BIOCHEM MC

Which statement about hydrogen bonds is not true?

Individual hydrogen bonds in liquid water exist for many seconds and sometimes for minutes.

The four covalent bonds in methane (CH4) are arranged around carbon to give which one of the following geometrics?

tetrahedral

The macromolecules that serve in the storage and transmission of genetic information are:

nucleic acids

Dr. Emil's office hours are on Tuesdays and Thursdays from:

11:00 am- 12:00 pm and also by appointment

The hydrophobic effect makes important energetic contributions to:

all of the answers are correct

\-binding of a hormone to its receptor protein

\-enzyme substrate interactions

\-membrane structure

\-three-dimensional folding of a polypeptide chain

In water, which substance would most force surrounding water molecules to become highly ordered?

CH4

What is the pH of 1 M HCl solution?

0 (pH= -log1)

The Henderson-Hasselbach equation

relates the pH of a solution to the pka and the concentrations of acid and conjugate base

When a nonpolar solute is dispersed in water, which will occur?

the entropy of the water decreases

Pyranose forms of monosaccharides are___

6-membered cyclic hemiacetals

Two monosaccharides that differ in stereochemistry at only a single asymmetric carbon are called:

epimers

\-also accepted= diastereomers

When the linear form of glucose cyclizes, the product is a(n):

hemiacetal

Which arrow correctly identifies the atom that will become the anomeric carbon?

the carbon with a hydrogen and double bonded O (H-C=O)

Which of the following compound(s) would undergo mutarotation in aqueous solution and therefore classified as reducing sugar(s)

I, II, and III (only contain OH no OCH3)

The compound that consists of ribose linked by an N-glycosidic bond to N-9 of adenine is:

adenosine

Purines have ___ ring(s), (each) containing___ nitrogens(s), whereas pyrimidines have ____ ring(s), (each) containing ____ nitrogens.

2; 2; 1; 2

A true statement about hydrophobic interactions is that they:

are the driving force in the formation of micelles of amphipathic compounds in water

Which of following is an anomeric pair?

alpha-D-glucose and beta-D-glucose

The aqueous solution with the lowest pH is:

0.1 M HCl

When forming the disaccharide maltose from two glucose monosaccharides:

both A and B

\-water is eliminated

\-a hemiacetal is converted to an acetal

Stereoisomers that differ in absolute configuration in at least one but not all chiral centers are known as:

diastereoisomers

B-form DNA in vivo is a ____ -handed helix, ___ armstrongs in diameter, with a rise of ____ armstrongs per base pair

right; 20; 3.4

In nucleotides and nucleic acids, syn and anti conformations relate to:

rotation around the sugar-base bond

The double helix of DNA in the B-form is stabilized by:

nonspecific base-stacking interaction between two adjacent bases in the same strand

Chargaff's rule state that in typical DNA

A+G = T+ C

Which of the following statements is (are) true about alpha-amino acids?

all of these

\-the amino and carboxylic acid groups are separated by one carbon atom

\-the amino group is connected to a carbon atom that is alpha to the carboxylic acid group

\-the alpha carbon can be a chirality center

which of the following amino acids is achiral?

glycine

two amino acids of the standard 20contain sulfur atoms. They are:

methionine and cysteine

which of the following naturally occurring amino acids does not have the S configuration

cysteine (has the CH2-S)

On the molecule, the arrow is pointing to the___ carbon

beta

\-one adjacent to the carbon attached to the NH2 and COO

Which pair of amino acids can be used to measure the concentration of proteins based on absorption of UV light?

tyrosine and phenylalanine

The MOST useful way to classify amino acids is by:

polarity

Amino acids without ionizable R groups can act as a zwitterion in a(n)____ solution

neutral

In the alpha helix the hydrogen bonds:

are roughly parallel to the axis of the helix

In an alpha helix, the R groups of the amino acid residues:

are found on the outside. of the helix spiral

Which of the following best represents the backbone arrangement of two peptide bonds?

