Lecture 11 notes Flashcards
how are codons read?
amino acids have to be ‘activated’ before incorporation in a protein
the activated form of the amino acid is attached to small RNA (tRNA)
transfer RNA
(tRNA) small RNA
- adaptors between codons and amino acids
- two ‘readings’: addition of correct amino acid to tRNA and antiparallel base pairing between codon in mRNA and anticodon in tRNa
- each tRNA can recognize multiple codons
- made from genes
- a mutation in a tRNA gene can alter the anticodon
aminoacyl-tRNA synthetastes
- attach amino acids to tRNAs
- reaction: aa + ATP + tRNA -> aminoacylated tRNA
- each amino acid has its own tRNA synthetase
wobble phenomenon
- base pairing rules are relaxes at 5’ position of anticodon
- contributions of relaxed rules: RNA structure and modified nucleotides in tRNA
- 5’ base of anticodon is modified
- I can pair with U, C or A
is it possible to have mutant tRNAs that suppress missense mutations?
yes but these are very unhealthy since many proteins will have incorrect amino acids from ‘misreading’ of the code
silent mutation
change in base pair that codes for the same amino acid
missense mutation
change in base pair codes for a different amino acid
nonsense mutation
change in base pair codes for stop codon
frameshift mutation
insertion/deletion of base pair causes next amino acids to change
genetic approach to understanding gene function
- mutate gene
- observe mutant phenptype
- infer wildtype function
loss of function alleles
- usually recessive to wild type
amorph: null allele
hypomorph: weak allele
gain of function alleles
*usually dominant to wild type
hyper morph: overactive
anti morph: dominant negative
neomorph: new function
amorph
no gene product, or no functional gene product
hypomorph
less of wild type gene product, or mutant gene product with less activity than normal gene product
a nonsense mutant would most likely be a:
a. hypomorph
b. amorph
amorph
