Chapter 3: dynamic study module
A final mRNA transcript of 300 nucleotides would code for ______ amino acids. 100 300 3 0
100 A final mRNA transcript of 300 nucleotides would code for 100 amino acids because 3 nucleotides = 1 codon = 1 amino acid. During transcription, each DNA triplet is transcribed into a complementary three-nucleotide sequence of mRNA called a codon. In essence, the codon is a complementary RNA "copy" of the DNA triplet. After transcription, the transcript, called pre-mRNA, is not yet ready to be sent out into the cytosol because it must first be modified in several ways. As part of this process, large portions of the pre-mRNA transcript are actually removed before it exits the nucleus. Recall that not all regions of a gene contain actual code, or exons, some of the gene instead consists of introns. The copied introns in the pre-mRNA must be removed and the exons spliced together before the final mRNA transcript is sent to the cytosol. Then during translation, each mRNA codon is matched with a specific amino acid.
How many homologous chromosome pairs are present in most human cells? 23 4 18 46
23 Twenty three (23) homologous chromosome pairs are present in most human cells. Most human cells contain two sets of 23 chromosomes (46 total), with one set of 23 chromosomes inherited from each parent. The maternal and paternal chromosomes are called homologous chromosomes (or simply homologs).
If a cell has 24 chromosomes during the G1 phase and undergoes mitosis, how many chromosomes would each daughter cell have? 24 12 48 60
24 Each daughter cell would have 24 chromosomes after undergoing mitosis. The process of mitosis divides the cell's replicated DNA between two daughter cells. At the beginning of mitosis, we have a cell with 48 chromatids, or 24 replicated chromosomes. At the end, we have two cells with identical sets of 24 chromosomes.
Transcribe mRNA from this strand of DNA: 5'-T A C G G T A G T-3'. 5'-A U G C C A U C A-3' 5'-A T G C C A T C A-3' 5'-U T G C C U T G U-3' 5'-U A G C C U A C U-3'
5'-A U G C C A U C A-3' Transcription of mRNA from this strand of DNA, 5'- T A C G G T A G T-3', produces 5'-A U G C C A U C A-3'. During transcription, each DNA triplet is transcribed into a complementary three-nucleotide sequence of mRNA called a codon. In essence, the codon is a complementary RNA "copy" of the DNA triplet. Complementary base pairing works as follows: The nucleotide bases C and G always pair with one another, and A always pairs with T (in DNA) or U (in RNA). The transcript is built with the help of an enzyme that serves as the cell's "copy machine," called RNA polymerase. When RNA polymerase binds to a gene, it brings in nucleotides one at a time that are complementary to the DNA strand and links them to build a polymer of messenger RNA (mRNA).
A ___________ is a three-nucleotide sequence of mRNA that specifies a single amino acid. codon triplet gene anticodon
A codon is a three-nucleotide sequence of mRNA that specifies a single amino acid. During transcription, each DNA triplet is transcribed into a complementary three-nucleotide sequence of mRNA called a codon. In essence, the codon is a complementary RNA "copy" of the DNA triplet. Then during translation, each mRNA codon is matched with an amino acid. A triplet is a group of three DNA nucleotides that code for an amino acid. Anticodon contains a sequence of three nucleotides on the tRNA that is complementary to a specific mRNA codon. Genes are segments of DNA that mostly specify the amino acid sequences of proteins.
What is the start codon sequence that initiates translation? AUG ATG UAC AAA
AUG The start codon has a sequence of AUG. Translation begins when an initiator tRNA binds the mRNA start codon in the ribosome. The initiation stage begins when both the mRNA transcript and a tRNA called the initiator tRNA, which carries the amino acid methionine, bind to a small ribosomal subunit. With this tRNA in place, the small ribosomal subunit moves down the mRNA transcript looking for a specific nucleotide sequence called the start codon. The start codon has a sequence of AUG that base pairs to the initiator tRNA's anticodon, UAC. At this point, the large ribosomal subunit binds to the small subunit, with the initiator tRNA in the P site. Initiation is now complete, and elongation can begin.
Which of the following factors is not an extracellular signal that regulates progression through cell cycle checkpoints? Amount of carbon dioxide in the extracellular fluid Density of cells in a tissue Growth factors in the extracellular fluid Nutrients in the extracellular fluid
Amount of carbon dioxide in the extracellular fluid Amount of carbon dioxide in the extracellular fluid is not an extracellular signal to regulate progression through cell cycle checkpoints. Our cells have a control system that determines how rapidly each cell passes through the stages of the cell cycle. Such control is necessary to balance cell division with cell death. Monitoring occurs at specific points in the cell cycle, called checkpoints, which act as stop- and-go signals. Researchers have worked out many of the extracellular signals that regulate progression through these checkpoints and completion of the cell cycle. Some of the extracellular signals include the following: nutrients in the extracellular fluid (ECF), growth factors in the ECF, density of cells in a tissue, and anchorage of cells within the tissue.
During which phase of mitosis are sister chromatids separated and pulled to opposite poles? Anaphase Metaphase Prophase Telophase
Anaphase During anaphase, the sister chromatids part, and the individual chromosomes, now called daughter chromosomes, are pulled to opposite poles of the cell. This movement occurs as the spindle fibers to which they are attached get progressively shorter. By the end of anaphase, each pole of the cell has the complete set of 46 daughter chromosomes. Note that some microtubules are not attached to chromosomes, and these microtubules lengthen rather than shorten, which elongates the cell. In addition, cytokinesis may start in this phase. During metaphase phase, spindle fibers from opposite poles of the cell tug the sister chromatids back and forth to eventually line up on the middle, or "equator," of the cell. During prophase of mitosis, the chromatin condenses into chromosomes and the mitotic spindle forms. The previously duplicated centrosomes, each containing a pair of centrioles, move to opposite poles of the cell and organize the spindle fibers. Spindle fibers from each centriole pair then attach to each sister chromatid at the centromere. The final phase of mitosis is telophase, during which daughter cells separate. The nuclear envelopes reassemble, the nucleoli reform, and the chromosomes become less visible as the DNA reassumes the looser structure of chromatin. While telophase is occurring, so is cytokinesis, which divides the cytosol and organelles equally between the two daughter cells. The cells are split at an indentation called a cleavage furrow, which forms along the cell equator and deepens like a belt tightening as the cell's actin filaments and myosin motor proteins pinch the cell in two.
Which of the following transmembrane proteins does not transport solutes using facilitated diffusion? Aquaporin Symporter Uniporter Antiporter
Aquaporin Aquaporins are not a basic type of carrier protein used in facilitated diffusion. Aquaporins are water channels that allow most of the water molecules to pass into and out of the cell during osmosis. During facilitated diffusion using carrier proteins, the carriers bind one or two specific solutes and "carry" them into or out of the cell. As the process is currently understood, when a solute binds to its carrier protein, the protein changes shape, allowing the solute to move across the membrane and into or out of the cell. There are three basic types of carrier proteins: (1) a uniporter, which transports a single solute; (2) an antiporter, which moves two different solutes in opposite directions, one into the cell and one out of the cell; and (3) a symporter, which moves two solutes in the same direction.
_____________ are channels that allow the majority of water to enter and exit the cell. Aquaporins Glycolipids Peripheral proteins Glycoproteins
Aquaporins Aquaporins are channels that allow the majority of water to enter and exit the cell. The plasma membrane contains water channels called aquaporins that allow water molecules to pass into and out of the cell. Most water that crosses the membrane does so through aquaporins during osmosis. Glycolipids and glycoproteins consist of carbohydrate chains (polysaccharides) covalently attached to membrane lipids or proteins, respectively. These polymers are found on the outside of the plasma membrane. They function in cell recognition or the ability of our cells to tell one cell type from another. Peripheral proteins are found on only one side of the membrane.
