Biochemistry: BCH 3053 Quiz 1 Flashcards


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Biochemistry
Chapters 1-4, 6
Subjects:
biobiochemistry, science, life sciences, biochemistry
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1

Assume that a protein exists either in a native state or in a denatured (unfolded) state. If ΔH and ΔS of denaturation are 570 kJ/mol and 1.9 kJ/K•mol, respectively, what is the temperature at which the denaturation becomes spontaneous?

42°C

37°C

27°C

11°C

16°C

27°C

2

A catalyst __________________.

increases the rate of a chemical reaction

decreases ΔG

increases the amount of product obtained from a chemical reaction

increases ΔGchanges the equilibrium of a reaction

increases the rate of a chemical reaction

3

Which of the following is a true property of aqueous solutions?

As pH decreases, hydroxide ion concentration increases.

Hydrogen bonds form readily in aqueous solutions.

Nonpolar molecules are generally more soluble than polar molecules in aqueous solutions.

A pH change from 4.5 to 6.5 reflects a decrease in hydronium ion concentration by a factor of 10

pH can be calculated by adding 7.0 to the pOH value

Hydrogen bonds form readily in aqueous solutions.

4

What is the pH of an acetic acid solution where the concentration of acetic acid is 4 mM and the concentration of sodium acetate is 20 mM. The pKa of acetic acid is 4.76.

5.46

4.46

6.00

9.52

11.83

5.46

We can solve this problem by using Henderson-Hasselbach's equation:

pH = pKa + log

We are already know all the required information, thus we input the data given by the problem:

pH = 4.76 + log(20/4)

And finally calculate the pH:

pH = 5.46

The pH of that acetic acid solution is 5.46.

5

If you have a 1L solution of 1M carbonate buffer with a pH of 6.0, what is the molar ratio of H2CO3 to HCO3-? (pKa = 6.37)

2.34

0.29

1.34

0.43

0.11

0.43

6

A solution at pH 7 contains a weak acid, HA, which has a pKa of 6.5. Which of the following is closest to the molar ratio of [A-]:[HA]?

Group of answer choices1:32:33:12:11:1

3:1

7

What is the overall charge of the following peptide at pH = 7.1? C-K-H-N-D

-1

+2

+1

0

-2

0

8

What is the isoelectric point of Histidine?

6.50

4.65

6.00

9.10

7.75

7.75

9

At what pH value (or values) would a solution of Glycine be most effective as a buffer solution?

7.0 only

9.5 only

7.0 and 9.5

2.3 only

2.3 and 9.5

2.3 and 9.5

10

Which group(s) on a polypeptide contribute the most to its overall acid-base properties?

The C-terminal carboxyl group

All α-carboxyl groups on the non-terminal amino acids

The R-groups

All α-amino groups on the non-terminal amino acids

The N-terminal amino group

The R-groups

11

The hydrogen bonds in an α-helix ______________.

are roughly parallel to the axis of the helix

only occur between electronegative atoms of the R-groups

occur between every other amino acid in the helixare roughly perpendicular to the axis of the helix

only occur near the N-terminus or C-terminus

are roughly parallel to the axis of the helix

12

Quaternary structure describes the:

relative orientation of polypeptides in a multi-subunit protein

size and shape of peptide bonds

overall charge of the protein

linear sequence of amino acids from N-terminus to C-terminusα-helices, β-sheets, and β-turns

relative orientation of polypeptides in a multi-subunit protein

13

All of the following can lead to protein denaturation EXCEPT:

Strong acids (e.g. HCl)

Low temperature

Chaotropic agents (e.g. guanidine or urea)

Strong bases (e.g. NaOH)

Detergents (e.g. SDS)

Low temperature

14

How many of these properties – amino acid composition, molecular weight, secondary structure, primary sequence, and isoelectric point – do the following peptides have in common?
AVVSTHPMALEKA and AVVSTHAMALEKP

2

0

3

4

1

3

15

Which of the following could hinder the formation of an α-helix?

Two Alanine in the residues side-by-side

A Proline residue in the helix

A positively charged Lysine residue in the helix

A nonpolar residue near the C-terminus

A negatively charged Arginine residue in the helix

A Proline residue in the helix