BIO 314 Exam #1

The Ca2+ pumps in the plasma membrane and the endoplasmic reticulum are examples of: A. ATP-driven pumps B. coupled transporters C. passive carrier proteins D. antiports E. symports

A. ATP-driven pumps

An amino acids you would expect to more frequently find on the outside of a folded globular protein would be:

A. Argine (Basic, Polar)

Molecules that cannot diffuse through a lipid bilayer include: A. Glucose B. Water

A. Glucose

Proteins can be modified by reaction with acetate which results in the addition of an acetyl group to lysine side chains as shown in the Figure below. The bond indicated in the acetylated lysine side chain is most like:

A. Peptide bond

Peptide bonds are: A. Planar B. Circular C. Tetrahedral D. Unstable E. Cis

A. Planar

Three phospholipids X, Y, and Z are distributed in the plasma membrane as indicated below. For which of these phospholipids does a flippase probably exist?

A. X and Y (both sides)

The common feature of alpha helices and beta sheets that make them universal building blocks for proteins is A. all of the N-H and C=O groups are engaged in hydrogen bonds B. they start with an initiating methionine C. they can be phosphorylated D. they are amphipathic E. all of the side-chains are involved in ionic interactions

A. all of N-H and C=O groups are engaged in hydrogen bonds.

Which of the following statements is false? A. The active site of an enzyme usually occupies only a small fraction of the surface. B. Catalysis by some enzymes involves the formation of a covalent bond between an amino acid side chain and a substrate molecule. C. An enzyme must have both beta-sheets and alpha helices. D. Allosteric enzymes have two or more binding sites. E. An enzyme is unchanged at the end of the reaction.

A. an enzyme must have both beta-sheets and alpha-helices

Secondary structures that are found in proteins include all of the following EXCEPT: A. peptide bonds B. alpha helix C. beta sheet D. beta barrel E. omega turn

A. peptide bonds

You are measuring the effect of temperature on the rate of an enzyme-catalyzed reaction. If you plot reaction rate against temperature, which of the graphs (1, 2, 3, or 4) would you expect your plot to resemble? A. 1 B. 2 C. 3 D. 4 E. none of the above

A.1

Which of the following statements about enzymes are correct? A. Catalysis of an energetically unfavorable reaction by an enzyme will enable that reaction to occur. B. An enzyme can direct a molecule along a particular reaction pathway. C. An enzyme can catalyze many chemically different reactions. D. An enzyme can bind to many structurally unrelated substrates. E. Enzymes are permanently altered after catalyzing a reaction.

B. An enzyme can direct a molecule along a particular reaction pathway.

Which of the following statements is correct? A. High-energy electrons (such as those found in the activated carriers NADH and NADPH) move faster around the atomic nucleus. B. Some activated carrier molecules can transfer energy and chemical groups. C. Cold-blooded animals have an energetic disadvantage because they give less heat to the environment than warm-blooded animals do. This slows their ability to make ordered macromolecules. D. Linking the reaction X -->Y to a second, favorable reaction Y --> Z will shift the equilibrium constant of the first reaction. E. A partially oxidized carbon atom has a somewhat larger diameter than a more reduced one.

B. Some activated carrier molecules can transfer energy and chemical groups.

Which of the following statements about proteins are true? A. The three-dimensional structure of a protein can usually be predicted from knowledge of its amino acid sequence. B. Two proteins having similar amino acid sequences will often have similar shapes. C. Proteins containing fewer than 100 amino acids cannot fold into stable structures. D. Most proteins contain more than 2000 amino acids. E. The detailed three-dimensional structure of a protein can usually be determined by electron microscopy.

B. Two proteins having similar amino acid sequences will often have similar shapes.

Which of the following statements is true? A. Enzymes are always comprised of protein. B. Enzymes reduce the activation energy of a reaction. C. Enzymes are able to catalyze reactions that decrease the entropy of the universe. D. Enzymes must go through covalent changes themselves to catalyze the reaction. E. Functional enzymes are heteromultimeric.