Which of the following functions is not associated with intermediate filaments within the cell? Associating with motor proteins to move vesicles and organelles throughout the cell Uniting adjacent cells in a tissue so that the tissue can withstand mechanical stresses Forming a network within the cytoplasm that gives the cell mechanical strength Forming a network under the membrane around the nucleus to support its shape and size
Associating with motor proteins to move vesicles and organelles throughout the cell Associating with motor proteins to move vesicles and organelles throughout the cell is the function of microtubules. The strength and stability of intermediate filaments enable them to have a variety of roles within the cell, which include the following: forming a network within the cytoplasm that gives the cell mechanical strength. forming a network under the membrane around the nucleus to support its shape and size. uniting adjacent cells in a tissue so that the tissue can withstand mechanical stresses.
What tRNA anticodon is complementary to the mRNA codon GUA? CAU GUA CTA CAT
CAU CAU is the correct tRNA anticodon that is complementary to this mRNA codon GUA. Anticodons contain a sequence of three nucleotides that is complementary to a specific mRNA codon. The opposite end of the tRNA carries the specific amino acid that corresponds to the anticodon. Recall how complementary base pairing works: the nucleotide bases C and G always pair with each other, and A always pairs with U in RNA.
__________ stabilize(s) the structure of the plasma membrane when the temperature changes. Cholesterol Integral proteins Phospholipids Glycolipids
Cholesterol Cholesterol, a lipid, stabilizes the structure of the plasma membrane when the temperature changes. This is critical because the plasma membrane must maintain a certain state of fluidity to function. Glycolipids consist of carbohydrate chains (polysaccharides) covalently attached to membrane lipids. These polymers are found on the outside of the plasma membrane. They function in cell recognition or the ability of our cells to tell one cell type from another. Integral proteins are membrane proteins that typically span the entire width of the membrane; when they do reach both sides of the membrane, they are known as transmembrane proteins. Phospholipids in the bilayer shift continually in a lateral, or sideways, direction, and do so extremely rapidly—adjacent phospholipids switch places an average of 10 million times per second. The ability of phospholipids and other components to move within the plane of the membrane, a property known as fluidity, is critical to many plasma membrane functions, such as cell movement, cell reproduction, and transport of substances across the membrane.
______________ are tightly coiled and condensed barlike structures that separate during anaphase. Chromosomes Chromatin Nucleoli Centromeres
Chromosomes Chromosomes are tightly coiled and condensed barlike structures that separate during anaphase. During cell division, the chromatin threads coil tightly and condense into bar like structures called chromosomes that are about 10,000 times more compact than the original strand of DNA. During anaphase, the sister chromatids part, and the individual chromosomes, now called daughter chromosomes, are pulled to opposite poles of the cell. Chromatin consists of one extremely long DNA strand and its associated proteins. Between rounds of cell division, the chromatin threads are loose and tangled together like an unwound ball of yarn. Nucleoli are dark-staining structures in the nucleoplasm where ribosomes are assembled. The paired and identical copies of a chromosome are called sister chromatids and are joined at a region of the chromosome known as the centromere.
Which of the following functions is not associated with the peroxisome? Digesting worn-out organelles Oxidizing toxic substances Synthesizing certain phospholipids Breaking down fatty acids
Digesting worn-out organelles Digesting worn-out organelles is not a function of peroxisomes. Lysosomes are able to digest the nutrients they take in, as well as old, worn-out organelles, and in some cases, other cells. A peroxisome uses molecular oxygen to oxidize and strip hydrogen atoms off certain organic molecules to produce hydrogen peroxide (H2O2). The hydrogen peroxide, along with oxidative enzymes, then performs various functions, including the following: Oxidizing toxic substances. Hydrogen peroxide oxidizes certain chemicals that would be toxic to the cell, including ethanol (alcohol). The oxidation reactions convert such chemicals into less toxic compounds, which are then eliminated from the body. This function is particularly important in kidney and liver cells, which perform most detoxification reactions in the body. Breaking down fatty acids. Many of the catabolic reactions that break down fatty acids into smaller molecules occur in the peroxisomes. The products of these reactions are sent either to the cytosol to participate in anabolic reactions or to the mitochondria to be oxidized to produce adenosine triphosphate (ATP). Synthesizing certain phospholipids. Some enzymes in peroxisomes catalyze the initial reactions that form certain phospholipids. These phospholipids are critical components of the plasma membrane of specific cells in the nervous system.
Which of the following structures is not a type of RNA? Enzymatic RNA (eRNA) Messenger RNA (mRNA) Ribosomal RNA (rRNA) Transfer RNA (tRNA)
Enzymatic RNA (eRNA) Enzymatic RNA (eRNA) is not a type of RNA. Ribosomal RNA (rRNA) is a type of RNA produced in the nucleolus that serves as a main component of ribosomes. Messenger RNA (mRNA) is a strand of RNA that contains a copy of an amino acid sequence of a single protein. The DNA that codes for the proteins does not leave the nucleus. Our cells make a copy of the gene, called a transcript, which is a strand of RNA that can exit the nucleus and enter the cytosol. Transfer RNAs (tRNA) are RNA molecules that contain an amino acid and an anticodon that binds to a specific mRNA codon to build a polypeptide.
Which of the following components is not one of the three main parts of a cell? Extracellular fluid Cytoplasm Nucleus Plasma membrane
Extracellular fluid Extracellular fluid is not one of the three main parts of a cell. Most animal cells have three basic components: the plasma membrane, cytoplasm, and nucleus. The plasma membrane physically isolates the cell from its surroundings. The body contains two fluid compartments: (1) the intracellular space, which is the space within our cells that contains the cytosol or intracellular fluid and (2) the extracellular space, which is the space outside our cells that contains fluid called extracellular fluid, or simply ECF. The plasma membrane forms a barrier between the ECF and the cytosol and keeps the two fluid compartments separate. Inside the plasma membrane is the cytoplasm. This consists of both the fluid cytosol and the structures embedded within it: the organelles and the cytoskeleton. Most cells contain a single roughly spherical structure called the nucleus. The nucleus is surrounded by a membrane similar to the plasma membrane, known as the nuclear envelope. The nucleus contains most of the cell's deoxyribonucleic acid (DNA) and is the primary location for producing much of the cell's ribonucleic acid (RNA). The DNA and RNA control cellular functions by coding for and creating proteins.
What is the name of the long cellular extension that moves in a whiplike manner to propel a whole cell? Flagellum Cilium Centriole Microvillus
Flagellum A flagellum is a long extension that moves in a whiplike manner to propel a whole cell. A cell generally has no more than one flagellum, and the only flagellated cell in the human body is the sperm cell in males. Although they are similar structurally, cilia and flagella differ in function. Cilia are shorter and move in a coordinated beating motion. They are present in large numbers on the surfaces of certain cells, where each cilium functions like a tiny broom; these "brooms" beat together to sweep substances over the cell surface. Centrioles are composed of a ring formed by nine groups of three modified microtubules and other proteins. Modified centrioles called basal bodies give rise to both cilia and flagella. Microvilli are tiny fingerlike extensions that increase the surface area of the plasma membrane up to about 30-40 times, which allows the cell to absorb substances more rapidly.
How many codons will result from the transcription of this DNA strand: T A C G G T A G T A C C? Four (4) Three (3) Six (6) Sixteen (16)
Four (4) Four (4) codons will result from the transcription of the DNA strand- T A C G G T A G T A C C. A codon is a three-nucleotide sequence of mRNA that specifies a single amino acid. During transcription, each DNA triplet is transcribed into a complementary three-nucleotide sequence of mRNA called a codon.
