04 January 2013

BIO 106 Test 3 Part 5 Answers

1) Which of the following types of molecules are the major structural components of the cell membrane?
A) nucleic acids and proteins    B) phospholipids and proteins   C) phospholipids and cellulose
D) proteins and cellulose          E) glycoproteins and cholesterol

2) Which of the following is a reasonable explanation for why unsaturated fatty acids help keep any membrane more fluid at lower temperatures?
A) The double bonds result in shorter fatty acid tails and thinner membranes.
B) The double bonds form kinks in the fatty acid tails, preventing adjacent lipids from packing tightly.
C) Unsaturated fatty acids have a higher cholesterol content and therefore more cholesterol in membranes.
D) The double bonds block interaction among the hydrophilic head groups of the lipids.
E) Unsaturated fatty acids are more polar than saturated fatty acids.

3) The primary function of polysaccharides attached to the glycoproteins and glycolipids of animal cell membranes is
A) to maintain membrane fluidity at low temperatures.            B) to mediate cell-to-cell recognition.
C) to actively transport molecules against their concentration gradients.
D) to facilitate diffusion of molecules down their concentration gradients.
E) to maintain the integrity of a fluid mosaic membrane.

4) Which of these are never embedded in the hydrophobic portion of the lipid bilayer at all?
A) transmembrane proteins                  B) glycoproteins                       C) integrins
D) integral proteins                              E) peripheral proteins

5) Why are lipids and proteins free to move laterally in membranes?
A) Lipids and proteins repulse each other in the membrane.
B) Molecules such as cellulose can pull them in various directions.
C) There are only weak hydrophobic interactions in the interior of the membrane.
D) Hydrophilic portions of the lipids are in the interior of the membrane.
E) The interior of the membrane is filled with liquid water.

6) What kinds of molecules pass through a cell membrane most easily?
A) ionic                                    B) large and hydrophobic         C) monosaccharides such as glucose
D) small and hydrophobic         E) large polar

7) Which of the following statements correctly describes the normal tonicity conditions for typical plant and animal cells?
A) The animal cell is in an isotonic solution, and the plant cell is in a hypertonic solution.
B) The animal cell is in an isotonic solution, and the plant cell is in a hypotonic solution.
C) The animal cell is in a hypotonic solution, and the plant cell is in an isotonic solution.
D) The animal cell is in a hypertonic solution, and the plant cell is in a hypotonic solution.
E) The animal cell is in a hypertonic solution, and the plant cell is in an isotonic solution.

8) White blood cells engulf bacteria through what process?
A) phagocytosis      B) pinocytosis         C) osmosis       D) exocytosis    E) receptor-mediated exocytosis

9) Ions diffuse across membranes through specific ion channels
A) down their chemical gradients.        B) down the osmotic potential gradients.         
C) down the electrical gradients.          D) down their electrochemical gradients.
E) down their concentration gradients.

10) The difference between pinocytosis and receptor-mediated endocytosis is that
A) pinocytosis can concentrate substances from the extracellular fluid, but receptor-mediated endocytosis cannot.
B) pinocytosis is nonselective in the molecules it brings into the cell, whereas receptor-mediated endocytosis offers more selectivity.
C) pinocytosis increases the surface area of the plasma membrane whereas receptor-mediated endocytosis decreases the plasma membrane surface area.
D) pinocytosis requires cellular energy, but receptor-mediated endocytosis does not.
E) pinocytosis brings only water molecules into the cell, but receptor-mediated endocytosis brings in other molecules as well.

