You have isolated two mutants of a normally pear-shaped microorganism that have lost their distinctive shape and are now round.

You have isolated two mutants of a normally pear-shaped microorganism that have lost their distinctive shape and are now round. One of the mutants has a defect in a protein you call A and the other has a defect in a protein you call B. First, you grind up each type of mutant cell and normal cells separately and separate the plasma membranes from the cytoplasm, forming the first cell extract. Then you set aside a portion of each fraction for later testing. Next, you wash the remaining portion of the membrane fractions with a low concentration of urea (which will unfold proteins and disrupt their ability to interact with other proteins) and centrifuge the mixture. The membranes and their constituent proteins form a pellet, and the proteins liberated from the membranes by the urea wash remain in the supernatant. When you check each of the fractions for the presence of A or B, you obtain the results given below.Which of the following statements are consistent with your results (more than one answer may apply)?

(a) Protein A is an integral membrane protein that interacts with B, a peripheral membrane protein that is part of the cell cortex.
(b) Protein B is an integral membrane protein that interacts with A, a peripheral membrane protein that is part of the cell cortex.
(c) Proteins A and B are both integral membrane proteins.
(d) The mutation in A affects its ability to interact with B.

Answer: 

The endothelial cells found closest to the site of an infection express proteins called lectins. Each lectin binds to a particular ____________ that is presented on the surface of a target cell.

The endothelial cells found closest to the site of an infection express proteins called lectins. Each lectin binds to a particular ____________ that is presented on the surface of a target cell.

(a) oligosaccharide
(b) aminophospholipid
(c) polysaccharide
(d) sphingolipid

Answer: 

Both glycoproteins and proteoglycans contribute to the carbohydrate layer on the surface of the cell. Which of the following is not true of glycoproteins?

Both glycoproteins and proteoglycans contribute to the carbohydrate layer on the surface of the cell. Which of the following is not true of glycoproteins?

(a) They can be secreted into the extracellular environment.
(b) They have only one transmembrane domain.
(c) They have long carbohydrate chains.
(d) They are recognized by lectins.

Answer: 

Which of the following statements about the carbohydrate coating of the cell surface is false?

Which of the following statements about the carbohydrate coating of the cell surface is false?

(a) It is not usually found on the cytosolic side of the membrane.
(b) It can play a role in cell-cell adhesion.
(c) The arrangement of the oligosaccharide side chains is highly ordered, much like the peptide bonds of a polypeptide chain.
(d) Specific oligosaccharides can be involved in cell-cell recognition.

Answer: 

Diversity among the oligosaccharide chains found in the carbohydrate coating of the cell surface can be achieved in which of the following ways?

Diversity among the oligosaccharide chains found in the carbohydrate coating of the cell surface can be achieved in which of the following ways?

(a) varying the types of sugar monomers used
(b) varying the types of linkages between sugars
(c) varying the number of branches in the chain
(d) all of the above


Answer: 

Consider the apical location of a particular protein expressed in epithelial cells, illustrated in Figure Q11-50A. When a molecule that chelates calcium is added to the cell culture medium, you observe a redistribution of that protein around the entire cell, shown in Figure Q11-50B. Which is most likely to be true about the role of calcium in maintaining an apical distribution of protein A?

Consider the apical location of a particular protein expressed in epithelial cells, illustrated in Figure Q11-50A. When a molecule that chelates calcium is added to the cell culture medium, you observe a redistribution of that protein around the entire cell, shown in Figure Q11-50B. Which is most likely to be true about the role of calcium in maintaining an apical distribution of protein A? 

(a) calcium is required to maintain the structural integrity of the junctional complex
(b) calcium is required for the binding of the junctional proteins to the cell cortex
(c) calcium is a structural component of protein A
(d) calcium inhibits intracellular transport of protein A


Answer:

Consider the apical location of a particular protein expressed in epithelial cells, illustrated in Figure Q11-49A. Which type of defect described below is the most likely to cause the redistribution of that protein around the entire cell, shown in Figure Q11-49B?

Consider the apical location of a particular protein expressed in epithelial cells, illustrated in Figure Q11-49A. Which type of defect described below is the most likely to cause the redistribution of that protein around the entire cell, shown in Figure Q11-49B?

(a) a nonfunctional protein glycosylase
(b) the deletion of a junctional protein
(c) the truncation of a protein found in the extracellular matrix
(d) a nonfunctional flippase

Answer: 

The lateral movement of transmembrane proteins can be restricted by several different mechanisms. Which mechanism best describes the process by which an antigen-presenting cell triggers an adaptive immune response?