What is the nondividing state called when cells get stalled indefinitely during the cell cycle? G0 phase S phase G1 phase G2 phase
G0 phase Cells get stalled indefinitely during G0 phase of the cell cycle. Some cells do not move through the cell cycle at all once the body's normal growth and development have ceased. Such cells are frozen in G1 phase indefinitely and are said to be in a nondividing state called the G0 phase. Cells in the human body in G0 phase include most mature muscle cells and nerve cells. Under certain limited conditions, these cells may divide, but generally they remain in G0 phase for life. During the G1 phase, or first gap phase, the cell is performing its normal metabolic functions as well as growing and carrying out rapid protein synthesis. The S phase is when DNA synthesis (replication) takes place. The G2 phase, or the second gap phase, is another period of cellular growth during which the proteins necessary for cell division are rapidly produced and the centrioles are duplicated.
Before export from the cell, products made by the endoplasmic reticulum are modified, sorted, and packaged by the ________________ Golgi apparatus. lysosomes. ribosomes. smooth endoplasmic reticulum.
Golgi apparatus. Within the Golgi apparatus, proteins and lipids produced by the endoplasmic reticulum (ER) are further modified, sorted, and packaged for export. When the processing of products in the Golgi apparatus is finished, they are packaged in vesicles bound for different destinations either within or outside the cell. Some of these secretory vesicles are ready for exocytosis from the plasma membrane. Some contain proteins to be inserted into the plasma membrane, and some go to lysosomes. Lysosomes contain digestive enzymes that break down substances taken into the cell by endocytosis, as well as worn-out organelles. Ribosomes are nonmembrane-enclosed organelles that are the site of protein synthesis. Smooth endoplasmic reticulum (SER) has no ribosomes on its surface. It stores calcium, synthesizes many lipids, and detoxifies certain substances.
What is the correct order of the phases in the cell cycle? Interphase, prophase, metaphase, anaphase, and telophase Prophase, interphase, anaphase, metaphase, and telophase Anaphase, telophase, prophase, metaphase, and interphase Interphase, metaphase, prophase, anaphase, and telophase
Interphase, prophase, metaphase, anaphase, and telophase Interphase, prophase, metaphase, anaphase, and telophase is the correct order of the phases in the cell cycle. The cell cycle is composed of two main phases: interphase and M phase, or cell division. M phase consists of mitosis, in which the genetic material divides. There are four stages in mitosis: prophase, metaphase, anaphase, and telophase.
What organelle degrades old, worn-out organelles for cellular recycling? Lysosome Peroxisome Rough endoplasmic reticulum Smooth endoplasmic reticulum
Lysosome Lysosomes contain digestive enzymes that break down substances taken into the cell by endocytosis, as well as worn-out organelles. Lysosomes are membrane-enclosed sacs that contain water and a set of enzymes called acid hydrolases that catalyze hydrolysis reactions. Lysosomes degrade old, worn-out organelles and cell components via a process called autophagy ("self-eating"). The components of the digested organelles are then returned to the cytosol to build new cell components, an example of cellular recycling. A peroxisome uses molecular oxygen to oxidize and strip hydrogen atoms off certain organic molecules to produce hydrogen peroxide (H2O2). The hydrogen peroxide, along with oxidative enzymes, then performs various functions, including the following: oxidize toxic substances and fatty acids and synthesize certain phospholipids. Rough endoplasmic reticulum (RER) has ribosomes attached to its surface, and it modifies and folds proteins made by the attached ribosomes. Smooth endoplasmic reticulum (SER) has no ribosomes on its surface. It stores calcium, synthesizes many lipids, and detoxifies certain substances.
Cell division occurs during __________. M phase G1 phase S phase G2 phase
M phase Cell division occurs during M phase. The cell cycle is composed of two main phases: interphase and M phase, or cell division. During interphase—which includes three subphases known as G1, S, and G2—the cell grows and prepares for the final M phase, which is the division of the nucleus (mitosis) and cytoplasm (cytokinesis).
Identify the phase of mitosis.
Metaphase is the correct phase pictured. Note that the spindle fibers have pulled the sister chromatids to align on equator of cell. In prophase, the chromatin condenses so sister chromatids become visible and the nuclear envelope begins to break apart. In anaphase, you will see the sister chromatids at opposite poles of the cell. The cell may elongate, but the indentation is not distinguishable at this phase. In telophase, the chromosomes become less visible, and an indentation called a cleavage furrow will be visible.
_____________ is the process of cancer cells spreading to other tissues. Metastasis Hyperplasia Apoptosis Cytokinesis
Metastasis Metastasis is the process of cancer cells spreading to other tissues. Cancer cells from malignant tumors are able to spread into other tissues in a process called metastasis, which results in the formation of other tumors throughout the body. This can cause widespread tissue destruction that, especially if untreated, may lead to death. Apoptosis is a process of programmed cell death. Hyperplasia results when the rate of cell division exceeds the rate of cell death, and the tissue may increase in cell number and size. This condition, called hyperplasia, can strain the surrounding tissues, robbing them of oxygen and nutrients. Cytokinesis divides the cytoplasm between the daughter cells and pinches the cell in two at the cleavage furrow.
Which cellular extensions can increase the surface area of the plasma membrane up to 40%? Microvilli Flagella Cilia Centrioles
Microvilli Microvilli are tiny fingerlike extensions that increase the surface area of the plasma membrane up to about 30-40 times, which allows the cell to absorb substances more rapidly. On microscopic examination, cells with microvilli resemble a brush, and so these extensions are sometimes referred to collectively as a brush border. Flagella are long extensions that move in a whiplike manner to propel a whole cell. A cell generally has no more than one flagellum, and the only flagellated cell in the human body is the sperm cell in males. Cilia are shorter than flagella and move in a coordinated beating motion. They are present in large numbers on the surfaces of certain cells, where each cilium functions like a tiny broom; these "brooms" beat together to sweep substances over the cell surface. Centrioles are composed of a ring formed by nine groups of three modified microtubules and other proteins. Modified centrioles called basal bodies give rise to both cilia and flagella.
Which organelle has a second inner membrane that has folds called cristae and a matrix? Mitochondrion Golgi apparatus Nucleus Rough endoplasmic reticulum
Mitochondrion The mitochondrion has a second inner membrane that has folds called cristae and a matrix. The organelles known as mitochondria are involved in energy production. There are actually two mitochondrial membranes: a smooth outer mitochondrial membrane and an inner mitochondrial membrane that has numerous folds called cristae, which significantly increase the inner surface area. This double-membrane structure creates two spaces within the mitochondrion: (1) the intermembrane space, which is the space between the two membranes, and (2) the matrix, which is the innermost space. The Golgi apparatus consists of a group of flattened membranous sacs filled with enzymes and other molecules. Within the Golgi apparatus, proteins and lipids produced by the endoplasmic reticulum (ER) are further modified, sorted, and packaged for export. The nucleus consists of three main structures: (1) an enclosing membrane, (2) DNA and its associated proteins, and (3) the nucleolus. Most of the time, DNA is found here in a loosely organized form called chromatin. Rough endoplasmic reticulum (RER) has ribosomes attached to its surface, and it modifies and folds proteins made by the attached ribosomes.
What process of the M phase divides the genetic material of a cell? Mitosis Interphase Cytokinesis Replication
Mitosis Mitosis is the division of the genetic material between the two daughter cells. The process of mitosis divides the cell's replicated DNA between two daughter cells. It requires a structure called the mitotic spindle, which is composed of microtubules organized into spindle fibers by the cell's centrosomes. Interphase, the phase of growth and preparation for division, includes the following three subphases: G1, S, and G2. The S phase is when DNA synthesis (replication) takes place. Interphase is not a part of the M phase. Cytokinesis is the division of the cell's proteins, organelles, and cytosol between the daughter cells.
