Chapter 3 - Cells: The Living Units
What is lipid bilayer made up of?
-75% phospholipids, which consist of two parts: phosphate heads and fatty acid tails -Phosphate heads: are polar (charged), so are hydrophilic (water-loving) -Fatty acid tails: are nonpolar (no charge), so are hydrophobic (water-hating) -5% glycolipids (lipids with sugar groups on outer membrane surface); these are carbs with lipids attached -20% cholesterol (increases membrane stability)
Receptors for signal transduction
-A membrane protein exposed to the outside of the cell may have a binding site that fits the shape of a specific chemical messenger, such as a hormone -When bound, the chemical messenger may cause a change in shape in the protein that initiates a chain of chemical reactions in the cell
Enzymatic activity
-A membrane protein may be an enzyme with its active site exposed to substances in the adjacent solution -A team of several enzymes in a membrane may catalyze sequential steps of a metabolic pathway as indicated (left to right) here
Plasma Membrane
-Acts as an active barrier separating intracellular fluid (ICF) from extracellular fluid (ECF) -Controls what enters and what leaves the cell -Also known as the "cell membrane"
Flagella
-Are longer extensions that propel the whole cell -Ex: tail of sperm (only one!)
Cilia
-Are whiplike, motile extensions on surfaces of certain cells (such as respiratory cells) -Thousands of cilia work together in sweeping motion to move substances (example: mucus) across cell surfaces in one direction
Sodium-potassium pump
-Basically is an enzyme, called Na+-K+ ATPase -Pumps 3 Na+ out of cell and 2 K+ back into cell! (how to remember: potassium is high in the cell and sodium has the inside of the cell more negative) -Located in all plasma membranes, but especially active in excitable cells (nerves and muscles) -Maintains electrochemical gradients, which involve both concentration and electrical charge of ions
Cytokinesis
-Begins during late anaphase and continues through mitosis (overlaps anaphase and telophase) -Two daughter cells are pinched apart (are genetically identical/clones) -Separation of cytoplasm and organelles
Mitochondria
-Called the "power plant" of cells because they produce most of cell's energy molecules (ATP) via aerobic (oxygen-requiring) cellular respiration -Contain their own DNA, RNA, and ribosomes
Transfer RNA (tRNAs)
-Carrier of amino acids -Anticodon of tRNA will complementary base-pair with codon of mRNA at ribosome, adding its specific amino acid to growing polypeptide chain (process is referred to as translation)
Rough Endoplasmic Reticulum (Rough ER)
-External surface appears rough because it is studded with attached ribosomes -Site of synthesis of proteins that will be secreted from cell! (proteins are modified or changed) -Site of synthesis of many plasma membrane proteins and phospholipids -Proteins enter cisterns, gets enclosed in a vesicle and sent to Golgi apparatus for further processing
Hypertonic solution
-Has higher osmolarity than inside cell, so water flows out of cell, resulting in cell shrinking (solution has more solute than the cell) -Shrinking is referred to as crenation (also used for shrivelling) -Hyper = more
Hypotonic solution
-Has lower osmolarity than inside cell, so water flows into cell, resulting in cell swelling (in swelling, the solution has less solute than the cell) -Can lead to cell bursting, referred to as lysing -Hypo = less
Isotonic solution
-Has same osmolarity as inside the cell, so volume remains unchanged (no net movement of H2O) -Iso = the same
What are the two types of membrane proteins?
-Integral proteins and peripheral proteins -Integral proteins function as transport proteins (channels and carriers), enzymes, or receptors -Peripheral proteins function as enzymes, motor proteins for shape change during cell division and muscle contraction, and cell-to-cell connections
Channel-mediated facilitated diffusion
-Leakage channels (always open) -Gated channels (controlled by chemical or electrical signals); need a trigger to open (ex. molecule bonded through receptor) -Ions pass through channels, but carriers!
