Lodish Ch 3: Protein Structure and Function

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Questions and Answers

Which of the following is defined as the tertiary structure of a protein?

the primary amino acid sequence

structural features such as a turn

folded structures such as an a helix

structural domains such as a DNA-binding domain (correct)

Monomeric proteins do not contain a:

secondary structure

primary structure

quaternary structure (correct)

tertiary structure

Which of the following is NOT part of a zinc-finger motif?

proline residue (correct)

histidine residue

zinc ion

cysteine residue

There are many important roles for the dynamic nature of proteins in a cell. Which of the following is NOT likely to describe one such reason?

Quaternary structures are usually very transient (occur for short periods of time). (A) Signup and view all the answers

You are studying an oligopeptide composed of eight amino acids. The four amino acids nearest the C terminus are nonpolar. The two amino acids nearest the N terminus are charged. The middle two amino acids are polar. Which amino acid is likely to be labeled as number 2?

lysine (D) Signup and view all the answers

A protein containing several proline residues is:

not likely to form alpha helices (D) Signup and view all the answers

Which of the following is true about protein folding?

Elements from the secondary structure are maintained in the tertiary structure. (C) Signup and view all the answers

When comparing domains and structural motifs, which of the following is NOT true?

Structural domains appear in different proteins with similar functions, while structural motifs have been less conserved over evolution. (C) Signup and view all the answers

You disrupt all hydrogen bonds in a protein. What level of structure will be preserved?

primary structure (D) Signup and view all the answers

Two proteins that have a similar function:

will share similar amino acid sequences if they are homologs (C) Signup and view all the answers

All the following statements about molecular chaperones are true EXCEPT:

they are found only in mammals (C) Signup and view all the answers

Hsp90 family members are present in all organisms EXCEPT:

archaea (C) Signup and view all the answers

What role does aberrant protein folding play in the development of a disease such as Alzheimer's disease?

Misfolding and subsequent proteolytic degradation of the amyloid precursor protein generates a short fragment called b-amyloid protein, which changes from an a-helical to a b-sheet conformation. (A) Signup and view all the answers

Which of the following does NOT impose limits on protein folding?

backbone sequence of the polypeptide (B) Signup and view all the answers

Eggs are protein-rich foods. An uncooked egg can catalyze a reaction that breaks down bacterial cell walls. After cooking, this activity is almost abolished. This is likely because:

the enzyme became denatured (C) Signup and view all the answers

The correct order for molecular chaperone-mediated protein folding is:

III, II, I, IV (C) Signup and view all the answers

All the following statements about enzymes are true EXCEPT:

a single enzyme typically reacts with many different substrates (A) Signup and view all the answers

The K for an enzyme-catalyzed reaction:

is a measure of the affinity of the substrate for the enzyme (A) Signup and view all the answers

For an enzyme-catalyzed reaction, doubling the concentration of enzyme will:

double the V (D) Signup and view all the answers

A small molecule that binds directly to the active site of an enzyme and disrupts its catalytic reaction is called:

a competive inhibitor (B) Signup and view all the answers

Changes in the conformational shape of an enzyme that diminish the size of its ligand-binding pocket are likely to affect an enzyme's:

specificity and affinity (D) Signup and view all the answers

Which of the following is true about enzymes?

Enzymes increase reaction rates by lowering the activation energy needed to reach the transition state. (A) Signup and view all the answers

Which of the following plays a role in the degradation of proteins?

b and c (C) Signup and view all the answers

Which of the following modifications marks a protein for degradation in proteasomes?

ubiquitinylation (D) Signup and view all the answers

Protein self-splicing:

is autocatalytic (B) Signup and view all the answers

Proteases that attack selected peptide bonds within a polypeptide chain are synthesized and secreted as inactive forms called:

zymogens (C) Signup and view all the answers

Which of the following is a mechanism for regulating protein activity?

all of the above (D) Signup and view all the answers

Protein kinase A is converted from an inactive state to an active state by binding:

cAMP (C) Signup and view all the answers

Kinases, which are responsible for the activation or inactivation of a number of proteins, add phosphate groups onto:

serine residues (D) Signup and view all the answers

The conversion of inactive chymotrypsinogen to active chymotripsin is an example of:

proteolytic activation (A) Signup and view all the answers

A misfolded protein targeted to the proteasome will undergo:

unfolding using energy released by ATPases (C) Signup and view all the answers

Modification of proteins by ubiquitin and ubiquitin-like E3 ligases can stimulate all of the following EXCEPT:

mRNA stability (C) Signup and view all the answers

GTPases serve in many signal transduction pathways and the presence of GTP or GDP dictates whether the pathway is on or off, respectively. Which of the following statements is true regarding guanine nucleotide exchange factors (GEF) and their role in these signaling pathways?

They catalyze the dissociation of GDP on the G-protein to therefore promote the replacement of GTP (C) Signup and view all the answers

Which of the following methods can separate proteins based on their mass?

centrifugation and SDS polyacrylamide gel electrophoresis (C) Signup and view all the answers

In two-dimensional gel electrophoresis, proteins are first resolved by and then by

IEF; SDS-PAGE (B) Signup and view all the answers

Gel filtration chromatography separates proteins on the basis of their:

mass (B) Signup and view all the answers

Starting with 1 mCi (milliCurie) of a phosphorus-32-labeled compound, how long would it take until only 0.125 mCi remains?

42.9 days (A) Signup and view all the answers

Western blotting is a method for detecting:

protein (C) Signup and view all the answers

A chunk of tissue is treated so that each cell's membrane is broken open to release the contents inside, and then subjected to differential centrifugation. Which of the following is true at the end of the centrifugation?

Proteins of similar density will be found in the same fraction (either pellet or supernatant) (C) Signup and view all the answers

Proteomics allows researchers to:

examine which proteins differ in abundance between a normal sample and a disease sample (C) Signup and view all the answers

Mass spectrometry techniques are used in proteomics for all of the following purposes EXCEPT:

identification of thousands of proteins' amino acid sequences within a single cell (C) Signup and view all the answers

Flashcards

Tertiary protein structure

The three-dimensional arrangement of a protein's polypeptide chain.

Monomeric proteins

Proteins composed of a single polypeptide chain.