Which of the following functions is associated with many plasma membrane proteins? Molecular transport through the membrane Oxygen transport Forms a lipid bilayer Promotes fluidity of the membrane
Molecular transport through the membrane Molecular transport through the membrane is a function of many plasma membrane proteins. Besides phospholipids, the main components of the plasma membrane are molecules called membrane proteins. Integral proteins typically span the entire width of the membrane; when they do reach both sides of the membrane, they are known as transmembrane proteins. Many transmembrane proteins serve as protein channels that allow certain substances to cross the membrane and pass into or out of the cell. Some integral proteins called carrier proteins bind and directly transport substances into and out of the cell. The phospholipid bilayer forms the basis of the plasma membrane in every one of our cells. The ability of phospholipids and other components to move within the plane of the membrane, a property known as fluidity, is critical to many plasma membrane functions, such as cell movement, cell reproduction, and transport of substances across the membrane. Simple diffusion mostly involves nonpolar solutes (such as hydrocarbons and lipids and gases such as O2 and CO2) that pass straight through the phospholipid bilayer without assistance from a membrane protein.
The _____________ is the organelle that produces most of our adenosine triphosphate (ATP). mitochondrion Golgi apparatus nucleus rough endoplasmic reticulum
Most of our adenosine triphosphate (ATP) is produced within the mitochondria. The organelles known as mitochondria (singular, mitochondrion) are involved in energy production. The main source of energy for cells is chemical energy, and the most ready supply of chemical energy for our cells is ATP. Although some ATP production occurs via glycolysis in the cytosol, most of our ATP is produced within the mitochondria, which is why they are often called the "power plants" of the cell. The Golgi apparatus consists of a group of flattened membranous sacs filled with enzymes and other molecules. Within the Golgi apparatus, proteins and lipids produced by the endoplasmic reticulum (ER) are further modified, sorted, and packaged for export. The nucleus consists of three main structures: (1) an enclosing membrane, (2) DNA and its associated proteins, and (3) the nucleolus. Most of the time, DNA is found here in a loosely organized form called chromatin. Rough endoplasmic reticulum (RER) has ribosomes attached to its surface, and it modifies and folds proteins made by the attached ribosomes.
Which of the following proteins is not a long filament found in the cytoskeleton? Myosin Microtubules Actin filaments Intermediate filaments
Myosin Myosin is not a type of long protein filament. Myosin is a motor protein associated with actin filaments that is capable of moving the entire cell. Many different types of myosin proteins exist, but all contain a globular head that uses energy from adenosine triphosphate (ATP) hydrolysis to move actin filaments or the myosin protein itself. Microtubules are composed of protein subunits called tubulins that can be rapidly added or removed from a microtubule, allowing it to change size as needed by the cell. Actin filaments (microfilaments) are composed of two intertwined strands of protein subunits called actin. Actin filaments provide structural support, bear tension (stretching forces), and help to maintain the cell's shape. Intermediate filaments are named "intermediate" because they are intermediate in size between the small actin filaments and the large microtubules. Intermediate filaments are made up of a diverse group of fibrous proteins, including keratin. The long strands are twisted together like a rope. An intermediate filament bends and twists easily but is quite strong and difficult to break.
Within the nucleus, where does ribosome assembly occur? Nucleolus Nucleoplasm Centromere Nuclear pore
Nucleolus Within the nucleus, ribosome assembly occurs in the nucleolus. Within the nucleoplasm of the nucleus is a dark-staining structure called the nucleolus (cells sometimes have more than one of these nucleoli). We can think of a nucleolus as a "ribosome factory"; this is where ribosomes are assembled. It is not enclosed by a membrane but rather is simply a large aggregate of proteins, DNA, and RNA. In the nucleolus we find segments of DNA-containing genes that do not code for a protein but instead just specify the nucleotide sequence of an RNA strand. Some of these segments, known as rRNA genes, code for ribosomal RNA (rRNA), which is a key component of ribosomes. The enclosing membrane, called the nuclear envelope, is pierced by occasional openings known as nuclear pores. Both the DNA and the nucleolus are located within a cytosol-like gel called the nucleoplasm. Nucleoplasm contains many different components, including water, free-floating nucleotides, enzymes and other proteins, and different types of RNA. The most notable component of the nucleoplasm, however, is our DNA. Most of the time, DNA is found here in a loosely organized form called chromatin. During cell division, the chromatin threads coil tightly and condense into chromosomes. The paired and identical copies of a chromosome are called sister chromatids and are joined at a region of the chromosome known as the centromere.
Where does transcription of genomic DNA into RNA occur? Nucleus Lysosomes Golgi apparatus Peroxisomes
Nucleus Transcription of DNA into RNA occurs in the nucleus. Most of a cell's DNA resides in the nucleus, and protein synthesis occurs on ribosomes, which are found outside the nucleus in the cytoplasm. This arrangement presents our cells with a problem: The DNA that codes for the proteins does not leave the nucleus, but the information must somehow leave and get into the cytosol so that it can be read there by the ribosomes. Our cells solve this problem by making a copy of the gene, called a transcript, which is a molecule of RNA that can exit the nucleus and enter the cytosol. The Golgi apparatus is a stack of flattened sacs. It receives vesicles from the endoplasmic reticulum (ER) and then modifies and packages these products to be secreted from the cell by exocytosis to become part of the plasma membrane, or to be incorporated into lysosomes. Lysosomes contain digestive enzymes that break down substances taken into the cell by endocytosis, as well as worn-out organelles. Peroxisomes use oxygen to carry out oxidation reactions that include oxidation of toxic substances and fatty acids and synthesis of certain phospholipids.
Which of the following types of membrane transport is not adenosine triphosphate (ATP) dependent? Osmosis Exocytosis Pinocytosis Sodium-potassium pump
Osmosis Osmosis is a type of passive transport in which the solvent moves across a selectively permeable membrane from a region of lower solute concentration to a region of higher solute concentration. The sodium-potassium pump is the primary active transport pump in the body. A pump binds a solute and transports it against its concentration gradient using the energy from the hydrolysis of ATP. The Na+ /K+ pump maintains the steep concentration gradient by transporting three sodium ions out of the cell for every two potassium ions it moves into the cell. There are two main types of vesicular transport: endocytosis to bring substances into the cell, and exocytosis to move substances out of the cell. Vesicular transport requires the energy from ATP hydrolysis to fuel several steps of the process, including vesicle formation. During pinocytosis, a type of endocytosis, coated pits in the plasma membrane form vesicles containing dissolved substances from the extracellular fluid (ECF). Pinocytosis produces smaller transport vesicles than phagocytosis. These vesicles bring nutrients and other substances dissolved in the ECF into the cell.
_____________ join amino acids together to build a polypeptide chain during translation. Peptide bonds Hydrogen bonds Metallic bonds Ionic bonds
Peptide bonds Amino acids are joined by peptide bonds to build a polypeptide chain during translation. During elongation, tRNAs bring in specific amino acids that will link together by special covalent bonds called peptide bonds to form a polypeptide. Hydrogen bonds are weak chemical bonds that hold complementary bases together in a DNA molecule or a RNA nucleotide to its complementary base in DNA during transcription. An ionic bond results from the transfer of electrons and results in an attraction between a positive metal cation and a negative nonmetal anion. A metallic bond is a type of chemical bond that occurs between atoms of metallic elements.