B. enzymes reduce the activation energy of a reaction

Carbon atoms CANNOT: A. form four covalent bonds to other atoms. B. form both covalent and ionic bonds. C. form double bonds. D. form chains of virtually unlimited size. E. form ring structures.

B. form both covalent and ionic bonds

The equilibrium constant for the binding of a protein to its ligand can depend on all of the following EXCEPT: A. the number of noncovalent bonds formed between the protein and the ligand. B. the concentration of the ligand. C. the exact fit of the binding site to the ligand. D. the temperature. E. the pH.

B. the concentration of the ligand

An amphipathic molecule is characterized by

Both hydrophobic and hydrophilic

Which of the following statements regarding lipid membranes are true? A. Phospholipids will spontaneously form liposomes in nonpolar solvents. B. A solution of pure fatty acids forms a lipid bilayer in a polar solvent. C. Membrane lipids move laterally within their own layer. D. Membrane lipids frequently move between one layer of the bilayer and the other. E. The preferred form of a lipid bilayer in water is a flat sheet with exposed edges.

C. Membrane lipids move laterally within their own layer.

Four samples of cells have membranes containing a uniform distribution of a fluorescently labeled phospholipid (sample 1) and three fluorescently labeled membrane proteins X, Y, and Z (samples 2-4), respectively. An intense beam of light is shone on each sample. The light beam destroys the fluorescent label in the illuminated area, but the intensity of fluorescence in the area recovers over time, as bleached molecules diffuse away and unbleached molecules diffuse in. The results of this experiment are shown below. Which of the following interpretations are INCONSISTENT with these results? A. X is a small freely diffusing protein. B. Y is a large freely diffusing protein. C. X and Y are part of the same large protein complex. D. Z is bound to a component of the cell cortex. E. none of the above

C. X & Y are part of the same large protein complex.

The lipid bilayer is held together primarily by: A. covalent bonding between membrane lipids. B. hydrogen-binding between the phospholipid tails. C. repulsion between the phospholipid tails and water. D. covalent bonding between the ends of phospholipid tails in opposite layers. E. hydrogen-bonding between the head groups of phospholipids.

C. repulsion between the phospholipid tails and water.

The most abundant intracellular cation is: A. Na+ B. Ca2+ C. H+ D. K+ E. positively charged macromolecules

D. K+

Which of the following CANNOT be a reason that cells use enzymes rather than heat to increase the rate of biochemical reactions? A. The temperature increase required to speed up a reaction by an appreciable extent is often huge. B. Reactions cannot be coupled without enzymes. C. An enzyme catalyzes just one or a small number of different reactions; heat would affect all the reactions in a cell. D. No organism can live at a temperature higher than 40 degrees centigrade. E. Enzymes can accelerate reactions to a much greater extent than can heat.

D. No organism can live at a temperature higher than 40 degrees centigrade.

Which of the following statements are false? A. All protein molecules function by binding specifically to other molecules. B. Many proteins can bind to more than one ligand. C. Binding between protein and ligand generally involves noncovalent bonds. D. Proteins are designed to bind their ligands as tightly as possible. E. Changes in the amino acid sequence of a protein can decrease binding to a ligand, even if the amino acid affected by the change does not lie in the binding site for the ligand.

