Chapter 3 - Proteins (Practice Quiz)

Match the basic protein functions with a specific example of that type of protein: enzyme

Carboxylase

Which of the following is not a feature commonly observed in ? sheets?

Coiled-Coil patterns

Which of the following statements is true?

Disulfide bonds stabilize but do not change a protein's final conformation.

Protein structures have several different levels of organization. The primary structure of a protein is its amino acid sequence. The secondary and tertiary structures are more complicated. Consider the definitions below and select the one that best fits the term "protein domain."

Elastase, Collagen, Keratin, elastin

GTP binding proteins typically have GTPase activity, and the hydrolysis of GTP transforms them to the "off" conformation.

False

ATPases generate ATP for the cell

False. ATPases hydrolyze ATP; they do not produce it. These enzymes enable the cell to harness the chemical energy stored in the high-energy phosphate bonds.

Antibodies are Y shaped and are composed of six different polypeptide chains.

False. Although antibodies are Y shaped, they are composed of four, not six, polypeptide chains. There are two heavy chains and two light chains.

Protein phosphorylation is another way to alter the conformation of an enzyme and serves exclusively as a mechanism to increase enzyme activity.

False. Although phosphorylation of a protein can change its conformation, this modification may be either as a positive or a negative regulator of enzyme activity, depending on the protein in question.

Feedback inhibition is defined as a mechanism of down-regulating enzyme activity by the accumulation of a product earlier in the pathway.

False. Feedback inhibition occurs when an enzyme acting early in a metabolic pathway is inhibited by the accumulation of a product late in the pathway. The inhibitory product binds to a site on the enzyme that lowers its catalytic activity.

The "polypeptide backbone" refers to all atoms in a polypeptide chain, except for those that form the peptide bonds.

False. Peptide bonds are planar amide bonds that are central to the polypeptide backbone formation. The atoms in the amino acid side chains are not considered to be part of the backbone.

The amino acids in the interior of a protein do not interact with the ligand and do not play a role in selective binding.

False. The interior amino acids form a structural scaffold that maintains the specific orientation for those that directly interact with the ligand. Changes to these interior amino acids can change the protein shape and render it nonfunctional.

Match the basic protein functions with a specific example of that type of protein: storage

Ferritin

Lysozyme is an enzyme that specifically recognizes bacterial polysaccharides, which renders it an Effective antibacterial agent. Into what classification of enzymes does lysozyme fall?

Hydrolase

Match the basic protein functions with a specific example of that type of protein: motor

Myosin

Which of the following statements is true?

Nonpolar amino acids tend to be found in the interior of proteins.

To study how proteins fold, scientists must be able to purify the protein of interest, use solvents to denature the folded protein, and observe the process of refolding at successive time points. What is the effect of the solvents used in the denaturation process?

The solvents break all noncovalent interactions.

The correct folding of proteins is necessary to maintain healthy cells and tissues. Unfolded proteins are responsible for such neurodegenerative disorders as Alzheimer's, Huntington's, and Creutzfeld Jacob disease (the specific faulty protein is different for each disease). What is the ultimate fate of these disease-causing, unfolded proteins?

They form protein aggregates

Generally, the total number of nonpolar amino acids has a greater effect on protein structure than the exact order of amino acids in a polypeptide chain.

True

Hexokinase recognizes and phosphorylates only one of the glucose stereoisomers.

True

The relative distribution of polar and nonpolar amino acids in a folded protein is determined largely by hydrophobic interactions, which favor the clustering of nonpolar side chains in the interior.