11) You are working on a team that is designing a new drug. In order for this drug to work, it must enter the cytoplasm of specific target cells. Which of the following would be a factor that determines whether the molecule selectively enters the target cells?
A) hydrophobicity of the drug molecule           B) blood or tissue type of the patient
C) lack of charge on the drug molecule             D) lipid composition of the target cells' plasma membrane
E) similarity of the drug molecule to other molecules transported by the target cells

12) Which of the following factors would tend to increase membrane fluidity?
A) a lower temperature
B) a greater proportion of relatively large glycolipids compared with lipids having smaller molecular masses
C) a greater proportion of saturated phospholipids
D) a greater proportion of unsaturated phospholipids
E) a relatively high protein content in the membrane

13) ______ are the major lipids of plasma membranes.
A) Mosaics                   B) Phospholipids           C) Steroids       D) Prostaglandins         E) Triglycerides

14) ______ code for the structure of proteins.
A) Phospholipids           B) Ribosomes                C) Carbohydrates         D) Genes           E) Lysosomes

15) According to the fluid mosaic model of membrane structure, proteins of the membrane are mostly
A) spread in a continuous layer over the inner and outer surfaces of the membrane.
B) free to depart from the fluid membrane and dissolve in the surrounding solution.
C) randomly oriented in the membrane, with no fixed inside-outside polarity.
D) confined to the hydrophobic interior of the membrane.
E) embedded in a lipid bilayer.

16) If a red blood cell is placed in a salt solution and bursts, what is the tonicity of the solution relative to the interior of the cell?
A) isotonic                   B) hypertonic               C) hypotonic                 D) osmotic

17) The permeability of a biological membrane to a specific polar solute may depend on which of the following?
A) the amount of cholesterol in the membrane            
B) the types of transport proteins in the membrane
C) the phospholipid composition of the membrane     
D) the presence of unsaturated fatty acids in the membrane
E) the types of polysaccharides present in the membrane

18) Which of the following statements about osmosis is correct?
A) Osmosis is the diffusion of water from a region of lower water concentration to a region of higher water concentration
B) If a solution outside the cell is hypertonic compared to the cytoplasm, water will move into the cell by osmosis
C) The presence of aquaporins (proteins that form water channels in the membrane) should speed up the process of osmosis
D) Osmotic movement of water out of a cell would likely occur if the cell accumulates water from its environment.
E) If a cell is placed in an isotonic solution, more water will enter the cell than leave the cell.

19) In facilitated diffusion, what is the role of the transport protein?
A) Transport proteins provide the energy for diffusion of the solute.
B) Transport proteins organize the phospholipids to allow the solute to cross the membrane.
C) Transport proteins provide a hydrophilic route for the solute to cross the membrane.
D) Transport proteins provide a low-resistance channel for water molecules to cross the membrane.
E) Transport proteins provide a protein site for ATP hydrolysis, which facilitates the movement of a solute across a membrane.

20) What distinguishes facilitated diffusion from simple diffusion?
A) Water moves through membranes by facilitated diffusion
B) No energy is used to move molecules across the membrane
C) Molecules move from a region of higher concentration to a region of lower concentration.
D Membrane proteins help move molecules across the membrane.

21) Which of the following statements is true about the net movement of an ion across a membrane by passive diffusion through a membrane channel?
A) The charge on the other side of the membrane is generally the opposite of the ion’s charge.
B) There is a higher concentration of ions on the side of the membrane toward which the ion diffuses.
C) The cell expends energy as the ion passes through the membrane.
D) For every ion that diffuses through the membrane, a different ion diffuses in the opposite direction.

22) Active and passive transport of solutes across a membrane typically differ in which of the following ways?
A) Active transport is ussually down the concentration gradient of the solute, whereas passive transport is always against the concentration gradient of the solute.
B) Active transport always involves the ultilization of cellular energy, whereas passive transport does not require cellular enrgy.
C) Active transport is always faster than passive transport.
D) Active transport uses protein carriers, wheras passive transport uses carbohydrate carriers.
E) Active transport is used for ions, passive transport is used for uncharged solutes.

23) A chemical reaction that has a positive ΔG is correctly described as
A) endergonic.  B) endothermic.           C) spontaneous.             D) exothermic.             E) enthalpic.

24) Why is ATP an important molecule in metabolism?
A) It provides energy coupling between exergonic and endergonic reactions.
B) Its terminal phosphate group contains a strong covalent bond that, when hydrolyzed, releases free energy.
C) Its terminal phosphate bond has higher energy than the other two.
D) It is one of the four building blocks for DNA synthesis.
E) Its hydrolysis provides an input of free energy for exergonic reactions.

