Lecture7- Translation Flashcards
What is translation
Its protein synthesis, in which the nucleotide code ( codon)of mRNA is translated into the amino acid sequence of proteins in the cytoplasm
What are the components of translation
1- ribosome - present in the cytoplasm as separate large or small unit
2- tRNA- the different ammoniacyl activated firms, carrying the amino acid eg tRNA ^met
3- mRNA- carries information in 3 base codons; recall that eukaryotic mRNA also has VARIOUS PROTEINS INVOLVED ( only in eukaryotes )eg: initiation factors , elongation factors, termination factors
Start codon for translation
AUG
Stop codon for translation
UAG
UAA
UGA
What is the function of 5’ cap in translation. How dies it help in the initiation of translation
Facilitate binding with the ribosomes
Translation is divided in 3 states
1- initiation
2- elongation
3- termination
Overview of initiation
Ribosomes bind with the DNA
- attachment of the small subunit
- bring in the first amino acid
- complete initiation complex
Overview of elongation
Extending if amino acid chain
- selection
- peptide bond formation
- translocation
- release of de acetyl tRNA
Overview of termination
Stopping of translation at stop codon
- encounter stop codon
- release factors bind
- dissociate of the complex
1 initiation of translation
-There are specific codon in mRNA that helps in starting translation and stopping it
-Initiation is the assembly of ribosomes at the beginning of the coding region of the mRNA
-Its important that the first codon is properly aligned to establish the right “reading frame” of triplet codon
Step 1- Eukaryotic initiation factors ( elf4 ) bond to the initiator tRNA met, which then binds with the small unit
Step 2- the pre initiation complex binds to the 5’ cap
Step 3- the small unit scans and position the first AUG in P site
Kozak sequence helps find the start codon
Step 4- after the initiator base pairs with the start codon, the large subunit , facilitated. By GTP hydrolysis
- poly A binding protein( PABP) binds the polyA stretch and can also bind elf4g
- elf4g is involved in translational initiation
- this is called complete initiation complex
2- Elongation
- EF delivers charged tRNA to the A site(trial and error)
- If the anticodon matches, then the Peptide bond forms between the amino acids at P site
- The mRNA advanced 3 nucleotides, the ribosome SS moves 3 nucleotide in 5’ to 3’
- Continuous until stop codon encountered
3- Termination in translation
- when the stop codon is encountered at A site, there is no tRNA for this
- instead of tRNA binding, release factor binds to the A site
- dissociation occurs 1- through release of the completed polypeptide, 2- ribosomes dissociate into two separate subunits
How does eukaryotes increase efficiency of translation
Because mRNA of eukaryotes is longer and requires more protein made therefore there is a cluster of many ribosomes -POLYRIBOSOME on the mRNA carrying out translation causing the mRNA to curl into a spiral and increasing the rate of translation