The lateral movement of transmembrane proteins can be restricted by several different mechanisms. Which mechanism best describes the process by which an antigen-presenting cell triggers an adaptive immune response?

(a) proteins are tethered to the cell cortex
(b) proteins are tethered to the extracellular matrix
(c) proteins are tethered to the proteins on the surface of another cell
(d) protein movement is limited by the presence of a diffusion barrier

Answer: 

The lateral movement of transmembrane proteins can be restricted by several different mechanisms. Which mechanism best describes the process by which nutrients are taken up at the apical surface of the epithelial cells that line the gut and released from their basal and lateral surfaces?

The lateral movement of transmembrane proteins can be restricted by several different mechanisms. Which mechanism best describes the process by which nutrients are taken up at the apical surface of the epithelial cells that line the gut and released from their basal and lateral surfaces?

(a) proteins are tethered to the cell cortex
(b) proteins are tethered to the extracellular matrix
(c) proteins are tethered to the proteins on the surface of another cell
(d) protein movement is limited by the presence of a diffusion barrier

Answer: 

The lateral movement of transmembrane proteins can be restricted by several different mechanisms. Which mechanism best describes the process by which neutrophils are recruited by endothelial cells?

The lateral movement of transmembrane proteins can be restricted by several different mechanisms. Which mechanism best describes the process by which neutrophils are recruited by endothelial cells?

(a) proteins are tethered to the cell cortex
(b) proteins are tethered to the extracellular matrix
(c) proteins are tethered to the proteins on the surface of another cell
(d) protein movement is limited by the presence of a diffusion barrier

Answer: 

The lateral movement of transmembrane proteins can be restricted by several different mechanisms. Which mechanism best describes the process by which focal adhesions are formed to promote cell motility?

The lateral movement of transmembrane proteins can be restricted by several different mechanisms. Which mechanism best describes the process by which focal adhesions are formed to promote cell motility?

(a) proteins are tethered to the cell cortex
(b) proteins are tethered to the extracellular matrix
(c) proteins are tethered to the proteins on the surface of another cell
(d) protein movement is limited by the presence of a diffusion barrier

Answer: 

The lateral movement of transmembrane proteins can be restricted by several different mechanisms. Which mechanism best describes the process by which a budding yeast cell designates the site of new bud formation during cell division?

The lateral movement of transmembrane proteins can be restricted by several different mechanisms. Which mechanism best describes the process by which a budding yeast cell designates the site of new bud formation during cell division?

(a) proteins are tethered to the cell cortex
(b) proteins are tethered to the extracellular matrix
(c) proteins are tethered to the proteins on the surface of another cell
(d) protein movement is limited by the presence of a diffusion barrier

Answer: 

Red blood cells have been very useful in the study of membranes and the protein components that provide structural support. Which of the following proteins is the principal fibrous protein in the cortex of the red blood cell?

Red blood cells have been very useful in the study of membranes and the protein components that provide structural support. Which of the following proteins is the principal fibrous protein in the cortex of the red blood cell?

(a) tubulin
(b) attachment proteins
(c) actin
(d) spectrin

Answer: 

Plasma membranes are extremely thin and fragile, requiring an extensive support network of fibrous proteins. This network is called the ____________.

Plasma membranes are extremely thin and fragile, requiring an extensive support network of fibrous proteins. This network is called the ____________.

(a) cortex.
(b) attachment complex.
(c) cytoskeleton.
(d) spectrin.



Answer: 

In the photosynthetic archaean Halobacterium halobium, a membrane transport protein called bacteriorhodopsin captures energy from sunlight and uses it to pump protons out of the cell. The resulting proton gradient serves as an energy store that can later be tapped to generate ATP. Which statement best describes how bacteriorhodopsin operates?

In the photosynthetic archaean Halobacterium halobium, a membrane transport protein called bacteriorhodopsin captures energy from sunlight and uses it to pump protons out of the cell. The resulting proton gradient serves as an energy store that can later be tapped to generate ATP. Which statement best describes how bacteriorhodopsin operates?

(a) The absorption of sunlight triggers a contraction of the ß barrel that acts as the protein's central channel, squeezing a proton out of the cell.
(b) The absorption of sunlight triggers a shift in the conformation of the protein's seven, membrane spanning a helices, allowing a proton to leave the cell.
(c) The absorption of sunlight triggers a restructuring of bacteriorhodopsin's otherwise unstructured core to form the channel through which a proton can exit the cell.
(d) The absorption of sunlight triggers the activation of an enzyme that generates ATP.

