Topic 5 Practice Problems Flashcards
Which of the following is NOT a general feature of the lipid bilayer in biological membranes?
A. The polar head groups of the membrane lipids face outwards to interact with the aqueous environment.
B. Individual lipid molecules are free to diffuse laterally within one leaflet of the bilayer.
C. The thickness of the bilayer depends on the length of the fatty acids in the lipids.
D. The bilayer is stabilized by covalent interactions between the lipid molecules and integral membrane proteins.
D. The bilayer is stabilized by covalent interactions between the lipid molecules and integral membrane proteins.
Which of the following forms bilayers spontaneously in water? A. Glycerophospholipids B. Triacylglycerols C. Cholesterol D. Fatty acids
A. Glycerophospholipids
Which one of the following is a general feature of the lipid bilayer in all biological membranes?
A. Individual lipid molecules are free to diffuse laterally in the bilayer.
B. Polar, but uncharged, compounds readily diffuse across the bilayer.
C. The bilayer is stabilized by covalent bonds between neighboring phospholipid molecules.
D. Individual lipid molecules in one face (monolayer) of the bilayer readily diffuse (flip-flop) to the other monolayer.
A. Individual lipid molecules are free to diffuse laterally in the bilayer.
Which of the following forms micelles spontaneously in water? A. Cholesterol B. Glycerophospholipids C. Fatty acids D. Triacylglycerols
C. Fatty acids
Which of the following statements regarding membrane proteins is FALSE?
A. Amino acid side chains positioned on the outside surface of the transmembrane domain of integral membrane proteins are non-polar.
B. Amino acid side chains positioned inside the transmembrane domain (region) of integral membrane proteins may be polar or non-polar.
C. Integral membrane proteins use either -helical or β-sheet secondary structure to satisfy the hydrogen-bonding requirements of backbone groups in portions of the protein that cross the bilayer.
D. Peripheral membrane proteins position hydrophilic amino acid side chains in the loop portions of their secondary structure, but integral membrane proteins do not.
D. Peripheral membrane proteins position hydrophilic amino acid side chains in the loop portions of their secondary structure, but integral membrane proteins do not.
Which of the following statements describing cholesterol in biological membranes is TRUE?
A. Cholesterol’s planar ring structure is highly flexible, which maximizes its interactions with the acyl tails of neighboring lipids.
B. Cholesterol is an important component of the plasma membrane in mammalian cells.
C. Cholesterol has no effect on the stability or transition temperature of a membrane.
D. Cholesterol is located between the polar head groups of the membrane lipids.
B. Cholesterol is an important component of the plasma membrane in mammalian cells.
Which of the following statements CORRECTLY describes triacylglycerols?
A. Triacylglycerols always contain three identical esterified fatty acids.
B. Triacylglycerols are molecules of energy storage.
C. Triacylglycerols form lipid bilayers in aqueous solutions.
D. Triacylglycerols are amphiphilic molecules.
E. Triacylglycerols have a polar head group.
B. Triacylglycerols are molecules of energy storage.
If polar amino acids are found in a membrane spanning -helical region, they are most likely _____.
A. mutations
B. modified with nonpolar groups by prenylation, methylation and/or acylation
C. hydrogen-bonded to other polar amino acids to prevent interaction with the membrane lipids
D. hydrogen-bonded with hydroxyl groups of the membrane fatty acids
E. none of the above
C. hydrogen-bonded to other polar amino acids to prevent interaction with the membrane lipids
Match the following:
Integral (intrinsic) membrane proteins Transmembrane protein Porins Lipid-linked proteins Peripheral (extrinsic) proteins
- Channel-forming proteins found in the outer membranes of bacteria, with a beta-barrel motif.
- Proteins that are associated with membranes, but can be dissociated by relatively mild procedures.
- Proteins that completely span the membrane.
- A general class of proteins that are tightly bound to membranes by hydrophobic interactions.
- Membrane-associated proteins that have covalently-bonded lipids.
Integral (intrinsic) membrane proteins 4. A general class of proteins that are tightly bound to membranes by hydrophobic interactions.
Transmembrane protein 3. Proteins that completely span the membrane.
