Biochem U7 (7.6-7.7)

Fundamental objectives on membrane proteins

Peripheral membrane proteins have which of the following properties?

Question 1 options:

Lipid-linked

Transmembrane helices

All of these options

Relatively weak association with the bilayer

Relatively weak association with the bilayer

A β-barrel is composed of which of the following molecules?

Question 2 options:

Amino acids

Lipid rafts

Fatty acids

Steroids

Amino acids

Where are GPI-linked proteins usually found?

Question 3 options:

None of these options

Anchored to the intracellular portion of a bilayer

Extended through the entire bilayer

Anchored to the extracellular portion of a bilayer

Anchored to the extracellular portion of a bilayer

Extrinsic (peripheral) proteins are where with respect to a membrane?

Question 4 options:

On the edge of the membrane with a lipid anchor inserted into the membrane

Entirely outside the membrane and interacting with the polar head groups

Mostly within the membrane

Inside a β-barrel

Entirely outside the membrane and interacting with the polar head groups

Non-mediated transport can also be described using which of the following terms?

Question 1 options:

Passive transport

Active transport

Facilitated diffusion

Passive-mediated transport

Passive transport

Which type of transport involves diffusion directly across a lipid bilayer?

Question 2 options:

Passive-mediated

There is insufficient information to answer this question

Active

Passive

Passive

Lipid anchors are described by which of the following statements?

Question 3 options:

A type of fatty acid

Lipids attached to proteins

Lipids attached to the lipid bilayer

Particularly heavy lipids

Lipids attached to proteins

Which type of protein is not strongly bound to the cell membrane?

Question 4 options:

Peripheral

GPI-linked

Lipid-linked

Integral

Peripheral

The expression RT * ln ([X]in/[X]out) + ZFΔψ is equal to which of the following values?

Question 1 options:

The equilibrium constant for transport

Membrane potential

ΔG_trans

The binding affinity for a transporter

ΔG_trans

Which type of structure is found inserted into the membrane?

Question 2 options:

β-barrel

All of these options

Transmembrane helix

GPI anchor

All of these options

Which type of protein extends through a lipid bilayer?

Question 3 options:

Lipid-linked

Peripheral

Integral

All of these options

Integral

The electrical potential that develops because a membrane divides two unequal concentrations of an ion is described by which of the following terms?

Question 4 options:

Membrane potential

ΔGtrans

Membrane fusion

Passive-mediated transport

Membrane potential

Which of the following structures is a transmembrane helix?

Question 1 options:

An α-helix that forms a lipid bilayer

A helical lipid within a lipid bilayer

A helical oligosaccaride in a lipid bilayer

An α-helix that extends through a lipid bilayer

An α-helix that extends through a lipid bilayer

Lipids attached to proteins can assist with which type of membrane association?

Question 2 options:

None of these options

Peripheral association

Lipid anchoring

Transmembrane helices

Lipid anchoring

Which of the following ideas does membrane potential refer to?

Question 3 options:

Isolated lipids before they assemble into a lipid bilayer

The membrane that will result following a membrane fusion event

The electrical potential that develops because a membrane divides two unequal concentrations of an ion

The ability of a membrane to prevent movement of non-polar molecules

The electrical potential that develops because a membrane divides two unequal concentrations of an ion

Which type of transport requires work?

Question 4 options:

There is insufficient information to answer this question

Active

Passive-mediated

Passive

Active

Which of the following statements describes an intrinsic membrane protein?

Question 1 options:

A protein containing a lipid anchor

A protein that associates with the surface of a bilayer

None of these options

A protein that extends through the bilayer

A protein that extends through the bilayer

Which type of transport moves a solute from high to low concentration through a channel?

Question 2 options:

Active

Passive-mediated

There is insufficient information to answer this question

Passive

Passive-mediated

Which of the following statements describes a prenylated protein?

Question 3 options:

A specific type of lipid anchor has been attached to the protein

The protein is part of a lipid raft

The protein has been inserted into the lipid bilayer

The protein is a sphingolipid

A specific type of lipid anchor has been attached to the protein

Which of the following statements describes an extrinsic membrane protein?

Question 4 options:

A protein that associates with the surface of a bilayer

A protein containing a lipid anchor

None of these options

A protein that extends through the bilayer

A protein that associates with the surface of a bilayer

Which type of lipid anchor is usually found extracellularly?

Question 2 options:

Mryistoylation

Palmitoylation

Prenylation

GPI-linked

GPI-linked

Facilitated diffusion is the same as which of the following processes?

Question 3 options:

Transport through the blood

Passive transport

Passive-mediated transport

Active transport

Integral membrane proteins are usually found where?

