Flashcards in Molecular Biochem Deck (9):
heterochromatin vs. euchromatin
heterochromatin: condensed, trascriptionally inactive, sterically inaccessible DNA. euchromatin: transcriptionally active, less condensed DNA
Where does DNA methylation take place? What are two main functions of DNA methylation?
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.
Histone methylation vs. acetylation
methylation usually represses DNA transcription, though it is occasionally activating. Histone acetylation is activating (it relaxes DNA coiling and allows for transcription).
What factors influence melting temperature of DNA?
the types of bonds. C-G bonds increase the melting time of DNA because they have 3 H bonds between them
General schema for purine vs. pyrmaidine synthesis
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
significance of carbamoyl phosphate
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.
Adenosine deaminase deficiency
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.
Lesch-Nyhan syndrome: pathophysiology
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