Which of the following organelles is not part of the endomembrane system? Peroxisomes Lysosomes Golgi apparatus Smooth endoplasmic reticulum
Peroxisomes Peroxisomes are not a part of the endomembrane system. A peroxisome uses molecular oxygen to oxidize and strip hydrogen atoms off certain organic molecules to produce hydrogen peroxide (H2O2). The hydrogen peroxide, along with oxidative enzymes, then performs various functions, including the following: oxidize toxic substances and fatty acids and synthesize certain phospholipids. Most of the cell's organelles are surrounded by phospholipid bilayer membranes that are similar to the plasma membrane. Some of these organelles form vesicles that exchange proteins and other molecules. The organelles that transfer molecules in this manner are part of a system called the endomembrane system, whose components together synthesize, modify, and package molecules produced by the cell. This system includes the plasma membrane, endoplasmic reticulum, the Golgi apparatus, and lysosomes. Also included in the endomembrane system is the nuclear envelope.
During which phase of the cell cycle does the mitotic spindle form? Prophase Anaphase Metaphase Telophase
Prophase During prophase of the M phase of the cell cycle, the mitotic spindle forms. During this process, the previously duplicated centrosomes, each containing a pair of centrioles, move to opposite poles of the cell and organize the spindle fibers. Spindle fibers from each centriole pair then attach to each sister chromatid at the centromere. During metaphase, spindle fibers from opposite poles of the cell tug the sister chromatids back and forth to eventually line up on the middle or "equator" of the cell. During anaphase, the sister chromatids part, and the individual chromosomes, now called daughter chromosomes, are pulled to opposite poles of the cell. This movement occurs as the spindle fibers to which they are attached get progressively shorter. During telophase the daughter cells separate. The nuclear envelopes reassemble, the nucleoli reform, and the chromosomes become less visible as the DNA reassumes the looser structure of chromatin. While telophase is occurring, so is cytokinesis, which divides the cytosol and organelles equally between the two daughter cells. The cells are split at an indentation called a cleavage furrow, which forms along the cell equator and deepens like a belt tightening as the cell's actin filaments and myosin motor proteins pinch the cell in two.
Which of the following functions does not relate to the smooth endoplasmic reticulum? Protein synthesis Lipid synthesis Calcium ion storage Detoxification reactions
Protein synthesis Protein synthesis does not relate to a function of the smooth endoplasmic reticulum, but it is a function of ribosomes. Smooth endoplasmic reticulum (SER) has no ribosomes on its surface. Because the SER is not associated with ribosomes, it plays essentially no role in protein synthesis. It stores calcium, synthesizes many lipids, and detoxifies certain substances. In most cells, the SER pumps calcium ions out of the cytosol and stores them for later release. The SER is very well developed in cells that detoxify drugs and harmful substances ingested by and produced in the body, particularly cells in the liver. The SER synthesizes the bulk of the cell's lipid membrane components, such as phospholipids and cholesterol, as well as steroid hormones and lipoproteins.
What is the role of RNA polymerase in transcription? RNA polymerase binds to the DNA promoter and builds an mRNA molecule. RNA polymerase catalyzes the unwinding of the DNA double helix. RNA polymerase carries information that specifies the amino acid sequence to the ribosomes. RNA polymerase signals the end of the mRNA molecule.
RNA polymerase binds to the DNA promoter and builds an mRNA molecule. RNA polymerase binds to the DNA promoter and builds an mRNA molecule. The process by which the mRNA strand is made is called transcription. Transcription begins when transcription factors bind to the DNA promoter. RNA polymerase then binds to the promoter as well, and a segment of DNA unwinds. RNA polymerase builds a complementary mRNA transcript with free nucleotides. The process continues until the RNA polymerase reaches a nucleotide sequence that signals the end of the gene. At this point enzymes catalyze the release of the mRNA transcript, and the RNA polymerase detaches from the DNA.
Where does protein synthesis occur? Ribosomes Peroxisomes Lysosomes Mitochondria
Ribosomes Ribosomes are the site of protein synthesis. Ribosomes are nonmembrane-bounded organelles that are the site of protein synthesis. Each ribosome consists of two subunits, one large and one small, that fit together like the top and bottom of a hamburger bun. Each subunit is made of a complex assembly of ribosomal proteins and a type of RNA called ribosomal RNA (rRNA). Peroxisomes oxidize toxic substances and fatty acids and synthesize certain phospholipids. Lysosomes contain digestive enzymes that break down substances taken into the cell by endocytosis, as well as worn-out organelles. Mitochondria are involved in energy production. The main source of energy for cells is chemical energy, and the most ready supply of chemical energy for our cells is ATP.
What organelle modifies polypeptides so they can fold into fully functional proteins? Rough endoplasmic reticulum Lysosomes Smooth endoplasmic reticulum Peroxisomes
Rough endoplasmic reticulum Rough endoplasmic reticulum (RER) modifies polypeptides so that they can fold into fully functional proteins. The polypeptides synthesized on bound ribosomes pass through the RER membrane into its lumen, where enzymes catalyze the reactions that fold these polymers into their correct three-dimensional shapes. The RER recognizes proteins that have folded into an incorrect shape and sends them to the cytosol, where they are degraded. Lysosomes contain digestive enzymes that break down substances taken into the cell by endocytosis, as well as worn-out organelles. Lysosomes are membrane-enclosed sacs that contain water and a set of enzymes called acid hydrolases that catalyze hydrolysis reactions. A peroxisome uses molecular oxygen to oxidize and strip hydrogen atoms off certain organic molecules to produce hydrogen peroxide (H2O2). The hydrogen peroxide, along with oxidative enzymes, then performs various functions, including the following: oxidize toxic substances and fatty acids and synthesize certain phospholipids. Smooth endoplasmic reticulum (SER) has no ribosomes on its surface. It stores calcium, synthesizes many lipids, and detoxifies certain substances.
Which of the following statements best describes the structure of the plasma membrane? The plasma membrane is a phospholipid bilayer surrounding the cell. The plasma membrane is composed of cristae. The plasma membrane is a double layer of protein enclosing the plasma. The plasma membrane is a single-layered membrane that surrounds the nucleus of the cell.
The plasma membrane is a phospholipid bilayer surrounding the cell. The plasma membrane is best described as a phospholipid bilayer surrounding the cell. Recall that phospholipids are a special class of lipid that is amphiphilic; they have both polar and nonpolar parts. Their phosphate-containing "heads" are relatively large, highly polar regions, and their fatty acid "tails" are large, nonpolar regions. The phospholipids rearrange themselves into two layers, so that their fatty acid tails still face away from the water molecules, forming a phospholipid "sandwich." The phosphate heads are the "bread" and align on both sides so that they are facing the water molecules. The fatty acid tails are the "cheese" in the middle, and they align so that they face each other and exclude water and polar molecules. This arrangement is known as a phospholipid bilayer. The nucleus is surrounded by a phospholipid bilayer similar to the plasma membrane, known as the nuclear envelope, but the nuclear envelope is a double membrane.
