Biochem 1 Flashcards
What makes up a nucleosome?
Negatively charged DNA loops twice around positively charged histone octamer.
Histones have a lot of what?
Rich in lysine and arginine
Purpose of H1
Binds to nucleosome and to linker DNA to stabilize the chromatin fiber: it is the only one NOT in the nucleosome core.
DNA and histone synthesis during what phase of mitosis
S phase
Nucleosome core histones
H2A, H2B, H3, H4 (each x2)
Heterochromatin
Highly condensed, not active
Euchromatin
Transcriptionally active
DNA methylation in prokaryotes
Template strand Cs and As are methylated to allow mismatch repair enzymes to distinguish parent from daughter strand.
DNA methylation in eukaryotes
CpG islands to repress transcription
What are CpG islands exactly?
Cytosine next to Guanine in a strand of DNA. The cytosine can be methylated, in fact most of the cytosines in CpG islands are.
Histone methylation
Usually reversible, represses transcription, but can occasionally activate it.
Histone acetylation
Relaxes DNA coiling, increasing transcription
What are the pyrmidines
Pyrimidines CUT
Thymine vs Uracil
Thymine has a methyl, uracil is a deaminated cytosine
Amino acids necessary for purine synthesis
GAG-Glycine, Aspartate, Glutamine
What makes up pyrimidines?
Carbamoyl phosphate and aspartate
Nucleoside vs. nucleotide
nucleoside is base + sugar, -tide has 3’-5’ phosphodiester bond linked phosphate(s)
Basic steps of Purine synthesis
- Star with sugar + phosphate (PRPP) 2. Add base
What is PRPP?
Phosphoribosyl pyrophosphate (it has a phosphate instead of a base attached to the ribose)
Basic steps of Pyrimidine synthesis
- Make temporary base (orotic acid) 2. Add sugar + phosphate (PRPP) 3. Modify base
What turns ribonucleotides to deoxyribonucleotides
Ribonucleotide reductase
Carbamoyl phosphate used in what metabolic pathways
De novo pyrimidine synthesis and the urea cycle
Purine base production steps
- Start with Ribose 5-P
- Turn to PRPP by PRPP synthetase
- Produce IMP through some steps
- AMP and GMP produced (GMP by IMP dehydrogenase?)
What does de novo purine synthesis require?
Aspartate, glycine, glutamine, and THF