Biochem2

Question 1

Autosomal recessive disease that is major cause of SCID?

Answer 1

Adenosine deaminase deficiency

(Severe Combined Immunodeficiency Disease) - SCID happens to KIDS

Question 2

Adenosine deaminase deficiency: Pathology

Answer 2

Excess ATP and dATP

Imbalances nucleotide pool via feedback inhibition of Ribonucleotide Reductase –>

Prevents DNA synthesis & DEcreased Lymphocyte count

**1st dz treated by human gene therapy

Question 3

What enzyme is absent in Lesch-Nyhan syndrome?

Answer 3

HGPRT

He’s Got Purine Recovery Trouble

Question 4

Lesch-Nyhan syndrome: Pathology

Answer 4

X-linked

Defective purine salvage d/t absence of HGPRT (converts hypoxanthine to IMP and guanine to GMP)

INcreased Uric acid production & de novo Purine synthesis

Question 5

Lesch-Nyhan syndrome: Findings

Answer 5

Retardation
Self-mutilation
Aggression
Hyperuricemia
Gout
Choreoathetosis

Question 6

What is the order of severity in Point Mutations in DNA?

Answer 6

Least to Most severe:

• Silent
• Missense
• Nonsense
• Frameshift

Question 7

What is a silent mutation?

Answer 7

Same amino acid, often base change in 3rd postion of codon (tRNA wobble)

Question 8

What is a missense mutation?

Answer 8

Changed amino acid (conservative – new amino acid is similar in chemical structure)

Question 9

What is a nonsense mutation?

Answer 9

Change resulting in early STOP codon

“Stop the Nonsense”

Question 10

What is a frameshift mutation?

Answer 10

Change resulting in misreading of ALL nucleotides downstream

Results in truncated, non-functional protein

Question 11

Helicase

Answer 11

Unwinds DNA template at Replication fork

Question 12

What prevents strands from reannealing?

Answer 12

Single-stranded binding proteins

Question 13

DNA topoisomerases

Answer 13

Create nick in helix to relieve supercoils created during replaction

Question 14

What inhibits DNA gyrase (prokaryotic topoisomerase II)

Answer 14

Fluoroquinolones

Question 15

What makes an RNA primer on which DNA polymerase III can initiate replication?

Answer 15

Primase

Question 16

DNA polymerase III

Answer 16

Elongates LEADING strand by adding deoxynucleotides to the 3’ end.

Elongates LAGGING strand until it reaches primer of preceding fragment

3’ –> 5’ EXONUCLEASE activity “proofreads” each added nucleotide

Question 17

What are the directions of DNA polymerase III synthesis and proofreading?

Answer 17

Synthesis - 5’ –> 3’

Proofreads - 3’ –> 5’ (w/ exonuclease)

Question 18

What degrades the RNA primer and replaces it with DNA?

Answer 18

DNA polymerase I

Same function as DNA Pol III but also EXCISES RNA primer with 5’ –> 3’ exonuclease

Question 19

DNA ligase

Answer 19

Catalyzes formation of phosphodiesterase bond within a strand of double-stranded DNA

i.e., Joins Okazaki Fragments (seals)

Question 20

What enzyme adds DNA to 3’ end of chromosomes to avoid loss of genetic material with every duplication?

Answer 20

Telomerase

Question 21

What are the 2 Purine Salvage Deficiencies?

Answer 21

Adenosine deaminase deficiency

Lesch-Nyhan syndrome

Question 22

What AAs are only encoded by 1 codon?

Answer 22

Methionine (AUG)

Tryptophan (UGG)