Quart Term 2 - CHEM 150

Version A

Which of the following chromatography techniques separates protein in function of their net charge?

lon exchange

Which of the following chromatography techniques would be best to separate a protein enzyme that has a high binding affinity for its substrate?

Affinity

Which chromatography technique would be best to separate positively charged proteins in function of their size and shape?

Size exclusion

Consider an aqueous solution at pH7 containing a mix of lysine, aspartate, and glutamine. You submit this mix to separation using an cation exchange chromatography column: which one of the 3 amino acids present in the solution will be eluted last?

lysine

The most direct method to determine the amino acid sequence of a short peptide is:

Edman degradation

When end-group analysis (Sanger’s method) was performed on the protein insulin, the results indicated that both glycine and phenylalanine were N-terminal amino acids. These results indicate that

Insulin consists of two separate polypeptide chains

The main thermodynamics-related difference between a catalyzed and a non-catalyzed reaction is that

the activation energy change of the catalyzed reactions is the lowest of the 2 reactions

First order kinetics means that

The rate of the reaction varies linearily with the concentration of reactant.

In the induced-fit model of substrate binding to enzymes

there is a conformational change of the catalytic site when the substrate binds

The Michaelis-Menten approach to model the kinetics of an enzyme-catalyzed reaction makes which of the following assumptions regarding the conversion of product into substrate?

The product is not converted to substrate to any appreciable extent.

If the y-intercept of a Lineweaver-Burk (double reciprocal) plot = 39.37 (sec/millimole) and the slope = 75.3 L/sec, Vmax equals

0.0254 millimoles per second

Refer to Exhibit 6A. What is the Km value of the enzyme?

10 uM

Refer to Exhibit 6A. What is the max value of the enzyme?

180 nM/s

Refer to Exhibit 6A. “Restrainin” is an inhibitor of the enzyme triose phosphate isomerase. When restrainin is added to cells at a concentration of 0.4 nM, the enzyme’s apparent Km for the substrate is increased to reach a value of 100 uM, but the Vmax is unchanged.

In the following graph, which line best represents the Lineweaver-Burk (double reciprocal) plot obtained in the presence of restrainin?

C

Refer to Exhibit 6A. “Hindrate” is an inhibitor of trios phosphate isomerase. When it is added to cells at a concentration of 0.1 nM, the enzyme’s Km for the substrate is unchanged, but the apparent Vmax is altered to 50 nM/sec. Is hindrate a:

Noncompetitive inhibitor?

Which of the following types of inhibitor binds reversibly to the enzyme at the same site than the substrate without altering the overall enzyme structure?

competitive inhibitor

Which of the following is true?

none of these is true

In order to trigger an allosteric effect, enzyme effectors…

always bind at a site different from the catalytic site

Inhibitors which bind covalently onto specific amino acids are useful to identify which amino acids residues are present in the catalytic site of an enzyme.

True

Refer to Exhibit 4A. Total hydrolysis of the peptide in HCl would yield to these products:

Ala, Arg, Cys, GIn, Gly, Met

Refer to Exhibit 4A. The amino terminal amino acid is:

Cys

Refer to Exhibit 4A. This peptide is digested with chymotrypsin which cleaves peptide chains at the C-terminus side of Group D amino acids. What are the sequences of the 2 products expected from this digestion?

Cys-Ala-Gly-Arg and GIn-Met

The typical order for the major steps of protein purification would be (from first to last):

Tissue homogenization, salt fractionation, column chromatography, electrophoresis.

Homotropic effects are associated with catalysis carried by

Allosteric enzymes

The critical serine residue and the critical histidine residue of the catalytic site of the enzyme chymotrypsin separated by 138 amino acids if considering the enzyme primary structure. This observation suggests that:

chymotrypsin tertiary structure is essential to its function

Which of the following statements about coenzymes is true?

All of these statements are true

Cyanogen bromide is a reagent which cleaves a peptide at the C-terminal of a methionine residue. This specificity is based on the presence of a sulfur atom in the structure of the methionine side chain. What other amino acid contains a sulfur atom in its side chain?

cysteine

What physico-chemical property is used to define lipids?

solubility in organic solvent

What does amphipathic mean?

having both hydrophilic and hydrophobic regions

Which of the following moieties is not present in a molecule of triacylglycerol?

Phosphate

Which of the following four fatty acids has the highest melting point?

CH,CH,CH,CH,CH,CH,CH,CH,CH,COOH

How does cholesterol affect membrane fluidity?

It tends to decrease membrane fluidity

Which of the following modes of transport is spontaneous?

Facilitated diffusion

Which of the following mode of transport across a membrane requires bio-energy?

Active Transport

The nucleotide sequence of DNA represents what level of structure?

primary

Which of the following nuclear bases is not found in DNA?

U

The fundamental differences between RNA and DNA are

at the nuclear bases and the ribose units levels only

The backbone of nucleic acids consists of

phosphodiester bond between the 3' and 5' hydroxyl groups of neighboring sugars

Which of the following statements is true for double-stranded DNA?

The amount of A is the same as the amount of T, and the amount of G is the same as the amount of C

The two strands in the DNA double helix

have their 3’ → 5’ directions opposed, i.e., they are anti-parallel

Which of the following RNA subtype has NOT been introduced in class?

epidermal RNA (eRNA)

Histones are basic proteins which are part of DNA quaternary structure in eukaryotes. These proteins contain large amounts of basic amino acids (Group D) such as?

lysine

Cell membranes

separate the cell from the outside world

Which of the following types of bonds are essential in the definition of the primary structure of nucleic acids?

covalent bonds

Membrane lipids in a lipid bilayer are held together primarily by

hydrophobic interactions

In nucleic acid primary structure, the bonds between each nucleotide residues in a single strand are

phosphodiester bonds

Membranes are generally symmetrical, i.e., the outer leaflet is composed of the same number and types of phospholipids than the inner leaflet.

False

Lipids differ from most other biomolecules because they are primarily defined on the basis of solubility criteria instead of molecular structure criteria.

True

Supercoiling of DNA

requires the action of topoisomerase enzymes

In the fluid mosaic model of membrane structure

the proteins “float” in the lipid bilayer