Cell Biology Quiz 2

Integral membrane proteins are those that A. directly associate with membrane lipids. B. associate with the membrane indirectly. C. do not span the lipid bilayer. D. None of the above

A

Phospholipid bilayers are permeable only to molecules that are _______ and _______. A. small; uncharged B. small; charged C. large; uncharged D. large; charged

A

Plasma membrane phospholipids are A. asymmetrically distributed between the two membrane halves. B. symmetrically distributed between the two membrane halves. C. located mostly in the inner leaflet of the bilayer. D. located mostly in the outer leaflet of the bilayer.

A

Active transport differs from facilitated diffusion in that A. active transport involves the transport of molecules up their concentration gradient. B. active transport involves a conformational change in the transport molecule. C. ions are not transported via active transport, only by facilitated diffusion. D. active transport requires a protein component, whereas facilitated diffusion occurs by simple diffusion through the plasma membrane.

A, Active transport is thus an energy-requiring process and is coupled to either ATP hydrolysis or to the passage of another substance in an energetically favorable direction.

Passive transport across a membrane refers to A. transport in the energetically favorable direction. B. transport out of a cell. C. simple diffusion across membranes, without the help of proteins such as channels or carriers. D. transport into the interior of a cell.

A, Passive transport refers to the transport of a molecule in the energetically favorable direction, taking into consideration concentration and electrochemical gradients via membrane channels or carrier proteins.

Channels form pores through which molecules of appropriate size and charge can cross a membrane. By contrast, carrier proteins A. actively transport molecules. B. selectively bind the molecule to be transported, change configuration, and release it on the other side. C. transport a molecule against its concentration gradient. D. require ATP.

B

A feature common to most transmembrane proteins is a(n) Selected Answer: A. phosphorylated exterior domain. B. α-helical region of about 20 to 25 hydrophobic amino acids. C. structure consisting almost exclusively of β-sheets. D. amino acid sequence rich in acidic residues.

B, At least one of these α-helical domains is present in almost all transmembrane proteins and functions as the membrane-spanning domain.

What is the primary reason that mammalian red blood cells are used in the study of the plasma membrane? A. They are of particular interest because they are made up of a lipid monolayer. B. They lack nuclei and membrane-bounded organelles. C. They contain larger plasma membranes than any other cell type. D. There are a lot of them and they are easily obtained.

B, Red blood cells are a good source of plasma membrane because the membranes can be isolated without risk of contamination from other types of membranes.

In the fluid mosaic model of biological membrane structure, transmembrane proteins are A. segregated into large protein clusters or rafts. B. embedded nearly randomly in the lipid bilayer. C. almost completely surrounded by membrane lipid. D. weakly held in place on the surface of the lipid bilayer.

B, Typically, only small, α-helical portions of the protein are embedded in the membrane, and individual proteins are distributed fairly randomly within the membrane bilayer.

ntroducing a double bond into a fatty acid puts a(n) _______ into the conformation of the molecule. A. reverse spiral B. kink C. branch D. amino acid bulge

B, the double bond introduces a kink in the hydrocarbon chain.

Active transport is transport in an energetically A. unfavorable direction, driven only by the flow of another molecule across a membrane. B. favorable direction, coupled to the hydrolysis of ATP. C. unfavorable direction, always coupled to another reaction or source of energy. D. unfavorable direction, always driven by hydrolysis of ATP.

C

Cholesterol is present in the membranes of all A. plant cells. B. cells. C. animal cells. D. eukaryotic cells.

C

Molecules that traverse a membrane against their concentration gradient do so by _______ transport. A. passive B. channel-mediated C. active D. carrier-mediated

C

The resting potential of a typical eukaryotic cell is _______ mV. A. 0 B. -100 C. -60 D. +60

C

While small, uncharged molecules can diffuse through the hydrophobic core of a phospholipid bilayer, larger polar molecules such as glucose must enter cells by binding to A. a nonphospholipid such as cholesterol. B. peripheral membrane proteins located on the inner side of the membrane. C. carrier proteins that facilitate the passage of specific molecules across membranes. D. the carbohydrate portion of glycolipids.

C, Through binding to a carrier protein, a transporter, glucose is placed in a hydrophilic environment and not exposed to the hydrophobic membrane lipids.

Cell membranes are composed principally of A. nucleic acids. B. proteins. C. carbohydrates. D. phospholipids.

D

Cholesterol affects membrane fluidity by Selected Answer: A. decreasing membrane fluidity at all temperatures. B. increasing membrane fluidity at high temperatures and decreasing membrane fluidity at low temperatures. C. increasing membrane fluidity at all temperatures. D. decreasing membrane fluidity at high temperatures and increasing membrane fluidity at low temperatures.

D

Common factors affecting membrane fluidity include A. length of phospholipid fatty acid chains. B. temperature. C. number of double bonds in the fatty acid chains. D. All of the above

D

Phospholipids in a membrane commonly A. move laterally in the plane of the bilayer. B. rotate within the bilayer. C. move from one bilayer to the other. D. Both a and b

D

The plasma membrane functions as a A. selective barrier to the passage of molecules. B. site for the uptake of macromolecules into the cell. C. site for cell-cell interactions. D. All of the above

D

Lipids with unsaturated fatty acids A. are present only on the inner side of the plasma membrane. B. decrease fluidity of membranes. C. increase the charge associated with the inner face of a membrane. D. increase fluidity of membranes.

D, Double bonds produce kinks in fatty-acid chains, causing them to pack irregularly, which increases the fluidity of membranes.

The sugar groups of glycolipids and glycoproteins are found on the outer surface of the plasma membrane. True or False

True