Porins 1. Channel-forming proteins found in the outer membranes of bacteria, with a beta-barrel motif.
Lipid-linked proteins 5. Membrane-associated proteins that have covalently-bonded lipids.
Peripheral (extrinsic) proteins 2. Proteins that are associated with membranes, but can be dissociated by relatively mild procedures.
Lipid-linked proteins come in three varieties: fatty acylated proteins, prenylated proteins, or glycosylphosphatidylinositol-linked proteins. True/False
True
When secreted in the human body, the hormone glucagon causes rapid degradation of glycogen in liver cells. This mobilization of glycogen is accomplished though a signaling pathway. What is the proper temporal sequence of the following steps in this reaction cascade?
A - displacement of GDP with GTP on the a-subunit of the G-proteins
B - phosphorolysis of glycogen
C - dissociation of the regulatory subunits activates protein kinase A
D - phosphorylation of glycogen phosphorylase
E - glucagons binds to a specific, transmembrane receptor
F – formation of cyclic-AMP by adenylyl cyclase
E-A-F-C-D-B
Which of the following statements concerning receptors is CORRECT?
A. They have a ligand binding site on the extracellular side of the membrane.
B. They have an active site on the extracellular side of the membrane.
C. They bind signal molecules in a non-specific manner.
D. They contain an enzyme activity for which the signal molecule is a substrate.
A. They have a ligand binding site on the extracellular side of the membrane.
Which of the following would diminish a hormone signal mediated via a G protein signal transduction system?
A. Addition of a substance which inhibits adenylate cyclase.
B. Greater than normal expression of the receptor in the cell membrane.
C. Addition of a substance such as caffeine, which inhibits phosphodiesterase.
D. Addition of a substance which inhibits the GTPase activity of the G protein.
A. Addition of a substance which inhibits adenylate cyclase.
Which of the following is never a second messenger? A. A protein. B. A carbohydrate derivative. C. A lipid. D. A calcium ion. E. A nucleotide.
A. A protein.
In a G protein signaling pathway, what would happen if phosphodiesterase were inactivated?
A. The first messenger (ligand) could not elicit its desired metabolic response.
B. Protein kinase A would remain active.
C. The G protein could no longer reassociate.
A and B
B and C
B. Protein kinase A would remain active.
Which of the following is NOT a general component of a signal transduction pathway? A. Target proteins (enzymes). B. G proteins. C. First messengers (ligand). D. Receptors E. The cell (plasma) membrane.
B. G proteins.
Which of the following would REDUCE a hormone signal mediated via the G protein signal transduction system?
A. Addition of a substance that activates protein phosphatases.
B. Addition of a substance that inhibits phsphodiesterase.
C. Addition of a substance that activates adenylate cyclase.
D. A and C
A. Addition of a substance that activates protein phosphatases.
In a G protein signal-transduction system, what role does the G protein play?
A. It produces the second messenger molecule.
B. It transmits the signal from the receptor to other components of the signaling system.
C. It activates a target protein (enzyme).
D. It reverses the activation of the receptor caused by ligand binding.
B. It transmits the signal from the receptor to other components of the signaling system.
Which of the following is not a function of nucleotides in living cells?
A. They are precursors of nucleic acid synthesis.
B. They are carriers of metabolic energy.
C. They can be intracellular signals.
D. They serve as cofactors in enzymes.
E. They can be the first messenger in a signaling pathway.
E. They can be the first messenger in a signaling pathway.
When a receptor loses its ability to transmit a signal following continuous exposure to a ligand, the receptor is said to be \_\_\_\_\_. A. saturated B. desensitized C. transduced D. specific E. none of the above
B. desensitized
Match the following:
Saturated fatty acid Unsaturated fatty acid Triacylglycerol Glycerophospholipid Sphingolipid Steroid Eicosanoid
- Cholesterol
- Prostaglandin H2
- Phosphatidylcholine
- Stearic acid
- 1-palmitoyl-2-linoleoyl-3-stearoyl-glycerol
- Oleic acid
- Sphingomyelin
Saturated fatty acid 4. Stearic acid
Unsaturated fatty acid 6. Oleic acid
Triacylglycerol 5. 1-palmitoyl-2-linoleoyl-3-stearoyl-glycerol
Glycerophospholipid 3. Phosphatidylcholine
Sphingolipid 7. Sphingomyelin
Steroid 1. Cholesterol
Eicosanoid 2. Prostaglandin H2
Palmitic acid is a _____ acid.
fatty
Polyunsaturated fatty acids contain multiple ______ bonds.
double
Fatty acid double bonds almost always have the _____ configuration.
cis
Phosphatidylethanolamine has a net charge of _____ at pH 7.0.