C (alpha)-C-N-C(alpha)-C-N

Proline residues are infrequently found in___ due to their___

alpha helices; decreased ability to serve as hydrogen-bond donors

For amino acids with neutral (non-ionizing) R groups, at any pH below the pI of the amino acid, the population of amino acids in solution will:

have a net positive charge

At the isoelectric pH of a tetrapeptide:

the total net charge is zero

In highly basic solution, pH=13, the dominant form of glycine is:

NH2-CH2-COO-

Which of the following is correct with respect to the amino acid composition of proteins?

proteins with different functions usually differ significantly in their amino acid composition

All of the following are considered "weak" interaction in proteins except:

peptide bonds

Two proteins bind to the same ligand, and protein A has half of its binding sites occupied when the ligand concentration is 0.5 mM, while protein B has half of its binding sites occupied when the ligand concentration is at 0.3 mM. Which protein binds the ligand more strongly, and what is the dissociation constant for that protein-ligand interaction?

protein B binds more strongly, and Kd= 0.3 mM

Proteins often have regions that can fold and function as an independent entity from the whole protein. These regions are called:

domains

In hemoglobin, the transition from T state to R state (low to high affinity) is triggered by:

oxygen binding

The chirality of an amino acid results from the fact that its alpha carbon:

is bonded to four different chemical groups

What is the biological advantage to the sigmoidal binding curve of hemoglobin for oxygen?

it allows hemoglobin to shift between low and high affinities for oxygen

A prosthetic group of a protein is a nonprotein structure that is____the protein

permanently associated with

Examine the binding curves for two proteins (A and B) that bind the same ligand. Which statement applies?

A= hyperbolic and B=sigmoidal

the dissociation constant for A is less than that of B

Patients with chronic hypoxia (low O2 levels) due to decreased lung function may adapt by increasing their circulating BPG levels. Predict which outcome will be true for such a patient.

p50 for O2 will be increased

Which statement is false?

collagen is a protein in which the polypeptides are mainly in the alpha-helical conformation

An average protein will NOT be denatured by:

iodoacetic acid

In aqueous solution, protein conformation is determined by two major factors. One is the formation of the maximum number of hydrogen bonds. The other is the:

placement of hydrophobic amino acid residues within the interior of the protein

Roughly how many amino acids are there in one turn of an alpha helix

4

According to the diagram, which is the BEST estimate of this amino acid's isoelectric point?

6.0 (find half)

Allosteric proteins

often display cooperativity

the relaxed form of an allosteric enzyme has___ affinity for the substrates than the tense form

higher

A Hill coefficient (nH) of 2 indicates that there:

is positive cooperativity in ligand binding

Select all that apply. The fetal hemoglobin has:

a lower binding affinity for 2,3-BPG than adult hemoglobin and a higher binding affinity for oxygen than adult hemoglobin

To calculate the turnover number of an enzyme, you need to know:

enzyme concentration and the velocity of the catalyzed reaction at [S]\>> Km

Which statement about a plot of V0 versus [S] for an enzyme that follows Michaelis-Menten kinetics is FALSE?

At very high \[S\], the velocity curve becomes a horizontal line that intersects the y-axis at Km

\-also accepted= The y-axis is a rate term with units of um/min...can be in M/sec for example

The benefit of measuring the initial rate of a reaction V0 is that, at the beginning of a reaction:

changes in [S] are negligible, so [S] can be treated as a constant

Which enzymes are NOT among the six internationally accepted classes of enzymes?

polymerases

The role of an enzyme in an enzyme-catalyzed reaction is to:

increase the rate at which substrate is converted into product

An enzyme's specificity constant (kcat/Km) has a maximum upper limit due to:

diffusion of the enzyme and substrate together

In competitive inhibition, an inhibitor:

binds reversibly at the active site

Phenyl-methane-sulfonyl-fluoride inactivates serine proteases by binding covalently to the catalytic serine residue at the active site; this enzyme-inhibitor bond is NOT cleaved by the enzyme. This is an example of what kind of inhibition?

irreversible

An enzyme inhibitor is a compound that?

can do all of the above

\-prevents a substrate from binding to the enzyme

\-deforms enzymes

\-binds to the active site of an enzyme

\-prevents an enzyme from functioning

Select the statement that BEST describes a key difference between competitive and noncompetitive inhibitors.

