L7: Translation

sequence of bases in mRNA that specifies the order in which amino acids are added to polypeptide chain

translation

factors required for translation

mRNA, initiation factors, elongation factors, release factors, aminoacyl tRNA synthetases, tRNA, ribosome (rRNA + ribosomal proteins)

structure of a ribosome

complex RNA + protein that bind mRNA to control translation; catalyze translation; consists of small & large subunit

binding sites for tRNA

A (aminoacyl), P (peptidyl), E (exit)

form complex with ribosomal proteins

rRNA

group of 3 adjacent nucleotides in mRNA that code of an amino acid

codon

site where ribosome begins reading nucleotide sequence

reading frame

compare eukaryotic and prokaryotic ribosomes

eukaryotic ribosomes are larger than prokaryotic ribosomes

carries translation of mRNA

tRNA

structure of tRNA

three clover with 1 anticodon loop; -CCA @ 3’end (AA attachment site)

enzyme that connects specific amino acids to specific tRNA; charges tRNAs

aminoacyl tRNA sythetase

charged tRNA

amino acid attached

uncharged tRNA

no amino acid attached

base pairing properties btwn codons and anti-codons

first base in codon of mRNA (5’) pairs with last base of anticodon of tRNA (3’); antiparallel

what is the codon that initiates translation

AUG

what is the amino acid that initiates transcription

methionine

how do codons determine their amino acid

by their genetic code

specified by more than 1 codon

degenerate

what tool is used to identify match correct amino acid with their codon

codon chart

where does the initiation complex form in eukaryotes

5’ cap

where does the initiation complex form in prokaryotes

shine dalgarno sequence

process of translation initiation and the role of initiation factors

• initiation factors bind to 5’ cap or shine dalgarno sequence

• sm ribosomal subunit is recruited

• brings tRNA charged with methionine

• initiation complex moves along mRNA until it reaches AUG (start codon)

• The anticodon (UAC) of an initiator tRNA (carrying methionine) binds to the start codon (AUG) on the mRNA by hydrogen bonds

• tRNA anticodon pairs with mRNA codon and recruits lg subunit

• initiation factors are released

• the initiator tRNA is now in the P site of the lg subunit

proteins involved in termination

release factors

which subunit are the 3 binding sites found in

large subunit

what units are the ribosomal subunits measured in

svedberg units (s)

are eukaryotic ribosomes more or less mobile than prokaryotic and why

less mobile because their ribosomal subunits are larger which makes them less mobile

which RNA molecule translates the codon message into amino acids

tRNA

binds complementary codons in mRNA

aniticodon

consists of 3 nucleotides in tRNA

anticodon loop

amino acid attachment site

CCA at 3’ end with 3’ -OH group of the A

what will the codon sequence be for a tRNA with anti-codon 5’ UCG 3’

5’ CGA 3’

how many amino acids are there

20

how many codons

64

stop codons

UAA, UAG, UGA

main stages in translation

initiation, elongation, termination

goal of initiation

get ribosome on start codon (AUG)

elongation

tRNA comes in and amino acids are added to the growing chain

termination

ribosome will reach stop codon and polypeptide chain leaves; ribosome will dissociate

t/f initiation is the same in prokaryotes and eukaryotes

false, eukaryote initiation factors bind to 5’ cap whereas prokaryote initiation factors bind to shine-dalgarno sequence

what is the anticodon for methionine

3’ UAC 5’

which subunit site is first charged tRNA in

P site

which sites do incoming tRNAs bind to

A site

what happens when new tRNA in A site enters

bond connecting MET to its tRNA is transferred to amino group of amino acid in A site & covalent peptide bond is formed; tRNA in P site is now uncharged

which site do tRNAs exit

E site

are tRNAs in E site charged or uncharged

uncharged

what is the catalyst for the formation of the peptide bond

rRNA in the large subunit

what happens when the ribosome shifts one codon to the right

• uncharged tRNA is moved to E site

• peptide-bearing tRNA is moved to P site

• A site is free for next charged tRNA

what happens during elongation

• tRNA in E site is ejected

• tRNA in P site is moved to E site

• tRNA in A site is moved to P site

  • A site is open for next tRNA

what proteins cause the polypeptide chain to release during termination

release factor proteins

where do release factors bind

A site

what does the breaking of the polypeptide bond result in

carboxyl terminus on polypeptide