First Aid: Molecular Biochem Flashcards
Telomere code
TTAAGGG
start codons + what they code for
usually AUG
rarely GUG
codes for Met in euk
for N-formyl Met in prok
Nucleotide excision repair
enzymes
when it happens
disease(s)
- endonucleases release the damaged bases; DNA polymerase and ligase repair
- happens in G1
- xeroderma pigmentosum
RNA polymerase types + inhibitors (4)
- RNAP 1 - makes rRNA; in nucleolus
- RNAP 2 - makes mRNA; alpha-amantin inhibits
- RNAP 3 - makes tRNA + 5s rRNA
- Prokaryotic RNAP - makes all kinds of RNA
rifampin inhibits DNA-dep RNAP in prokaryotes; actinomycin D inhibits RNAP in prok/euk
what 3 processes are done to hnRNA (heterogenous nuclear) in the nucleus before it becomes mRNA?
- 7-methylguanosine capping - 5’ end
- polyadenylation - 3’ end; ~200 As
- intron splicing
Base Excision Repair enzymes
what kind of damage do they repair + when?
what are they?
Repair spontaneous / toxic deamination throughout whole cell cycle
- Glycosylase - removes altered base -> apurinic/-pyrimidinic site made
- AP-Endonuclease - cleave 5’ to remove 1+ NTs
- Lyase - cleaves 3’
- DNA-Polymerase-beta - fills gap
- Ligase - seals
- (mnemonic = GEL PLease)
Mismatch Repair Enzymes
how they work + when?
defective in what disease?
- in S phase > recognize new strand, remove mismatched NTs, fill + seal gap
- defective in Lynch Syndrome (Hereditary Nonpolyposis Colorectal Cancer, HNPCC)
Double stranded DNA repair types (2)
how they work + diseases in which they are defective
-
NHEJ - brings together 2 ends of DNA fragments; no homology req; may lose DNA
- def. in ataxia telangectasia + Fanconi anemia
-
Homologous Recomb. - 2 homolog DNA duplexes > damaged dsDNA strand repaired using complementary strand from homolog; no loss of NTs
- defective in BRCA1 mut. (breast/ovary cc.)
Missense mutation
what is it + ex of disease
- mutation that changes an AA
- “conservative” if new AA is similar structure
- sickle cell anemia is Glu > Val missense
Diff btwn promoters + enhancers + silencers
- Promoter - RNA pol II and TFs bind upstream from gene (AT-rich, TATA or CAAT box)
- Enhancer/Silencer - activator/repressor proteins bind sites close to/far from/within intron of gene
RNA processing
3 processes (where?)
initial hnRNA (heterogenous nuclear) is modified in nucleus to become mRNA
- 5’ cap - with methyl-guanosine
- polyadenylation - 3’ tail of ~200 As
- intron splicing
mRNA quality control
where + how?
at cytoplasmic processing bodies (P-bodies)
- exonucleases, decapping enzymes and miRNAs
- mRNA may then be degraded or stored in p-body for later translation
explain process of pre-mRNA splicing
3 steps
- Spliceosome formation - primary transcript combines with snRPs and other proteins
- 5’ cleavage - 5’ end of intron cleaved; forms looped intermediate
- 3’ cleavage - releases intron loop + exon ends join
examples of diseases of abnormal alternative splicing
(4)
- beta thalassemia
- Gaucher disease
- Tay-Sachs disease
- Marfan syndrome
as well as some cancers
miRNAs
what are they, what do they do, how do they affect disease
- small, conserved, noncoding RNA
- posttranscriptionally reg gene expression by targeting 3’ UTR on some mRNAs for degradation and translation repression
- abnormal expr. of miRNAs targeting tumor suppressor gene products > cancer
