Chapter 4 - Cell Membranes and Signalling Flashcards
1
Q
What is the fluid mosaic model?
A
Model proposing that the membrane consists of a fluid phospholipid bilayer in which proteins are embedded and float freely.
2
Q
What is the freeze-fracture technique?
A
Technique in which experimenters freeze a block of cells rapidly and then fracture the block to split the lipid bilayer and expose the hydrophobic membrane interior.
3
Q
What are fats?
A
Neutral lipid that is semisolid at biological temperatures.
4
Q
What are phospholipids?
A
A phosphate-containing lipid.
5
Q
What is a hydrocarbon?
A
Molecule consisting of carbon linked only to hydrogen atoms.
6
Q
What are alcohols?
A
A molecule of the form R—OH in which R is a chain of one or more carbon atoms, each of which is linked to hydrogen atoms.
7
Q
What is amphipathic?
A
Containing a region that is hydrophobic and a region that is hydrophilic.
8
Q
What is unsaturated?
A
Fatty acid with one or more double bonds linking the carbons.
9
Q
What is micelle?
A
A sphere composed of a single layer of lipid molecules.
10
Q
What are saturated fatty acids?
A
Fatty acid with only single bonds linking the carbon atoms.
11
Q
What are sterols?
A
Steroid with a single polar —OH group linked to one end of the ring framework and a complex, nonpolar hydrocarbon chain at the other end.
12
Q
What is cholesterol?
A
The predominant sterol of animal cell membranes.
13
Q
What is Signal transduction?
A
The series of events by which a signal molecule released from a controlling cell causes a response (affects the function) of target cells with receptors for the signal. Target cells process the signal in the three sequential steps of reception, transduction, and response.
14
Q
What are integral membrane proteins?
A
Protein embedded in a phospholipid bilayer.
15
Q
What is a secondary structure?
A
Regions of alpha helix, beta strand, or random coil in a polypeptide chain.
16
Q
What is a primary structure?
A
The sequence of amino acids in a protein.
17
Q
What are peripheral membrane proteins?
A
Protein held to membrane surfaces by noncovalent bonds formed with the polar parts of integral membrane proteins or membrane lipids.
18
Q
What are ionic bonds?
A
Bond that results from electrical attractions between atoms that have lost or gained electrons.
19
Q
What is Passive transport?
A
The transport of substances across cell membranes without expenditure of energy, as in diffusion.
20
Q
What is diffusion?
A
The net movement of ions or molecules from a region of higher concentration to a region of lower concentration.
21
Q
What is a solute?
A
The molecules of a substance dissolved in water.
22
Q
what is a concentration gradient?
A
The concentration difference that drives diffusion.
23
Q
What is simple diffusion?
A
Mechanism by which certain small substances diffuse through the lipid part of a biological membrane.
24
Q
What is facilitated diffusion?
A
Mechanism by which polar and charged molecules diffuse across membranes with the help of transport proteins.
25
What are channel proteins?
Transport protein that forms a hydrophilic channel in a cell membrane through which water, ions, or other molecules can pass, depending on the protein.
26
What is a gated channel?
Ion transporter in a membrane that switches between open, closed, and intermediate states.
27
What are carrier proteins?
Transport protein that binds a specific single solute and transports it across the lipid bilayer.
28
What is osmosis?
The passive transport of water across a selectively permeable membrane in response to solute concentration gradients, a pressure gradient, or both.
29
What is hypotonic?
Solution containing dissolved substances at lower concentrations than the cells it surrounds.
30
What is hypertonic?
Solution containing dissolved substances at higher concentrations than the cells it surrounds.
31
What is isotonic?
Refers to the state of equal concentration of water inside and outside cells.
32
What is active transport?
The mechanism by which ions and molecules move against the concentration gradient across a membrane, from the side with the lower concentration to the side with the higher concentration.
33
What is membrane potential?
The electrical potential across a cell membrane due to the unequal distribution of positively and negatively charged molecules; it is negative under resting conditions.
34
What is primary active transport?
Transport in which the same protein that transports a substance also hydrolyzes ATP to power the transport directly.
35
What is secondary active transport?
Transport indirectly driven by ATP hydrolysis.
36
What is a calcium pump (Ca2+ pump)?
Pump that pushes Ca2+ from the cytoplasm to the cell exterior and from the cytosol into the vesicles of the endoplasmic reticulum.
37
What is an electrochemical gradient?
A difference in chemical concentration and electric potential across a membrane.
38
What is antiport?
A secondary active transport mechanism in which a molecule moves through a membrane channel into a cell and powers the active transport of a second molecule out of the cell. Also referred to as exchange diffusion.
39
What is bulk-phase endocytosis?
Mechanism by which extracellular water is taken into a cell together with any molecules that happen to be in solution in the water.
pinocytosis
40
What is receptor-mediated endocytosis?