D. Proteins are designed to bind their ligands as tightly as possible.

Disulfide bonds: A. are formed by the cross-linking of methionine residues B. are formed mainly in proteins that are retained within the cytosol. C. stabilize but do not change a protein's final conformation D. can be broken by reduction (for example, by -mercaptoethanol) E. rarely form in extracellular proteins

D. can be broken by reduction

van der Waals attractions and hydrogen bonds are similar in that: A. they both require specific groups to attract B. they both involve polar bonds C. they both involve chelated metals D. they both are short range interactions that only come into play when molecules are close E. they both involve ionic interactions

D. they both are short range interactions that only come into play when molecules are close

Which statement below about the sodium-potassium pump is false? A. moves 2 K+ ions into the cell for every 3 Na+ ions moved out of the cell B. hydrolyses ATP C. undergoes allosteric change D. uses the electrochemical gradient of Na+ to pump K+ into the cell E. has an Na+ binding site on the intracellular domain and a K+ binding site on the extracellular domain

D. uses the electrochemical gradient of Na+ to pump K+ into the cell

A stretch of amino acids you might expect to find in a transmembrane domain would be: A. E-G-T-Y-H-W-D-S-A-N-M-E-L-W-D-T-Y-I-S-A B. P-G-G-A-L-P-S-V-T-M-F-L-N-V-S-W-H-P-S-N C. G-N-Q-A-L-R-Y-T-W-K-N-K-W-I-L-R-Q-A-G-F D. K-K-L-V-A-A-V-L-I-K-L-V-A-A-V-V-I-L-R-R E. A-M-G-I-I-V-M-L-L-A-S-G-L-A-L-V-I-A-V-M

E. A-M-G-I-I-V-M-L-L-A-S-G-L-A-L-V-I-A-V-M transmembrane domains have non polar amino acids

The membrane potential of a typical animal cell favors the inward flux of: A. water. B. glucose. C. Cl-. D. ATP. E. Ca2+.

E. Ca2+

Which of the following reactions are energetically favorable? a. base + sugar + phosphate --> nucleotide b. amino acid + amino acid --> peptide c. CO2 + H2O --> sugar d. N2 + H2 --> ammonia e. sucrose --> CO2 + H2O

E. SUCROSE -> CO2 + H2O

Which of the following is not true about K+ channels? A. Carbonyl groups in the selectivity filter make it energetically favorable for K+ ions to shed their water shell. B. The amphipathic S4 domain senses the change in membrane potential and rotates within the membrane, resulting in an allosteric change of the channel from closed to open configuration. C. K+ channels are responsible for repolarization of the membrane. D. In the inactivated state, a domain of the channel called the "inactivation peptide" binds to the opening to block it, in what is called a "ball and chain" model. E. Since Na+ ions are smaller than K+ ions but also have a single positive charge, they in theory would be able to interact with the carbonyls and also pass through the K+ channel but do not because of the chemical gradient in the cell.

E. Since Na+ ions are smaller than K+ ions but also have a single positive charge, they in theory would be able to interact with the carbonyls and also pass through the K+ channel but do not because of the chemical gradient in the cell.

Which of the following statements is not correct about lipids in a lipid bilayer? A. lipids rotate rapidly around their long axis B. lipids rapidly exchange positions with respect to one another in the plane of the membrane C. lipids do not flip-flop readily from one lipid monolayer to the other D. hydrogen bonds are continually broken and re-formed between lipid head groups and water molecules E. The composition of the phospholipid heads is the same on both inner and outer leaves of the lipid bilayer.

E. The composition of the phospholipid heads is the same on both inner and outer leaves of the lipid bilayer.

Which of the following statements about hydrogen bonds are true? A. They are weak covalent bonds that are easily disrupted by heat B. They are weak bonds formed between hydrocarbons in water. C. They are weak bonds formed between nonpolar groups. D. They are weak bonds only formed in the presence of water. E. They are weak bonds involved in maintaining the 3-D structure of macro- molecules

E. They are weak bonds involved in maintaining the 3-D structure of macromolecules.

Ion channels: A. only open in response to a signal of some kind. B. require input of energy in order to function. C. have no limit to the rate at which they can transport ions. D. can transport both positive and negative ions through the same channel. E. allow passage of ions in both directions.

E. allow passage of ions in both directions

A common means of providing energy to an energetically unfavorable reaction in a cell is by: A. generation of a higher temperature by the cell. B. transfer of a phosphate group from the substrate to ADP. C. enzyme catalysis of the reaction. D. coupling of the synthesis of ATP to the reaction. E. coupling of ATP hydrolysis to the reaction.