0
Lipid molecules are the only essential components of biological membranes. True/False
False
The chemical structure of Vitamin D is closely related to cholesterol. True/False
True
The chemical structure of Vitamin D is closely related to cholesterol. True/False
True
Which is not a structural feature of cholesterol? A. Alcohol group B. Rigidity C. Octyl group D. Aromatic ring
D. Aromatic ring
Match the following:
Spheroidal micelles Liposomes Broadens phase transitions Thinner, fluid bilayer Thicker, gel-like bilayer
- Cholesterol
- Above the transition temperature
- Phospholipids
- Below the transition temperature
- Detergents
Spheroidal micelles 5. Detergents
Liposomes 3. Phospholipids
Broadens phase transitions 1. Cholesterol
Thinner, fluid bilayer 2. Above the transition temperature
Thicker, gel-like bilayer 4. Below the transition temperature
Lipids in bilayers have high rates of ______ diffusion.
Lateral
Biological membranes contain both lipids and_____ . .
Proteins
Geometrical considerations influence the types of micelles that lipids form. True/False
True
In a bilayer, lipids diffuse rapidly, both laterally and transversely. True/False
False
In biological membranes, the fatty acyl chains of lipids tend to remain fully-extended and well-packed. True/False
False
The transition temperature of a bilayer depends upon the composition of lipids. True/False
True
Match the following:
Integral (intrinsic) membrane proteins Transmembrane protein Porins Lipid-linked proteins Peripheral (extrinsic) proteins
- Channel-forming proteins found in the outer membranes of bacteria, with a beta-barrel motif.
- Proteins that are associated with membranes, but can be dissociated by relatively mild procedures.
- Proteins that completely span the membrane.
- A general class of proteins that are tightly bound to membranes by hydrophobic interactions.
- Membrane-associated proteins that have covalently-bonded lipids.
Integral (intrinsic) membrane proteins 4 Transmembrane protein 3 Porins 1 Lipid-linked proteins 5 Peripheral (extrinsic) proteins 2
α-helices and β-sheets allow transmembrane proteins to maximize hydrophobic interactions with lipids and minimize hydrophilic exposure to the lipids in the membrane. True/False
True
Which statement does NOT accurately describe integral membrane proteins?
A. Integral proteins are bound to membranes through hydrophobic interactions.
B. Integral proteins typically have covalently-bound lipids.
C. Integral proteins typically have transmembrane α-helices or β-strands.
D. Integral proteins tend to aggregate in aqueous solutions unless detergents are present. (Incorrect. This is true.)
B. Integral proteins typically have covalently-bound lipids.
Integral proteins tend to be completely buried in membranes. True/ FAlse
False
1) What are the characteristics of most unsaturated fatty acids found within a human cell?
A) protonated carboxylic acid and trans double bonds
B) deprotonated carboxylic acid and trans double bonds
C) protonated carboxylic acid and cis double bonds
D) deprotonated carboxylic acid and cis double bonds
E) none of the above
D) deprotonated carboxylic acid and cis double bonds
2) Which of the following is considered an omega-3 fatty acid?
A) 9,12-Octadecadienoic acid B) 9,12,15-Octadecatrienoic acid C) 6,9,12-Octadecatrienoic acid D) 8,11,14-Eicosatrienoic acid E) 5,8,11,14-Eicosatetraenoic acid
B) 9,12,15-Octadecatrienoic acid
3) The major lipid component of cell membranes are _____.
A) triacylglycerols B) cholesterol C) glycerophospholipids D) plasmologens E) gangliosides
C) glycerophospholipids
4) Which of the following alcohols is esterified to the phosphate group of glycerophospholipids?
