Cell Biology Chapter 11 Membrane Structure

1.Which is NOT found in a cell membrane? A. Lipid B. DNA C. Protein D. Cholesterol

B

5.Which parts of the phospholipid face the outside of the membrane? A. The head B. The tail C. The belly

A

Short, rigid lipid molecule present in large amounts in the plasma membranes of animal cells, where it makes the lipid bilayer less flexible.

cholesterol

The space inside a hollow or tubular structure; can refer to the cavity in a tissue or within an organelle.

lumen

Functionally and structurally specialized region in the membrane of a cell or organelle; typically characterized by the presence of specific proteins.

membrane domain

A protein associated with the lipid bilayer of a cell membrane.

membrane protein

T/F a lipid bilayer can be formed by a single tailed phospholipid

False (a miscelle is formed)

T/F the two layers of the plasma membrane have the same lipid compositions because they serve the same function

False - different composition - different functions

T/F The lipid bilayer is symmetrical

False the lipid bilayer is asymmetrical

T/F small hydrophobic molecules cannot create membrane potential

False: they cannot cross but can create membrane potential

Two dimensional fluid

Lipid molecules can move freely in one plane. Cannot freely flip flop from one lipid monolayer to another

How many cell membranes do bacterium have?

One

Common phospholipid present in abundance in most cell membranes; uses choline attached to a phosphate as its head group.

phosphatidylcholine

A major type of lipid molecule in many cell membranes. Generally composed of two fatty acid tails linked to one of a variety of phosphate-containing polar groups.

phospholipid

12.How does cholesterol in animal cell membranes affect the fluidity of the bilayer? A. Cholesterol tends to stiffen the bilayer. B. Cholesterol tends to make the bilayer more fluid. C. Cholesterol has little effect on membrane fluidity.

A

3.The tails of phospholipids are: A. hydrophobic. B. hydrophilic. C. amphipathic.

A

7.In a lipid bilayer, which behaves like a two-dimensional fluid, lipids rapidly diffuse: A. (A) within the plane of one monolayer in the bilayer. B. (B) back and forth from one monolayer to the other in the bilayer. C. Both A and B D. Neither A nor B

A

Amphipathic

A molecule that has both a hydrophilic region and a hydrophobic region.

10.Margarine is made from vegetable oils in which the hydrocarbon tails have had what treatment? A. Decreasing the number of single bonds (i.e., changing them to double bonds and removing hydrogen atoms) B. The removal of double bonds (i.e., changing them to single bonds and adding hydrogen atoms) C. The addition of carbon atoms D. The removal of carbon atoms

B

11.Double bonds in hydrocarbon tails have what effect on the rigidity of fats and phospholipid bilayers? A. Double bonds increase the ability of hydrocarbon tails to pack together into a rigid mass. B. Double bonds decrease the ability of hydrocarbon tails to pack together into a rigid mass. C. Double bonds have little effect on the rigidity of fats and phospholipid bilayers.

B

13.In eukaryotic cells, new phospholipids are manufactured byenzymes bound to which part of the endoplasmic reticulum membrane? A. The monolayer that faces the lumen of the endoplasmic reticulum B. The monolayer that faces the cytosol C. Both monolayers

B

14.What type of enzyme moves phospholipids from one monolayer to the other in a biological membrane? A. Phospholipase B. Flippase C. No enzyme-this action happens spontaneously and relatively quickly

B

15.When a vesicle fuses with the plasma membrane, the monolayer that was facing the inside of the vesicle will face: A. the cell cytoplasm. B. the outside of the cell.

B

16.How much of the mass of the plasma membranes is constituted by proteins? A. 25% B. 50% C. 75%

B

17.Which of the following is NOT a function of membrane proteins? A. Transport molecules across the membrane B. Generate the energy required for lipids to diffuse through the membrane C. Transmit extracellular signals to the cell interior D. Serve as anchors to attach the cell to the extracellular matrix

B

19.In the /alpha helices of transmembrane proteins, the hydrophobic side chains are facing: A. the inside of the membrane-spanning helix. B. the outside of the membrane-spanning helix.

B

20.Porin proteins-which form large, water-filled pores in mitochondrial and bacterial membranes-fold into /beta barrel structures. The amino acids that face the outside of the barrel have what kind of side chains? A. Hydrophilic B. Hydrophobic

B

21.Which statement about phospholipids and detergents is NOT true? A. Phospholipids have two hydrocarbon tails, whereas detergents have just one. B. Phospholipids are amphipathic, whereas detergents are hydrophobic. C. Phospholipids form bilayers, whereas detergents tend to form micelles.

