Benzten 9 - Translation Flashcards
What is translation?
The process of converting genetic information stored in nucleic acid sequences into protein. Sequences of mRNA are translated into unique sequence of amino acids in polypeptide chain (linear order is preserved throughout)
What direction is the mRNA read in the ribosome during translation?
In the 5’ to 3’ direction
Which terminus of the growing polypeptide chain are amino acids attached to? Which end of the polypeptide chain is ejected into the cytosol?
The carboxyl terminus. Which stays in the ribosome until the polypeptide is complete. The amino end is ejected into the cytosol.
What are 6 requirements for translation in prokaryotes?
- mRNA template
- tRNA
- Amino acids (bound to tRNAs)
- Ribosomes
- Many accessory proteins
- Energy provided by ATP hydrolysis
The amino acid attachment site is the same for all tRNA molecules, what is its sequence?
5’-CCA-3’ on the acceptor arm
How does tRNA read information in a mRNA sequence?
The anticodon on the anti-codon arm reads the information in a mRNA sequence by base pairing with a codon
What is a RNA-protein complex called?
Ribonucleoprotein
How many RNA molecules does a prokaryotic ribosome have?
3
What determines sedimentation velocity (S) in an ultracentrifuge (with RNA)?
How many base pairs in a RNA molecule. This was used to determine the two sub-units of ribosomes. More base pairs means higher sedimentation velocity
Which subunit holds mRNA during translation?
The small subunit
Which subunit does the growing polypeptide exit through?
A tunnel in the large subunit
How many amino acids per second do ribosomes add in prokaryotes? Eukaryotes?
20 amino acids per second in prokaryotes, 2 per second in eukaryotes.
Which subunit of ribosomes uses catalytic activity to join amino acids together to form peptide bonds?
Large subunit, the amino acid at the end of a tRNA makes contact with this catalytic region
How to antibiotics attack translational apparatuses?
Binding to tRNA sites and blocking exit tunnel
The growing polypeptide (in translation) is always attached to _____ during translation
a tRNA
What are the four steps of translation?
- tRNA charging
- Initiation
- Elongation
- Termination
What is tRNA charging?
Attachment of an amino acid to the tRNA
What part of the tRNA are amino acids attached to during tRNA charging?
Adenine (A) nucleotide in the 3’ end acceptor stem
What group of the amino acid is attached to what group of the A nucleotide of the tRNA?
Amino acid: carboxyl group
tRNA A nucleotide: hydroxyl group on 3’ carbon
What supplies energy for binding aa (aminoacyl) to tRNA?
ATP hydrolysis
What does aminoacyl-tRNA synthetase do?
Correctly attaches an amino acid to the appropriate tRNA using ATP, there are 20 different aminoacyl tRNA synthetases, one for each amino acid
What are the key steps of initiation (in translation)?
- Assembly of ribosomal subunits at the translation start site
- Base pairing of initiatory-tRNA anticodon with start site codon in the mRNA
What are the requirements of initiation in translation?
- mRNA
- small and large ribosome subunits
- initiator tRNA
- Initiation factors (IFs)
What does initiation factor do in initiation step of translation?
Binds to the large ribosome subunit to prevent the small subunit from binding. This allows the mRNA to bind with the small subunit
Which subunit does mRNA bind to in initation? What part of it binds?
The small ribosomal subunit (16S rRNA). There is complementary base pairing between the small subunit and the Shine-Dalgarno sequence of prokaryotic mRNA. rRNA binds to mRNA in an antiparallel fashion.
What anticodon of initiator tRNA base pairs with what mRNA codon in initiation (in translation)?
initiator tRNA anticodon: 3’ UAC 5’
mRNA initiator/start codon: 5’ AUG 3’
What amino acid charges tRNA?
fMet
What does IF-3 do in initiation?
Keeps the small and large ribosomes separated
What do IF-1 and IF-2 do?
Facilitate initiator-tRNA binding to the correct site
What lets the large ribosome subunit bind to the small ribosome subunit? What does this form?
When initiator factor proteins dissociate, the large subunit binds to the small, this forms the 70S initiation complex.
What is the sedimentation velocity (S) of the large rRNA subunit and small rRNA subunit. What is the sedimentation velocity of the initiation complex?
Small subunit: 30S
Large subunit: 50S
Initiation complex: 70S
What are three key steps of elongation in translation?
- entry of aa-tRNA into the A site of the ribosome
- Peptide bond formation
- Ribosome translocation
What are the 4 requirements for elongation in translation?
- aa-tRNAs (or charged tRNAs)
- 70S initiation complex
3. Elongation factors (EFs)
4. GTP
What are the three sites on ribosomes used by tRNAs?
E (exit), P (peptidyl) and A (aminoacyl) sites
What is the A-site of the ribosome?
The aminoacyl site accepts the incoming aa-tRNA carrying the next amino acid to be added to the chain
What is the P-site of the ribosome?
The peptidyl site holds the tRNA carrying the growing polypeptide
What is the E-site on the ribosome?
The exit site is where discharged tRNAs leave the ribosome from this site
Where does the initiator tRNA bind to the 70S initiator complex?
The P (peptidyl) site
Where is aa-tRNA delivered on the ribosome?
To the A (aminoacyl) site
What guides the incoming aa-tRNA to the correct site?
Elongation factors (EF)
What catalyses peptide bond formation in ribosomes?
Peptidyl transferase
What is a ribozyme?
A RNA that has nucleic activity and catalytic activity
How much does your boyfriend care about you?
ALOT - and always will xoxo
What releases the amino acid from the tRNA at the P-site?
Peptide bond formation
At what areas in order does the amino acid touch in the ribosome? (sites)
A to P to E
What is translocation?
Ribosome movement along the mRNA in the 5’ to 3’ direction
What facilitates translocation?
Elongation factors
What causes protein synthesis to terminate?
When the ribosome translocates to a stop codon
What does release factor (RF) protein do?
- Binds to the A site of a ribosome
2. Triggers release of the polypeptide from the P-site tRNA
What facilitates ribosome binding to mRNA in eukaryotes?
The 5’ cap and 3’ Poly(A) tail. There is no consensus sequence for ribosome binding in eukaryotes
How are prokaryotic and eukaryotic ribosomes different?
Eukaryotic contains more proteins and rRNA with a greater sedimentation velocity. The assembled ribosome in a prokaryote is 70S and in eukaryotes 80S
