Biochem 1 (DNA Basics)

Question 1

What are the nuclesome components and how many times is the DNA wrapped?

Answer 1

• H2 A/B, H3, and H4

- The DNA is wrapped around the 8 protein core twice

Question 2

What is the charge of the histone proteins?

Answer 2

Positive due to lysine and arginine (DNA is negative due to phosphate groups)

Question 3

What is the function of H1 protein?

Answer 3

H1 joins consecutive nucleosomes to create chromatin

Question 4

How is Uracil made?

Answer 4

Deamination of Cytosine

Question 5

Which DNA sequences have the highest melting temperature?

Answer 5

G-C rich sequences (3 hydrogen bonds vs 2 in A-T)

Question 6

Where do the carbons for Purines come from?

Answer 6

Glycine, THF, and CO2

Question 7

Where do the nitrogens for purine synthesis come from?

Answer 7

Glutamine and Aspartate

Question 8

What are the four molecules necessary to make pyrimidines?

Answer 8

Glutamine - Nitrogen
CO2 - Carbon
ATP - Energy
-These combine to make carbamoyl phosphate

Question 9

What is the rate limiting step in pyrimidine synthesis?

Answer 9

CPS-II (in cytosol)

Question 10

What is the difference in order between pyrimidine and purine synthesis?

Answer 10

Pyr = 1) Base (orotic acid) 2) Phosphate/sugar (PRPP)
Purine = 1) Sugar (Ribose-5-P) 2) Base (IMP)

Question 11

In Orotic Aciduria (impaired de-novo pyrimidine synthesis) what are the clinical features? What enzyme(s) is detective? How is it treated?

Answer 11

1) Megaloblastic anemia that is not corrected by B12 or Folate, growth retardation, neurological abnormalities
2) OMP decarboxylase/Orate phosphoribosyl transferase (2 parts/same protein)
3) Give uridine to bypass and inhibit CPS-2