case 3 translation proces

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the primary advantage of coupled transcription and translation in prokaryotes?

It allows for post-translational modifications.

Ribosomes can only translate fully processed mRNA.

Ribosomes can immediately start translating mRNA before transcription is complete. (correct)

It enables transcription to occur in the nucleus.

What is a polysome and its significance in prokaryotic translation?

A structural component of the nucleus during transcription.

An mRNA strand that has undergone extensive processing.

A single ribosome translating multiple mRNA strands.

A complex of multiple ribosomes translating a single mRNA strand. (correct)

Where do transcription and translation occur in eukaryotic cells?

Both in the mitochondria

Transcription in the cytoplasm and translation in the nucleus

Transcription in the nucleus and translation in the cytoplasm (correct)

Both in the lysosome

During translation initiation in prokaryotes, what role does the ribosome play?

It binds to tRNA for amino acid delivery. Signup and view all the answers

Which of the following is NOT a post-translational modification?

Translation Signup and view all the answers

What is the primary role of the Shine-Dalgarno sequence in prokaryotic translation?

It facilitates binding of the ribosomal subunit to mRNA. Signup and view all the answers

Which component recognizes the AUG initiation codon during translation initiation?

Initiator tRNA Signup and view all the answers

During the elongation phase of translation, where does the aminoacyl tRNA first enter the ribosome?

A-site Signup and view all the answers

What is the function of peptidyl transferase during translation?

To catalyze peptide bond formation Signup and view all the answers

In eukaryotic translation, how does the process of initiation differ from that in prokaryotes?

There are no shine-dalgarno sequences involved. Signup and view all the answers

What role does EF-G play during translation termination?

It hydrolyzes GTP to facilitate translocation. Signup and view all the answers

What is the role of RF1 and RF2 in translation termination?

To recognize stop codons and trigger release of the polypeptide. Signup and view all the answers

After the polypeptide is released during termination, what happens to the ribosomal subunits?

They dissociate from mRNA and can bind to another mRNA. Signup and view all the answers

Which of the following correctly describes the composition of ribosomes in prokaryotes?

35% proteins and 65% ribosomal RNA Signup and view all the answers

What is the direction of mRNA translation during protein synthesis?

5'-3' Signup and view all the answers

Which site on the ribosome is responsible for holding the growing protein chain during translation?

P-site Signup and view all the answers

In eukaryotic cells, which RNA polymerase is responsible for transcribing tRNA genes?

RNA polymerase III Signup and view all the answers

What type of interactions are crucial for the clover-leaf shape of tRNA?

Hydrogen bonds Signup and view all the answers

Which of the following is true about the initiation of translation in prokaryotes?

The small subunit of the ribosome binds to the ribosome binding site (RBS). Signup and view all the answers

Which type of tRNA is involved in attaching the amino acid during translation elongation?

Aminoacyl-tRNA Signup and view all the answers

During translation termination, what recognition factor is typically involved?

Release factor Signup and view all the answers

Which of the following structures contributes to the site for tRNA exit after translation?

E-site Signup and view all the answers

How many types of rRNA molecules are typically found in eukaryotic ribosomes?

4 types Signup and view all the answers

What is the role of eukaryotic initiator factor (eIF-4E) in translation initiation?

It binds to the 5' cap of mRNA. Signup and view all the answers

During translation elongation, what occurs at the A-site of the ribosome?

Aminoacyl-tRNA enters with a specific amino acid. Signup and view all the answers

What is the purpose of the poly-A tail in eukaryotic mRNA translation?

It stabilizes the mRNA and aids in translation. Signup and view all the answers

What triggers the termination of translation?

The recognition of a STOP codon by the ribosome. Signup and view all the answers

Which of the following correctly describes the scanning model of translation initiation in eukaryotes?

The ribosome scans until it finds the start codon AUG. Signup and view all the answers

What is the primary location for translation in prokaryotes?

Cytoplasm Signup and view all the answers

What happens to the uncharged tRNA during the translocation phase of translation?

It is released into the cytoplasm. Signup and view all the answers

Which factor helps the ribosome recognize STOP codons during translation termination?

Releasing factor (RF) Signup and view all the answers

How is peptide bond formation catalyzed during elongation?