25) Which of the following is most similar in structure to ATP?
A) a pentose sugar        B) a phospholipid          C) an amino acid with three phosphate groups attached
D) a DNA nucleotide     E) an RNA nucleotide

26) When chemical, transport, or mechanical work is done by an organism, what happens to the heat generated? 
A) It is transported to specific organs such as the brain.    B) It is used to store energy as more ATP.
C) It is lost to the environment.                                           D) It is used to power yet more cellular work.
E) It is used to generate ADP from nucleotide precursors.

27) Which of the following statements is true about enzyme-catalyzed reactions?
A) Enzyme-catalyzed reactions require energy to activate the enzyme.
B) The reaction is faster than the same reaction in the absence of the enzyme.
C) Enzyme-catalyzed reactions release more free energy than noncatalyzed reactions.
D) The free energy change of the reaction is opposite from the reaction that occurs in the absence of the enzyme.
E) The reaction always goes in the direction toward chemical equilibrium.

28) Reactants capable of interacting to form products in a chemical reaction must first overcome a thermodynamic barrier known as the reaction's
A) endothermic level.                           B) entropy.                   C) free-energy content.           
D) activation energy.                            E) equilibrium point.

29) According to the induced fit hypothesis of enzyme catalysis, which of the following is correct?
A) The binding of the substrate changes the shape of the enzyme's active site.
B) The binding of the substrate depends on the shape of the active site.
C) The active site creates a microenvironment ideal for the reaction.
D) Some enzymes change their structure when activators bind to the enzyme.
E) A competitive inhibitor can outcompete the substrate for the active site.

30) When you have a severe fever, what grave consequence may occur if the fever is not controlled?
A) removal of the amino acids in active sites of your enzymes  B) removal of amine groups from your proteins
C) binding of your enzymes to inappropriate substrates   D) destruction of your enzymes' primary structure
E) change in the tertiary structure of your enzymes

31) The mechanism in which the end product of a metabolic pathway inhibits an earlier step in the pathway is most precisely described as
A) allosteric inhibition.            B) reversible inhibition.            C) feedback inhibition.
D) metabolic inhibition.            E) noncooperative inhibition.
32) Besides turning enzymes on or off, what other means does a cell use to control enzymatic activity?
A) hydrophobic interactions                             B) connecting enzymes into large aggregates                       
C) cessation of cellular protein synthesis         D) exporting enzymes out of the cell
E) localization of enzymes into specific organelles or membranes 

Rate of an enzyme-catalyzed reaction as a function of varying reactant concentration, with the concentration of enzyme constant.

33) For the enzyme-catalyzed reaction shown in the figure above, which of these treatments will cause the greatest increase in the rate of the reaction, if the initial reactant concentration is 1.0 micromolar?  
A) doubling the activation energy needed         B) cooling the reaction by 10°C
C) doubling the enzyme concentration
D) increasing the concentration of reactants to 10.0 micromolar, while reducing the concentration of enzyme by 1/2
E) doubling the concentration of the reactants to 2.0 micromolar

34) In the figure above, why does the reaction rate plateau at higher reactant concentrations?
A) The reaction nears equilibrium at high reactant concentrations.
B) The rate of the reverse reaction increases with reactant concentration.
C) Most enzyme molecules are occupied by substrate at high reactant concentrations.
D) The activation energy for the reaction increases with reactant concentration.
E) Feedback inhibition by product occurs at high reactant concentrations.

A series of enzymes catalyze the reaction X  Y  Z  A. Product A binds to the enzyme that converts X to Y at a position remote from its active site. This binding decreases the activity of the enzyme.

35) What is substance X?
A) a coenzyme       B) a substrate        C) an allosteric inhibitor     D) the product      E) an intermediate

36) With respect to the enzyme that converts X to Y, substance A functions as 
A) a coenzyme.                                     B) an intermediate.                   C) an allosteric inhibitor.
D) a competitive inhibitor.                    E) the substrate.

Succinate dehydrogenase catalyzes the conversion of succinate to fumarate. The reaction is inhibited by malonic acid, which resembles succinate but cannot be acted upon by succinate dehydrogenase. Increasing the ratio of succinate to malonic acid reduces the inhibitory effect of malonic acid.

