BI203 Chapter 2 Quiz

Phospholipids consist of a 3-carbon core to which fatty acids and a phosphate group are linked. The most common 3-carbon core is a. dihydroxyacetone. b. glyceraldehyde. c. glycerol. d. serine.

c. glycerol.

Proteins must have more than one _______ to have a quaternary structure. a. α helix b. β sheet c. polypeptide chain d. transmembrane segment

c. polypeptide chain

Whereas small uncharged molecules can diffuse through the hydrophobic core of a phospholipid bilayer, a larger polar substance such as glucose must enter cells by binding to a. a non-phospholipid such as cholesterol. b. the carbohydrate portion of glycolipids. c. peripheral membrane proteins located on the inner side of the membrane. d. carrier proteins that facilitate the passage of specific molecules across membranes.

d. carrier proteins that facilitate the passage of specific molecules across membranes.

Molecules that are partly water-soluble and partly water-insoluble are a. hydrophilic. b. amphipathic. c. hydrophobic. d. allosteric.

b. amphipathic.

The lock-and-key and induced-fit models are two alternative models that can explain how enzymes and substrates interact. These two models can be distinguished from each other according to changes in the a. viscosity of the reaction solution as the substrate and enzyme bind. b. shape as the substrate and enzyme bind. c. reaction solution temperature as a result of the endothermic cooling that occurs during substrate binding. d. reaction solution color as the substrate and enzyme bind.

b. shape as the substrate and enzyme bind.

Which of the following classes of amino acids is buried within the folded structure of the protein? a. Acidic b. Basic c. Nonpolar d. Polar

c. Nonpolar

The α (alpha) helix is an example of which level of protein structure? a. Primary b. Quaternary c. Secondary d. Tertiary

c. Secondary

Which of the following is not one of the four major classes of organic molecules in the cell? a. Carbohydrates b. Lipids c. Water d. Proteins

c. Water

All of the following are ways in which enzyme activity can be regulated except a. by binding to an allosteric site. b. through feedback inhibition. c. by modulation of intracellular sucrose concentrations. d. through phosphorylation.

c. by modulation of intracellular sucrose concentrations.

Lipids with unsaturated fatty acids a. decrease the fluidity of membranes. b. increase the charge associated with the inner face of a membrane. c. increase the fluidity of membranes. d. are present only on the inner side of the plasma membrane.

c. increase the fluidity of membranes.

About 50% of the mass of most biological membranes consists of lipids and about 50% consists of proteins. Therefore, a. the membranes contain fewer molecules of lipid than of protein. b. the membranes contain equal numbers of lipid and protein molecules. c. the membranes contain more molecules of lipid than of protein. d. only a few membrane proteins are exposed at the cell surface.

c. the membranes contain more molecules of lipid than of protein.

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

c. transport in the energetically favorable direction.

What is the major carbohydrate-storage molecule in plants? a. Starch b. Cellulose c. Glycogen d. Deoxyribonucleic acid

a. Starch

A disulfide bond is formed between _______ residues. a. cysteine b. glycine c. methionine d. tyrosine

a. cysteine

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

a. embedded nearly randomly in the lipid bilayer.

Cholesterol, a membrane lipid in animals, has a chemical structure similar to a. estradiol. b. phosphatidylinositol. c. thymine. d. triacylglycerol.

a. estradiol.

What is the effect of a β barrel on the permeability of a membrane? a. It decreases permeability. b. It increases permeability. c. It has no effect. d. β barrels are never found in membranes.

b. It increases permeability.

Introducing a double bond into a fatty acid has the effect of putting a(n) _______ into the conformation of the molecule. a. amino acid bulge b. kink c. reverse spiral d. reinforcing rod

b. kink

Chymotrypsin, trypsin, elastase, and thrombin are all grouped together as members of the serine protease family because each a. has similar charge and shape properties in its substrate insertion pockets. b. can form a heptahedral complex with its substrate. c. uses the same catalytic mechanism involving the same key amino acids. d. can be modified by the cell-wall biosynthetic degradative enzyme chitinase.

c. uses the same catalytic mechanism involving the same key amino acids.

Enzymes affect the transition state of a chemical reaction by a. binding to the substrate(s). b. providing a surface on which the reactions converting substrate to product can occur more rapidly. c. altering the conformation of the substrate(s) to approach that of the transition state. d. All of the above

d. All of the above

Which of the following bases is not found in DNA? a. Adenine b. Cytosine c. Thymine d. Uracil

d. Uracil

The three-dimensional structure of a protein is analyzed most definitively by a. electron microscopy. b. light microscopy. c. subcellular fractionation. d. X-ray crystallography.

d. X-ray crystallography.

Enzymes act by a. lowering the overall change in the free energy of a reaction. b. decreasing the distance that reactants must diffuse to find one another. c. increasing the activation energy. d. decreasing the activation energy.

d. decreasing the activation energy.

Transport across biological membranes is speeded by what class of biological molecules? a. Carbohydrates b. Lipids c. Nucleic acids d. Proteins

d. proteins

Coenzymes are chemically related to a. amino acids. b. inorganic phosphate. c. glucose. d. vitamins.

d. vitamins.

The most abundant molecule in cells is a. aspartic acid. b. DNA. c. sucrose. d. water.

d. water.

Which of the following is not true of coenzymes? a. Chemically, they are branched amino acids. b. They serve as carriers of several types of chemical groups. c. They transfer specific chemical groups among a wide range of substrates. d. They work together with enzymes to enhance chemical reactions without being irreversibly altered.

a. Chemically, they are branched amino acids.

How many common amino acids are there? a. 5 b. 10 c. 20 d. 25

c. 20