What are the two major steps of gene expression that produce a protein from a gene? Transcription and translation Replication and translation Mitosis and cytokinesis Replication and transcription
Transcription and translation The two major steps of gene expression that produce a protein from a gene are transcription and translation. During transcription, the code specified by a gene is copied, creating a molecule of messenger RNA (mRNA). In translation, ribosomes read the nucleotide sequence of the mRNA molecule and synthesize a polypeptide chain containing the correct amino acid sequence. During DNA replication, the chromatin unwinds from the histone proteins, and the entire set of 3.2 billion base pairs is duplicated by a process that builds new DNA strands using each "old" DNA strand as a template. Such replication is called semiconservative replication because one of the original strands of DNA is included in each newly formed double helix. The ordered series of events from cell formation to cell division is called the cell cycle. The cell cycle consists of two main phases: interphase and cell division (M phase). Interphase includes three subphases: G1, S, and G2. During S phase, DNA synthesis or replication, a cell's entire set of chromosomes is duplicated. The M phase of interphase consists of mitosis, in which the genetic material divides, and cytokinesis, in which the cell divides into two daughter cells. Mitosis divides the cell's replicated DNA between the two daughter cells. There are four stages in mitosis: prophase, metaphase, anaphase, and telophase. Cytokinesis occurs simultaneously with anaphase and telophase; it divides the cytoplasm between the daughter cells and pinches the cell in two at the cleavage furrow.
What brings amino acids to the ribosome during translation? Transfer RNA (tRNA) Ribosomal RNA (rRNA) RNA polymerase Messenger RNA (mRNA)
Transfer RNA (tRNA) Transfer RNA's job is to pick up a specific amino acid from the cytosol and transfer it to the growing polypeptide chain at the ribosome during transcription. Transfer RNA (tRNA) is a RNA molecule that contains an amino acid and an anticodon that binds to a specific mRNA codon to build a polypeptide. Ribosomal RNA (rRNA) is a type of RNA produced in the nucleolus that serves as a main component of ribosomes. Messenger RNA (mRNA) is a strand of RNA that contains a copy of an amino acid sequence of a single protein. The DNA that codes for the proteins does not leave the nucleus. Our cells make a copy of the gene, called a transcript, which is a strand of RNA that can exit the nucleus and enter the cytosol. RNA polymerase binds to the DNA promoter and builds an mRNA molecule.
What protein subunits comprise microtubules? Tubulin Actin Myosin Kinesin
Tubulin Microtubules are composed of protein subunits called tubulins that can be rapidly added or removed from a microtubule, allowing it to change size as needed by the cell. Actin filaments (microfilaments) are composed of two intertwined strands of protein subunits called actin. Actin filaments provide structural support, bear tension (stretching forces), and help to maintain the cell's shape. The motor protein associated with actin filaments, called myosin, is capable of moving the entire cell. The motor proteins, called dynein and kinesin, move along microtubules, carrying their "cargo," in the same way a train moves along a track.
What RNA sequence is complementary to the DNA sequence-A T G C C A T C G? U A C G G U A G C A T G C C A T C G T A C G G T A G C T U C G G T U G C
U A C G G U A G C U A C G G U A G C is the transcribed strand from the DNA strand A T G C C A T C G. Recall how complementary base pairing works: the nucleotide bases C and G always pair with each other, and A always pairs with U in RNA. During transcription, each DNA triplet is transcribed into a complementary three-nucleotide sequence of mRNA called a codon.
What is transported across a membrane during osmosis? Water Solutes Salts Sugars
Water Water is transported across a membrane during osmosis. The process of osmosis refers to the movement of solvent, the dissolving medium, across a selectively permeable membrane from a solution with a lower solute concentration to a solution with a higher solute concentration. In the human body, the solvent is water. Remember from chapter 2, solutes are substances that are dissolved by a solvent in a solution.
Simple diffusion requires __________. a concentration gradient the use of energy protein channels carrier proteins
a concentration gradient Simple diffusion requires a concentration gradient. Diffusion, a type of passive transport, is defined as the movement of solute molecules (those that are dissolved) from an area of higher solute concentration to an area of lower solute concentration without the expenditure of energy from the cell. The basic force that drives diffusion is called a concentration gradient. Diffusion allows solutes to move into and out of the cell using the potential energy of a concentration gradient. A solute is said to move down or "with" its concentration gradient (from a higher to a lower concentration) during the process of diffusion. Simple diffusion mostly involves nonpolar solutes (such as hydrocarbons and lipids and gases such as O2 and CO2) that pass straight through the phospholipid bilayer without assistance from a membrane protein.
A cell is placed into a 3% dextrose solution. At that concentration, the solution is isotonic to the cell. If the concentration of dextrose in the solution is increased to 5%, the cell is now in __________ a hypertonic solution a less concentrated solution an isotonic solution a hypotonic solution
a hypertonic solution A cell is placed into a 3% dextrose solution. At that concentration, the solution is isotonic to the cell. If the concentration of dextrose in the solution is increased to 5%, the cell is now in a hypertonic solution. In a hypertonic solution, the extracellular fluid (ECF) has a greater ability to cause osmosis because of the presence of higher numbers of solute particles that do not cross the plasma membrane (hyper = "more"). A hypertonic solution drives osmosis; so a cell in a hypertonic ECF loses water as it leaves the cell and enters the ECF. Such water loss causes the cell to shrivel, or crenate, and possibly die. A cell immersed in a hypotonic solution has a lower ability to cause osmosis because of fewer solutes (hypo = "less"). The cytosol now has a greater ability to drive osmosis, so water moves from the ECF into the cytosol. This causes the cell to swell and possibly rupture, or lyse. The body's ECF is isotonic (iso = "same") to the cytosol of a cell, meaning that the ECF and the cytosol have the same ability to cause osmosis. Under these conditions, water enters and leaves the cell at the same rate, so the cell has no net gain or loss of water over time and its volume remains the same.
Because phospholipids have both polar and nonpolar parts, they are classified as ___________. amphiphilic hydrophilic hydrophobic ionic
amphiphilic Phospholipids are a special class of lipids that are amphiphilic; they have both polar and nonpolar parts. Their phosphate-containing "heads" are relatively large, highly polar regions, and their fatty acid "tails" are large, nonpolar regions. The polar hydrophilic phosphate heads line up so that they face the water, whereas the nonpolar hydrophobic fatty acid tails point away from the water. Compounds with ionic bonds and compounds with polar covalent bonds are both hydrophilic, able to interact with water. Yet ionic compounds would not make good material for our barrier because they dissociate in water.
A molecular machine that performs a specific function for the cell is __________. an organelle the cytoskeleton cytosol the plasma membrane
an organelle Molecular machines that perform specific functions for the cell are organelles. Just as each of our organs has a unique structure that enables it to perform specific functions, so does each of a cell's organelles. Organelles are vital to a cell because they compartmentalize the cell's functions. Compartmentalization is essential for efficiency; it enables the cell to keep related enzymes and proteins together in one place so that they are not scattered throughout the cell. Most animal cells have three basic components: plasma membrane, cytoplasm, and nucleus. The cytoplasm consists of both the fluid cytosol and the structures embedded within it: the organelles and the cytoskeleton. Cytoskeleton consists of a network of protein filaments. The cytoskeleton supports the cell, helps create and maintain its shape, and holds the organelles in place.
A long, thin strand of DNA and its associated proteins is called ___________. chromatin a chromosome a centromere a nucleolus
chromatin Chromatin consists of one extremely long DNA strand and its associated proteins. Between rounds of cell division, the chromatin threads are loose and tangled together like an unwound ball of yarn within the nucleus. During cell division, the chromatin threads coil tightly and condense into barlike structures called chromosomes that are about 10,000 times more compact than the original strand of DNA. Nucleoli are dark-staining structures in the nucleoplasm where ribosomes are assembled. The paired and identical copies of a chromosome are called sister chromatids and are joined at a region of the chromosome known as the centromere.