37) Based on this information, which of the following is correct?
A) Succinate dehydrogenase is the enzyme, and malonic acid is the substrate.
B) Succinate dehydrogenase is the enzyme, and fumarate is the substrate.
C) Succinate is the substrate, and fumarate is the product.
D) Fumarate is the product, and malonic acid is a noncompetitive inhibitor.
E) Malonic acid is the product, and fumarate is a competitive inhibitor.

38) What is malonic acid's role with respect to succinate dehydrogenase?
A) It blocks the binding of fumarate. B) It is a competitive inhibitor.            C) It is an allosteric regulator.
D) It is able to bind to succinate.         E) It is a noncompetitive inhibitor.

39) Some bacteria are metabolically active in hot springs because
A) their enzymes have high optimal temperatures.
B) their enzymes are completely insensitive to temperature.
C) they use molecules other than proteins or RNAs as their main catalysts.
D) they are able to maintain a lower internal temperature.
E) high temperatures make catalysis unnecessary.

40) Which of these is exhibiting kinetic energy?
A) a rock on a mountain ledge                                       B) a space station orbiting Earth
C) a person sitting on a couch while watching TV          D) an archer with a with a flexed bow
E) the high-energy phosphate bonds of a molecule of ATP

41) Which of the following would be unlikely to contribute to the substrate specificity of an enzyme?
A) A similar shape exists between a pocket on the surface of the enzyme and a functional group on the substrate
B) A hydropobic group on the substrate interacts with several hydrophobic amino acids on the enzyme
C) A positive charge on the substrate is attached to a negative charge in the active site of the enzyme.
D) The enzyme has the ability to change its confirmation in response to the substrate binding.
E) The enzyme has an allosteric regulatory site.

42) Which of the following is NOT a way in which an enzyme can speed up the reaction that it catalyzes?
A) The enzyme binds a cofactor that interacts with the substrate to facilitate the reaction.
B) Binding of the substrate to the active site can streatch bonds in the substrate that need to be broken.
C) The active site of the enzyme can provide a microenvironment with a different pH that facilitates the reaction.
D) The binding of two substrates in the active site provides the correct orientation for them to react to form the product.
E) The active site can provide heat from the environment that raises the energy content of the substrate.

43) Aerobic means with ______.
A) carbohydrate          B) oxygen         C) ATP                         D) light                        E) carbon dioxide

44) The waste products of cellular respiration include ______.
A) carbon dioxide        B) water           C) glucose         D) water and carbon dioxide    E) water and glucose

45) The binding of a compound to an enzyme is observed to slow down or stop the rate of the reaction catalyzed by the enzyme. Increasing the substrate concentration reduces the inhibitory effects of this compound. Which of the following could account for this observation?
A) The compound is a competitive inhibitor.
B) The compound is a negative allosteric regulator.
C) The compound causes a cofactor to be lost from the enzyme.
D) The compound forms a bond with one of the amino acid residues needed for enzyme activity.
E) The compound reduces disulfide bonds, causing the enzyme molecules to partially unfold.

46) What compound directly provides energy for cellular work?
A) fat              B) rubisco                     C) ATP                         D) DNA            E) C6H12O6

47) Respiration ______, and cellular respiration ______. 
A) produces glucose . . . produces oxygen          B) is gas exchange . . . produces ATP
C) produces ATP . . . is gas exchange                D) produces glucose . . . is gas exchange
E) uses glucose . . . produces glucose

48) Which of these equations describes aerobic cellular respiration?
A) glucose + lactose  galactose + water                      B) glucose  lactic acid + energy
C) energy + carbon dioxide + water  glucose + oxygen + water
D) glucose  ethyl alcohol + carbon dioxide + energy
E) glucose + oxygen  carbon dioxide + water + energy

49) The energy released from glucose by the process of cellular respiration is in the form of ______.
A) ATP and NADH        B) oxygen only              C) ATP and heat           D) heat only     E) ATP only