Intercellular joining
-Membrane proteins of adjacent cells may be hooked together in various kinds of intercellular junctions -Some membrane proteins (cell adhesion molecules or CAMs) of this group provide temporary binding sites that guide cell migration and other cell-to-cell interactions
Translation
-mRNA decoded to assemble polypeptides -The step of protein synthesis where the language of nucleic acids (base sequence) is translated into the language of proteins (amino acid sequence) -Process involves: mRNA, tRNA, and rRNA
16. What is the function of the organelle indicated by B? (HW #3 Question)
modification and packaging of proteins -This function is handled by the Golgi apparatus within the endomembrane system; it functions in the sorting and modifying of membrane-bound proteins being transported to various cellular locations.
Prophase
Can be broken into two parts: Early prophase and Late Prophase
Selective Permeability
Determines manner in which substances enter or exit the cell
10. Which of the following statements is true? (HW #3 Question)
During exocytosis, substances from inside the cell are moved outside. -Vesicular transport processes that eject substances from the cell interior into the extracellular fluid are called exocytosis. Exocytosis is a form of active transport; thus, it requires energy, usually in the form of ATP.
Active processes
Energy (ATP) required to cross membrane
11. Which of the following processes allows cells to concentrate specific material that is present only in very small amounts in the extracellular fluid? (HW #3 Question)
receptor-mediated endocytosis -Receptor-mediated endocytosis is the main mechanism for the specific endocytosis and transcytosis of most macromolecules by body cells, and it is exquisitely selective. The mechanism also allows cells to concentrate material that is present only in very small amounts in the extracellular fluid.
Primary Active Transport
Required energy comes directly from ATP hydrolysis
Secondary Active Transport
Required energy is obtained indirectly from ionic gradients created by primary active transport
17. What can we infer if we see a large number of mitochondria in a cell? (HW #3 Question)
The cell has a great metabolic demand. -Mitochondria are threadlike or lozenge-shaped membranous organelles. In living cells they squirm, elongate, and change shape almost continuously. They are the power plants of a cell, providing most of its ATP supply.
22. Drag the appropriate labels to their respective targets. Label processes on the right in PURPLE, and all other components on the left. (HW #3 Question)
Transcription, RNA processing, Translation, DNA, Pre-mRNA, mRNA, Ribosome, and Polypeptide
13. In their resting state, all body cells exhibit a resting membrane potential; therefore, all cells are polarized. (HW #3 Question)
True -All cells have a resting membrane potential (RMP), such that the inside (interior surface) of the cell membrane has a net negative charge while the outside (external surface) of the membrane has a net positive charge. Given the different (opposite) charges on either side of the cell membrane, the cell is considered to be polarized. This RMP, which results from separation of charged particles (ions) across the cell membrane, can be measured in millivolts (typically ranging from −50 to −90 mV depending on the cell type).
14. What is a membrane potential? (HW #3 Question)
a voltage or electrical charge across the plasma membrane -The membrane potential is the electrical potential energy (measured in millivolts) resulting from the separation of oppositely charged ions across the plasma membrane. At rest, membrane potentials are typically negative, ranging from − 50 to minus 100 mV, with more anions (than cations) concentrated along the internal surface of the membrane, and more cations (than anions) concentrated along the external surface.
6. Ions are transported across plasma membranes using __________, which requires __________. (HW #3 Question)
channel-mediated facilitated diffusion; kinetic energy -Ions travel through aqueous channels down their concentration gradients. Kinetic energy drives this process.
3. Which of the following names the three main parts of a human cell? (HW #3 Question)
cytoplasm, plasma membrane, and nucleus -Human cells have three main parts: the plasma membrane, the cytoplasm, and the nucleus.
4. What is the force driving all of these transport mechanisms?
diffusion down a concentration gradient -Transport by diffusion of a molecule down its concentration gradient is a spontaneous process that requires no energy input.
21. What process allows for the production of molecule B from a template consisting of molecule A? (HW #3 Question)
transcription -Transcription is the synthesis of RNA using DNA as a template.
