Molecule Test 4

1. Histones are usually rich in _______ and ________ residues as they are positively charged at physiological pH and can form ion pairs with the negatively charged phosphate groups on the backbone of the DNA molecule.

Lysine, Arginine

Arginine, Leucine

Uracil, Thymine

Glycine, Proline

Glutamate, Aspartate

2. Why is the decreased affinity of fetal hemoglobin for BPG advantageous to the fetus?

With fewer BPG molecules bound there are more heme residues available for O2 binding

Decreased BPG binding biases the fetal hemoglobin toward the T state

BPG is available to bind to fetal myoglobin, helping to release O2 in fetal muscle tissue

It reduces fetal hemoglobin's P50

3. Transketolase catalyzed reaction follows a

Ping-pong mechanism

Second order reaction mechanism

Hills reaction mechanism

Allosteric activation mechanism

Random mechanism

4. Which of the following statements does not apply to collagen?

It contains hydroxylated amino acids.

One single polypeptide forms a left-handed helix.

Cross-links between neighbouring hydroxylated Lys residues stabilize the helix.

Glycine at every third position is essential for the stability of the triple helical structure.

The triple helical structure twists in the right-handed direction.

5. Which of the following accurately describes the effects of a competitive inhibitor on km

Km decreases because the inhibitor binds to ES to form ESI which decreases ES

Km unchanged; inhibitor binding does not affect S binding

Km increases because the inhibitor is decreasing the probability of the substrate's binding to the active site

Km increases because the inhibitor binds to ES to form ESI which decreases ES

None of the rest

6. The isoelectric point of Ala-His-Asp-Arg-Val-Gln is

7.95

11.17

4.97

7.0

3.03

7. Which of the following has the smallest KI towards adenosine deaminase

Adenosine

Inosine

1,6 Dihydroinosine

Malonate

PCNA

8. DIPF is a ________ inhibitor of serene proteases

Competitive

Noncompetitive

Uncompetitive

Reversible

Irreversible

9. According to Figure 4, which of the following is not likely to be a serine protease?

Thrombin

Factor XIa

Factor IXa

Tissue factor

Factor VIIa

10. Which of the following statements about a plot of V0 vs [S] for and enzyme that follows Michaelis-Menten kinetics is FALSE

Km is the [S] at which V0 = 0.5 Vmax

The shape of the curve is a hyperbola.

The y-axis is initial reaction velocity

As [S] increases, the initial velocity of reaction, V0, also increases.

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

11. Which of the following statements is correct?

The replication machinery is stationary and the template DNA is reeled through it.

The replication machinery move along the template DNA like a train on tracks.

Positive supercoiling facilitates initiation of DNA replication.

Introduction of negative supercoiling to DNA by helicase is dependent on ATP hydrolysis.

Introduction of negative supercoiling to DNA by helicase is independent on ATP hydrolysis.

12. Which of the following is the best competitive inhibitor to adenosine deaminase catalyzed reaction

Adenosine

Inosine

1,6 Dihydroinosine

Malonate

PCNA

13. Which of the following corresponds to an enzyme catalyzed reaction with a noncompetitive inhibitor

Figure 10

Figure 5

Figure 6

Figure 8

None of the rest

14. The active compound in Aspirin is acetylsalicylic acid (ASA), which inhibits the cyclooxygenase (COX) enzyme involved in synthesis of prostaglandins. The structure of ASA and COX's natural substrate, arachidonic acid, are given next to Figure 4. Based on this information, you would be right to say ASA is a ___ inhibitor of COX.

Competitive

Allosteric

Dephosphorylating

Co-structural

Dissociative

15. Which of the following corresponds to an enzyme catalyzed reaction with a competitive inhibitor

Figure 6

Figure 7

None of the rest

Figure 9

Figure 10

16. Which of the following increases the processivity of a DNA polymerase

Adenosine

Inosine

1,6 Dihydroinosine

Malonate

PCNA

17. According to Figure 12, one of the Mg2+ ions interacts with ____ to _____ its nucleophilicity as it attack(s) the incoming nucleotide

The 3'O atoms, enhance

The 2'O atoms, enhance

The 3'O atoms, reduce

The 2'O atoms, reduce

The phosphates, enhance

18. Which of the following best describes the kinetics of DIPF on serine protease catalyzed reaction

Figure 10 with alpha = alpha'

Figure 9

Figure 8 with alpha = 2

Figure 8

Figure 9 with alpha' = 2

19. If 20% of the DNA in a relaxed circular-covalently-closed plasmid is induced to change from B-DNA to Z-DNA and then treated by an enzyme that has type IA topoisomerase activity, what happens to the value of the linking number?

Decreases

Increases

Remains the same

Cannot be calculated without knowing the size of the plasmid

None of the answers

20. The isoelectric point of Tyr-Arg is

9.83

11.46

5.51

10.46

12.48

21. The isoelectric point of Arg is

5.40

7.15

10.73

12.48

1.82

22. A plasmid with 4000 bp of closed circular duplex DNA was isolated from E. coli. It has a 300-bp segment of alternating C and G residues. Upon transfer to a high salt solution, this segment undergoes a transition from the B conformation to the Z conformation. Given that B-DNA contains one right-handed turn per 10 base pairs, Z-DNA contains one left-handed turn per 12 base pairs and linking number (L) equals twist (T) plus writhing number (W). Which of the followings is correct if the process include a further treatment with a type IB topoisomerase that is active at high salt solution?

Its linking number is not changed

The change in its writhing number is 55

Its original linking number is 400

The change in its twist is -55

All answers are correct

23. Which of the following is true

Telomerase adds DNA sequence repeats to the 5’ end of the DNA strands in the telomere regions

Telomerase joins Okazaki fragments on the lagging strand

In the circular chromosomes of bacteria, DNA replication begins at multiple origins

In prokaryotes DNA ligase is activated by ATP

In eukaryotes DNA ligase is activated by ATP

24. Which of the following corresponds to an enzyme catalyzed reaction with a uncompetitive inhibitor

Figure 5

Figure 7

Figure 9

Figure 10

None of the rest

25. An individual is diagnosed with a deficiency of DNA repair enzymes that resolve deamination to hypoxanthine. What changes will be seen in this individual's DNA if these deaminations are left unrepaired?

A G:C base pair will become an A:T base pair

An A:T base pair will become a G:C base pair

A G:C base pair will become a U:T base pair

An A:T base pair will become a U:T base pair

There will be no change seen in the individual's DNA