The short structures located in respiratory passages that sweep out mucus containing inhaled debris are called: cilia. flagella. microvilli. microtubules.
cilia. The cells that line our respiratory passages have cilia that sweep out mucus littered with dust and debris we have inhaled. Cilia are shorter than flagella and move in a coordinated beating motion. They are present in large numbers on the surfaces of certain cells, where each cilium functions like a tiny broom; these "brooms" beat together to sweep substances over the cell surface. Microvilli are tiny fingerlike extensions that increase the surface area of the plasma membrane up to about 30-40 times, which allows the cell to absorb substances more rapidly. On microscopic examination, cells with microvilli resemble a brush, and so these extensions are sometimes referred to collectively as a brush border. Flagella are long extensions that move in a whiplike manner to propel a whole cell. A cell generally has no more than one flagellum, and the only flagellated cell in the human body is the sperm cell in males. Microtubules form the core of cellular extensions called cilia and flagella.
The indentation that forms during telophase of mitosis is called a _____________. cleavage furrow sister chromatid mitotic spindle centrosome
cleavage furrow The indentation that forms during telophase of mitosis is called a cleavage furrow. While telophase is occurring, so is cytokinesis, which divides the cytosol and organelles equally between the two daughter cells. The cells are split at an indentation called a cleavage furrow, which forms along the cell equator and deepens like a belt tightening as the cell's actin filaments and myosin motor proteins pinch the cell in two. Mitosis and cytokinesis are now complete, and the result is two daughter cells with identical genetic material. Sister chromatids are two identical copies of a replicated chromosome. A centrosome is a central area of a cell from which microtubules emanate. It contains a pair of centrioles that play an important role in cell division. A mitotic spindle is a structure that forms during prophase of mitosis and aids in dividing the sister chromatids. During metaphase, the spindle fibers from opposite poles of the cell tug the sister chromatids back and forth to eventually line up on the middle, or "equator," of the cell. During anaphase, the spindle fibers get progressively shorter and pull the sister chromatids to opposite poles of the cell.
A blood cell placed in a hypertonic solution will _____________. crenate swell burst not change
crenate A red blood cell placed in a hypertonic solution will crenate. When a red blood cell is placed in a hypertonic solution, the extracellular fluid (ECF) has a greater ability to cause osmosis because of the presence of higher numbers of solute particles that do not cross the plasma membrane. A hypertonic solution drives osmosis, so a cell in a hypertonic ECF loses water as it leaves the cell and enters the ECF. Such water loss causes the cell to shrivel, or crenate, and possibly die. A red blood cell immersed in a hypotonic solution causes the cell to swell and possibly rupture, or lyse. The cytosol has a greater ability to drive osmosis, so water moves from the ECF into the cytosol. In isotonic solutions, water enters and leaves the cell at the same rate, so the cell has no net gain or loss of water over time and its volume remains the same.
Human cells that lack centrioles cannot __________. divide move synthesize proteins metabolize sugars
divide Human cells that lack centrioles cannot divide. Centrioles are composed of a ring formed by nine groups of three modified microtubules and other proteins. The centrioles play a critical role in cell division. During prophase of mitosis, centrioles move to opposite poles of the cell and organize the spindle fibers. Spindle fibers from each centriole pair then attach to each sister chromatid at the centromere. The movement of chromosomes occurs as the spindle fibers to which they are attached get progressively shorter.
Two types of active transport via vesicles are __________. endocytosis and exocytosis primary active transport and secondary active transport diffusion and osmosis simple diffusion and facilitated diffusion
endocytosis and exocytosis Two types of active transport via vesicles are endocytosis and exocytosis. Larger particles are transported into or out of the cell in small sacs called vesicles. A vesicle is enclosed by a membrane made of a phospholipid bilayer, just like the plasma membrane that encloses the cell. In fact, vesicles form from pinched-off parts of cell membranes, so they can fuse with the plasma membrane and also with the membranes surrounding the organelles found in the cytoplasm. Transport that uses vesicles is an active process called vesicular transport. Vesicular transport requires the energy from adenosine triphosphate (ATP) hydrolysis to fuel several steps of the process, including vesicle formation. There are two main types of vesicular transport: endocytosis to bring substances into the cell and exocytosis to move substances out of the cell. Diffusion is a type of passive transport during which molecules move down their concentration gradient until equilibrium is reached. Simple diffusion refers to the movement of molecules directly through the phospholipid bilayer. Facilitated diffusion refers to movement of polar and ionic molecules across a membrane through a protein channel or with the help of a carrier protein. Osmosis is a type of passive transport in which water (the solvent) moves across a selectively permeable membrane from a region of lower solute concentration to a region of higher solute concentration until equilibrium is reached. Active transport processes use energy in the form of ATP to move a solute against its concentration gradient from a low concentration to a high concentration. During primary active transport, a membrane protein uses the energy from ATP to "pump" a solute against its concentration gradient. One of the body's main primary active transport pumps is the Na+/K+ pump, or ATPase, which pumps three sodium ions out of and two potassium ions into the cell. Secondary active transport uses a primary active transport pump to create a concentration gradient and then uses potential energy from that concentration gradient to pump another solute into or out of the cell against its concentration gradient.
Neurotransmitters are released from secretory vesicles in neurons by a process called ____________. exocytosis phagocytosis pinocytosis transcytosis
exocytosis Neurotransmitters are released from secretory vesicles in neurons by a process called exocytosis. Exocytosis is the process by which large substances are packaged into a vesicle that fuses with the plasma membrane and are released from the cell. Many molecules are released from the cell in this manner, including components of the extracellular fluid (ECF), such as glycoproteins and enzymes. In addition, cells that release large volumes of products—including nerve, gland, and digestive cells—release products such as hormones, neurotransmitters (the chemical messengers of nerve cells) and enzymes by a process known as secretion. The products of secretion are packaged in specialized vesicles called secretory vesicles. During phagocytosis, a type of endocytosis, cells ingest large particles such as bacteria, dead body cells, or parts of cells. In humans only certain cells of the immune system called phagocytes carry out phagocytosis. Phagocytosis requires the energy from adenosine triphosphate (ATP) hydrolysis to fuel several steps of the process, including vesicle formation. During pinocytosis, coated pits in the plasma membrane form vesicles containing dissolved substances from the ECF. Pinocytosis produces smaller transport vesicles than phagocytosis. These vesicles bring nutrients and other substances dissolved in the ECF into the cell. Some molecules are brought into the cell by endocytosis, transported through the cell, and released from the cell's other side by exocytosis, a process known as transcytosis.
Sodium ions move across the plasma membrane through a carrier protein using no energy in __________________. facilitated diffusion simple diffusion osmosis the sodium-potassium pump
facilitated diffusion Sodium ions move across the plasma membrane through a carrier protein using no energy in facilitated diffusion. Facilitated diffusion involves charged or polar solutes (such as ions and glucose) that cross the phospholipid bilayer with the help of a membrane protein. Facilitated diffusion is still a type of passive transport, even though it requires the help of membrane proteins. The cell expends no more energy in facilitated diffusion than it does in simple diffusion. Both processes rely on the potential energy of the concentration gradient to drive each solute's movement. Simple diffusion mostly involves nonpolar solutes (such as hydrocarbons and lipids and gases such as O2 and CO2) moving with their concentration gradient that pass straight through the phospholipid bilayer without assistance from a membrane protein. Osmosis is a type of passive transport in which the solvent moves across a selectively permeable membrane from a region of lower solute concentration to a region of higher solute concentration. The sodium-potassium pump is the primary active transport pump in the body. A pump binds a solute and transports it against its concentration gradient using the energy from the hydrolysis of ATP. The Na+ /K+ pump maintains the steep concentration gradient by transporting three sodium ions out of the cell for every two potassium ions it moves into the cell, both against their concentration gradients.