Transport
- A protein (left) that spans the membrane may provide a hydrophilic channel across the membrane that is selective for a particular solute -Some transport proteins (right) hydrolyze ATP as an energy source to actively pump substances across the membrane
M (mitotic) phase
-Cell division/cell divides into two -Consists of 2 distinct events: mitosis and cytokinesis -Mitosis is the division of nucleus, in which the duplicated DNA is distributed to new daughter cells (genetically identical to each other; there are 2) -Four stages of mitosis ensure each cell receives a full copy of replicated DNA: Prophase, Metaphase, Anaphase, and Telophase (PMAT) -Where cells are replaced and division of DNA/nucleolus occurs -The human body has 46 chromosomes, and there are no longer only 23 because each have a replicated cell
Interphase
-Cell grows and carries on its usual activities -Nuclear material is in uncondensed chromatin state (is unwound) -Consists of subphases, which include the process of DNA replication -Most life is here; it's doing its normal function
Metaphase
-Centromeres of chromosomes are precisely aligned at cell's equator -The imaginary plane midway between poles is called metaphase plate
Anaphase
-Centromeres of chromosomes split simultaneously—each sister chromatid now becomes a separate chromosome (either go to the left or right) -Chromosomes are pulled toward their respective poles (one chromosome of each original pair goes to opposite poles) -HOW TO REMEMBER: The movie Frozen, where Anna and Elsa were sisters but went in different directions
Facilitated Diffusion
-Certain molecules (ex. glucose, amino acids, and ions) are transported passively down their concentration gradient -Are transported by: carrier-mediated facilitated diffusion (substances bind to protein carriers) and channel-mediated facilitated diffusion (substances move through water-filled channels); no binding -Are large, polar, and hydrophilic (water-loving)
Early Prophase
-Chromosomes become visible, each with two chromatids joined at centromere -Centrosomes separate and migrate toward opposite poles (also replicate during interphase) Mitotic spindles and asters form
Structure of Plasma Membrane
-Consists of membrane lipids that form a flexible lipid bilayer -Specialized membrane proteins float through this fluid membrane, resulting in constantly changing patterns -Surface sugars form glycocalyx -Membrane structures help to hold cells together through cell junctions
Transcription
-DNA information coded in mRNA -The process of transferring code held in DNA gene base sequence to complementary base sequence of mRNA -A part of protein synthesis
S (synthetic)
-DNA replication occurs -is one of the three subphases of interphase alongside G1 (gap 1) and G2 (gap 2); these locations are where growth occurs
Desmosomes
-Desmosomes allow "give" between cells, reducing the possibility of tearing under tension; still holds cells together -Allows fluids and most molecules to move in between cells
Osmosis
-Diffusion of a solvent, such as water, across a selectively permeable membrane -Water diffuses through plasma membranes, through lipid bilayer (even though water is polar!) and specific water channels called aquaporins (AQPs), which is how H2O is moved across the membrane faster -Water moves by osmosis from areas of low solute (high water) concentration to high areas of solute (low water) concentration -Water is attracted to solute!
What are the two types of passive transport?