E. coupling of ATP hydrolysis to the reaction,

All of the following are characteristic of some integral membrane proteins EXCEPT: A. they often have one or more -helical transmembrane segments. B. they might be amphipathic. C. they might diffuse freely in the lipid bilayer. D. they might be tethered in the lipid bilayer. E. they often can be extracted from the membrane with high salt.

E. they often can be extracted from the membrane with high salt

True or False: Elements common in living organisms have filled outer shells and can participate in chemical reactiona

False *They have unfilled shells

The alpha helix and beta sheet are found in many different proteins because they are formed by:

Hydrogen bonding between atoms of polypeptide backbone

A general term for an enzyme that catalyzes a hydrolytic cleavage reaction is:

Hydrolase

Where are the Mitochondrial inner matrix proteins translocated across?

Inner and outer membranes simultaneously

A general term for an enzyme that catalyzes the addition of a phosphate group to molecules is:

Kinase

Hydrogen bonds determine the solubility of:

Molecule in water

Which of the following reactions will occur only if coupled to a second, energetically favorable reaction?

NTP -> DNA

For the following peptide: R-K-S-F-R-A-L Overall it has what kind of charge?

Positive

An amino acid that would not participate in ionic bonding?

Proline

Ion channels can have the following properties except being:

Salt extractable

Advantages of membranes in a cell:

They compartmentalize the cell.

Which of the following statements regarding membrane proteins are false? a. In transmembrane proteins that form an aqueous pore through the membrane, the pore is lined with hydrophobic amino acid side chains b. Integral membrane proteins often precipitate (form insoluble aggregates) in aqueous solutions lacking detergents. c. Strong detergents can completely unfold both membrane and no membrane proteins. d. Some transmembrane domains have amino acids with charged amino acid side chains. e. Some hydrophobic amino acids in membrane proteins are not in contact with the lipid bilayer.

a. In transmembrane proteins that form an aqueous pore through the membrane, the pore is lined with hydrophobic amino acid side chains.

The energy input required to initiate an energetically favorable reaction is called the: a. activation energy. b. kinetic energy. c. free energy. d. potential energy. e. chemical bond energy.

a. activation energy

An enzyme can increase the rate of conversion of substrate (S) to product (P) for the reaction depicted below by: a. decreasing a b. decreasing b and c by the same amount. c. decreasing a and b by the same amount. d. decreasing c. e. decreasing b.

a. decreasing a

Forces that determine the folding of a macromolecule into distinct shape include all of the following except: a. magnetic interactions b. hydrogen bonds c. van der Waals forces d. hydrophobic interactions e. ionic interactions

a. magnetic interactions

The plasma membrane of an animal cell is symmetric with regard to: a. the distribution of cholesterol in each half of the lipid bilayer b. the orientation of membrane proteins in the lipid bilayer. c. the distribution of glycolipids in the lipid bilayer d. the distribution of different phospholipids in each half of the lipid bilayer. e. All of the above

a. the distribution of cholesterol in each half of the lipid bilayer.

Living organisms require a continual supply of energy to exist because: a. they are creating order out of disorder inside their cells b. they convert it into heat energy which powers biosynthetic reactions. c. they are closed systems isolated from the rest of the universe. d. they are defying the laws of thermodynamics. e. they are causing the entropy in the universe to decrease.

a. they are creating order out of disorder inside their cells

All of the following statements about channel proteins are true EXCEPT: a. they can move ions up an electrochemical gradient. b. they move ions at faster rates than carrier proteins. c. they are integral membrane proteins. d. they fluctuate between open and closed states. e. they might have amphipathic transmembrane segments.

a. they can move ions up an electrochemical gradient

Which of the following processes must be coupled to an energetically favorable reaction in order to occur? a. Formation of a bilayer from phospholipids in water. b. Polymerization of amino acids into polypeptides. c. Conversion of glucose to carbon dioxide and water. d. The hydrolysis of ATP. e. Conversion of protein into amino acids

b. Polymerization of amino acids into polypeptides.

