Question 1

Which protein in the Question above is likely to be buried within the membrane?
A)Protein W
B)Protein X
C)Protein Y
D)Protein Z
E)Protein A

Accepted Answer

B

Question 2

What word below characterizes the amino acids that are found in an $\alpha$-helical segment that spans a membrane?
A)exclusively circular
B)predominantly hydrophilic
C)predominantly hydrophobic
D)predominantly antiparallel
E)totally parallel

Accepted Answer

A segment that spans a membrane is likely part of a transmembrane protein or a membrane-anchored protein, where the hydrophobic region of the protein interacts with the hydrophobic core of the membrane. Therefore, amino acids that are predominantly hydrophobic would be favored in this segment.

Question 3

What kind of membrane protein penetrates into the hydrophobic part of the lipid bilayer?
A)integral protein
B)lipid-anchored protein
C)peripheral proteins
D)transmembrane protein
E)both integral protein and transmembrane protein

Accepted Answer

Integral proteins and transmembrane proteins both penetrate the hydrophobic core of the lipid bilayer, with transmembrane proteins being a subtype of integral proteins that span the entire membrane.

Question 4

Gorter and Grendel extracted lipids from human red blood cells.They calculated the total surface area for these red blood cells and found it to be 36 µ2.How much surface area would these lipids cover once they were spread across the surface of water?
A)72 µ2
B)36 µ2
C)18 µ2
D)144 µ2
E)30 µ2

Accepted Answer

Gorter and Grendel's experiment demonstrated that the lipids extracted from red blood cells form a bilayer when spread on water. Therefore, the lipids would cover twice the surface area of the cells, which is 72 µ2.

Question 5

How are the new "stealth liposomes" protected from immune system phagocytes?
A)They are kept cold before use.
B)They are coated with carbohydrates.
C)They are given a synthetic polymer coating that protects them from immune destruction.
D)They are loaded with radioactive isotopes.
E)They are colored red.

Accepted Answer

Stealth liposomes are protected from immune system phagocytes by being given a synthetic polymer coating that protects them from immune destruction. This coating helps the liposomes evade recognition and clearance by the immune system, allowing them to reach their target tissue or organ more effectively. Therefore, choice C is the best option.

Question 6

What are the building blocks of a phosphoglyceride,specifically phosphatidic acid?
A)glycerol + 2 phosphate groups + 1 fatty acid
B)glycerol + 1 phosphate group + 2 fatty acids
C)glycerol + 1 phosphate group
D)glycerol + 3 fatty acids
E)glycerol + 1 phosphate group + 3 fatty acids

Accepted Answer

Phosphoglycerides, including phosphatidic acid, are composed of a glycerol backbone, one phosphate group, and two fatty acids. Therefore, option B is the correct answer. Option A is incorrect as it includes two phosphate groups instead of one. Option C is incorrect as it only includes a glycerol backbone and one phosphate group, but does not include any fatty acids. Option D is incorrect as it includes three fatty acids, but only one phosphate group is present in a phosphoglyceride. Option E is incorrect as it includes three fatty acids and one phosphate group, but phosphoglycerides typically have two fatty acids.

Question 7

What did Davson and Danielli add to their model of enzyme structure to explain the passage of polar solutes and ions through the membrane and to account for their selective permeability?
A)They proposed protein-lined pores.
B)They proposed lipid-lined pores.
C)They proposed carbohydrate-lined pores.
D)They proposed a protein coating on the cytoplasmic surface of the membrane.
E)They proposed a carbohydrate coating on the external surface of the membrane.

Accepted Answer

Davson and Danielli proposed protein-lined pores to account for the selective permeability of ions and polar solutes through the membrane. This allowed for the passage of these polar molecules, while still maintaining the overall hydrophobic nature of the lipid bilayer.