A) choline B) ethanolamine C) glycerol D) serine E) all of the above
E) all of the above
5) The most notable difference between _____ and other lipids is the presence of four fused rings.
A) cholesterol B) arachidonic acid C) gangliosides D) plasmologens E) triacylglycerols
A) cholesterol
6) Which of the following terms describes all glycerophospholipid?
A) zwitterionic B) amphipathic C) nonpolar D) amphoteric E) none of the above
B) amphipathic
7) Which of the following is the primary building block for the synthesis of molecules like cholesterol or ubiquinone?
A) acetyl-CoA B) palmitic acid C) choline D) isoprene E) sphingosine
D) isoprene
8) A type of lipid that commonly forms a waterproof barrier and is composed of a fatty acid and a fatty alcohol is called a _____.
A) terpenoid B) ganglioside C) capsaicin D) steroid E) wax
E) wax
9) Which of the following vitamins is derived from cholesterol?
A) vitamin A B) vitamin D C) vitamin E D) vitamin K E) none of the above
B) vitamin D
10) What two molecules are used in the synthesis of sphingosine?
A) arachidonic acid and serine B) stearic acid and isoprene C) palmitic acid and choline D) linoleic acid and isoprene E) palmitic acid and serine
E) palmitic acid and serine
11) Which of the following explains why free fatty acids do not form bilayers?
A) the width of the polar head is greater than the nonpolar tail
B) the width of the polar head is less than the nonpolar tail
C) the width of the polar head is equal to the nonpolar tail
D) the width of the nonpolar head is greater than the polar tail
E) the width of the nonpolar head is less than the polar tail
A) the width of the polar head is greater than the nonpolar tail
12) As temperatures grow colder with the onset of winter, animals will adapt by changing the fatty acid composition of cell membranes. What characteristics of fatty acids will be seen?
A) longer chains with greater unsaturation
B) longer chains with greater saturation
C) shorter chains with greater unsaturation
D) shorter chains with greater saturation
E) chain length and saturation do not change in a cell membrane
C) shorter chains with greater unsaturation
13) A membrane raft is a(n) _____ in the lipid bilayer of a cell membrane.
A) transmembrane protein
B) integral membrane protein oriented to the intracellular side
C) integral membrane protein oriented to the extracellular side
D) region of high cholesterol and sphingolipid content
E) none of the above
D) region of high cholesterol and sphingolipid content
14) Which of the following is true regarding membrane asymmetry?
A) transverse diffusion occurs very quickly
B) lateral diffusion occurs very slowly
C) a flippase causes lateral diffusion to occur very rapidly
D) carbohydrates attached to membrane lipids are usually found on the cytosolic side of the membrane
E) none of the above
E) none of the above
15) In an -helical protein that spans a cell membrane, _____ would likely be in the center of the membrane while _____ would likely be associated with the polar head groups and _____ would likely be associated with the aqueous environment
A) Trp; Asn; Ala B) Leu; Gln; Asp C) Tyr; Glu; Gly D) Ile; Arg; Gln E) Val; Ser; Thr
B) Leu; Gln; Asp
16) Which of the following statements describes integral membrane proteins?
A) they never completely span the lipid bilayer
B) they are easily removed by changes in pH or high salt
C) amino acids that contact the core of the membrane are hydrophobic
D) they tend to be water soluble
E) their association with the membrane is through an attached fatty acyl or prenyl group
C) amino acids that contact the core of the membrane are hydrophobic
17) If a transmembrane domain of protein contains -sheet structure, the overall structure of the transmembrane portion is likely a ____________.
A) -barrel B) -tube C) -turn D) -helix E) none of the above
A) -barrel
18) Which fatty acid is commonly attached to proteins to allow membrane localization?
A) eicosapentaenoic acid (EPA) B) arachidonic acid C) linoleic acid D) myristic acid E) farnesylic acid
D) myristic acid
19) If polar amino acids are found in a membrane spanning -helical region, they are most likely _____.
A) mutations
B) modified with nonpolar groups by prenylation, methylation and/or acylation
C) hydrogen-bonded to other polar amino acids to prevent interaction with the membrane lipids
D) hydrogen-bonded with hydroxyl groups of the membrane fatty acids
E) none of the above
C) hydrogen-bonded to other polar amino acids to prevent interaction with the membrane lipids
20) Which of the following is a characteristic of integral membrane proteins?
