Translation Flashcards
Where does translation take place?
Prokaryotes (bacteria and archaea) –> in the cytoplasm (they don’t have a nucleus), directly.
Eukaryotes –> in the cytoplasm, following mRNA export from the nucleus, more specifically in the ER.
Where are eukaryotic ribosomes made?
where do components translocate?
In the nucleolus.
rRNA translocated from the nucleoplasm,
while ribosomal proteins translocate from
the cytoplasm.
what are the 3 stem loops formed by tRNA
Forms three stem-loop structures (D-loop, T-loop. Anticodon loop = cloverleaf structure.
Ribosomal Features
- same shape in prokaryotes and eukaryotes but EUKARYOYIC ones are LARGER
- The ‘A’ site = Acceptor Site
- Two subunits come together only when ribosomes is actively synthesising proteins.
BOOK- image
tRNA charging- also known as aminoacylation
What is it?
What us it mediated by?
What is formed as a result?
What does the enzyme bind to?
What does the activated amino acid do?
Charged tRNA does what?
Amino acids need to be attached to the
appropriate tRNA with correct anticodon loop.
This process is Mediated by enzymes called aminoacyl tRNA synthETASE –
one specific enzyme for each amino acid ensuring specificity and accuracy.
The enzyme catalyzes the reaction, forming an aminoacyl-AMP intermediate.
The enzyme binds to the amino acid, ATP and
the anticodon loop of the appropriate tRNA.
The activated amino acid is then transferred to the 3’end of tRNA, forming the charged tRNA called tRNA aminoacyl-tRNA.
The charged tRNA is now ready to participate in translation- where it delivers its amino acids to the growing polypeptide chain.
Aminoacyl tRNA
- Each amino acid is attached to a particular tRNA.
- There are 20 amino acids.
- There are 64 different codon sequences available.
why are there 64 possible codon sequences?
There are four available bases, and each codon is made up of three bases.
1 base → 4 different possible codons (A, C, G, T) → 4
2 bases → 16 different possible codons (AA, AC, AG, AT, CA, CC, CG, etc) → 4x4
3 bases → 64 different possible codons (AAA, ACA, AGA, ATA, AAC, ACC, ACG, etc) → 4x4x4
Why is genetic code describes as degenerate.
The genetic code is described as degenerate because most amino acids are encoded by more than one codon. This means that there are multiple codons that can specify the same amino acid
start codons
stop codons
- Methionine – AUG – start codon – only
one codon. - Stop codons – UAA UAG UGA.
using codon table, translate UGUGCCACA
CAT- Cysteine, Alanine, Threonine
How do ribosomes bind to mRNA in PROKARYOTES.
The small subunit (30S) associates with the mRNA at the ribosome binding site (RBS).
The shine-Dalgarno Sequence (found upstream of the start codon) helps align the ribosome with the start codon (AUG) - indicating where translation will starts(initiate translation).
This sequence is complementary to a portion of the 16S rRNA in the 30S subunit, ensuring proper binding.
The initiation factor 3 (IF3) facilitates the binding of the 30S subunit to the mRNA. It also stops the 30S subunit from prematurely associating with the large subunit (50S) before the mRNA is correctly positioned.
How do ribosomes bind to mRNA in EUKARYOTES?
The small subunit (40s) binds to 5’mRNA cap via initiation factors.
Sequence surrounding the start codon=called
Kozac sequence – indicates where
translation will start.
Translation Initiation- PROKARYOTES- E.coli
How does it begin?
what is the recruitment facilitated?
what other factor facilitates this process?
what other factor is released?
how are he other two factors released?
what happens before translation can begin?
The first (initiator) aminoacyl-tRNA, which carries the amino acid methionine (the initiator tRNA), is recruited to the start codon (AUG) at the P site of the ribosome.
This recruitment is facilitated by IF2 (initiation factor 2) that is bound to GTP. IF2 helps ensure that the correct initiator tRNA is positioned at the start codon.
IF1 also binds to the A site of the small ribosomal subunit (30S), preventing any other tRNAs from entering prematurely.
With the initiator tRNA correctly positioned at the start codon, IF3 is released.
The binding of the initiator tRNA triggers the hydrolysis of GTP, which leads to the release of both IF2 and IF1.
With the initiation factors released, the large ribosomal subunit (50S) can now join the complex, completing the formation of the functional ribosome and allowing translation to begin.
Translation elongation Prokaryotes- E.coli
How does the process begin?
Role of enzyme?
How is the chain released?
what happens once the peptide bonds are formed?
what happens before termination?
SAME BASIC MECHANISM IN BOTH EUKARYOTES AND PROKARYOTES !
The process begins with the recruitment of the second aminoacyl-tRNA to the A site of the ribosome.
The enzyme peptidyl transferase, catalyzes the formation of a new peptide bond between the incoming amino acid (attached to the tRNA in the A site) and the growing polypeptide chain (attached to the tRNA in the P site).
The growing polypeptide is transferred from the tRNA in the P site to the amino acid on the tRNA in the A site, facilitated by a reaction with tRNA deacylase. This process releases the growing chain from the tRNA in the P site.
After the peptide bond is formed, the peptidyl-tRNA in the A site translocates to the P site. This movement shifts the ribosome along the mRNA, allowing the next codon to enter the A site.
The spent tRNA, which is now without an amino acid, is released from the E site of the ribosome, freeing up the A site for the next aminoacyl-tRNA.
Translation Termination
How does the process begin?
what the effect of the first step?
what happens once the polypeptide is released?
Role of RF3?
When the RIBOSOME reaches a stop codon (UAA, UAG, or UGA) in the mRNA, release factors (RF1 or RF2) bind to the A site. These factors recognize the stop codons and trigger the termination process.
he binding of the release factors activates the peptidyl transferase, which releases newly synthesized polypeptide from the tRNA in the P site via the exit tunnel.
After the polypeptide is released, the spent tRNA leaves the ribosome from the E site, making space for the next steps in recycling.
RF3 helps clear the A site by promoting the release of the release factors and facilitating the disassembly of the ribosomal complex, allowing them to be used for new rounds of translation (recycling).
