bio ch4
Which of the following statements correctly describes a common characteristic of cell walls and the cell extracellular matrix?
Both are external to the plasma membrane. -A common characteristic of cell walls and the cell extracellular matrix is that both are external to the plasma membrane. All cells are bounded by a selective barrier called the plasma membrane. Plants have a cell wall outside the plasma membrane. The wall protects the plant cell, maintains its shape, and prevents excessive uptake of water. Outside an animal cell plasma membrane is the extracellular matrix (ECM). The main ingredients of the ECM are glycoproteins and other carbohydrate-containing molecules secreted by the cells. (Recall that glycoproteins are proteins with covalently bonded carbohydrates.) Plants do not have an extracellular matrix. The most abundant glycoprotein in the ECM of most animal cells is collagen, which forms strong fibers outside the cells. Collagen is an animal protein and is not a component of cell walls. Cell walls are composed of carbohydrates, specifically cellulose, not lipids. The nucleolus is a nonmembranous structure involved in the production of ribosomes. It is not directly involved in the production of the cell wall or extracellular matrix.
Which of the following correctly compares the extracellular matrix (ECM) of animal cells to cell walls of plant cells?
Both the ECM and the plant cell wall are composed of varying mixtures of proteins and carbohydrates. -Both the ECM and the plant cell wall are composed of varying mixtures of proteins and carbohydrates. The extracellular matrix (ECM) of animal cells to cell walls of plant cells are both composed of varying mixtures of proteins and carbohydrates. Although animal cells lack walls akin to those of plant cells, they do have an elaborate extracellular matrix (ECM), which functions in support, adhesion, movement, and regulation. The main ingredients of the ECM are glycoproteins and other carbohydrate-containing molecules secreted by the cells. (Recall that glycoproteins are proteins with covalently bonded carbohydrate, usually short chains of sugars.) The most abundant glycoprotein in the ECM of most animal cells is collagen, which forms strong fibers outside the cells. The cell wall is an extracellular structure of plant cells that distinguishes them from animal cells. Plant cell walls are much thicker than the plasma membrane. Microfibrils made of the polysaccharide cellulose are synthesized by an enzyme called cellulose synthase and secreted to the extracellular space, where they become embedded in a matrix of other polysaccharides and proteins. This combination of materials, strong fibers in a "ground substance" (matrix), is the same basic architectural design found in steel-reinforced concrete and in fiberglass.
Which of the following structures is found in animal cells but not plant cells?
Centrioles -Centrioles are structures that are found in animal cells but not plant cells. Most animal cells have a centrosome, a region near the nucleus where the cell's microtubules are initiated, within which is a pair of centrioles. Before an animal cell divides, the centrioles replicate. Although centrosomes with centrioles may help organize microtubule assembly in animal cells, they are not essential for this function in all eukaryotes; fungi and almost all plant cells lack centrosomes with centrioles but have well-organized microtubules. Apparently, other microtubule organizing centers play the role of centrosomes in these cells. All cells are enclosed by a plasma membrane. The Golgi apparatus is an organelle active in synthesis, modification, sorting, and secretion of cell products possessed by eukaryotic cells. Along with the Golgi apparatus, the rough endoplasmic reticulum is part of the endomembrane system of animals, plants, and other eukaryotes. The mitochondria of animals, plants, and other eukaryotes are sites of cellular respiration where most ATP is generated.
Which of the following is/are possible site(s) of protein synthesis in a typical eukaryotic cell?
Cytoplasm, rough endoplasmic reticulum, and mitochondria -In a typical eukaryotic cell, the possible sites of protein synthesis are cytoplasm, rough endoplasmic reticulum, and mitochondria. Ribosomes are tiny complexes that make proteins according to instructions from genes. Ribosomes are present in the cytoplasm, on the rough ER, and in mitochondria (and chloroplasts); therefore, all of these are possible sites of protein synthesis. Endoplasmic reticulum (ER) is a membranous system of interconnected tubules and flattened sacs called cisternae. Rough ER is studded on its outer surface with ribosomes. Ribosomes build proteins in two cytoplasmic locales. At any given time, free ribosomes are suspended in the cytosol, while bound ribosomes are attached to the outside of the endoplasmic reticulum or nuclear envelope. In addition, free cytoplasmic ribosomes are most likely to be involved in the process of producing proteins for a chloroplast or mitochondrion. Like prokaryotes, mitochondria and chloroplasts contain ribosomes as well as circular DNA molecules attached to their inner membranes. The DNA in these organelles programs the synthesis of some of their own proteins, which are made on the ribosomes inside the organelles.
What is the most likely pathway taken by a newly synthesized protein that will be secreted by a cell?