A competitive inhibitor binds to the active site, and a noncompetitive inhibitor does not.

Which of the following is NOT a cofactor?

carbonic anhydrase

Which statement about allosteric control of enzymatic activity is false?

heterotropic allosteric effectors compete with substrate for binding sites

The allosteric enzyme ATCase is regulated by CTP, which binds to the T state of ATCase. CTP is a:

negative regulator (heterotropic inhibitor)

One of the enzymes involved in glycolysis, aldolase, requires Zn2+ for catalysis. When the enzyme lacks zinc, it is referred to as the:

apoenzyme

Chymotrypsin catalyzes the cleavage of proteins at peptide bonds adjacent to aromatic amino acid residues by using which catalytic mechanism?

both general acid-base catalysis and covalent catalysis

Which amino acid is NOT capable of using its side chain (R group) to participate in general acid-base catalysis

Val (valine)

The site on an enzyme where the reaction that is catalyzed by the enzyme occurs is the___

active site

What term describes the substance that is bound by an enzyme and converted to product?

substrate

What term describes an enzyme without its required cofactor?

apoenzyme

If a reaction is exergonic at specific reactant concentrations, it is considered___

spontaneous

What type of enzymes often display sigmoidal plots of activity versus substrate concentration?

allosteric enzymes

What type of binding is indicated by a sigmoidal-shaped binding curve?

cooperative

Which statement about allosteric control of enzymatic activity is FALSE?

heterotropic allosteric effectors compete with substrate for binding sites

Multiple substrate enzyme reactions are divided into two classes which are called

sequential (single) displacement and double (ping pong) displacement

What is the Bohr effect?

the regulation of hemoglobin-binding by hydrogen ions and carbon dioxide

Which of the following is correct concerning the oxygenation plot of proteins X and Y shown below?

X= higher sigmoidal

Y=lower sigmoidal

Protein X corresponds to fetal hemoglobin, and protein Y corresponds to normal adult hemoglobin

What regulatory mechanism relies on inhibition of the first step of the pathway by the final product of the pathway?

feedback inhibition

What term describes multiple forms of homologous enzymes found within an organism?

isoenzymes

What term describes enzymes that are activated by proteolytic cleavage?

zymogens

Which type of enzyme specifically catalyzes protein phosphorylation

protein kinases

Removal of protein phosphates is catalyzed by protein___

phosphatase

What is (are) the most common strategy(ies) for enzymatic regulation?

reversible covalent modification

Which of the following is an example of a zymogen?

all of the answers are correct

\-pepsinogen

\-procarboxypeptidase

\-trypsinogen

\-proelastase

A regulatory mechanism that is NOT readily reversible is

proteolytic cleavage

Which molecules of substances contain, or are derived from, fatty acids?

all of these contain or are derived from fatty acids

\-beeswax

\-galactolipids

\-sphingolipids

\-triacylgylcerols

Trriacylglycerols are composed of:

a glycerol backbone with ester links to three fatty acids

Which factor is NOT a consequence of partial hydrogenation of vegetable oils?

lower melting temperature

Which is the abbreviated nomenclature for octadecenoic acid with two double bonds?

18:2

Which is the abbreviated nomenclature for a 14-carbon omega 3-fatty acid that contains no other double bonds

14:1 (delta 11)

Which gives the advantages to using triacylglycerols, rather than polysaccharides, to store energy?

the carbon atoms of triacylgylcerols are more reduced, and since triacylgylcerols are hydrophobic, excess water does not need to be stored along with them

Waxes are best described as:

esters of one long-chain fatty acid and one long-chain alcohol