50) During cellular respiration, the energy in glucose is ______.
A) transferred to starch B) carried by electrons C) used to manufacture glucose by exergonic reactions
D) released all at once              E) none of the above

51) During redox reactions, ______. 
A) the loss of electrons from one substance is called reduction
B) electrons are lost from one substance and added to another substance
C) a substance that gains electrons is said to be oxidized
D) protons from one molecule replace the electrons lost from another molecule
E) none of the above

52) Which of the following statements is completely true?
A) Lactic acid is a product of aerobic respiration; ethyl alcohol is a product of fermentation.
B) Oxygen is a product of cellular respiration; carbon dioxide is a product of photosynthesis.
C) Oxidation is the loss of electrons; reduction is the gain of electrons.
D) Glucose is a product of aerobic respiration; lactic acid is a product of anaerobic respiration.
E) Oxidation is the gain of electrons; reduction is the loss of electrons.

53) The final electron acceptor of aerobic respiration is ______.
A) NAD+           B) lactic acid                C) ATP                         D) oxygen                     E) carbon dioxide

54) A product of glycolysis is ______.
A) O2               B) lactic acid                C) ethyl alcohol            D) NAD+           E) pyruvic acid

55) Where in the cell does glycolysis occur?
A) along the outside of the outer mitochondrial membrane      B) ER                C) cytosol
D) between the inner and outer mitochondrial membrane
E) within the fluid just inside the inner mitochondrial membrane

56) Which of the following is a correct sequence of stages in cellular respiration?
A) citric acid cycle, glycolysis, electron transport chain         
B) electron transport chain, citric acid cycle, glycolysis
C) citric acid cycle, electron transport chain, glycolysis
D) electron transport chain, glycolysis, citric acid cycle
E) glycolysis, citric acid cycle, electron transport chain

57) What must pyruvic acid be converted to before it can enter the citric acid cycle?
A) ethyl alcohol           B) acetyl CoA               C) citric acid    D) NADH          E) lactic acid

58) Energy is transferred from ATP to other molecules by transferring a(n)   ______.
A) adenosine    B) phosphate group       C) heat             D) photon                     E) spring

59) Which part of cellular respiration produces the most NADH?
A) electron transport chain      B) Calvin cycle  C) citric acid cycle       D) hydrogenation          E) glycolysis

60) In cellular respiration, most ATP is produced directly as a result of ______. 
A) glycolysis     B) the electron transport chain            C) fermentation            D) the citric acid cycle
E) the movement of hydrogen ions across the inner mitochondrial membrane

61) Anaerobic respiration produces a maximum of ______ ATP per glucose.
A) 36               B) 4                  C) 2                  D) 38                E) 10

62) Some friends are trying to make wine in their basement. They've added yeast to a sweet grape juice mixture and have allowed the yeast to grow. After several days they find that sugar levels in the grape juice have dropped, but there's no alcohol in the mixture. The most likely explanation is that ______.
A) the mixture needs less oxygen; yeast only produce alcohol in the absence of oxygen
B) the mixture needs less sugar; high sugar concentrations stimulate cellular respiration, and alcohol is not a by-product of cellular respiration
C) the mixture needs more oxygen; yeast need oxygen to break down sugar and get enough energy to produce alcohol
D) the mixture needs more sugar; yeast need a lot of energy before they can begin to produce alcohol
E) none of the above

63) What waste product do yeast produce under anaerobic conditions?
A) ethyl alcohol           B) lactic acid                C) pyruvic acid                         D) creatine                   E) glucosamine

64) If you were able to stop the process of cellular respiration after completion of electron transport but prior to chemiosmosis, you would find the pH of a mitochondrion to be at its lowest ______.
A) in the cytoplasm                              B) on the inner membrane         C) in the intermembrane space
D) in the mitochondrial matrix             E) on the outer membrane

This graph represents an exergonic reaction with and without an enzyme catalyst.

65) Which letter represents the ΔG of the reaction?

66) Which letter represents the activation energy required for the enzyme-catalyzed reaction?

67) Which letter represents the activation energy required for a noncatalyzed reaction?

68) Which letter represents the difference between the free-energy content of the reaction and the free-energy content of the products?

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