Molecular Biochemistry Flashcards
Sickle Cell disease mutations in DNA
Missense - Nucleotide substitution resulting in changed amino acid
Silent Mutations in DNA
Nucleotide substtions but codes for the same amino acid; often base changed in 3rd position of codon
Nonsense Mutations in DNA
nucleotide substition in early stop codon. Stop the nonsense!
Duchenne muscular atrophy DNA mutation type
Frameshift - deletion or insertion of a number of nucleotides not divisible by 3, resulting in mistreading of all nucleotides downstream, usually resulting in a truncated, nonfunctional protein
Order of severity of DNA mutations
Silent «_space;missense < nonsense < frameshift
Why is nucleotide exicision repair defective in xeroderma pigmentosum?
Prevents repair of pyrimidine dinners because of ultraviolet light exposure
Nucleotide excision repair
specific endonucleases releasethe oligonucleotide-containing damage bases; DNA polymerase and ligase fill and reseak the gap, respecitively. Repairs bulky helix-distorting lesions
Base excision repair
Base-specfic glycosylase recognizes altered base and creates AP sites (apurinic/apyrimidinic). One or more nucleotides are removed by AP-endonuclease, which cleaves the 5’ end. Lyase cleaves the 3’ end. DNA polymerase-betafills the gap and DNA ligase seals it
Nonhomologous end joining - double strand
Brings tighter 2 ends of DNA fragments to repair double-stranded breaks
Chain Terminator
3’ OH
DNA/RNA synthesis direction
5’ to 3’
Triphosphate bone end
5’
mRNA start codons
AUG (rarely GUG)
Eukaryotes code for…
methionine
Prokaryotes code for…
formylmethionine (f-met)
mRNA stop codons
UGA, UAA, UAG
UGA = U Go Away
UAA = U Are Away
UAG = U Are Gone
Promotor
Site where RNA polymerase and multiple other transcription factors bind to DNA upstream from gene locus. Promoter mutation commonly results in dramatic decrease in level of gene transcription
Enhancer
Stretch of DNA that alters gene expression by binding transcription factors
Silencer
Site where negative regulators (repressors) bind
Eukaryotes - RNA polymerase I, II, III make…
I - rRNA (most numerase, Rampant)
II - mRNA (largest RNA, Massive)
III - tRNA (smallest RNA, Tiny)
Steps to make hnRNA to mRNA
Capping fo 5’ end (addition of 7-methylguanosine cap)
Polyadenylation of 3’ end (~200 A’s)
Splicing out of introns
Capped, tailed, and spliced transcript is called mRNA
What is AAUAAA?
Polyadenylation signal for RNA processing (eukaryotes)
Splicing of pre-mRNA
- Primary transcript combines with small nuclear ribonucleoproteins (snRNPs) and other proteins to form spliceosome
- Lariat shaped (looped) intermediate is generated
- Lariat is released to precisely remove intron and join to exons
What antibodies are highly specific for SLE?
Antibodies to spliceosomal snRNPs (anti-Smith antibodies)
What antibodies are highly associated with mixed connective tissue disease?
Anti-U1 RNP antibodies
Exons
Contain actual genetic information coding for protein
INtrons are Intervening sequences and stay IN the nucleus, whereas EXons Exit and are EXpressed
Introns
Intervening noncoding segments of DNA
INtrons are Intervening sequences and stay IN the nucleus, whereas EXons Exit and are EXpressed
Chaperone protein
intracellular protein involved in facilitating and/or maintaining protein folding
Protein synthesis Eukaryotic initiation
40S + 60S = 80S (Even)
Protein synthesis Prokaryotic initiation
30S + 50S = 70S (Odd)
Protein synthesis Elongation
A Site - activation (tRNA enters with AA)
P site - accommodates growing peptide
E site - holds Empty tRNA as it exits
Protein synthesis termination
Stop codon is recognized by release factor, and completed polypeptide is released from ribosome
