Deck 6: Bio-membrane Structure

Question 1

Peripheral proteins bound to the exoplasmic face of the plasma membrane can also bind to:

A)cytoskeletal proteins.
B)proteins of the ECM.
C)the hydrophobic core of the phospholipid bilayer.
D)proteins of the outer mitochondrial membrane.

Answer 1

B

Question 2

Sphingolipids are considered amphipathic glycolipids if:

A)their polar head groups are sugars that are not linked to the tails via a phosphate group.
B)they are phospholipids with a one-chain hydrophobic tail.
C)have one fatty acyl chain attached to carbon 2 of glycerol.
D)none of the above

Answer 2

A

Question 3

Describe how you would prepare liposomes from a biological membrane.

Answer 3

The first step would be to treat the biological membrane with an organic solvent such as a mixture of chloroform and methanol.This would dissolve phospholipids and cholesterol,but not proteins or carbohydrates.Once the dissolved lipids were separated from the proteins and carbohydrates,you would evaporate the solvent.The final step would be to disperse the residue (which consists of phospholipids and cholesterol)in water to form liposomes.

Question 4

When using immunofluorescence microscopy with labeled Annexin V antibodies you found that there is a change in the distribution of the fluorescence when the cells were treated with tumor necrosis factor,an apoptosis-inducing agent.Your data show that this increase in Annexin V fluorescence increases specifically in the:

A)mitochondria.
B)exoplasmic face of the plasma membrane.
C)Golgi.
D)endoplasmic reticulum.

Question 5

Human alkaline phosphatase protein is attached to the plasma membrane by a GPI anchor.In an experiment you treat cells with each of the following enzymes and find one of them inhibits the activity of the protein because it releases it into the extracellular matrix.Which specific enzyme led you to conclude that this anchor on alkaline phosphatase was both necessary and sufficient for binding the protein to the membrane where it can perform its normal activity?

A)glycosyltransferases
B)phospholipase C
C)flippases
D)none of the above

Question 6

What experimental evidence supports the fluid mosaic model of biomembranes?

Question 7

What type of simple-pass membrane protein would contain a hydrophobic membrane-spanning α-helix?

A)transmembrane protein
B)integral membrane protein
C)peripheral protein
D)transmembrane protein and integral membrane protein

Question 8

Which of the cellular organelles are enclosed by two cellular membranes?

A)Golgi
B)lysosome
C)nucleus
D)endoplasmic reticulum

Question 9

Cholesterol mixes with phospholipids in a biomembrane because cholesterol molecules are

A)amphipathic.
B)steroid derivatives.
C)entirely hydrophobic.
D)phospholipid derivatives.

Question 10

Proteins can be attached to the phospholipid bilayer plasma membrane by covalently linked hydrocarbon groups.Which of the following mechanisms are employed in this anchoring?

A)GPI
B)prenylation
C)acylation
D)all of the above

Question 11

How do animal cells maintain membrane fluidity,and hence membrane function,in response to decreased temperature?

Question 12

An investigator wants to use FRAP to quantify the lateral movement of a specific plasma membrane protein,but to do so this investigator must first:

A)focus a laser on one region of the cell surface.
B)measure the intensity of the fluorescence of the cell surface.
C)label the cell with a fluorescent reagent that binds specifically to the cell surface.
D)add detergents to make the cell surface more fluid.

Question 13

Which of the following classes of lipids is (are)present in biomembranes?

A)phosphoglycerides
B)sphingolipids
C)sterols
D)all of the above

Question 14

Which two organelles are responsible for producing phospholipids and sphingolipids?

A)mitochondria and proteasome
B)endoplasmic reticulum and mitochondria
C)Golgi complex and persoxisome
D)endoplasmic reticulum and Golgi complex

Question 15

Lipid droplets arise from the

A)endoplasmic reticulum.
B)plasma membrane.
C)cytosol.
D)exoplasm.

Question 16

Phospholipids with short or unsaturated fatty acyl chains

A)decrease membrane fluidity.
B)increase membrane fluidity.
C)cause biomembranes to become thicker.
D)allow hydrophilic molecules to diffuse across the lipid bilayer.