Answer: 

We know the detailed molecular structure and mechanism of action of the transmembrane protein bacteriorhodopsin. This protein uses sunlight as the source of energy to pump ______ out of the cell.

We know the detailed molecular structure and mechanism of action of the transmembrane protein bacteriorhodopsin. This protein uses sunlight as the source of energy to pump ______ out of the cell. 

(a) ATP
(b) H+
(c) K+
(d) Na+

Answer: 

Unlike soluble, cytosolic proteins, membrane proteins are more difficult to purify. Which of the following substances is most commonly used to help purify a membrane protein?

Unlike soluble, cytosolic proteins, membrane proteins are more difficult to purify. Which of the following substances is most commonly used to help purify a membrane protein?

(a) high salt solution
(b) sucrose
(c) detergent
(d) ethanol

Answer: 

The amino acid sequences below represent the sequences of transmembrane helices. The characteristics of a helices that form a channel are different from those that form a single transmembrane domain. Select the helix that forms a single transmembrane domain.

The amino acid sequences below represent the sequences of transmembrane helices. The characteristics of a helices that form a channel are different from those that form a single transmembrane domain. Select the helix that forms a single transmembrane domain.

(a) VGHSLSIFTLVISLGIFVFF
(b) IMIVLVMLLNIGLAILFVHF
(c) ILHFFHQYMMACNYFWMLCE
(d) VTLHKNMFLTYILNSMIIII

Answer: 

Porin proteins form large, barrel-like channels in the membrane. Which of the following is not true about these channels?

Porin proteins form large, barrel-like channels in the membrane. Which of the following is not true about these channels?

(a) They are made primarily of a helices.
(b) They are made primarily of ß sheets.
(c) They cannot form narrow channels.
(d) They have alternating hydrophobic and hydrophilic amino acids.

Answer: 

A group of membrane proteins can be extracted from membranes only by using detergents. All the proteins in this group have a similar amino acid sequence at their C-terminus: -KKKKKXXC (where K stands for lysine, X stands for any amino acid, and C stands for cysteine). This sequence is essential for their attachment to the membrane. What is the most likely way in which the C-terminal sequence attaches these proteins to the membrane?

A group of membrane proteins can be extracted from membranes only by using detergents. All the proteins in this group have a similar amino acid sequence at their C-terminus: -KKKKKXXC (where K stands for lysine, X stands for any amino acid, and C stands for cysteine). This sequence is essential for their attachment to the membrane. What is the most likely way in which the C-terminal sequence attaches these proteins to the membrane?

(a) The cysteine residue is covalently attached to a membrane lipid.
(b) The peptide spans the membrane as an a helix.
(c) The peptide spans the membrane as part of a ß sheet.
(d) The positively charged lysine residues interact with an acidic integral membrane protein.

Answer: 

Membrane proteins, like membrane lipids, can move laterally by exchanging positions with other membrane components. Which type of membrane proteins is expected to be the least mobile, based on their function?

Membrane proteins, like membrane lipids, can move laterally by exchanging positions with other membrane components. Which type of membrane proteins is expected to be the least mobile, based on their function?

(a) channels
(b) anchors
(c) receptors
(d) enzymes



Answer: 

Membrane curvature is influenced by the differential lipid composition of the two membrane monolayers. Which factor do you think has the largest impact on the curvature of biological membranes?

Membrane curvature is influenced by the differential lipid composition of the two membrane monolayers. Which factor do you think has the largest impact on the curvature of biological membranes?

(a) amount of cholesterol
(b) charge of the lipid head group
(c) length of the hydrocarbon tails
(d) size of the lipid head group



Answer: 

Membrane synthesis in the cell requires the regulation of growth for both halves of the bilayer and the selective retention of certain types of lipids on one side or the other. Which group of enzymes accomplishes both of these tasks?

Membrane synthesis in the cell requires the regulation of growth for both halves of the bilayer and the selective retention of certain types of lipids on one side or the other. Which group of enzymes accomplishes both of these tasks?

(a) flippases
(b) phospholipases
(c) convertases
(d) glycosylases



Answer: 

New membrane phospholipids are synthesized by enzymes bound to the _____________ side of the _________________ membrane.

New membrane phospholipids are synthesized by enzymes bound to the _____________ side of the _________________ membrane.

(a) cytosolic, mitochondrial
(b) luminal, Golgi
(c) cytosolic, endoplasmic reticulum
(d) extracellular, plasma



Answer: 

Most animal fats form a solid at room temperature, while plant fats remain liquid at room temperature. Which of the following is a feature of lipids in plant membranes that best explains this difference?