Which of the following elements is least abundant in living organisms? A. Oxygen B. Sulfur C. Carbon

b. Sulfur

The possible effects of adding sugars to a protein include all of the following EXCEPT: a. Sugar moieties spread out in aqueous solution, maximizing H-bonding. b. The hydrophobic nature of sugars reduces the tendency of a protein to aggregate. c. Addition of sugars provides molecular diversity to proteins. d. Glycosylation protects a protein from degradation. e. Addition of sugars may regulate protein/receptor interactions

b. The hydrophobic nature of sugars reduces the tendency of a protein to aggregate.

A strain of bacteria secretes a toxin that can lyse human red blood cells. You are able to partially purify the toxin and find that it is a small protein. Furthermore, the toxin is capable of rendering liposomes made of pure phospholipids permeable to many different ions. What type of protein is the bacterial toxin likely to be? A. a flippase. B. a beta-barrel protein. C. a protease. D. a protein containing a single hydrophobic alpha helix. E. An enzyme that adds carbohydrate groups to lipids.

b. beta-barrel protein

H bonds can form between a a. between two hydrogens bound to a carbon atoms b. between a nitrogen atom and a hydrogen bound to an oxygen atom c. between a nitrogen atom and a hydrogen bound to a carbon atom d. between a sulfur atom and a nitrogen atom e. between an oxygen atom and a nitrogen atom

b. between a nitrogen atom and a hydrogen bound to an oxygen

A helical structure: a. can form either within a single large molecule or from an assembly of separate molecules. b. can form only by joining together a string of identical protein molecules. c. has to have free ends on each side. d. will contain two, three, four, or some other exact number of subunits per each turn of the helix. e. that is right-handed if viewed from one end will appear to be left-handed if viewed from its other end.

b. can form only by joining together a string of identical protein molecules

Which of the following statements describe the typical biomembrane: a. all lipids and proteins in the biomembrane are equally mobile b. it may include different kinds of lipid molecules c. the lipid molecules are attached to each other through covalent bonds d. it contains a hydrophilic core e. it is a symmetrical structure

b. it may include different kinds of lipid molecules

Which of the following are the same in all atoms of an element? a. Number of neutrons. b. number of protons c. mass d. atomic weight e. number of neutrons plus protons

b. number of protons

Atoms form covalent bonds with each other by: a. attraction of positive and negative charges. b. sharing electrons. c. sharing protons. d. transferring electrons from one atom to the other. e. sharing neutrons.

b. sharing electrons

The generation and maintenance of a membrane potential depends on all of the following EXCEPT: a. ATP. b. voltage-regulated ion channels. c. a selectively permeable membrane. d. active pumping of the permeant ions. e. passive diffusion.

b. voltage-regulated ion channels

Which of the following statements are correct? a. Since the structure of a protein is determined solely by its amino acid sequence, a genetically engineered protein of the reverse sequence would have the same structure as the original protein. b. A alpha sheet can contain up to five strands, but no more. c. amino acids behave as acids and bases. d. The tertiary structure is the localized folding arrangement of a polypeptide chain. e. Alpha helices are depicted as flattened arrows on a ribbon diagram.

c. Amino acids behave as acids and bases.