Question 8

What kind of membrane protein penetrates into the hydrophobic part of the lipid bilayer?
A)integral protein
B)lipid-anchored protein
C)peripheral proteins
D)phosphatidylcholine
E)galactocerebroside

Accepted Answer

Integral proteins are membrane proteins that extend across or penetrate into the hydrophobic part of the lipid bilayer. This allows them to interact with the hydrophobic fatty acid tails of the phospholipids. Lipid-anchored proteins are attached to the membrane by a covalently attached lipid but do not typically penetrate the bilayer. Peripheral proteins are located on the exterior surface of the membrane and do not penetrate the bilayer. Phosphatidylcholine and galactocerebroside are both types of phospholipids and are not proteins.

Question 9

Which of the following is not a function of membranes?
A)transporting solutes
B)scaffold for biochemical activities
C)energy transduction
D)signal transition
E)signal transduction

Accepted Answer

"Signal transition" is not a recognized function of membranes, whereas the other options are established functions.

Question 10

What technique allows an investigation of the microheterogeneity of a membrane so that one can see localized differences in different parts of the membrane?
A)freeze-denture replication
B)freeze-fracture replication
C)X-ray crystallography
D)circular dichroism
E)tasty-freeze replication

Accepted Answer

Freeze-fracture replication allows for the investigation of the internal structure of membranes, including the microheterogeneity and localized differences in different parts of the membrane. This technique involves freezing a sample and then fracturing it, allowing for replication of the internal surfaces of the membrane.

Question 11

What kind of membrane protein is found entirely outside the bilayer on either the extracellular or cytoplasmic surface? These proteins are covalently linked to a membrane lipid situated within the bilayer.
A)integral protein
B)lipid-anchored protein
C)peripheral proteins
D)carbohydrate-anchored protein
E)transmembrane

Accepted Answer

Lipid-anchored proteins are covalently linked to a membrane lipid situated within the bilayer and found entirely outside the bilayer on either the extracellular or cytoplasmic surface. Integral proteins span the entire bilayer and transmembrane proteins have segments that pass all the way through the lipid bilayer. Peripheral proteins are not embedded in the bilayer and are found on the surface of the membrane. Carbohydrate-anchored proteins are covalently linked to a carbohydrate group on a membrane lipid or protein.

Question 12

Why did liposomes not work against diseases as hoped when they were first tried?
A)They were degraded in the bloodstream.
B)Immune system phagocytes removed them from the bloodstream before they could exert an effect.
C)They leaked before getting to their target.
D)They were targeted incorrectly.
E)They expanded osmotically and lysed before reaching their target.

Accepted Answer

Liposomes were initially removed by the immune system's phagocytes before they could reach their target and exert their therapeutic effect.

Question 13

What word describes a molecule that contains both hydrophilic and hydrophobic portions?
A)amphoteric
B)ambidextrous
C)amphipathic
D)rings
E)straight

Accepted Answer

A molecule that contains both hydrophilic and hydrophobic portions is called amphipathic.

Question 14

Glycolipids have been shown to play roles in certain disease states in humans and other mammals.Which of the situations below illustrate the ways in which this can happen?
A)failure to add a sugar to the glycolipid.
B)inhibition of glycolipid synthesis.
C)they are the site at which bacterial toxins like those that cause botulism and cholera first bind cells.
D)they are the site at which the influenza virus first binds a cell.
E)All of these are correct.

Accepted Answer

Failure to add a sugar to a glycolipid or inhibition of glycolipid synthesis can result in diseases such as Tay-Sachs disease and Gaucher's disease. Additionally, glycolipids can serve as the site for the binding of bacterial toxins and influenza virus, leading to pathogenic outcomes. Therefore, all of the choices are correct answers.

Question 15

Why are integral membrane proteins difficult to study?
A)They are difficult to isolate in soluble form due to their hydrophobic transmembrane domains.
B)They are difficult to isolate in soluble form due to their hydrophilic transmembrane domains.
C)They are so small.
D)They are so large.
E)None of these are correct.

Accepted Answer

Integral membrane proteins are difficult to study because they are embedded in the lipid bilayer of cell membranes, and often have hydrophobic transmembrane domains that are difficult to solubilize and isolate in a biologically active form. Their hydrophobic nature also makes them prone to aggregation, making it difficult to obtain high-resolution structural information by traditional techniques such as X-ray crystallography or NMR spectroscopy.

Question 16

On average,how many amino acids engaged in predominantly hydrophobic $\alpha$- helices does it take to cross the hydrophobic part of the membrane?
A)about 10 amino acids
B)about 20 amino acids
C)at least 40 amino acids
D)about 2 - 3 amino acids
E)None of these are correct.

Accepted Answer

Predominantly hydrophobic F1F1F1S1F1F1F10- helices usually consist of around 20 amino acids that are involved in crossing the hydrophobic region of the membrane.

Question 17

Once the structure of one member of a membrane protein family has been determined,researchers can usually apply a strategy called __________ to learn about the structure and activity of other members of the family.For example,solution of the structure of the bacterial potassium channel KcsA provided a lot of data that could be applied to the structure and mechanism of action of the much more complex eukaryotic potassium channels.
A)heterology modeling
B)homology mapping
C)homology modeling
D)protein mapping
E)homologous characterization

Accepted Answer

Homology modeling involves using the known structure of one protein to predict the structure of other proteins that share a similar amino acid sequence. This strategy is often used for membrane protein families where determining the structure of every member is difficult or impossible. By using the known structure of one protein as a template, researchers can predict the structure and activity of other family members. This was done with the bacterial potassium channel KcsA, where the structure was used as a template to predict the structures and mechanisms of eukaryotic potassium channels.

Question 18

What evidence convinced Overton that membranes were composed of lipids?
A)He could see the lipids in the microscope.
B)Membranes were destroyed by enzymes that degraded lipids.
C)He found that more lipid-soluble solutes enter root hair cells faster than polar solutes.
D)Membranes dissolved in gasoline.
E)Membranes did not dissolve in water.

Accepted Answer

Overton observed that lipid-soluble substances entered cells more rapidly than polar substances, suggesting that cell membranes were composed of lipids.

Question 19

Which of the following is a function of membranes?
A)compartmentalization
B)selectively permeable barrier
C)mediates intercellular interactions
D)helps cells respond to external stimuli
E)All of these are correct.

Accepted Answer

All of the options listed are correct functions of membranes. Membranes compartmentalize organelles within cells and separate different compartments of the cell from the external environment. They are selectively permeable barriers that control the movement of ions and molecules into and out of cells. Membranes also mediate intercellular interactions by providing a surface for cells to attach to and communicate with neighboring cells, and they help cells respond to external stimuli by transmitting signals from the extracellular environment to the interior of the cell.

Question 20

You treat some cells with a proteolytic enzyme that is too large to penetrate the cell membrane (Set 1).Another group of cells is made permeable before treatment with the enzyme (Set 2).A third set of cells was not treated with the enzyme at all (controls).Proteins are then extracted from the three different sets of cells and applied to an SDS-PAGE gel.Protein W migrates to the same distance on a gel of proteins from Set 1 and Set 2; Protein W migrates a shorter distance on gels of proteins extracted from the control group than on gels of proteins extracted from Set 1 and Set 2 treated cells.Protein X migrates to the same distance on a gel of proteins from control cells and the gels of the proteins from Set 1 and Set 2.Protein Y migrates a longer distance when extracted from Set 1 cells than does protein Y in the controls; Protein Y moves an even larger distance in the gel of the extracts from Set 2.Protein Z migrates the same distance on gels of proteins from the controls and the proteins extracted from Set 1,but it migrates a longer distance in extracts from Set 2 cells.Which protein is exposed only on the exterior of the cell?
A)Protein W
B)Protein X
C)Protein Y
D)Protein Z
E)Protein K

Accepted Answer

Protein W migrates the same distance on gels of proteins from Set 1 and Set 2, which implies that the proteolytic enzyme did not affect its mobility. However, Protein W migrates a shorter distance on gels of proteins extracted from the control group than on gels of proteins extracted from Set 1 and Set 2 treated cells. This suggests that Protein W is only exposed on the exterior of the cell and is protected from the proteolytic enzyme in Set 1 and Set 2 cells but not in control cells.

Quiz 4: The Structure and Function of the Plasma Membrane

Which protein in the Question above is likely to be buried within the membrane?

What word below characterizes the amino acids that are found in an $\alpha$ -helical segment that spans a membrane?

What kind of membrane protein penetrates into the hydrophobic part of the lipid bilayer?

Gorter and Grendel extracted lipids from human red blood cells.They calculated the total surface area for these red blood cells and found it to be 36 µ2.How much surface area would these lipids cover once they were spread across the surface of water?

How are the new "stealth liposomes" protected from immune system phagocytes?

What are the building blocks of a phosphoglyceride,specifically phosphatidic acid?

What did Davson and Danielli add to their model of enzyme structure to explain the passage of polar solutes and ions through the membrane and to account for their selective permeability?

What kind of membrane protein penetrates into the hydrophobic part of the lipid bilayer?

Which of the following is not a function of membranes?

What technique allows an investigation of the microheterogeneity of a membrane so that one can see localized differences in different parts of the membrane?

What kind of membrane protein is found entirely outside the bilayer on either the extracellular or cytoplasmic surface? These proteins are covalently linked to a membrane lipid situated within the bilayer.

Why did liposomes not work against diseases as hoped when they were first tried?

What word describes a molecule that contains both hydrophilic and hydrophobic portions?

Glycolipids have been shown to play roles in certain disease states in humans and other mammals.Which of the situations below illustrate the ways in which this can happen?

Why are integral membrane proteins difficult to study?

On average,how many amino acids engaged in predominantly hydrophobic $\alpha$ - helices does it take to cross the hydrophobic part of the membrane?

What evidence convinced Overton that membranes were composed of lipids?

Which of the following is a function of membranes?

Quiz 4: The Structure and Function of the Plasma Membrane

Which protein in the Question above is likely to be buried within the membrane?

What word below characterizes the amino acids that are found in an α\alphaα -helical segment that spans a membrane?

What kind of membrane protein penetrates into the hydrophobic part of the lipid bilayer?

Gorter and Grendel extracted lipids from human red blood cells.They calculated the total surface area for these red blood cells and found it to be 36 µ2.How much surface area would these lipids cover once they were spread across the surface of water?

How are the new "stealth liposomes" protected from immune system phagocytes?

What are the building blocks of a phosphoglyceride,specifically phosphatidic acid?

What did Davson and Danielli add to their model of enzyme structure to explain the passage of polar solutes and ions through the membrane and to account for their selective permeability?

What kind of membrane protein penetrates into the hydrophobic part of the lipid bilayer?

Which of the following is not a function of membranes?

What technique allows an investigation of the microheterogeneity of a membrane so that one can see localized differences in different parts of the membrane?

What kind of membrane protein is found entirely outside the bilayer on either the extracellular or cytoplasmic surface? These proteins are covalently linked to a membrane lipid situated within the bilayer.

Why did liposomes not work against diseases as hoped when they were first tried?

What word describes a molecule that contains both hydrophilic and hydrophobic portions?

Glycolipids have been shown to play roles in certain disease states in humans and other mammals.Which of the situations below illustrate the ways in which this can happen?

Why are integral membrane proteins difficult to study?

On average,how many amino acids engaged in predominantly hydrophobic α\alphaα - helices does it take to cross the hydrophobic part of the membrane?

What evidence convinced Overton that membranes were composed of lipids?

Which of the following is a function of membranes?

What word below characterizes the amino acids that are found in an $\alpha$ -helical segment that spans a membrane?

On average,how many amino acids engaged in predominantly hydrophobic $\alpha$ - helices does it take to cross the hydrophobic part of the membrane?