ER—Golgi—vesicles that fuse with plasma membrane -The most likely pathway taken by a newly synthesized protein that will be secreted by a cell is ER, Golgi apparatus, then vesicles that fuse with the plasma membrane. Many of the different membranes of the eukaryotic cell are part of the endomembrane system, which includes the nuclear envelope, the endoplasmic reticulum, the Golgi apparatus, lysosomes, various kinds of vesicles and vacuoles, and the plasma membrane. This system carries out a variety of tasks in the cell, including synthesis of proteins, transport of proteins into membranes and organelles or out of the cell, metabolism and movement of lipids, and detoxification of poisons. The membranes of this system are related either through direct physical continuity or by the transfer of membrane segments as tiny vesicles (sacs made of membrane). Endoplasmic reticulum (ER) is a membranous system of interconnected tubules and flattened sacs called cisternae; the ER is also continuous with the nuclear envelope. The membrane of the ER encloses a continuous compartment called the ER lumen (or cisternal space). Transport vesicles bud off from a region of the rough ER called transitional ER and travel to the Golgi apparatus and other destinations. After leaving the ER, many transport vesicles travel to the Golgi apparatus. Think of the Golgi as a warehouse for receiving, sorting, shipping, and even some manufacturing. Here, products of the ER, such as proteins, are modified and stored and then sent to other destinations. A Golgi stack has a distinct structural directionality, with the membranes of cisternae on opposite sides of the stack differing in thickness and molecular composition. The two sides of a Golgi stack are referred to as the cis face and the trans face; these act, respectively, as the receiving and shipping departments of the Golgi apparatus. The cis face is usually located near the ER. Transport vesicles move material from the ER to the Golgi apparatus. A vesicle that buds from the ER can add its membrane and the contents of its lumen to the cis face by fusing with a Golgi membrane. The trans face gives rise to vesicles that pinch off and travel to other sites or fuse with the plasma membrane to release their cargo outside the cell.
In terms of cellular function, what is the most important difference between prokaryotic and eukaryotic cells?
Eukaryotic cells possess specialized membrane-bounded organelles. -In terms of cellular function, the most important difference between prokaryotic and eukaryotic cells is that eukaryotic cells possess specialized membrane-bounded organelles. A major difference between prokaryotic and eukaryotic cells is the location of their DNA. In a eukaryotic cell, most of the DNA is in an organelle called the nucleus, which is bounded by a double membrane. In a prokaryotic cell, the DNA is concentrated in a region that is not membrane-enclosed called the nucleoid. In addition, within the cytoplasm of a eukaryotic cell, suspended in cytosol, are a variety of other organelles of specialized form and function including mitochondria, chloroplasts, endoplasmic reticulum, and Golgi apparatus. Eukaryotic cells are generally much larger than prokaryotic cells. All cells have ribosomes, tiny complexes that make proteins according to instructions from the genes. Prokaryotic cells preceded eukaryotic cells. Prokaryotes, including bacteria, are extremely abundant and widespread.
A researcher made an interesting observation about a protein made by the rough endoplasmic reticulum (ER) and eventually found in a cell's plasma membrane. The protein in the plasma membrane was actually slightly different from the protein made in the ER. The protein was probably altered in the .
Golgi apparatus -A researcher made an interesting observation about a protein made by the rough endoplasmic reticulum (ER) and eventually found in a cell's plasma membrane. The protein in the plasma membrane was actually slightly different from the protein made in the ER. The protein was probably altered in the Golgi apparatus. After leaving the ER, many transport vesicles travel to the Golgi apparatus. We can think of the Golgi as a warehouse for receiving, sorting, shipping, and even some manufacturing. Here, products of the ER, such as proteins, are modified and stored and then sent to other destinations such as the plasma membrane. Not surprisingly, the Golgi apparatus is especially extensive in cells specialized for secretion.
A researcher wants to film the movement of chromosomes during cell division. Which type of microscope should she choose, and why is it the best choice?
Light microscope because the specimen is alive -A researcher wants to film the movement of chromosomes during cell division. She should choose a light microscope because the specimen is alive. If a researcher wants to film the movement of chromosomes during cell division, then the type of microscope she should choose is the light microscope because the viewed specimen can be alive. A disadvantage of electron microscopy is that the methods used to prepare the specimen kill the cells. In the past several decades, light microscopy has been revitalized by major technical advances. In addition, both confocal and deconvolution microscopy have sharpened images of three-dimensional tissues and cells. Finally, over the past 10 years, a group of new techniques and labeling molecules have allowed researchers to "break" the resolution barrier and distinguish subcellular structures as small as 10 to 20 nm across. As this "super-resolution microscopy" becomes more widespread, the images we'll see of living cells may well be as awe-inspiring to us as van Leeuwenhoek's were to Robert Hooke 350 years ago.
Which of the following categories best describes the function of the rough endoplasmic reticulum?