Predict which of the following organisms will have the highest percentage of unsaturated phospholipids in their membranes.—unsaturated = double bonds = increases fluidity a. Thermophilic bacterium b. Human being c. Antarctic fish d. Desert snake e. Polar bear

c. Antarctic fish

Which of the following reactions does the underlined atom undergo an oxidation? a. Na+ -> Na b. Cl -> Cl- c. CH3CHO -> CH3COOH d. CH3CH2OH -> CH3CHO

c. CH3CHO -> CH3COOH

New membrane synthesis occurs by: A. the spontaneous aggregation of free phospholipids into a new bilayer in the aqueous environment of the cell. B. incorporation of phospholipids into both faces of a preexisting membrane by enzymes attached to each face. C. incorporation of phospholipids into one face of a preexisting membrane and their random redistribution to both faces by flippases. D. de novo biosynthesis of phospholipids within a preexisting membrane by enzymes. E. incorporation of phospholipids into one face of a preexisting membrane and their specific redistribution by flippases.

c. Incorporation of phospholipids into one face of a preexisting membrane and their random redistribution to both faces by flippases.

Which of the following statements are true? a. Resting cells do not produce any heat. b. Enzymes that couple unfavorable reactions to favorable reactions cause a decrease in total entropy. c. Life is a thermodynamically spontaneous process. d. The only processes that can occur to any significant degree are those that decrease the disorder in the universe. e. Growing cells release less heat to the environment than resting cells because they use more energy.

c. Life is a thermodynamically spontaneous process.

In a typical animal cell, which of the following types of transport occurs through a channel protein?—channel protein = passive transport = solutes moving spontaneously across membranes down concentration gradient a. Movement of glucose out of a starved cell. b. Movement of amino acids into a cell. c. Movement of Na+ into a cell. d. Movement of Na+ out of a cell. e. Movement of glucose into a starved cell.

c. Movement of Na+ into a cell.

Which of the following statements regarding the fatty acid tails of phospholipids are false? a. Most membrane phospholipids have one fully saturated tail. b. Saturated phospholipid tails pack more tightly against each other than do unsaturated tails. c. Fatty acid tails vary in length. d. Phospholipids with unsaturated tails make the bilayer more fluid because the tails contain fewer hydrogens and thus form fewer hydrogen bonds with each other. e. Phospholipid tails in a membrane can interact with each other via van der Waals interactions.

c. Phospholipids with unsaturated tails make the bilayer more fluid because their tails contain fewer hydrogens and thus form fewer hydrogen bonds with each other.

Which of the following pairs of atoms do you expect to be able to form double bonds with each other? a. Mg/Ca b. C/Cl c. S/O d. C/H e. He/O

c. S/O

An action potential depends directly on all of the following EXCEPT: a. activation of voltage-dependent ion channels. b. chemical gradients of permeant ions. c. activation of the Na+-K+ ATPase. d. inactivation of voltage-dependent ion channels. e. a rapid change in membrane potential

c. activation of Na+-K+-ATPase

The energy required by a human cell to grow and reproduce is provided by: A. the generation of order inside it. B. its anabolic metabolism. C. its catabolic metabolism D generation of heat. E. its biosynthetic reactions.

c. its catabolism metabolism

For a reaction to occur spontaneously" A. deltaG must be positive B. the reaction must be energetically unfavorable C. the products must have a lower energy than the reactants D. an input of energy must be provided. E. an enzyme must be present.

c. the products must have a lower energy than the reactants

An ionic bond between two atoms is formed as a result of: a. sharing of electrons. b. loss of a proton from one atom. c. transfer of electrons from one atom to the other. d. loss of a neutron from one atom. e. loss of electrons from both atoms.

c. transfer of electrons from one atom to the other

During an action potential, a sodium ion channel goes through the following states:

closed -> open -> inactivated -> closed

Which of the following is NOT a benefit of using a chain of neurons and chemical synapses rather than a direct connection between the site of stimulus and the site of response? a. Chemical synapses allow neurons to receive and integrate input from more than one source. b. Modification of different ion channels at synapses can be used to generate memory on the cellular level. c. Use of chemical synapses increases the variety of messages the presynaptic cell can send to the postsynaptic cell. d. Diffusion of small molecules is more rapid than propagation of an electric signal; thus the signal is speeded up by having more synapses. e. Each chemical synapse represents an opportunity for the organism to modify the signal being sent.

