Prin of Biochem Exam 1 (Jiaxu Li @MSU)

Select the coenzyme that DOES NOT participate in electron transfer reactions.

ATP

The class of enzyme that catalyzes the following reaction.

transferase

What is the maximum number of hydrogen bonds that one water molecule can have with neighboring water molecules?

4

Which of the following amino acids is involved in disulfide bonds?

cysteine

an apoenzyme combines with a coenzyme to form a...

haloenzyme

the alteration of enzyme structure on binding of a substrate to an active site is referred to as...

induced fit

Which of the following properties is NOT a characteristic of enzymes?

alter the equilibrium constant of the the reaction

Primary protein structure refers to

linear amino acid sequence

Which of the following statements about a plot of the initial velocity (Vo) vs. the concentration of substrate ([S]) for an enzyme that follows Michaelis-Menten kinetics is FALSE?

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

Which amino acid is considered as basic?

lysine

The Km of an enzymatic reaction is equal to

the concentration of substrate at 1/2 max velocity (Vmax)

In competitive inhibition, an inhibitor...

binds reversibly at the active site

For an enzyme obeying Michaelis/Menten kinetics, what is the Vmax if Vo = 35 mole/min when [s] = Km?

70

Secondary protein structure refers to...

repeated pattern of folding

The cleft in the surface of an enzyme where a substrate binds to is know as the...

active site

Hydrogen bonds can occur when hydrogen is covalently bonded to atoms like nitrogen and oxygen. What property of nitrogen and oxygen is important for this?

electronegativity

Succinic acid dehydrogenase is active only in combination with a nonprotein organic molecule called flavin adenine dinucleotide (FAD). FAD is called a...

coenzyme

The following data were obtained in a study of an enzyme known to follow the Michaelis-Menten kinetics.

Vo. substrate added (mM)

217 0.8

325 2

433 4

488 6

645 100

650 1,000

The Km for this enzyme is approximately...

2 mM

To what level of structure do a-helices and B-sheets belong?

secondary structure

According to the Henderson- Hasselbalch equation, when the concentrations of proton acceptor and proton donor are the same, then....

pH = pKa

The bonds linking amino acids to form proteins are called...

peptide bonds

A denaturing agents disrupt the three-dimensional structures of macromolecules by...

breaking hydrogen bonds

Allosteric effectors...

All of the above

Buffer systems are effective when the pH values are within _____ pH unit(s) of the pKa value.

1

The amino acid glycine titration curve reveals a pK1 of 2.34, a pI (isoelectric point) of 5.97, and a pK2 of 9.60. When dissolved in water, which ionic species is most likely to predominate at pH = 5.97

+NH3---CH2---COO-

Hydrogen bonds between amino acids in a polypeptide occur between which chemical groups?

the C=O and N-H grouds

The pH inside cells is normally near pH 7 which statement is true about the charges (ionization state) of the alpha-amino groups of an amino acid?

the alpha- carboxyl group is 1- and the alpha-amino group is 1+

What is the primary force that stabilizes repeating secondary structures as found in a-helices and B-turns?

hydrogen bonds

The effect of an enzyme is to...

lower activation energy

What is the isoelectric point, pI, of glycine? given: pKa1=2.3, pKa2=9.6

5.95

Most enzymes are...

proteins

The chirality of an amino acid results from the fact that its an a-carbon...

is bonded to four different chemical groups

Hemoglobin is made up of four polypeptide chains (subunits). The maximum degree of protein structure shown by hemoglobin is...

quaternary

Based on the Henderson- Hasselbalch equation, calculate the pH when the ratio of acetic acid to acetate is 10 to 1 (the pKa of acetic acid is 4.76)

3.76

The pH of a blood sample is 7.4, while gastric juice is 1.4. The blood sample has:

a million (10^6) times lower [H+] than the gastric juice

In a highly basic solution, pH=12, the dominant form of glycine is:

NH2---CH2---COO-

The three-dimensional structure (native conformation) of proteins is determined primarily by...

its amino acid sequence

Which of the following forced contributes MOST to the primary structure of a protein?

covalent bonds

Which of the following describes the overall three-dimensional folding of a polypeptide chain?

tertiary structure

Which of the following amino acids has a net positive charge at pH 7?

lysine