tRNA rRNA translation Flashcards
difference between RNA and DNA
ribose vs deoxyribose sugar
found in nucleus and cytoplasm vs only in the nucleus
uracil (1 less methyl group) vs thymine –> able to bond with other base pairs due to lack of methyl group
functional reason for having both DNA and RNA
DNA more stable less reactive, needed for whole lifetime without degrading
RNA can’t coil as tightly as DNA, more accessible for translation
primary and secondary structures
primary: sequence of ribonucleotides from 5’ to 3’
secondary: intrastrand base pairing via H bonds
folded RNA has enzymatic or structural roles
types of RNA
coding: mRNA
non-coding: rRNA, tRNA, lncRNA
lncRNA function
coats DNA and turns of transcription of 1 X chromosome in females
rRNA structure in ribosome and synthesis
synthesised in the nucleolus from 2 separate genes
have specific secondary structure, hence hanve catalytic activity
ribosome is 50% rRNA and 50% protein –> assembed in the nucleolus and continues to be processed in the cytoplasm before subunits combine
codon definitions, start stop codon
group of 3 nucleotides from 5’ to 3’
start: AUG
stop: UAA, UAG, UGA
degenerate and overlapping DNA codes
almost every amino acid (not Met and Trp) are encoded by more than 1 codon
given codon only codes for 1 AA
open reading frames
bounded by a start and stop codon
tRNA structure and function
cloverleaf secondary structure
binds with AA at the AA matching codon (read from 5’ to 3’)
binds with mRNA at anticodon loop (antiparallel to mRNA codon)
transfer amino acids to ribosome and bind mRNA
how are tRNA and AA attached
bound together by aminoacyl-tRNA synthetase (specific to each AA), forming acylated-tRNA
ATP converted into AMP, provides energy to attach carboxyl C of AA to 3’ -OH of tRNA
attaching base is always adenine on tRNA
3 tRNA binding sites on ribosome
aminoacyl - ensures correct tRNA
peptidyl - peptide bond formation
exit - deacylated tRNA released
isoaccepting tRNA and codon-anticodon wobble
tRNAs that bind the same AA but have different anticodons
wobble position is on the third nt of the codon (3rd base degeneracy)
A and C are fussy
G and U pair with 2
initiation - before finding start codon
- (eIFs unwind secondary structure of mRNA, ready for translation, use GTP for energy)
- Met-tRNA binds P site in small subunit
- eIF4G recognises mRNA 5’ cap
- complex moves along mRNA until start codon found and bound by anticodon
- eIFs dissociate
- large ribosomal subunit binds
elongation
- aminoacyl-tRNA binds to A site
- peptide bond forms
large subunit moves, leaving the 2 tRNAs in hybrid sites - small subunit moves
- deacylated-tRNA ejected from E site
termination
- stop codon reached by A site
- release factor protein binds to A site
- hydrolysis of P site amino acid, translated protein released
- ribosome dissociates
polyribosomes
multiple ribosomes translating the same mRNA, hence producing lots of the same protein
