Chapter 6: 6.6 Translation into Proteins Flashcards
Translation of mRNA is done by…
Ribosomes (a cellular organelle)
Describe the structure of:
Ribosomes
Composed of:
* A small subunit
* A large subunit
Both made from rRNA and proteins
What sites do ribosomes contain?
- A (aminoacyl) site
- P (peptidyl) site
- E (exit) site
What do the different sites of a ribosome do?
- A site: The acceptor site for an aminoacyl-tRNA
- P site: The site where the peptide bond forms between the amino acid and the growing polypeptide chain
- E site: The site where the tRNAs exit the ribosome
What steps does translation occur through?
- Initiation
- Elongation
- Termination
State the 3 steps of:
Initiation in Translation
- When the mRNA enters the cytosol, the 5’ end of the mRNA binds to the small subunit of the ribosome
- A tRNA carrying the amino acid methionine arrives at the P site of the ribosome and binds to the start codon
- Next, the large subunit binds and completes the intiation complex
In what order does the mRNA bind to the small and large subunit of a ribosome?
First small subunit, then large subunit
What is the base pair sequence for the start codon?
AUG
State:
Elongation in Translation
- A tRNA for the next codon attaches the A site
- The ribosome performs translocation
- The A site is now available for another tRNA
In the Elongation phase of Translation:
Describe how the tRNA for the next codon attaches to the A site
The carboxyl end (C-terminus) of the methionine forms a peptide bond with the amine end (N-terminus) of the amino acid at the A site (catalyzed by peptidyl transferase)
In the Elongation phase of Translation:
In the A site:
1. What kind of bond is formed?
2. Where is the bond formed?
3. What is it catalyzed by?
- Peptide bond
- Between C-terminus and N-terminus of methionine
- Peptidyl transferase
In the Elongation phase of Translation:
What is translocation? Describe the process
The process by which ribosomes shifts three nucleotides toward the 3’ end of the mRNA
* Shifts the tRNA that held the methionine to the E site
* The tRNA carrying the dipeptide moves from the A site to the P site
In the Elongation phase of Translation:
From the start codon, in the translocation process:
1. Where does the start codon/methionine go?
2. How do the other dipeptides move?
- tRNA that held the methionine shifts to the E site
- tRNA carrying the dipeptide moves from the A site to the P site
How does termination work in translation?
When a stop codon is reached:
* Release factor proteins bind to the A site
* Causes releasing of polypeptide from the tRNA and ribosome
State the differences between:
Eukaryotic and Prokaryotic Translation:
* Ribosomes
Eukaryote
* 80S ribosome
* Made up of a 60S subunit bound to a 40S subunit
Prokaryote
* 70S ribosome
* Made up of a 50S subunit bound to a 30S subunit