Cytosol is also known as __________
intracellular fluid (ICF) blood plasma the cytoskeleton extracellular fluid (ECF) Cytosol is also known as intracellular fluid (ICF). The cytosol, or ICF, is the fluid portion of the cytoplasm that makes up about half of the cell's total volume. It is a watery gel with many proteins, different forms of RNA, and dissolved solutes. The body contains two fluid compartments: (1) the intracellular space, which is the space within our cells that contains the cytosol or ICF and (2) the extracellular space, which is the space outside our cells that contains fluid called extracellular fluid, or simply ECF. The plasma membrane forms a barrier between the ECF and the cytosol and keeps the two fluid compartments separate.
A 0.9% normal saline solution is often administered with intravenous medication because it is __________ to the bloodstream. isotonic hypotonic hypertonic catatonic
isotonic A 0.9% NaCl solution, also called normal saline, is isotonic to human blood. Under normal isotonic conditions, water enters and leaves the cell at the same rate, so the cell has no net gain or loss of water over time and its volume remains the same. Blood cells would remain normal or return to normal if used when administrating intravenous medication or to replenish fluids and ions when dehydrated. A cell in a hypertonic extracellular fluid (ECF) loses water as it leaves the cell and enters the ECF. Such water loss would cause blood cells to shrivel, or crenate, and possibly die. A hypotonic extracellular solution would cause blood cells to swell and possibly rupture, or lyse. A catatonic solution does not exist.
Muscle cells require an abundant amount of ATP to function. Therefore, muscle cells have numerous __________. mitochondria ribosomes lysosomes peroxisomes
mitochondria Muscle cells have a higher demand for adenosine triphosphate (ATP) and therefore require more mitochondria. Mitochondria are involved in energy production. The main source of energy for cells is chemical energy, and the most ready supply of chemical energy for our cells is ATP. Peroxisomes oxidize toxic substances and fatty acids and synthesize certain phospholipids. Ribosomes are small, granular, nonmembrane-enclosed organelles with two subunits that synthesize proteins. Lysosomes contain digestive enzymes that break down substances taken into the cell by endocytosis, as well as worn-out organelles.
Most of a cell's DNA is located in its __________. nucleus Golgi apparatus ribosomes lysosomes
nucleus Most of a cell's DNA is located in its nucleus. The nucleus contains most of the cell's deoxyribonucleic acid (DNA) and is the primary location for producing much of the cell's ribonucleic acid (RNA). The DNA and RNA control all of the more specific organelle functions by coding for and creating proteins. Ribosomes are small, granular, nonmembrane-enclosed organelles with two subunits that synthesize proteins. Lysosomes contain digestive enzymes that break down substances taken into the cell by endocytosis, as well as worn-out organelles. The Golgi apparatus, located between the rough endoplasmic reticulum (RER) and the plasma membrane, consists of a group of flattened membranous sacs filled with enzymes and other molecules. Within the Golgi apparatus, proteins and lipids produced by the endoplasmic reticulum (ER) are further modified, sorted, and packaged for export.
Reactions of oxidative catabolism, or aerobic respiration, occur in the mitochondrion only in the presence of _____________. oxygen calcium sodium carbon dioxide
oxygen Reactions of oxidative catabolism, or aerobic respiration, occur in the mitochondrion only in the presence of oxygen. The mitochondrial matrix contains enzymes and proteins that break down organic fuels via a series of reactions known collectively as oxidative catabolism. The reactions of oxidative catabolism can proceed only in the presence of oxygen. For this reason, these reactions are also referred to as aerobic respiration.
Ingesting cellular debris occurs in a process called _________________. phagocytosis pinocytosis exocytosis receptor-mediated endocytosis
phagocytosis During phagocytosis, a type of endocytosis, cells ingest large particles such as bacteria, dead body cells, or parts of cells. In humans only certain cells of the immune system called phagocytes carry out phagocytosis. Phagocytosis requires the energy from adenosine triphosphate (ATP) hydrolysis to fuel several steps of the process, including vesicle formation. During pinocytosis, coated pits in the plasma membrane form vesicles containing dissolved substances from the extracellular fluid (ECF). Pinocytosis produces smaller transport vesicles than phagocytosis. These vesicles bring nutrients and other substances dissolved in the ECF into the cell. Exocytosis is the process by which large substances are packaged into a vesicle that fuses with the plasma membrane and are released from the cell. During receptor-mediated endocytosis, specific ligands bind to their receptors on the plasma membrane and become concentrated in protein-coated pits.
Active transport of solutes across the plasma membrane __________. requires cells to expend energy (ATP) moves solutes with or along their concentration gradients moves solutes through the phospholipid bilayer without the use of integral proteins moves solutes from a higher concentration to a lower concentration
requires cells to expend energy (ATP) Active transport of solutes across the plasma membrane requires cells to expend energy (ATP). This use of energy is necessary because solutes are moved against their concentration gradients during active transport, from a lower concentration to a higher one. Because the concentration gradient does not provide energy to drive the molecules' movement, energy must be supplied from the hydrolysis of ATP. There are two types of active transport: primary active transport and secondary active transport, both of which require carrier proteins called pumps in the plasma membrane. Diffusion is defined as the movement of solute molecules (those that are dissolved) from an area of higher solute concentration to an area of lower solute concentration. The basic force that drives diffusion is called a concentration gradient. Simple diffusion mostly involves nonpolar solutes (such as hydrocarbons and lipids and gases such as O2 and CO2) that pass straight through the phospholipid bilayer without assistance from a membrane protein.
Carbon dioxide is a small molecule that moves through the phospholipid bilayer with its concentration gradient by __________. simple diffusion facilitated diffusion osmosis primary active transport
simple diffusion Carbon dioxide is a small molecule that moves through the phospholipid bilayer with its concentration gradient by simple diffusion. Simple diffusion mostly involves nonpolar solutes (such as hydrocarbons and lipids and gases such as O2 and CO2) that pass straight through the phospholipid bilayer without assistance from a membrane protein. Facilitated diffusion involves charged or polar solutes (such as ions and glucose) that cross the phospholipid bilayer with the help of a membrane protein. Osmosis is a type of passive transport in which water (the solvent) moves across a selectively permeable membrane from a region of lower solute concentration to a region of higher solute concentration until equilibrium is reached. Active transport processes use energy in the form of adenosine triphosphate (ATP) to move a solute against its concentration gradient from a low concentration to a high concentration.
The Na+/K+ pump transports __________ out of the cell for every _______ moved into the cell. three sodium ions; two potassium ions two potassium ions; three sodium ions two sodium ions; two potassium ions three sodium ions; two calcium ions
three sodium ions; two potassium ions The Na+/K+ pump transports three sodium ions out of the cell for every two potassium ions moved into the cell. The Na+ /K+ pump maintains this steep concentration gradient by transporting three sodium ions out of the cell for every two potassium ions it moves into the cell, both against their concentration gradients. The major primary active transport pump in the body is the antiport pump known as the sodium-potassium pump, or Na+/K+ pump (also called the Na+/K+ ATPase). Normally the concentration of sodium ions in the extracellular fluid (ECF) is about 10 times greater than that in the cytosol. The reverse is true for potassium ions; their concentration in the cytosol is about 10 times higher than their concentration in the ECF. It is absolutely critical to maintain the concentration gradients of sodium and potassium ions. These gradients are required for skeletal muscles to contract, the heart to beat, nerves to send impulses, cells to maintain their osmotic balance, and more.
The main component(s) of the cytosol is(are) __________. water organelles sugars the nucleus
water The main component of the cytosol is water. The cytosol, or intracellular fluid (ICF), is the fluid portion of the cytoplasm that makes up about half of the cell's total volume. The ICF consists largely of water with dissolved ions and organic compounds of varying size and concentrations.