The selective uptake of macromolecules that bind to cell surface receptors concentrated in clathrin-coated pits.
41
What is a coated pit?
A depression in the plasma membrane that contains receptors for macromolecules to be taken up by endocytosis.
42
What is clathrin?
The network of proteins that coat and reinforce the cytoplasmic surface of cell membranes.
43
What is reception in signal transduction?
The binding of a signal molecule with a specific receptor in a target cell.
44
What is transduction?
In cell signalling, the process of changing a signal into the form necessary to cause the cellular response. In prokaryotes, the process in which DNA is transferred from donor to recipient bacterial cells by an infecting bacteriophage.
45
What is response in signal transduction?
the last stage in which the transduced signal causes the cell to change according to the signal and to the receptors on the cell. In the nervous system, the output resulting from the integration of neural messages.
46
What is protein kinases?
Enzyme that transfers a phosphate group from ATP to one or more sites on particular proteins.
47
What is protein phosphatases?
Enzyme that removes phosphate groups from target proteins.
48
What is amplification?
An increase in the magnitude of each step as a signal transduction pathway proceeds.
49
What is symport?
The transport of two molecules in the same direction across a membrane. Also referred to as cotransport.
50
Which of the following statements about the fluid mosaic model is true?
a. The lipids within the membrane form a continuously moving mosaic.
b. The proteins are symmetrically distributed.
c. The lipids can spin, vibrate, move laterally, and flip from one side to the other.
d. The proteins can move within the membrane.
d. The proteins can move within the membrane.
51
Which of these factors contributes to the "mosaic" description of the plasma membrane as "fluid mosaic"?
a. its toughness
b. its embedded proteins
c. its permeability
d. its phospholipid bilayer
b. its embedded proteins
52
Which of these factors contributes to the "fluid" description of the plasma membrane as "fluid mosaic"?
a. its rigidity
b. its instability
c. its embedded proteins
d. its phospholipid bilayer
d. its phospholipid bilayer
53
Which of the following are found in animal plasma membranes but not in plant plasma membranes?
a. phospholipids
b. fatty acids
c. cholesterol
d. varying levels of saturation and unsaturation
c. cholesterol
54
Why do phospholipids spontaneously assemble into bilayers in aqueous environments?
a. because of the hydrophilic effect
b. because they are amphipathic
c. because this gives the highest energy state
d. because they contain fatty acids
b. because they are amphipathic
55
Which of the following would cause a reduced gelling temperature?
a. increasing the amounts of saturated lipids
b. increasing the unsaturation of lipid fatty acids
c. decreasing the transcription levels of desaturases
d. removing desaturases from the cell
b. increasing the unsaturation of lipid fatty acids
56
Suppose that you expose a cell to a higher temperature and it survives. What would most likely be the composition of the cell's membrane?
a. It would contain no hydrocarbon tails.
b. It would contain both saturated and unsaturated hydrocarbon tails.
c. It would contain more saturated hydrocarbon tails.
d. It would contain more unsaturated hydrocarbon tails.
c. It would contain more saturated hydrocarbon tails.
57
Which of the following statements about desaturases is correct?
a. Their expression is increased at higher temperatures.
b. They remove two hydrogen atoms from non-adjacent carbon atoms in fatty acids.
c. They create triple bonds in the fatty acids of lipids.
d. They are enzymes that help maintain a fluid membrane.
d. They are enzymes that help maintain a fluid membrane.
58
Which of the following is NOT one of the functions of membrane proteins?
a. transport
b. recognition/attachment
c. diffusion barrier
d. receptor
c. diffusion barrier
59
Which of the following is a feature unique to transmembrane proteins?
a. contain stretches of 17-20 hydrophobic amino acids in the primary sequence
b. may function in recognition
c. may function in attachment
d. contain hydrophilic surface domains
a. contain stretches of 17-20 hydrophobic amino acids in the primary sequence
60
Which of the following statements about integral membrane proteins is true?
a. They contain polar head groups.
b. They often have only one stretch of hydrophobic amino acids.
c. The folded protein has only hydrophobic surface regions.
d. They can have enzymatic activity.
d. They can have enzymatic activity.
61
Which of these statements most accurately explains diffusion?
a. It is the net movement of a substance from a region of higher concentration to a region of lower concentration.
b. It is the net movement of a substance from a region of lower concentration to a region of higher concentration.
c. It is the movement of a dissolved substance in any direction within a liquid medium.
d. It is the stagnation of a substance dissolved in a liquid medium
a. It is the net movement of a substance from a region of higher concentration to a region of lower concentration.
62
Which of the following would likely cross the membrane through simple diffusion?
a. small uncharged sugars such as glucose
b. oxygen and carbon dioxide
c. very small ions
d. large molecules such as starch
b. oxygen and carbon dioxide
63
Which of the following statements about diffusion is true?
a. Minimum entropy is reached at equilibrium.
b. The movement of solutes stops when equilibrium is reached.
c. The process is driven by entropy.
d. There is an indirect expenditure of energy.
c. The process is driven by entropy.