True

Match the basic protein functions with a specific example of that type of protein: structural

Tubulin

Studies conducted with a lysozyme mutant that contains an Asp?Asn change at position 52 and a Glu?Gln change at position 35 exhibited almost a complete loss in enzymatic activity. What is the most likely explanation for the decrease in enzyme activity in the mutant?

absence of negative charges in the active site

Enzymes catalyze a chemical reaction by lowering the __, because they provide conditions favorable for the formation of a high energy intermediate called the transition state.

activation energy

Purified antibodies are useful for a variety of experimental purposes, including protein purification using __ chromatography.

affinity

The human immune system produces billions of different immunoglobulins, also called __, which enable the immune system to recognize and fight germs by specifically binding one or a few related antigens.

antibodies

Which of the following mechanisms best describes the manner in which lysozyme lowers the energy required for its substrate to reach its transition state conformation?

by speeding up the rate at which water molecules collide with the substrate

Match the basic protein functions with a specific example of that type of protein: special purpose

green fluorescent protein

Match the basic protein functions with a specific example of that type of protein: transport

hemoglobin

Match the basic protein functions with a specific example of that type of protein: gene regulatory

homeodomain proteins

Although all protein structures are unique, there are common structural building blocks that Are referred to as regular secondary structures. Some have ? helices, some have ? sheets, and still others have a combination of both. What makes it possible for proteins to have these common structural elements?

hydrogen bonds along the protein backbone

Proteins bind selectively to small molecule targets called ligands. The selection of one ligand out of a mixture of possible ligands depends on the number of weak, noncovalent interactions in the protein's ligand-binding site. Where is the binding site typically located in the protein structure?

inside a cavity on the protein surface

The enzyme hexokinase is so specific that it reacts with only one of the two __ of glucose.

isomers

Which of the following is not a feature commonly observed in ? helices?

left-handedness

The hypervariable structural element that forms the ligand-binding site is comprised of several __.

loops

On being heated, a protein molecule will become denature as a result of breakage of __ bonds.

noncovalent

A protein such as hemoglobin, which is composed of more than one protein subunit, has __ structure.

quantinary

A newly synthesized protein generally folds up into a stable conformation. All the information required to determine a protein's conformation is contained in its amino acid

sequence

The three-dimensional conformation of a protein is its __ structure.

tertiary

You have two purified samples of protein Y: the wild-type (nonmutated) protein and a mutant version with a single amino acid substitution. When washed through the same gel-filtration column, mutant protein Y runs through the column more slowly than the normal protein. Which of the following changes in the mutant protein is most likely to explain this result?

the loss of a binding site on the mutant protein surface through which protein Y normally forms dimers

If an enzyme's allosteric binding site is occupied, the enzyme may adopt an alternative conformation that is not optimal for catalysis

true

The chemical properties of amino acid side chains include charged, uncharged polar, and nonpolar.

true

Fully folded proteins typically have polar side chains on their surfaces, where electrostatic attractions and hydrogen bonds can form between the polar group on the amino acid and the polar molecules in the solvent. In contrast, some proteins have a polar side chain in their hydrophobic interior. Which of following would not occur to help accommodate an internal, polar side chain?

A hydrogen bond forms between a polar side chain and an aromatic side chain.

The process of generating monoclonal antibodies is labor-intensive and expensive. An alternative is to use polyclonal antibodies. A subpopulation of purified polyclonal antibodies that recognize a particular antigen can be isolated by chromatography. Which type of chromatography is used for this purpose?

Affinity

Match the basic protein functions with a specific example of that type of protein: signal

Insulin

Any substance that will bind to a protein is known as its __.

Ligand

On removal of urea, an unfolded protein can become renatured. The final folded conformation adopted by a protein is that of __ energy.

Lowest

A protein's amino acid sequence is known as its __ structure.

Primary

Once the reaction is completed, the enzyme releases the __ of the reaction.

Products

For some proteins, small molecules are integral to their structure and function. Enzymes can synthesize some of these small molecules, whereas others, called vitamins, must be ingested in the food we eat. Which of the following molecules is not classified as a vitamin but does require the ingestion of a vitamin for its production?

Rentinal

Match the basic protein functions with a specific example of that type of protein: receptor

Rhodopsin

The three-dimensional coordinates of atoms within a folded protein are determined experimentally. After researchers obtain a protein's structural details, they can use different techniques to highlight particular aspects of the structure. What visual model best displays a protein's secondary structures (? helices and ? sheets)?

Ribbon

The ? helices and ? sheets are examples of protein __ structure.

Secondary