By peptidyl transferase. Signup and view all the answers

Which sequence is essential for the ribosome to accurately find the start codon?

Kozak sequence Signup and view all the answers

Study Notes

Translation Initiation in Prokaryotes

Ribosomal subunit (30S) with initiation factors (IF-1 and IF-3) binds to mRNA's AUG start codon.
Shine-Dalgarno sequence (RBS) on mRNA guides the 30S subunit to the correct binding site.
Initiator tRNA (tRNA.fMET) carries the first amino acid, formyl methionine (fMET), and recognizes AUG.

Translation Elongation in Prokaryotes

mRNA is read from 5' to 3'.
Polypeptide chain synthesis proceeds from N-terminus to C-terminus.
Elongation factors bind to tRNA after the correct amino acid is attached.

Codon Recognition

Aminoacyl tRNA with its specific amino acid enters the ribosome at the A-site.
Ribosome ensures correct base pairing between the tRNA anticodon and mRNA codon.

Peptide Bond Formation

In the P-site, adjacent amino acids form peptide bonds.
The bond between tRNA and its amino acid is broken first, then the amino acid is attached to the adjacent amino acid in the A-site via a peptide bond.
This process is catalyzed by peptidyl transferase.

Translocation

The ribosome moves along the mRNA one codon at a time, shifting from the P-site to the A-site.
Uncharged tRNA moves to the E-site.
Requires the activity of EF-G (elongation factor).
EF-TU-GTP complex binds to the ribosome, GTP is hydrolyzed, and translocation occurs.

Translation Termination in Prokaryotes

Release factors (RF1 and RF2) bind to stop codons (UAA, UAG, UGA), triggering peptidyl transferase to release the polypeptide from the P-site.
RF3-GDP binds to the ribosome triggering the release of RF from the stop codon and the ribosome.
GDP is converted to GTP, and RF3 hydrolyzes the GTP, detaching it from the ribosome.
Ribosome recycling factor (RRF) mimics rRNA and binds to the A-site.
EF-G binds, leading to translocation.
RRF moves to the P-site and the uncharged tRNA to the E-site.
Release of tRNA, EF-G, and RRF occurs, causing the ribosome subunits to dissociate from the mRNA.

Translation Initiation in Eukaryotes

Eukaryotic initiation factor 4E (eIF-4E) binds to the 5' cap of mRNA.
Scanning model: 40S subunit with MET-tRNA, multiple eIFs, and GTP binds to mRNA and scans for the start codon (AUG) within the Kozak sequence.
Upon finding AUG, the 40S subunit binds, and the 60S subunit joins, replacing eIFs except for eIF-4F. This forms the 80S initiation complex.
Initiator MET-tRNA binds to the mRNA at the P-site of the ribosome.
Poly-A tail binds to PABPII (poly A binding protein II), which interacts with eIF-4G at the 5' cap, facilitating a loop in the mRNA.

Translation Elongation in Eukaryotes

mRNA is read from 5' to 3'.
Polypeptide chain synthesis proceeds from N-terminus to C-terminus.
Elongation factors bind to tRNA after the correct amino acid is attached.

Codon Recognition (Eukaryotes)

Aminoacyl tRNA with its specific amino acid enters the ribosome at the A-site.
Ribosome ensures correct base pairing between the tRNA anticodon and mRNA codon.

Peptide Bond Formation (Eukaryotes)

In the P-site, adjacent amino acids form peptide bonds.
The bond between tRNA and its amino acid is broken first, then the amino acid is attached to the adjacent amino acid in the A-site via a peptide bond.
This process is catalyzed by peptidyl transferase.

Translocation (Eukaryotes)

The ribosome moves along the mRNA one codon at a time, shifting from the P-site to the A-site.
Uncharged tRNA moves to the E-site.
Requires the activity of EF-G (elongation factor).
EF-TU-GTP complex binds to the ribosome, GTP is hydrolyzed, and translocation occurs.

Translation Termination in Eukaryotes

STOP-codon is recognized (UAG, UAA, UGA), signaling the end of translation.
These codons do not code for any amino acid, and no tRNA has an anticodon for them.
The ribosome recognizes the stop codon with the help of release factors (RFs).

