E7 Translation and protein synthesis Flashcards
what is a gene?
- a section of DNA that directs the synthesis of one or more overlapping mature RNA molecules (including parts of DNA that are not transcribed themselves but are necessary for transcription)
- genes can overlap with each other
describe how tRNA, mRNA and rRNA are involved in translation
mRNA contains the code
- need a start and stop codon within the mRNA strand
tRNA is the decoder
- brings the correct amino acid to the correct codon using complementary base pairing
rRNA links the amino acids in the polypeptide
what does the ribosome do at the start of translation?
- scans for ATG start codon
- starts translation there
which direction does a ribosome translate mRNA in?
5’ to 3’
contrast ribosomes in eukaryotes and prokaryotes size-wise
eukaryotes = 80S
60S and 40S subunits
prokaryotes = 70S
50S and 30S subunits
what are the 3 main steps of protein synthesis?
- initiation
- elongation
- termination
describe initiation as a step of protein synthesis
- finding the start codon (ATG) and assembling the ribosome with the first tRNAs
describe elongation as a step of protein synthesis
- aminoacyl tRNA binding (codon recognition)
- peptidyl transfer (peptide bond formation, mediated by ribosome)
- translocation (moving to next codon)
describe aminoacyl tRNA binding in translation elongation
- codon is read
- correct tRNA binds
- tRNA-mRNA base pairing (between codon and anticodon) is recognised by the ribosome and shifts along by a conformational change
describe peptidyl transfer in translation elongation
- catalysed by the ribosomal RNA
- amino acid is added and polypeptide is elongated
- allows old tRNA molecule (without amino acid) to detach and have a new amino acid attached
describe translocation in translation elongation
- ribosome changes conformation
- mRNA and tRNAs have moved by one codon relative to the ribosome (ribosome is ready for next aminoacyl-tRNA and doesn’t interact with the old one)
describe the termination step of translation
- no tRNA molecule binds to a stop codon
- tRNA shaped protein called a release factor recognises stop codon
- peptidyl-tRNA bond is hydrolysed
- release factors and protein are released
what concept allows for the targeting of prokaryotic ribosomes by antibiotics?
- the differences between eukaryotic and prokaryotic ribosomes
- different RNAs, different subunits
how do antibiotics typically work?
- prevent translation by preventing elongation
- inhibits the main enzyme for replication and growth
state the 4 basic synthetic genetic processes
- replication
- transcription
- RNA processing
- translation