Molecular Flashcards
(44 cards)
Chromatin structure
Nucleosomes have H2A, H2B, H3, H4 – H1 histone is outside of nucleosome and binds to linker DNA to package it into a more compact form — DNA and histone synthesis occur during S phase
Heterochromatin
Highly Condensed and heavily methylated (inactive) – example is Barr bodies
Euchromatin
Less condense, active
DNA methylation
Cytosine and adenine are methylated to distinguish between old and new strands — represses transcription at CpG islands
Histone methylation
(Methylation = mute) Reversibly represses DNA transcription
Histone acetlyation
(Acetylation = active) – relaxes DNA coiling to allow transcription
Nucleotides
PURe As Gold (Purines, A, G, 2 rings) — CUT the PY (Pyrimidines, CUT, 1 ring) — Thymine has a meTHYl — Uracil in RNA, thymine in DNA — GC bond is stronger than AT bond so more GC means higher melting temperature
Purine synthesis
Requires GAG (Glycine, Aspartate, Glutamine) — start with sugar + PRPP and add a base
Pyrmidine synthesis
Requires Aspartate — Make temporary base (orotic acid), add sugar and phosphate, modify base — involves carbamoyl phosphate synthetase II (rate limiting) — thymidylate synthase requires folate so deficiency leads to decreased dTMP (thymidine supplementation can moderately increase it)
Adenosine deaminase deficiency
Excess ATP and dATP prevents DNA synthesis and decreases lymphocyte count – autosomal recessive cause of SCID
Lesch Nyhan syndrome
Defective purine salvage due to abscent HGPRT (converts hypoxanthine to IMP and guanine to GMP) — HGPRT (Hyperuricemia, Gout, Pissed off (self mutilation), Retardation, dysTonia) — X linked recessive – Tx: allopurinol
DNA helicase
Unwinds DNA template at replication fork
DNA topoisomerases
Create a single or double strand break in helix to add or remove supercoils (Fluoroquinolones inhibit topoisomerase II)
Primase
Makes an RNA primer on which DNA polymerase III can initiate replication
DNA polymerase III
Prokaryotic only – elongates leading strand by adding to 3’ end, elongates lagging strand until it reaches primer of preceding fragment – 3’ -> 5’ exonuclease activity proofreads
DNA polymerase I
Prokaryotic only - degrades RNA primer and replaces it with DNA – 5’ to 3’ synthesis, proofreads with 3’ to 5’ exonuclease, and excises RNA primer with 5’ to 3’ exonuclease
DNA ligase
Forms phosphodiester bond to join strands
Telomerase
RNA dependent DNA polymerase (has reverse transcriptase activity) that adds DNA (TTAGGG) to 3’ ends of chromosomes (eukaryotes only) - found on stem cells and cancer cells
Silent mutation
Nucleotide substition but codes for same amino acid (tRNA wobble)
Missense mutation
Changed amino acid (Sickle cell disease)
Nonsense mutation
Early stop codon
Frameshift mutation
Deletion or insertion of nucleotides not divisible by 3 (Duchenne muscular dystrophy)
Lac operon
Low glucose: increases adenylyl cyclase (glucose normally inhibits), increase cAMP, activate CAP protein and induce transcription — High lactose: unbinds represor protein from repressor/operator site and induces transcription
Nucleotide excision repair
Endonucleases releasing damaged bases, DNA polymerase and ligase fill and reseal gap (G1 phase) — defective in xeroderma pigmentosum (UV damage prevents repair of pyrimidine dimers)