Polysomes

Multiple ribosomes simultaneously translate a single mRNA strand, increasing the efficiency of protein synthesis in both prokaryotes and eukaryotes.

Prokaryotic vs. Eukaryotic Translation

Prokaryotes:
- Translation can begin even before transcription is complete because there is no nucleus.
- Transcription and translation occur in the cytoplasm.
- Coupled Transcription and Translation: Ribosomes can bind to the 5' end of the growing mRNA and begin translating almost simultaneously with transcription.
- Polysomes: Multiple ribosomes translate a single mRNA strand.
Eukaryotes:
- Transcription occurs in the nucleus, and translation occurs in the cytoplasm.
- mRNA undergoes processing (capping, splicing, polyadenylation) before translation.

Post-Translational Modifications

Enhance the functional diversity of the proteome.
Involve covalent addition of functional groups, proteolytic cleavage of regulatory subunits, or degradation of the entire protein.

Types of Post-Translational Modifications

Phosphorylation: Addition of phosphate groups to amino acid side chains, often regulating protein activity.
Glycosylation: Attachment of sugars to amino acids, affecting protein folding, stability, and cell signaling.
Ubiquitination: Tagging proteins with ubiquitin, a small polypeptide chain, for degradation by the proteasome.

The Proteasome

Known as the "protein shredder".
Degrades ubiquitinated proteins.
Involves three enzymes: E1 (activating ubiquitin), E2 (ubiquitin conjugating enzyme), and E3 (ubiquitin ligase).

Ubiquitination Process

Ubiquitin binds to E1 using ATP.
E3 binds to the target protein and E2.
E1 and E2 bind together.
Ubiquitin is transferred from E1 to E2.
Ubiquitin is transferred to the target protein.
E1 detaches from E2 and binds to a new ubiquitin molecule.
This process repeats, adding multiple ubiquitin molecules to the target protein, marking it for degradation by the proteasome.

Structure of tRNA

All tRNA molecules have the sequence 5'-CCA-3' at their ends.
They have chemically modified bases, contributing to their unique identity.
tRNA exhibits a clover-leaf shape due to complementary base pairing within the RNA strand.
Four loops are formed, with the second loop containing the anticodon sequence.
Loop 1 is the D-arm, and loop 3 is the T-arm.

tRNA in Bacteria

Not found in numerous copies in the genome.
Transcribed by RNA polymerase.
During transcription, pre-tRNA is produced.

tRNA in Eukaryotes

Genes are repeated multiple times in the genome.
Transcribed by RNA polymerase III.
During transcription, pre-tRNA is produced, which can contain introns.

Amino Acid Attachment to tRNA

The amino acid attaches to the 3' end of tRNA through a covalent linkage between the carboxyl group of the amino acid and the 3' or 2'-OH group of the ribose sugar in the adenine at the tRNA's 3' end.

Aminoacyl-tRNA Synthetases

These enzymes couple the correct amino acid to its corresponding tRNA molecule.

Wobble Pairing

Explains how a single tRNA can recognize multiple codons that differ only in their third position.
Allows for flexibility in the base pairing between the third position of the codon and the first position of the anticodon.

Ribosomes

Composed of approximately 35% proteins and 65% ribosomal RNA (rRNA).
Prokaryotes have three types of rRNA, while eukaryotes have four.
Ribosomes read mRNA from 5' to 3'.
Eukaryotic ribosomes can be found in the cytoplasm, attached to the endoplasmic reticulum, or on the outside of the nuclear envelope.
Composed of two subunits that come together to translate mRNA.

Ribosomal Subunits

Prokaryotes:
- Small subunit: 30S
- Large subunit: 50S
Eukaryotes:
- Small subunit: 40S
- Large subunit: 60S

Ribosomal Sites

A-site (aminoacyl-tRNA site): Part of both the large and small subunits. Entry point for tRNA molecules with attached amino acids.
P-site (peptidyl-tRNA site): Part of both the large and small subunits. Holds the growing polypeptide chain and its associated tRNA.
E-site (exit site): Only part of the large subunit. Exit site for uncharged tRNA molecules and the newly synthesized polypeptide chain.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.