Manufacturing -The function of the rough endoplasmic reticulum is best described as manufacturing. Endoplasmic reticulum (ER) is a membranous system of interconnected tubules and flattened sacs called cisternae. The membrane of the ER encloses a continuous compartment called the ER lumen (or cisternal space). There are two distinct, though connected, regions of the ER that differ in structure and function: rough ER and smooth ER. Smooth ER is so named because its outer surface lacks ribosomes. Rough ER is studded on its outer surface with ribosomes. Ribosomes assemble proteins. Enzymes of the smooth ER are important in the synthesis of lipids, including oils, steroids, and new membrane phospholipids. Among the steroids produced by the smooth ER in animal cells are the sex hormones of vertebrates and the various steroid hormones secreted by the adrenal glands. Lysosomes are digestive organelles where macromolecules are hydrolyzed. Mitochondria are the organelles of energy processing where cellular respiration occurs and most ATP is generated. The cytoskeleton provides structural support to the cell. In eukaryotic cells, the nucleus contains most of the DNA, the molecule of information storage.
Which structure is common to plant and animal cells?
Mitochondrion -The mitochondrion is a structure common to plant and animal cells. The mitochondria are membrane-bounded organelles within which cellular respiration occurs and most ATP is generated. Lysosomes, centrosomes with centrioles, and flagella are present in animal cells but not plant cells. In contrast, chloroplasts, central vacuoles, cell walls, and plasmodesmata are present in plant cells but not animal cells.
Cilia and flagella move due to the interaction of the cytoskeleton with which of the following?
Motor proteins -Cilia and flagella move due to the interaction of the cytoskeleton with motor proteins. Each motile cilium or flagellum has a group of microtubules sheathed in an extension of the plasma membrane. Nine doublets of microtubules are arranged in a ring with two single microtubules in its center. This arrangement, referred to as the "9 + 2" pattern, is found in nearly all eukaryotic flagella and motile cilia. Flexible cross-linking proteins, evenly spaced along the length of the cilium or flagellum, connect the outer doublets to each other and to the two central microtubules. Each outer doublet also has pairs of protruding proteins spaced along its length and reaching toward the neighboring doublet; these are large motor proteins called dyneins, each composed of several polypeptides. Dyneins are responsible for the bending movements of the organelle. A dynein molecule performs a complex cycle of movements caused by changes in the shape of the protein, with ATP providing the energy for these changes. Actin bears tension (pulling forces) as a component of the cytoskeleton. Tubulin is the globular protein of which microtubules are constructed. Mitochondria are organelles also containing DNA that function in cellular respiration. Pseudopodia are thin cell extensions used in cell locomotion.
Which type of cell is likely to have the most mitochondria?
Muscle cells in the legs of a marathon runner -Muscle cells in the legs of a marathon runner are likely to have the most mitochondria. In eukaryotic cells, mitochondria and chloroplasts are the organelles that convert energy to forms that cells can use for work. Mitochondria (singular: mitochondrion) are the sites of cellular respiration, the metabolic process that uses oxygen to generate ATP by extracting energy from sugars, fats, and other fuels. Mitochondria are found in nearly all eukaryotic cells, including those of plants, animals, fungi, and most protists. Some cells have a single large mitochondrion, but more often a cell has hundreds or even thousands of mitochondria; the number correlates with the cell's level of metabolic activity. For example, cells that move or contract have proportionally more mitochondria per volume than less active cells.
Which of the following features do prokaryotes and eukaryotes have in common?
Ribosomes, plasma membrane, and cytoplasm -Ribosomes, plasma membrane, and cytoplasm are common features in prokaryotes and eukaryotes. All cells share certain basic features. They are all bounded by a selective barrier called the plasma membrane. Inside all cells is a semifluid, jellylike substance called cytosol in which subcellular components are suspended. All cells contain chromosomes, which carry genes in the form of DNA. And all cells have ribosomes, tiny complexes that make proteins according to instructions from the genes. A major difference between prokaryotic and eukaryotic cells is the location of their DNA. In a eukaryotic cell, most of the DNA is in an organelle called the nucleus, which is bounded by a double membrane. In a prokaryotic cell, the DNA is concentrated in a region that is not membrane-enclosed called the nucleoid. Within the cytoplasm of a eukaryotic cell, suspended in cytosol, are a variety of organelles of specialized form and function including the mitochondria in which cellular respiration occurs. These membrane-bounded structures are absent in prokaryotic cells.
What is the functional connection between the nucleolus, nuclear pores, and the nuclear membrane?