-Diffusion: Simple diffusion, carrier- and channel-mediated facilitated diffusion, and osmosis -Filtration: Type of transport that usually occurs across capillary walls (ex. fluid leaving blood vessels)
Telophase
-Each set of chromosomes (at opposite ends of cell) uncoils to form chromatin -New nuclear membranes form around each chromatin mass (was previously removed in prophase) -Nucleoli reappear (will create RNA) -Spindle disappears (have already done their job in prophase)
Resting Membrane Potential (RMP)
-Electrical potential energy produced by separation of oppositely charged particles across plasma membrane in all cells (physically separating internal and external environment/separates charge) -Voltage = difference in electrical charge between two points (ex. batteries and their volts) -Cells that have a charge are said to be polarized -Membrane voltages range from -50 to -100 mV in different cells (negative sign (-) indicates inside of cell is more negative relative to outside of cell); RMP is a negative potential
Attachment to the cytoskeleton and extracellular matrix
-Elements of the cytoskeleton (cell's internal supports) and the extracellular matrix (fibers and other substances outside the cell) may anchor to membrane proteins, which helps maintain cell shape and fix the location of certain membrane proteins -Others play a role in cell movement or bind adjacent cells together
Smooth Endoplasmic Reticulum (Smooth ER)
-Network of looped tubules continuous with rough ER -Doesn't have ribosomes -Enzymes found in its plasma membrane (integral proteins) function in: Lipid metabolism, detoxification of certain chemicals, and storage and release of calcium
Simple Diffusion
-Nonpolar lipid-soluble (hydrophobic) substances diffuse directly through phospholipid bilayer -Are nonpolar, small, and hydrophobic (water-hating) -Will slip through the layers with the help of anything else (going down concentration gradient) -Ex: oxygen, carbon dioxide, fat-soluble vitamins
Late Prophase
-Nuclear envelope breaks up -Microtubules attach to kinetochore, which holds DNA together, of centromeres and pull chromosomes to center (equator) of cell -Remaining nonkinetochore microtubules push against each other, causing poles of cell to move farther apart (cells get longer)
Tight Junctions
-Prevent fluids and most molecules from moving in between cells -Act as protective barrier in our intestines -Shown in image A
Lysosomes
-Spherical membranous bags containing digestive enzymes (acid hydrolases) -Digest ingested bacteria, viruses, and toxins
Ribosomal RNA (rRNA)
-Structural component of ribosomes, the organelle where protein synthesis occurs -Along with tRNA, helps to translate message from mRNA into polypeptide
Osmotic pressure
-Tendency of water to move into cell by osmosis -The more solutes inside a cell, the higher the osmotic pressure (created attraction/pull for fluid to go into the cell)
Messenger RNA (mRNA)
-The code from the DNA template strand is copied with complementary base pairs, resulting in a strand of mRNA (process is referred to as transcription- the process of making an RNA copy, with original copy of DNA, of a gene sequence) -Only one single strand of DNA is copied
Diffusion
-The tendency of molecules or ions to move from an area of high concentration to an area of lower concentration (the difference is called a concentration gradient); energy is not required -Speed of diffusion is influenced by size (smaller = faster) of molecule and temperature (warmer = faster) -Image shows dye pellet --> diffusion occuring --> dye evenly distributed
Gap Junctions
-Transmembrane proteins (connexons) form tunnels that allow small molecules (charged and nutrients) to pass from cell to cell -Used to spread ions, simple sugars, or other small molecules between cells -Allows electrical signals to be passed quickly from one cell to next cell (used in cardiac and smooth muscle cells); all cells share signals that allow them to contract together -Shown in image C
Human cells have three basic parts:
1. Plasma membrane- flexible outer boundary 2. Cytoplasm- intracellular fluid containing organelles 3. Nucleus- DNA containing control center
What tasks do membrane proteins perform?
1. Transport 2. Receptors for signal transduction 3. Attachment to the cytoskeleton and extracellular matrix 4. Enzymatic activity 5. Intercellular joining 6. Cell-cell recognition
Tonicity
Ability of a solution to change the shape or tone of cells by altering the cells' internal water volume (based on where the water is going); a force of osmotic pressure
12. What is the difference between active and passive transport across the plasma membrane? (HW #3 Question)
Active transport is ATP dependent, whereas passive transport uses only the kinetic energy of the particles for movement across the plasma membrane. -In active transport, the cell provides the metabolic energy (ATP) needed to move substances across the plasma membrane (against their concentration gradient). In passive transport, substances cross the plasma membrane (down their concentration gradient) using kinetic energy, without any energy input from the cell.
Communication
Allows cell-to-cell recognition (ex. of egg by sperm) and interaction
Electrochemical Gradient
Generates and helps to maintain the electrochemical gradient required for muscle and neuron function
5. Drag the appropriate labels to their respective targets. (HW #3 Question) (types of solutions)
Isotonic, Hypertonic, and Hypotonic solutions
20. What must happen before a body cell can begin mitotic cell division? (HW #3 Question)
Its DNA must be replicated exactly so that identical copies of the cell's genes can be passed on to each of its offspring. -Before a body cell begins mitosis, it must replicate its DNA so that each daughter cell will have the same DNA as the parent cell.
Functions of the Plasma Membrane
Mechanical barrier, selective permeability, electrochemical gradient, communication, and cell signaling
Peroxisomes
Membranous sacs (vesicles) containing powerful detoxifying substances that neutralize toxins; also break these toxins apart
Golgi Apparatus
Modifies, concentrates, and packages proteins and lipids received from rough ER
7. Assume that Na+ is being transported across a membrane via facilitated diffusion. Which of the following conditions would allow for the most transport of Na+ across that membrane? (HW #3 Question)
Na+ diffusing toward the side of the membrane with Cl− and 50% less Na+ -A larger concentration gradient will provide greater kinetic energy to drive diffusion and Na+ will be electrically attracted to the Cl−; this will create a large electrochemical gradient.
Passive processes
No energy required to cross membrane
Ribosomes
Nonmembranous organelles that are site of protein synthesis (either freely floating or rough)
2. Drag the appropriate labels to their respective targets (second half of eukaryotic cell). (HW #3 Question)
Nuclear envelope, Plasma membrane, Chromatin, Nucleolus, Cytosol, Microtubule, and Intermediate filaments
1. Drag the appropriate labels to their respective targets (first half a eukaryotic cell). (HW #3 Question)
Nucleus, Rough endoplasmic reticulum, Ribosome, Golgi apparatus, Smooth endoplasmic reticulum, Lysosome, Mitochondria, and Centrioles
Cell Signaling
Plasma membrane proteins interact with specific chemical messengers and relay messages to the cell interior
Hydrostatic pressure
Pressure of water inside cell pushing on membrane
Mechanical Barrier
Separates two of the body's fluid compartments
Cell-cell recognition
Some glycoproteins (proteins bonded to short chains of sugars which help to make up the glycocalyx) serve as identification tags that are specifically recognized by other cells
18. Which organelle is responsible for synthesizing proteins? (HW #3 Question)
ribosomes -Proteins are synthesized at ribosomes. Free ribosomes float freely in the cytoplasm and produce soluble proteins that function in the cytosol, as well as those imported into mitochondria and some other organelles. Fixed ribosomes, which stud the rough endoplasmic reticulum, synthesize proteins destined either for incorporation into the cell membrane or lysosomes, or for export from the cell.
9. How would a small, nonpolar molecule likely diffuse across a cell membrane? (HW #3 Question)
simple diffusion -Nonpolar (or lipid-soluble) molecules dissolve into the phospholipid regions of the cell membrane and will pass with no additional protein transporters required.
19. Which of the following organelles is correctly paired with its function? (HW #3 Question)
smooth endoplasmic reticulum: metabolism of lipids -The smooth ER also plays a role in synthesizing steroid hormones, absorbing and transporting fats, detoxifying toxins, and breaking down glycogen.
15. What major function occurs on the specific membranes indicated by A? (HW #3 Question)
synthesis of proteins -Structure A is the rough endoplasmic reticulum (ER). The figure illustrates how proteins are synthesized on ribosomes bound to the rough ER before being modified and secreted or packaged.
23. __________ is a molecule that brings amino acids to the ribosome during translation. (HW #3 Question)
t-RNA -Transfer RNA (tRNA) are small, roughly L-shaped molecules that ferry amino acids to the ribosomes. There they decode mRNA's message for the amino acid sequence of the polypeptide to be built, a process called translation.
8. In a patient with severely burned skin, the damaged cells that have lost fluid cannot be properly rehydrated because _________. (HW #3 Question)
the disruption of selective permeability allows water molecules that enter these damaged cells to also leave the cytoplasm -Skin is an organ made up of tissues, and tissues are made up of cells. Selective permeability requires an intact cell membrane.