A) most of their movement is by lateral diffusion
B) transverse diffusion occurs often but rather slowly
C) interactions between proteins makes the membrane highly rigid
D) all have carbohydrates attached to the extracellular domain
E) none of the above
A) most of their movement is by lateral diffusion
21) The carbohydrate portion of a membrane spanning glycoprotein is found _____.
A) spanning the membrane
B) on both the cytoplasmic and extracellular sides of the membrane
C) only on the cytoplasmic side of the membrane
D) only on the extracellular side of the membrane
E) carbohydrates are not found on membrane spanning glycoproteins
D) only on the extracellular side of the membrane
22) Which of the following aspects of membrane protein movement is explained by the fluid mosaic model?
A) proteins that are immobile are often esterified to cholesterol via an Asp residue
B) proteins that are mobile only in a small area are sequestered by proteins attached to the cytoskeleton
C) proteins that freely diffuse through the membrane often undergo flip-flopping
D) proteins confined to a lipid raft are linked to phosphatidylserine via and amide bond
E) none of the above
B) proteins that are mobile only in a small area are sequestered by proteins attached to the cytoskeleton
When GTP is bound to G proteins (alpha subunit) the complex is _______.
active
How do heterotrimeric G-proteins work?
A. Ligand binding to a receptor activates the G-protein, by allowing GDP to exchange for GTP at the α subunit, while the β and γ subunits dissociate. )
B. Ligand binding to a receptor activates the G-protein, by allowing GTP to exchange for GDP at the α subunit, while the β and γ subunits dissociate.
C. cAMP binding to adenylate cyclase activates the G-protein, by allowing GTP to exchange for GDP at the α subunit, while the β and γ subunits dissociate.
D. Ligand binding to a receptor activates the G-protein, by allowing GTP to exchange for GDP at the β subunit, while the α and γ subunits dissociate.
B. Ligand binding to a receptor activates the G-protein, by allowing GTP to exchange for GDP at the α subunit, while the β and γ subunits dissociate.
How does cAMP function as a second messenger?
A. cAMP is produced by cAMP phosphodiesterase in response to G-protein activation, it activates many enzymes through cAMP-dependent protein kinase, and it is eliminated through cAMP phosphodiesterase.
B. cAMP is produced by adenylate cyclase in response to G-protein activation, it activates many enzymes through cAMP-dependent protein kinase, and it is eliminated through cAMP phosphodiesterase.
C. cAMP is produced by adenylate cyclase in response to G-protein deactivation, it activates many enzymes through cAMP-dependent protein kinase, and it is eliminated through cAMP phosphodiesterase.
D. cAMP is produced by adenylate cyclase in response to G-protein activation, it activates many enzymes through cAMP-dependent protein phosphatase, and it is eliminated through cAMP phosphodiesterase.
B. cAMP is produced by adenylate cyclase in response to G-protein activation, it activates many enzymes through cAMP-dependent protein kinase, and it is eliminated through cAMP phosphodiesterase.
1) Hormones bind to _____ with _____ affinity.
A) ligands; low B) agonists; high C) antagonists; low D) G proteins; low E) receptors; high
E) receptors; high
2) When a receptor loses its ability to transmit a signal following continuous exposure to a ligand, the receptor is said to be _____.
A) saturated B) desensitized C) transduced D) specific E) none of the above
B) desensitized
3) Which of the following can be a hormone?
A) amino acid derivatives B) steroids C) polypeptides D) eicosanoids E) all of the above
E) all of the above
4) A sample of cells with a total receptor concentration of 50 M was incubated with a ligand concentration of 100 M. Following the incubation period, the concentration of unbound receptors was determined to be 15 M. What is the Kd for the receptor-ligand interaction?
A) 28 M B) 43 M C) 143 M D) 217 M E) 333 M
A) 28 M
5) A small molecule produced inside a cell in response to a hormone binding to its receptor is called a(n) _____.
A) inside messenger B) agonist C) antagonist D) second messenger E) G protein
D) second messenger
6) Which of the following is a ligand of the 2-adrenergic receptor?