64
Which of the following is least likely to cross a plasma membrane by simple diffusion?
a. O2
b. H2O
c. CO2
d. Na+
d. Na+
65
Which of these characteristics is shared by both diffusion and facilitated diffusion?
a. Energy is required to go ahead.
b. Energy is not required to go ahead.
c. There is movement of molecules against their concentration gradient.
d. Proteins are required to assist the movement of molecules.
b. Energy is not required to go ahead.
66
Which of the following describes aquaporins?
a. They bind a molecule of water and transport it after undergoing a conformational change.
b. They use Na+ as a driving ion in symport.
c. They are voltage-gated channels.
d. They form a substrate-specific hydrophilic channel.
d. They form a substrate-specific hydrophilic channel.
67
Which of the following examples is NOT energy-dependent?
a. K+ voltage-gated channel
b. Na+-K+ pump
c. receptor-mediated endocytosis
d. symport
a. K+ voltage-gated channel
68
In a two-compartment system separated by cellophane, compartment A is filled with a 0.5 M sucrose solution and compartment B is filled with a 1 M sucrose solution. Given that cellophane is permeable only to the water, which of the following describes compartment B relative to compartment A?
a. B is hypotonic
b. B is isotonic
c. B is hypertonic
c. B is hypertonic
69
In a two-compartment system separated by cellophane, compartment A is filled with a 0.5 M sucrose solution and compartment B is filled with a 1 M sucrose solution. Compartment A is contained in a cellphone bag and suspended in a beaker of solution B. Given that cellophane is permeable only to the water, which of the following describes what happens when the bag is suspended in the beaker?
a. There would be no net movement of water.
b. There would be net movement of water from A to B.
c. There would be net movement of sucrose from B to A.
b. There would be net movement of water from A to B.
70
In a two-compartment system separated by cellophane, compartment A is filled with a 0.5 M sucrose solution and compartment B is filled with a 1 M sucrose solution. Compartment A is contained in a cellphone bag and suspended in a beaker of solution B. Given that cellophane is permeable only to the water, which of the following is true?
a. Water would move from B to A until the bag could not swell any further.
b. Movement across the cellophane barrier is through active transport.
c. Movement would stop completely once equilibrium was reached.
d. At equilibrium there would be maximum entropy.
d. At equilibrium there would be maximum entropy.
71
Which of the following would be transported through primary active transport?
a. glucose
b. Ca2+
c. chlorine
d. H2O
b. Ca2+
72
What is the result of the Na+/K+ pump?
a. The charge inside the cell is negative versus the outside.
b. The charge inside the cell is positive versus the outside.
c. The charge inside the cell is negative as well as the outside.
d. The charge inside the cell is positive as well as the outside.
a. The charge inside the cell is negative versus the outside.
73
Which of the following statements about calcium pumps is true?
a. They use light for energy.
b. They push calcium into the cytoplasm.
c. They are rare in animal cells.
d. Their activity generates an electrochemical gradient.
d. Their activity generates an electrochemical gradient.
74
Which of the following is true of secondary active transport?
a. It may simultaneously transport two solutes in the same direction.
b. The transporter relies on glucose gradients to drive transport.
c. ATP provides the direct energy to drive transport.
d. No energy is required.
a. It may simultaneously transport two solutes in the same direction.
75
Which of the following is associated with receptor-mediated endocytosis?
a. It involves binding of the substrate by clathrin.
b. The endocytic vesicle fuses with mitochondria.
c. The solute binds to a specific cell surface receptor.
d. The process does not require energy.
c. The solute binds to a specific cell surface receptor.
76
Which statement about exocytosis is true?
a. It is often called pinocytosis.
b. It forms endocytic cells.
c. It is prevalent in glandular/secretory cells.
d. It is a type of phagocytosis.
c. It is prevalent in glandular/secretory cells.
77
Which of these processes would most likely occur if a cell needs to import specific molecules from outside of its plasma membrane?
a. receptor-mediated endocytosis
b. phagocytosis
c. pinocytosis
d. exocytosis
a. receptor-mediated endocytosis
78
What is the purpose of membrane receptors in cell signalling?
a. to produce ATP
b. to acquire energy
c. to bind to the signal molecule
d. to directly cause the downstream cellular response
c. to bind to the signal molecule
79
What is the correct order of events associated with signal transduction?
a. reception, response, transduction
b. transduction, reception, response
c. reception, transduction, response
d. response, reception, transduction
c. reception, transduction, response
80
Lipid molecules within a bilayer can vibrate, spin, move sideways, and flip-flop between the two layers.
a. True
b. False
b. False
81
Membranes with higher amounts of saturated fatty acids will remain fluid and functional at higher temperatures.
a. True
b. False
a. True