Most animal fats form a solid at room temperature, while plant fats remain liquid at room temperature. Which of the following is a feature of lipids in plant membranes that best explains this difference?

(a) unsaturated hydrocarbons
(b) longer hydrocarbon tails
(c) higher levels of sterols
(d) larger head groups


Answer: 

Cholesterol serves several essential functions in mammalian cells. Which of the following is not influenced by cholesterol?

Cholesterol serves several essential functions in mammalian cells. Which of the following is not influenced by cholesterol?

(a) membrane permeability
(b) membrane fluidity
(c) membrane rigidity
(d) membrane thickness

Answer: 

There are two properties of phospholipids that affect how tightly they pack together: the length of the hydrocarbon chain and the number of double bonds. The degree of packing, in turn, influences the relative mobility of these molecules in the membrane. Which of the following would yield the most highly mobile phospholipid (listed as number of carbons and number of double bonds, respectively)?

There are two properties of phospholipids that affect how tightly they pack together: the length of the hydrocarbon chain and the number of double bonds. The degree of packing, in turn, influences the relative mobility of these molecules in the membrane. Which of the following would yield the most highly mobile phospholipid (listed as number of carbons and number of double bonds, respectively)?

(a) 24 carbons with 1 double bond
(b) 15 carbons with 2 double bonds
(c) 20 carbons with 2 double bonds
(d) 16 carbons with no double bonds

Answer: 

Membrane lipids are capable of many different types of movement. Which of these does not occur spontaneously in biological membranes?

Membrane lipids are capable of many different types of movement. Which of these does not occur spontaneously in biological membranes?

(a) switching between lipid layers
(b) lateral movement
(c) rotation
(d) flexing of hydrocarbon chains

Answer: 

Water molecules readily form hydrogen bonds with other polar molecules, and when they encounter nonpolar molecules they must form hydrogen-bonding networks with neighboring water molecules. Which of the following molecules will cause a "cage" of water to form?

Water molecules readily form hydrogen bonds with other polar molecules, and when they encounter nonpolar molecules they must form hydrogen-bonding networks with neighboring water molecules. Which of the following molecules will cause a "cage" of water to form?

(a) 2-methylpropane
(b) acetone
(c) methanol
(d) urea

Answer: 

Where does most new membrane synthesis take place in a eukaryotic cell?

Where does most new membrane synthesis take place in a eukaryotic cell?

(a) in the Golgi apparatus
(b) in the endoplasmic reticulum
(c) in the plasma membrane
(d) in the mitochondria
(e) on ribosomes

Answer: 

Three phospholipids X, Y, and Z are distributed in the plasma membrane as indicated in Figure Q11-14. For which of these phospholipids does a flippase probably exist?

Three phospholipids X, Y, and Z are distributed in the plasma membrane as indicated in Figure Q11-14. For which of these phospholipids does a flippase probably exist?

(a) X only
(b) Z only
(c) X and Y
(d) Y and Z

Answer: 

Which of the following phospholipid precursors is the most hydrophobic?

Which of the following phospholipid precursors is the most hydrophobic?

(a) triacylglycerol
(b) diacylglycerol
(c) phosphate
(d) glycerol

Answer: 

Some lipases are able to cleave the covalent bonds between the glycerol backbone and the attached fatty acid. What final products do you expect to accumulate through the action of the enzyme monoacylglycerol lipase?

Some lipases are able to cleave the covalent bonds between the glycerol backbone and the attached fatty acid. What final products do you expect to accumulate through the action of the enzyme monoacylglycerol lipase?

(a) phosphoglycerol and free fatty acid
(b) sterol and glycerol
(c) free phosphate and glycerol
(d) glycerol and free fatty acid

Answer: 

A bacterium is suddenly expelled from a warm human intestine into the cold world outside. Which of the following adjustments might the bacterium make to maintain the same level of membrane fluidity?

A bacterium is suddenly expelled from a warm human intestine into the cold world outside. Which of the following adjustments might the bacterium make to maintain the same level of membrane fluidity?

(a) Produce lipids with hydrocarbon tails that are longer and have fewer double bonds.
(b) Produce lipids with hydrocarbon tails that are shorter and have more double bonds.
(c) Decrease the amount of cholesterol in the membrane.
(d) Decrease the amount of glycolipids in the membrane.

Answer: 

Which of the following statements is true?

Which of the following statements is true?

(a) Phospholipids will spontaneously form liposomes in nonpolar solvents.
(b) In eukaryotes, all membrane-enclosed organelles are surrounded by one lipid bilayer.
(c) Membrane lipids diffuse within the plane of the membrane.
(d) Membrane lipids frequently flip-flop between one monolayer and the other.

