Molecular Biochem

Question 1

heterochromatin vs. euchromatin

Answer 1

heterochromatin: condensed, trascriptionally inactive, sterically inaccessible DNA. euchromatin: transcriptionally active, less condensed DNA

Question 2

Where does DNA methylation take place? What are two main functions of DNA methylation?

Answer 2

DNA may be methylated on cytosine and adenosine. 2 functions of methylation: when CpG islands are methylated, there is repression of DNA transcription. Methylation also allows mismatch repair enzymes in prokaryotes to distinguish btw old and new strands.

Question 3

Histone methylation vs. acetylation

Answer 3

methylation usually represses DNA transcription, though it is occasionally activating. Histone acetylation is activating (it relaxes DNA coiling and allows for transcription).

Question 4

What factors influence melting temperature of DNA?

Answer 4

the types of bonds. C-G bonds increase the melting time of DNA because they have 3 H bonds between them

Question 5

General schema for purine vs. pyrmaidine synthesis

Answer 5

purine: start with sugar and phosphate (PRPP). Add base
pyramidine: make a temporary base (orotic acid), then add sugar and phosphate (PRRP), then modify the base

Question 6

significance of carbamoyl phosphate

Answer 6

involved in both the urea cycle and de novo pyrimidine synthesis. may be produced from NH3and CO2 by carbamoyl phosphate synthetase I or from glutamine and CO2 by carbamoyl phosphate synthetase II. Both reactions require 2 ATP.

Question 7

Adenosine deaminase deficiency

Answer 7

adenosine deaminase helps convert adensoine to a form that can eventually be excreted as uric acid. in adenosine deaminase deficiency, there is an excess of ATP and dATP. This imbalances the nucleotide pool via feedback inhibition of ribonucleotide reductase (helps make deoxyribonucleic acids). this prevents DNA synthesis and reduces lymphocyte counts. one of the major causes of SCID.

Question 8

Lesch-Nyhan syndrome: pathophysiology

Answer 8

defective purine salvage d/t a defiency of HGPRT. HGPRT converts hypoxanthine to IMP and guanine to GMP. results in excess uric acid production and de novo purine synthesis. X-linked recessive

Question 9

Lesch-Nyhan syndrome

Answer 9

HGPRT: hyperuricemia, gout, pissed off (aggression, self-mutilation), retardation/intellectual diability, dysTonia