d. Diffusion of small molecules is more rapid than propagation of an electric signal; thus the signal is speeded up by having more synapses

Which of the following movements can a membrane protein make by lateral diffusion through the lipid bilayer? a. Movement from the outer nuclear membrane to the inner nuclear membrane. b. none of the above. c. Movement from the outer nuclear membrane to the endoplasmic reticulum d. Movement from the outer mitochondrial membrane to the inner mitochondrial membrane e. Movement from the apical plasma membrane to the basal plasma membrane in a gut epithelial cell.

d. Movement from the outer mitochondrial membrane to the inner mitochondrial membrane

Which of the following might act as an ER "signal sequence"? a. NH3+-M- A-N-L- L-H-A-L-V-R-R-R-R-L-V-G-A-L-V- b. NH3+-M- A-N-L- L-H-R-L-D-A-Q-S-K-L-S-S c. ------KKKKKKK d. NH3+-M- A-N-L- L-H-A-L-V-A-I-G-A-L-V-G-A-L-V e. ----KDEL ---- ER retention signal (Lys-Asp-Glu-Leu-COO-)

d. NH3+-M-A-N-L-L-H-A-L-V-A-I-G-A-L-V-G-A-L-V

Which of the following statements is true? a. A protein chain ends in a free amino group at the C-terminus. b. The sequence of the atoms in the polypeptide backbone varies between different proteins. c. Peptide bonds are the only covalent bonds that can link together two amino acids d. Nonpolar amino acids tend to be found in the interior of proteins. e. The polypeptide backbone of some proteins is branched.

d. Non polar amino acids tend to be found in the interior of proteins

Based on what you know about the properties of water, which of the following statements about methanol (CH3OH) are true? a. Methanol molecules form more hydrogen bonds than water molecules do. b. Methanol is a more cohesive liquid than water. c. The boiling point of methanol is higher than that of water. d. Salts such as NaCl are less soluble in methanol than in water. e. Methanol has a higher surface tension than water.

d. Salts such as NaCl are less soluble in methanol than in water.

Which of the following statements is not true? a. At the resting membrane potential, ion channels fluctuate between open and closed conformations. b. Facilitated transport does not require energy. c. Passive transport can be mediated by conformational change of a membrane protein. d. The facilitated diffusion of glucose across the cell membrane depends on membrane proteins called gated channels. e. Absorption of a photon of light can drive active transport.

d. The facilitated diffusion of glucose across the cell membrane depends on membrane proteins called gated channels

Gut intestinal epithelial cells, as illustrated below, have several characteristics essential for their function, including: a. a Na+-K+ pump that pumps Na+ into the cell to maintain the Na+ electrochemical gradient. b. free diffusion of glucose carriers throughout the cell so glucose can be both brought into the cell from the gut and flow out of the cell to the extracellular fluid. c. a glucose carrier protein on the basal membrane that uses active transport to transfer glucose to the extracellular fluid d. a glucose carrier protein on the apical membrane that uses active transport to bring sugar into the cell. e. microvilli on their basal membranes, to increase the surface area for more efficient absorption of glucose

d. a glucose carrier protein on the apical membrane that uses active transport to bring sugar into the cell

Energetically favorable reactions are those that: A. decrease the entropy of a system. B. increase the free energy of a system. C. have a positive DeltaG. D. decrease the free energy of a system. E. create order in a system.

d. decrease the free energy of a system

The action potential travels in one direction because: a. depolarization of the membrane causes voltage-gated K+ channels to open. b. voltage-gated Na+-channels spend less time in the open conformation when the membrane returns to the resting potential. c. the K+ leak channels allow K+ to flow out, restoring the membrane to resting potential. d. voltage-gated Na+ channels adopt a transitory inactive conformation after being opened. e. The Na+-K+ pump restores the concentrations of Na+ and K+ to their original levels.

d. voltage-gated Na+ channels adopt a transitory inactive conformation after being opened.