Subunits of ribosomes are assembled in the nucleolus and pass through the nuclear membrane via the nuclear pores. -The functional connection between the nucleolus, nuclear pores, and the nuclear membrane is that subunits of ribosomes are assembled in the nucleolus and pass through the nuclear membrane via the nuclear pores. The nuclear envelope (or nuclear membrane) encloses the nucleus, separating its contents from the cytoplasm. The nuclear envelope is a double membrane. The two membranes are each a lipid bilayer with associated proteins. A prominent structure within the nondividing nucleus is the nucleolus (plural: nucleoli). Here a type of RNA called ribosomal RNA (rRNA) is synthesized from instructions in the DNA. Also in the nucleolus, proteins imported from the cytoplasm are assembled with rRNA into large and small subunits of ribosomes. These subunits then exit the nucleus through the nuclear pores to the cytoplasm, where a large and a small subunit can assemble into a ribosome. At the lip of each pore, the inner and outer membranes of the nuclear envelope are continuous. An intricate protein structure called a pore complex lines each pore and plays an important role in the cell by regulating the entry and exit of proteins and RNAs as well as large complexes of macromolecules.
Your intestine is lined with individual cells that absorb nutrients. No fluids leak between these cells from the interior of the intestine. Why?
The intestinal cells are bound together by tight junctions. -Your intestine is lined with individual cells that absorb nutrients. No fluids leak between these cells from the interior of the intestine because the intestinal cells are bound together by tight junctions. At tight junctions, the plasma membranes of neighboring cells are very tightly pressed against each other, bound together by specific proteins. Forming continuous seals around the cells, tight junctions prevent leakage of extracellular fluid across a layer of epithelial cells. For example, tight junctions between skin cells make us watertight. Due to tight junctions, multiple adjacent cells can act as a barrier similar to a single large cell. Gap junctions (also called communicating junctions) provide cytoplasmic channels from one cell to an adjacent cell and in this way are similar in their function to the plasmodesmata in plants. Gap junctions consist of membrane proteins that surround a pore through which ions, sugars, amino acids, and other small molecules may pass. Desmosomes (also called anchoring junctions) function like rivets, fastening cells together into strong sheets. Intermediate filaments made of sturdy keratin proteins anchor desmosomes in the cytoplasm. Desmosomes attach muscle cells to each other in a muscle. The extracellular matrix spans the outside of animal cells and is composed of glycoproteins and other carbohydrate-containing molecules secreted by the cells.
Dye injected into a plant cell might be able to enter an adjacent cell through
plasmodesmata -Dye injected into a plant cell might be able to enter an adjacent cell through plasmodesmata. Plant cell walls are usually perforated by channels between adjacent cells called plasmodesmata. The cytoplasm of one plant cell is continuous with the cytoplasm of its neighbors via plasmodesmata, which are cytoplasmic channels through the cell walls. The cell walls themselves would be barriers to transport between cells. Gap junctions are cytoplasmic connections between adjacent animal cells. Forming continuous seals around animal cells, tight junctions establish a barrier that prevents leakage of extracellular fluid across a layer of epithelial cells. Microtubules are hollow but are components of the cytoskeleton rather than connections between cells.
Dye injected into a plant cell might be able to enter an adjacent cell through .
plasmodesmata -Dye injected into a plant cell might be able to enter an adjacent cell through plasmodesmata. Plant cell walls are usually perforated by channels between adjacent cells called plasmodesmata. The cytoplasm of one plant cell is continuous with the cytoplasm of its neighbors via plasmodesmata, which are cytoplasmic channels through the cell walls. The cell walls themselves would be barriers to transport between cells. Gap junctions are cytoplasmic connections between adjacent animal cells. Forming continuous seals around animal cells, tight junctions establish a barrier that prevents leakage of extracellular fluid across a layer of epithelial cells. Microtubules are hollow but are components of the cytoskeleton rather than connections between cells.
You would expect a cell with an extensive Golgi apparatus to
secrete a lot of protein -You would expect a cell with an extensive Golgi apparatus to secrete a lot of protein. After leaving the ER, many transport vesicles travel to the Golgi apparatus. We can think of the Golgi as a warehouse for receiving, sorting, shipping, and even some manufacturing. Here, products of the ER, such as proteins, are modified and stored and then sent to other destinations. Not surprisingly, the Golgi apparatus is especially extensive in cells specialized for secretion.
Cell fractionation
separates cells into their component parts -Cell fractionation separates cells into their component parts. Cell fractionation is commonly used to isolate (fractionate) cell components based on size and density. Cells are homogenized in a blender to break them up. The resulting mixture (homogenate) is centrifuged. The supernatant (liquid) is poured into another tube and centrifuged at a higher speed for a longer time. This process is repeated several times. This "differential centrifugation" results in a series of pellets, each containing different cell components. This method is commonly used in cell biology. Cell fractionation does not require the use of strong acids or other solutions that could chemically alter cell structure. Scanning electron microscopes reveal many subcellular structures that are impossible to resolve with light microscopes, but the methods used to prepare specimens kill the cells.