A) tyrosine B) serotonin C) norepinephrine D) caffeine E) adenosine
C) norepinephrine
7) Activation of a G protein in response to hormone binding requires binding of _____ to the _____ subunit.
A) GDP; b B) GTP; a C) GDP; g D) GTP; b E) GDP; a
B) GTP; a
8) What enzyme is activated by association with an active G protein?
A) adenylate cyclase B) cAMP phosphodiesterase C) protein kinase A D) protein kinase G E) all of the above
A) adenylate cyclase
9) The second messenger _____ is produced by the enzyme _____.
A) nitric oxide; arginase
B) cGMP; GTP cyclase
C) cAMP; adenylate cyclase
D) triacylglycerol; phospholipase C
E) inositol diphosphate; phospholipase C
C) cAMP; adenylate cyclase
10) cAMP binds to the _____ subunits of protein kinase A allowing the tetramer to dissociate into _____.
A) active subunits; an active dimer and two inactive monomers
B) active subunits; two active monomers and an inactive dimer
C) regulatory subunits; an active dimer and two inactive monomers
D) regulatory subunits; two active monomers and an inactive dimer
E) regulatory subunits; two active monomers and two inactive monomers
D) regulatory subunits; two active monomers and an inactive dimer
11) What two amino acid residues are the targets of protein kinase A?
A) Asn and Gln B) Thr and Ser C) Tyr and Thr D) Ser and Tyr E) Cys and Ser
B) Thr and Ser
12) Desensitization of a G protein-coupled receptor is caused by phosphorylation of the receptor by a specific kinase. What protein recognizes the phosphorylated receptor?
A) phospholipase C B) the G protein subunit C) cAMP phosphodiesterase D) adenosine receptor E) arrestin
E) arrestin
13) The second messenger _____ opens Ca2+ channels in the endoplasmic reticulum.
A) inositol trisphosphate B) diacylglycerol C) cAMP D) cGMP E) nitric oxide
A) inositol trisphosphate
14) Ligand binding to a receptor tyrosine kinase causes _____ of the receptor which then _____ the next protein in the signaling pathway.
A) methylation; hydrolyzes B) hydrolysis; inhibits C) phosphorylation; phosphorylates D) acylation; activates E) none of the above
C) phosphorylation; phosphorylates
15) The _____ receptor is a receptor tyrosine kinase.
A) 1- adrenergic B) 2-adrenergic C) calmodulin D) insulin E) cortisol
D) insulin
16) Activity of the Ras protein is analogous to the _____ in terms of its ability to bind GTP.
A) G protein a subunit B) G protein b subunit C) G protein g subunit D) calmodulin E) all of the above
A) G protein a subunit
17) Where are the ultimate targets of the Ras-dependent signaling cascade located within the cell?
A) cytoplasm B) nucleus C) endoplasmic reticulum D) mitochondria E) cell membrane
B) nucleus
18) The ability for some receptor tyrosine kinases to ultimately activate phospholipase C is an example of _____.
A) antagonism B) desensitization C) autophosphorylation D) poor receptor-ligand specificity E) cross-talk
E) cross-talk
19) Which of the following hormones is able to cross biological membranes and thus the receptor is found inside the cell, not on the cell surface?
A) insulin B) glucagon C) cortisol D) epinephrine E) platelet derived growth factor
C) cortisol
20) The complex formed between a lipid hormone and its receptor binds to _____ which are specific DNA sequences.
A) transcription factors B) nuclear localization sequences C) DNA-binding domains D) hormone response elements E) none of the above
D) hormone response elements
21) The eicosanoids are derived from the membrane fatty acid _____.
A) stearic acid B) linoleic acid C) -linolenic acid D) arachidonic acid E) docosahexaenoic acid (DHA)
D) arachidonic acid
22) Which of the following is an inhibitor of cyclooxygenase?
A) acetaminophen B) aspirin C) eicosanoic acid D) thromboxane E) progesterone
B) aspirin
23) Which of the following can be regulated by eicosanoids?
A) blood pressure B) blood coagulation C) inflammation D) fever E) all of the above
E) all of the above