Which of the following statements about the basic chemistry of cells are true? a. All cells contain exactly the same proteins. b. All organisms contain the same genes. c. All proteins are constructed from the same 22 amino acids. e. All genetic instructions in cells are stored in DNA

e. All genetic instructions in cells are stored in DNA

Peripheral membrane proteins can be attached to the membrane by all of the following except: a. Electrostatic interactions with phospholipids. b. An isoprene (farnesyl) tail attached to a CAX box at its C-terminus. c. A GPI (glycophosphatidylinositol) tail attached to its C-terminus. d. Partial penetration of the lipid bilayer. e. Association with microtubules.

e. Association with microtubules

Which statement below is true? a. Carrier proteins allow solutes to cross a membranes at much faster rates than do channel proteins. b. A symport would function as an antiport if its orientation in the membrane were reversed (i.e., if the portion of the molecule normally exposed to the cytosol faced outside the cell instead). c. The plasma membrane is highly impermeable to all charged molecules. d. Channel proteins must first bind to solute molecules before they can select those that they will allow to pass. e. Certain H+ pumps are fueled by light energy.

e. Certain H+ pumps are fueled by light energy

Which of the following pairs of elements are likely to form ionic bonds? Use the following Figure if necessary a. Carbon and oxygen b. Sulfur and hydrogen c. Hydrogen and hydrogen. d. Carbon and chlorine e. Magnesium and chlorine.

e. Magnesium and chlorine

Which of the following statements about amino acids are true? a. Not all amino acids have R groups. b. D- and L-amino acids are found in proteins. c. Twenty-two amino acids are commonly found in proteins. d. Most of the amino acids used in protein biosynthesis have charged side chains. e. Proline is formally not an amino acid but an imino acid

e. Proline is formally not an amino acid but an imino acid.

Carrier proteins can be classified into different types listed below EXCEPT: a. Uniporters b. Symporters c. Antiporters d. Coupled transporters e. Quasiporters

e. Quasiporters

Where does the most new membrane synthesis take place in a eukaryotic cell? a. The Golgi apparatus. b. The plasma membrane. c. Cytoplasmic membrane vesicles. d. The mitochondria. e. The endoplasmic reticulum.

e. The endoplasmic reticulum

The polar property of water is important for all of the following EXCEPT: a. the hydration shells of free ions b. the clustering of hydrophobic residues of a polypeptide in solution. c. the ionization of water d. the hydrogen bond formation between neighboring water molecules. e. the contraction of volume when water freezes

e. the contraction of volume when water freezes

All of the proteins listed below are enzymes EXCEPT: a. nuclease b. polymerase c. ATPase d. kinase e. antibody

e. antibody

Assembling the individual enzymes required for a multistep process into a protein machine is likely to increase the efficiency with which the entire process is carried out in all of the following ways EXCEPT: a. by coordinating the regulation of the individual enzymes. b. by increasing the rate at which the individual enzymes encounter their substrates. c. by coordinating the movement of the enzymes. d. by ordering the reactions sequentially. e. by increasing the Vmax of the individual enzymes.

e. by increasing the Vmax of the individual enzymes

The specificity of macromolecular assembly is influenced by multiple weak interactions provided by all of the following except: A. hydrogen bonding B. van der Waals interactions C. ionic interactions D. hydrophobic interactions E. disulfide bonds

e. disulfide bonds

All known proteins in cells adopt a stable conformation because: A. any chain of amino acids can fold up into only one stable conformation. B. they are complexed with other molecules that keep them in that one particular conformation. C. once folded, proteins are surrounded by a cage of water molecules that keep them in that one particular conformation. D. chaperone proteins prevent the protein from adopting a preferred unstable conformation. E. protein chains that can adopt many different conformations have been weeded out by natural selection.

e. protein chains that can adopt many different conformations have weeded out by natural selection.