Answer: 

Formation of a lipid bilayer is energetically favorable. How does this arrangement result in higher entropy for the system, and thus make bilayer formation energetically favorable?

Formation of a lipid bilayer is energetically favorable. How does this arrangement result in higher entropy for the system, and thus make bilayer formation energetically favorable?

(a) Polar head groups form a hydrogen-bonding network at the interface with water.
(b) Water molecules form cagelike structures around hydrophobic molecules.
(c) Hydrogen bonds form between neighboring polar head groups in the bilayer.
(d) Fatty acid tails are highly saturated and flexible.

Answer: 

Which of the following membrane lipids does not contain a fatty acid tail?

Which of the following membrane lipids does not contain a fatty acid tail?

(a) phosphatidylcholine
(b) a glycolipid
(c) phosphatidylserine
(d) cholesterol

Answer: 

Which type of lipids are the most abundant in the plasma membrane?

Which type of lipids are the most abundant in the plasma membrane?

(a) phospholipids
(b) glycolipids
(c) sterols
(d) triacylglycerides

Answer: 

The plasma membrane serves many functions, many of which depend on the presence of specialized membrane proteins. Which of the following roles of the plasma membrane could still occur if the bilayer were lacking these proteins?

The plasma membrane serves many functions, many of which depend on the presence of specialized membrane proteins. Which of the following roles of the plasma membrane could still occur if the bilayer were lacking these proteins?

(a) intercellular communication
(b) selective permeability
(c) cellular movement
(d) import/export of molecules

Answer: 

Which of the following phenomena will be observed if a cell's membrane is pierced?

Which of the following phenomena will be observed if a cell's membrane is pierced?

(a) the membrane reseals
(b) the membrane collapses
(c) a tear is formed
(d) the membrane expands

Answer: 

All of the following are signs of sudden exercise abstinence syndrome EXCEPT:

All of the following are signs of sudden exercise abstinence syndrome EXCEPT: 

A. Irregular respiratory rate
B. Irregular heartbeat
C. Depression
D. Sleep disorders

Answer: 

Which of the following reactions to injury is present when the length of rehabilitation is greater than 4 weeks?

Which of the following reactions to injury is present when the length of rehabilitation is greater than 4 weeks? 

A. Anger
B. Acceptance
C. Denial
D. Depression



Answer: 

During _____ stress, the threat is immediate and the body's response is instantaneous.

During _____ stress, the threat is immediate and the body's response is instantaneous.

A. chronic
B. acute
C. anxiety
D. exhaustive


Answer: 

Who developed a system to change an individual's irrational ideas and beliefs?

Who developed a system to change an individual's irrational ideas and beliefs? 

A. Benson
B. Jacobson
C. Ellis
D. Cyriax


Answer: 

Which of the following statements is true of progressive muscle relaxation techniques?

Which of the following statements is true of progressive muscle relaxation techniques? 

A. They require athletes to become aware of the tension in their body and progressively increase muscle contraction for up to an hour.
B. They are primarily designed to deal with a person's internal dialogue.
C. They are uncommon because athletes are required to tense their muscles for prolonged periods of time before relaxing them.
D. They can be practiced in a reclining position or while seated in a chair.

Answer: 

During meditation, all of the following are performed EXCEPT:

During meditation, all of the following are performed EXCEPT: 

A. Muscles are tensed and then relaxed.
B. Several deep breaths are taken.
C. A word is repeated several times.
D. Eyes are closed.


Answer: 

In which of the phases of rehabilitation does the patient feel fearful and may be in denial?

In which of the phases of rehabilitation does the patient feel fearful and may be in denial? 

A. Immediate postinjury
B. Advanced rehabilitation
C. Early postoperative
D. Post rehabilitation



Answer: 

Which of the following is the basic premise of rational emotive therapy?

Which of the following is the basic premise of rational emotive therapy? 

A. Individuals who are under severe stress should not explore their self-talk.
B. Actual events do not create emotions.
C. Rational self-talk causes anxiety, anger, and depression.
D. Focusing the mind on undesired events prepares it to face such events with ease.

Answer: 

Personality disorders include all of the following EXCEPT:

Personality disorders include all of the following EXCEPT: 

A. Paranoia
B. Obsessive-compulsive disorder
C. Posttraumatic stress disorder
D. Neurosis


Answer: 

Which of the following mood disorders can be treated with light therapy?

Which of the following mood disorders can be treated with light therapy? 

A. Panic attacks
B. Posttraumatic stress disorder
C. Phobia
D. Seasonal affective disorder

Answer: