Question 1

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

B

Question 2

What technique below is often used to identify transmembrane segments of integral proteins?
A)Lineweaver-Burk plot
B)Michaelis-Menten plot
C)hydrophilicity plot
D)hydropathy plot
E)titration plot

Accepted Answer

Hydropathy plot is often used to identify transmembrane segments of integral proteins. It plots the hydrophobicity or hydrophilicity of amino acids along the protein sequence, allowing the identification of stretches of hydrophobic amino acids that are likely to be embedded in the lipid bilayer.

Question 3

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

All of these situations illustrate the ways in which glycolipids can play roles in certain disease states. Failure to add a sugar to the glycolipid or inhibition of glycolipid synthesis can lead to certain diseases like Tay-Sachs, while bacteria toxins like those causing botulism and cholera first bind to glycolipids on cell surfaces. The influenza virus also first binds to glycolipids on cell surfaces before infecting the host.

Question 4

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

The answer of Which of the following is not a...

Question 5

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 is the technique that allows for the investigation of the microheterogeneity of a membrane so that one can see localized differences in different parts of the membrane. This technique involves freezing the sample and then fracturing it with a knife, revealing the inner structure of the membrane. Replicas are then obtained by evaporating metal onto the fractured surface, allowing for visualization under an electron microscope.

Question 6

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. Amphi- means both or double, and -pathic means relating to feelings or emotions. Therefore, amphipathic means the molecule has both love and hate (in this case, attraction and repulsion) towards water.

Question 7

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 the cell membrane and have hydrophobic transmembrane domains. This makes them difficult to isolate in soluble form for study.

Question 8

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 to be hydrophobic in order to interact with the hydrophobic lipid bilayer. Therefore, the amino acids in this segment would be predominantly hydrophobic.

Question 9

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.

Question 10

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 explain the passage of polar solutes and ions through the membrane and to account for their selective permeability.

Question 11

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

It typically takes around 20 amino acids to form a transmembrane helix that can span the hydrophobic interior of the membrane.

Question 12

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 penetrate into (or fully span) the hydrophobic part of the lipid bilayer, interacting with the lipid tails. This allows them to have various functions, such as transporters, channels, receptors, and enzymes, that require direct access to both sides of the membrane. Lipid-anchored proteins, on the other hand, are attached to the bilayer through covalent bonds to specific lipids, but do not cross it. Peripheral proteins are non-covalently bound to either the inner or outer surface of the bilayer, typically interacting with integral proteins or lipids. Phosphatidylcholine and galactocerebroside are both major lipids found in membranes, but are not proteins.

Question 13

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 these are correct. Membranes serve all these functions, which are essential for the maintenance of cellular homeostasis and survival.

Question 14

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 is a strategy where the structure of one member of a protein family is used to generate models for other members of the family. This is based on the assumption that related proteins will have similar structures and functions. Therefore, once the structure of one member is known, it can be used as a template to build models of other members of the family which can provide insights into their structure and function.

Question 15

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 typically protected from immune system phagocytes by coating them with synthetic polymers such as polyethylene glycol (PEG). This PEG coating helps the liposomes evade recognition by the immune system, as it makes them less recognizable to immune cells like macrophages.

Question 16

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, specifically phosphatidic acid, are composed of a glycerol molecule linked to a phosphate group and two fatty acids. Choice B accurately describes the building blocks of phosphatidic acid.

Question 17

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

The answer of Which protein in the Question above is...

Question 18

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 within the bilayer and are found entirely outside the bilayer on either the extracellular or cytoplasmic surface. Integral proteins, transmembrane proteins, peripheral proteins, and carbohydrate-anchored proteins are not all found exclusively outside the bilayer.

Question 19

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

The answer of What evidence convinced Overton that membranes were...

Question 20

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.

Quiz 4: The Structure and Function of the Plasma Membrane

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

What technique below is often used to identify transmembrane segments of integral proteins?

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?

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

Why are integral membrane proteins difficult to study?

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

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?

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

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

Which of the following is a function of membranes?

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

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

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

What evidence convinced Overton that membranes were composed of lipids?

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

Quiz 4: The Structure and Function of the Plasma Membrane

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

What technique below is often used to identify transmembrane segments of integral proteins?

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?

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

Why are integral membrane proteins difficult to study?

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

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?

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

Which of the following is a function of membranes?

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

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

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

What evidence convinced Overton that membranes were composed of lipids?

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

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?