Question 4 options:

With a non-polar portion inserted into the bilayer on one side only

Completely within the bilayer, contacting only the hydrophobic region

Extending through the entire bilayer

On the outside of the bilayer

Extending through the entire bilayer

Which type of structure is found inserted into the membrane?

Question 4 options:

Transmembrane helix

GPI anchor

All of these options

β-barrel

All of these options

Which type of protein is not strongly bound to the cell membrane?

Question 1 options:

Integral

GPI-linked

Peripheral

Lipid-linked

Peripheral

Lipids attached to proteins can assist with which type of membrane association?

Question 4 options:

Transmembrane helices

Peripheral association

Lipid anchoring

None of these options

Lipid anchoring

Which of the following statements regarding protein associations with membranes is true (select all correct answers)?

Question 1 options:

The ability of lipid anchors to associate proteins with the membrane is an example of the hydrophobic effect

All proteins associated with the membrane have an α-helical domain to insert into the bilayer

Proteins inserted into a lipid bilayer tend to have a hydrophilic core surrounded by a hydrophobic surface

The interaction of peripheral proteins with the phosphates of glycerophospholipids is an example of the hydrophobic effect

The ability of lipid anchors to associate proteins with the membrane is an example of the hydrophobic effect

Proteins inserted into a lipid bilayer tend to have a hydrophilic core surrounded by a hydrophobic surface

Addition of a lipid anchor to a protein causes which of the following outcomes (select all correct answers)?

The "inside-out" arrangement of hydrophobic amino acids observed in integral membrane proteins

The overall asymmetric distribution of lipids in a membrane

Attachment of a protein to a lipid bilayer while leaving the protein outside the bilayer

Formation of a transmembrane helix

Attachment of a protein to a lipid bilayer while leaving the protein outside the bilayer

Which of the following actions would cause the total cell membrane potential to become more negative (select all correct answers)?

Question 3 options:

Exporting Mg2+ from a cell while simultaneously importing an equal amount of Cl-

Exporting Na+ from a cell

Exporting Na+ from a cell while simultaneously importing an equal amount of K+

Importing glucose into a cell

Exporting Mg2+ from a cell while simultaneously importing an equal amount of Cl-

Exporting Na+ from a cell

Which of the following approaches can be used to associate a protein with a cellular membrane (select all correct answers)?

Attach a fatty acid to a Cys residue in the protein

Include only polar residues in the protein

Include several positively charged residues on the surface of the protein

Insert an α-helix of hydrophobic resides into the membrane

Attach a fatty acid to a Cys residue in the protein

Include several positively charged residues on the surface of the protein

Insert an α-helix of hydrophobic resides into the membrane

Which of the following amino acids is likely to be on the surface of a porin protein that is embedded in the cell membrane (select all correct answers)?

Question 1 options:

Met

Asn

Arg

Ser

Leu

Met

Leu

Write the 3-letter abbreviation of an amino acid that is likely to be found on the surface of an integral membrane protein interacting with the lipids.

Val

Which of the following functions do lipid anchors have?

Question 4 options:

To provide a location for cholesterol in membranes

To help associate proteins with membranes

None of these options

To protect membranes from hydrophilic substances

To help associate proteins with membranes

When a membrane potential exists, what is the sign of ΔG due to concentration differences?

Question 3 options:

Negative

Either positive or negative

Positive

Zero

Either positive or negative

Which of the following lipids is correctly matched to its role in protein anchoring to membranes (select all correct answers)?

Question 4 options:

Fatty acid (myristoylation and palmitoylation) - used in different combinations to direct proteins to particular locations

Prenylation - extracellular or intracellular anchoring of proteins

Steroid-linked - for intracellular anchoring

GPI - extracellular anchoring of proteins

Fatty acid (myristoylation and palmitoylation) - used in different combinations to direct proteins to particular locations

GPI - extracellular anchoring of proteins

Why is it beneficial for organisms to have several types of lipid anchors (select all correct answers)?

Question 1 options:

To direct proteins to different regions of the cell

There is no particular difference between the anchors, there are just several lipids available so nature uses them all

The isoprenoid lipid anchors prefer to interact with regions of isoprenoid lipids clustered together in a membrane whereas fatty acid anchors tend to interact with glycerophospholipids

Larger proteins require larger anchors

To direct proteins to different regions of the cell

Assuming no changes to ion distribution, how does a fever change the standard membrane potential of -70 mV?

The potential becomes more negative

It depends on which ions are separated by the membrane

There is no effect

The potential becomes more positive

The potential becomes more negative