Translation Flashcards
ribosomes read the genetic message in mRNA and produce a polypeptide chain
translation
immediate product of translation
polypeptide chain
translation machinery
- mRNA
- tRNA
- ribosomes
- protein factors
translation in prokaryotes
- initiation, elongation, termination
- control
- antibiotics
translation in eukaryotes
- initiation, elongation, termination
- control
- protein targeting
- post-translational modifications
- template for translation
- open reading frame
mRNA
start codon
AUG
open reading frame
start codon -> stop codon
correspondence between the mRNA/codon and amino acid
genetic code
genetic code is the correspondence between what?
- mRNA/codon
- amino acid
Properties of the genetic code
- almost universal
- degenerate
- contiguous
- unambiguous
the same for all organisms with few exceptions
universal
there is more than one codon for some amino acids
degenerate
codons do not overlap and have no spacers in between
contiguous
each codon specify only one amino acid
unambiguous
non-standard base pair can form between third base of codon and first base of anticodon
wobble hypothesis
wobble hypothesis
non-standard base pair between 3rd base codon and 1st base anticodon
what is reduced in wobble hypothesis
no. of tRNAs needed to read
wobble hypothesis:
in mRNA, __ in the wobble position can pair with __ in the tRNA anticodon
G - wobble
U/C - tRNA anticodon
wobble hypothesis:
in tRNA, __ in the wobble position can pair with __ in the tRNA anticodon
inosine - wobble
U/C/A - mRNA codon
contain multiple open reading frame
polycistronic
- AGGAGGU
- found upstream from the start codon
- prokaryotes
Shine-Dalgarno sequence
Shine-Dalgarno sequence
AGGAGGU
contain single ORF
monocistronic mRNA
protect and stabilize eukaryotic mRNA
- 5’ cap
- polyA tail
- transfers amino acid to the ribosome
- adaptor molecule
- its anticodon decodes the codon in the mRNA
tRNA
length of tRNA
~ 75-95 nucleotides long
characteristic secondary structure of the tRNA
clover-leaf structure
parts of tRNA
- acceptor arm
- D or DHU arm
- anticodon arm
- variable arm
- TYCG arm
the 5’-CCA-3’ terminal that binds the amino acid the anticodon specify
acceptor stem/arm
have 3-4 bp stem and a loop that contain dihydrouridine
D or DHU arm
what does the D or DHU arm contain
dihydrouridine
5bp stem with a loop that contain the anticodon that is complementary to teh codon it recognizes
anticodon arm
length of anticodon arm
5 bp
have 3-20 bases that may form a step of up to 7 bp
variable arm
no. of base in variable arm
3-20 bases
5 bp stem ending in a loop containing the invariant residues of TYCG
TYCG arm
bp of TYCG arm
5 bp
tertiary structure of the tRNA that is formed by 9 h-bonds mainly between the invariant bases
L-shape structure
forms tertiary structure of tRNA
9 H-bonds mainly between invariant bases
amino acid + tRNA + ATP –> aminoacyl-tRNA + AMP + PPi
tRNA activation/aminoacylation
enzyme in tRNA activation
aminoacyl-tRNA synthetase
rRNA + ribosomal proteins = ?
ribosomes
composition of ribosomes
- large subunit
- small subunit
- contains the peptidyl transferase center
- factor-binding center
large subunit
catalyzes peptide bond formation in P site
peptidyl transferase center
- contains the decoding center
- 2 narrow channels where the mRNA enters and exits
small subunit
Three tRNA binding site in a ribosome
- A site
- P site
- E site
binding site for the amino-acyl tRNA
A site
A site is the binding site for what
aminoacyl-tRNA
binding site for peptidyl tRNA
P site
P site is the binding site for what
peptidyl tRNA
binding site for the uncharged tRNA
E site
E site is the binding site of what
uncharged tRNA
meaning of S in ribosome
- sedimentation coefficient
- measure of rate of sedimentation in ultracentrifuge
S is measured in __
Svedberg units
prokaryotic ribosomes
70 S
large subunit of prokaryotic ribosomes
50S
50 S of large subunit of prokaryotic ribosomes
31 proteins + 23S RNA + 5S RNA
small subunit of prokaryotic ribosomes
30S
30S of small subunit of prokaryotic ribosomes
21 proteins + 16S RNA
eukaryotic ribosomes
80S
large subunit of eukaryotic ribosomes
60S
60S of large subunit of eukaryotic ribosomes
50 proteins + 28S RNA + 5.8S RNA + 5S
small subunit of eukaryotic ribosomes
40S
40S of small subunit of eukaryotic ribosomes
33 proteins + 18S RNA
consist of a cluster of ribosomes that are held simultaneously by a strand of messenger RNA (mRNA) in rosette or helical group
polyribosome