B

22.Bacteriorhodopsin is a membrane transport protein that uses sunlight to do what? A. Hydrolyze ATP molecules B. Pump H+ out of the cell and generate a H+ gradient across the plasma membrane C. Pump photons into the cell and generate a deep purple color D. Convert CO2 into sugar during photosynthesis

B

24.Which is not a mechanism for restricting the movement of proteins in the membrane? A. Using barriers such as tight junctions B. Coating proteins with carbohydrates C. Tethering proteins to the cell cortex D. Tethering proteins to the extracellular matrix E. Tethering proteins to the surface of another cell

B

25.On what side of the membrane are the carbohydrate chains of glycoproteins, proteoglycans, and glycolipids located? A. Cytosolic side B. External (noncytosolic) side

B

6.Why do lipids form bilayers in water? A. The hydrophobic head is attracted to water while the hydrophilic tail shuns water. B. The hydrophilic head is attracted to water while the hydrophobic tail shuns water. C. The hydrophobic tail is attracted to water while the hydrophilic head shuns water. D. The hydrophobic head shuns water and the hydrophilic tail attracts water.

B

8.In one second, a lipid in an artificial bilayer may diffuse as far as what distance? A. 2 nanometers (the width of a DNA double helix) B. 2 microns (the length of a large bacterial cell) C. 500 microns (the length of a typical amoeba)

B

9.Phospholipids with which of the following hydrocarbon tails will produce the most fluid bilayer? A. Tails with 18 carbon atoms, fully saturated B. Tails with 18 carbon atoms and two double bonds C. Tails with 20 carbon atoms, fully saturated D. Tails with 20 carbon atoms and two double bonds

B

18.Which is NOT an integral membrane protein? A. A transmembrane protein that spans the lipid bilayer B. A monolayer associated protein tucked into the inner leaflet of the lipid bilayer C. A protein attached to the membrane by non-covalent interactions with other membrane proteins D. A lipid-linked protein anchored to the outer leaflet of the membrane

C

2.The cell membrane is NOT involved in: A. cell communication. B. import and export of molecules. C. DNA Replication. D. cell growth and motility.

C

23.The shape of a cell and the mechanical properties of its plasma membrane are determined by a meshwork of fibrous proteins called: A. basal lamina. B. carbohydrate layer. C. cell cortex. D. tight junction.

C

4.The entire phospholipid molecule is: A. hydrophobic. B. hydrophilic. C. amphipathic.

C

26.What do carbohydrates attached to cell-surface proteins and lipids provide a cell? A. Protection from mechanical and chemical damage B. A slimy coat that prevents cells from sticking to one another C. A distinctive identity in cell-cell recognition D. All of the above

D

Membrane lipids form bilayers in water through what type of interactions

Electrostatic

What would be required for a lipid flip flop to occur?

Enzyme catalyst

Polypeptides chains cross the bilayer as a

Helix

Three classes of membrane lipid molecules

Phospholipids, settles, and glycolipids

Which structure is more favorable - planar phospholipid bilayer or a sealed compartment formed by a phospholipid bilayer

Sealed compartment formed by a phospholipid bilayer

What type of molecules is a lipid bilayer permeable to?

Small nonpolar molecules / very small polar molecules Ex: Oxygen, Carbondioxide / water

T/F Some cells adjust their membrane fluidity by modifying the lipid composition of their membranes.

True

T/F eukaryotes have many internal membranes

True

T/F the lipid bilayer provides the basic structure and barrier function of all cell membranes

True

Having both hydrophobic and hydrophilic regions, as in a phospholipid or a detergent molecule.

amphipathic

Pigmented protein found in abundance in the plasma membrane of the salt-loving archaeon Halobacterium halobium; pumps protons out of the cell in response to light

bacteriorhodopsin

Protective layer of sugar residues, including the polysaccharide portions of proteoglycans and oligosaccharides attached to protein or lipid molecules, on the outer surface of a cell. Also called the glycocalyx.

carbohydrate layer

Soapy substance used to solubilize membrane proteins.

detergent

Protective layer of carbohydrates on the outside surface of the plasma membrane formed by the sugar residues of membrane glycoproteins, proteoglycans, and glycolipids.

glycocalyx

Describes an organic molecule that contains a full complement of hydrogen; in other words, no double or triple carbon-carbon bonds.

saturated

Describes an organic molecule that contains one or more double or triple bonds between its carbon atoms.

unsaturated