Question 17

In immunofluorescence studies you always see the small G-protein Ras in a specific region of the cell and,given its protein sequence along with many other proteins localized to this area,you hypothesize that their C-terminal Cys-Ala-Ala-X (X can be any amino acid)motifs may be responsible for targeting these proteins to this subcellular region.To test this hypothesis,you genetically engineer the sequence encoding this motif onto a cDNA encoding green fluorescent protein.When immunofluorescence is used,where specifically would you expect to see GFP localized in the cell?

A)in the nucleus
B)in the cytoplasm
C)in the Golgi
D)at the plasma membrane

Question 18

Which of the following is TRUE regarding lipid-anchored membrane proteins?

A)They are only present on the exoplasmic leaflet of the cell.
B)They are only present on the endoplasmic leaflet of the cell.
C)They are only present on the cytosolic leaflet of the cell.
D)They can be present on either the cytosolic or exoplasmic leaflet of the cell.

Question 19

The plasma membrane around a eukaryotic cell is composed of:

A)hydrophilic fatty acyl side chains.
B)hydrophobic phospholipids.
C)a phospholipid bilayer.
D)none of the above

Question 20

All the following statements describe biomembranes except:

A)Different biomembranes may contain different proportions of the same phospholipids.
B)The two leaflets of a biomembrane may contain different phospholipids.
C)Some biomembranes have free edges.
D)Some phospholipids and cholesterol may cluster to form lipid rafts.

Question 21

Glycolipids and glycoproteins are especially abundant in the

A)nucleus.
B)mitochondrial inner membrane.
C)cytosol.
D)plasma membrane.

Question 22

Free and unesterified fatty acids bind to one of a number of chaperone proteins in order to be transported in the aqueous environment of the cytosol.Which of the following facilitates this intracellular transport?

A)fatty acid-binding proteins
B)aquaporins
C)flippases
D)fatty acid synthase

Question 23

Cholesterol,bile acids,ergosterol,and stigmasterol share all the following common structural features except

A)a four-ring structure.
B)a hydroxyl group on first ring.
C)a carboxylic acid group.
D)a multiple carbon chain extending off the ring structure.

Question 24

The ________________________are transmembrane proteins.

A)lipid-anchored membrane proteins
B)integral membrane proteins
C)peripheral membrane proteins
D)extracellular matrix proteins

Question 25

Describe how charged amino acids guide the assembly of membrane complexes such as the T-cell receptor.

Question 26

Peripheral membrane proteins

A)contain many hydrophobic amino acid residues.
B)contain membrane spanning domains.
C)have covalently attached lipid or fatty acid anchors.
D)may noncovalently interact with phospholipid heads.

Question 27

How are cholesterol and phospholipids transported between organelles?

Question 28

There are several enzymes involved in cholesterol biosynthetic pathway.Which of these is subject to feedback regulation? How does this enzyme sense cholesterol levels?

Question 29

The enzyme in cholesterol biosynthesis subject to feedback inhibition is

A)ABCB4.
B)desaturase.
C)fatty acid synthase.
D)HMG CoA reductase.

Question 30

Phosphate-containing lipids include all of the following except

A)plasmalogen.
B)phospholipids.
C)sphingolipid.
D)triglyceride.

Question 31

Movement of phospholipids from one leaflet to the other

A)occurs routinely.
B)requires cholesterol.
C)requires flippases.
D)is impossible.

Question 32

When examined by fluorescence recovery after photobleaching (FRAP),certain integral membrane proteins are significantly less mobile than others.What accounts for this reduced mobility?

Question 33

The major site of lipid synthesis in eukaryotic cells is the

A)nucleus.
B)endoplasmic reticulum (ER).
C)peroxisome.
D)mitochondria.

Question 34

Describe how unesterified fatty acids unlinked to CoA are able to move through the aqueous environment of the cytoplasm.

Question 35

Porins

A)are peripheral membrane proteins.
B)contain no hydrophobic amino acid residues.
C)have many hydrophobic α-helical regions.
D)allow small hydrophilic molecules to pass through a membrane.

Question 36

Cholesterol and phospholipids are transported between organelles by

A)Golgi-dependent mechanisms.
B)incompletely characterized vesicle populations.
C)direct contact between membranes and,to some extent,small,soluble lipid-transfer proteins.
D)b and c

Question 37

What are the primary functions of the plasma membrane in all cells?