Translation Flashcards

Questions and Answers

What does 16S rRNA do in the small ribosomal subunit?

It interacts with the RBS to position the AUG in the P-site.

What is the Shine-Dalgarno sequence?

It is a sequence element that acts as a ribosome binding site found just upstream of the start codon in many prokaryotic genes.

What binds to the Shine-Dalgarno sequence during translation?

The small ribosomal subunit recognizes the sequence, specifically a region of the 16S RNA.

Describe how the Shine-Dalgarno sequence can vary.

It can vary in sequence and distance from the start codon, affecting translation efficiency. Signup and view all the answers

What is the role of the 5′ cap during eukaryotic translation?

eIFs recognize the 5′ cap and recruit the small subunit of the ribosome to the mRNA. Signup and view all the answers

What happens to mRNA molecules that are missing a cap?

They are rapidly destroyed by exonucleases. Signup and view all the answers

What are the steps by which aminoacyl tRNA synthetases charge tRNAs?

The steps are adenylation and tRNA charging. Signup and view all the answers

How can some organisms have fewer than 20 synthetases and still charge tRNAs with all 20 amino acids?

They charge tRNAs with fewer than 20 amino acids and use other enzymes to modify them. Signup and view all the answers

Explain how EF-Tu escorts charged tRNA to the A-site.

EF-Tu binds charged tRNA and, upon correct codon-anticodon interaction, releases it in the ribosome. Signup and view all the answers

How do eukaryotic cells recognize the stop codon during translation?

The stop codon is recognized by class I release factors RF1 and RF2. Signup and view all the answers

How does recognition of the codon lead to the termination of protein synthesis?

It leads to the release of the polypeptide and dissociation of the ribosomal subunits. Signup and view all the answers

How does the degree of translation accuracy compare to DNA replication and transcription?

Translation has a higher error rate than transcription and DNA replication. Signup and view all the answers

What three key events must occur for the correct addition of an amino acid during translation elongation?

The correct aminoacyl-tRNA enters the A-site, a peptide bond is formed, and the tRNA must translocate to the P-site. Signup and view all the answers

Is translation elongation identical between prokaryotes and eukaryotes?

False Signup and view all the answers

To which of the three tRNA binding sites does the initiator tRNA bind?

P-site. Signup and view all the answers

What are the four components of the translation machinery?

mRNA, tRNAs, aminoacyl-tRNA synthetases, ribosome. Signup and view all the answers

What is meant by ORF?

An open reading frame is a coding sequence specifying a single polypeptide chain. Signup and view all the answers

Explain the structure of tRNA.

tRNA has a 3' terminus 5'-CCA, contains an anticodon, and has dihydrouridines. Signup and view all the answers

What type of 3D structure does tRNA have?

It resembles an L-shape. Signup and view all the answers

What is the size of the ribosome for prokaryotes and eukaryotes?

Prokaryotic ribosomes are 70 S (30 S + 50 S), eukaryotic ribosomes are 80 S (40 S + 60 S). Signup and view all the answers

The large and small subunits undergo association and dissociation during each cycle of translation.

True Signup and view all the answers

What are the names of the different sites in the ribosome?

A = aminoacylated-tRNA, P = peptidyl-tRNA, E = exit. Signup and view all the answers

What does it mean for tRNA to be charged?

It means that an amino acid is attached to the tRNA. Signup and view all the answers

What is the function of each subunit in the ribosome?

The small subunit is the decoding center; the large subunit forms peptide bonds. Signup and view all the answers

What is the error rate of translation?

The error rate is between 10^-3 and 10^-4. Signup and view all the answers

What type of catalysis occurs when forming a peptide bond?

Entropic catalysis. Signup and view all the answers

What catalyzes the peptidyl transferase reaction?

The 23S rRNA of the large subunit. Signup and view all the answers

What mechanisms ensure that the correct aminoacyl-tRNA is inserted?

Hydrogen bonds between 16S rRNA and codon-anticodon pair, GTP hydrolysis, and tRNA accommodation. Signup and view all the answers

Study Notes

16S rRNA and Shine-Dalgarno Sequence

16S rRNA helps position the AUG start codon in the P-site of the ribosome by interacting with the ribosome binding site (RBS).
The Shine-Dalgarno sequence (5′-GGAGG-3′) is crucial for translation initiation in prokaryotes, typically found 3 to 9 nucleotides upstream of the start codon.
Recognition of the Shine-Dalgarno sequence by the small ribosomal subunit is facilitated by complementary sequences in 16S RNA.

Variability of the Shine-Dalgarno Sequence

Variations in the Shine-Dalgarno sequence can affect translation efficiency.
Sequences closely matching the ideal Shine-Dalgarno sequence display higher activity, while deviations generally reduce activity.
Proper distance from the start codon also influences translation efficiency.

Eukaryotic Translation Initiation

The 5′ cap on mRNA is recognized by eIFs, recruiting the small ribosomal subunit and assisting in scanning for the start codon.
mRNA lacking a cap is vulnerable to degradation by exonucleases, underscoring the protective role of the cap.

Charging tRNA by Aminoacyl tRNA Synthetases

Aminoacyl tRNA synthetases charge tRNAs in two steps: adenylation (binding amino acid to AMP) and tRNA charging (transferring the amino acid to tRNA).
Some organisms have fewer than 20 synthetases yet can charge all amino acids by modifying others.

Role of EF-Tu in Translation

Charged tRNA is bound to EF-Tu-GTP, which delivers it to the ribosome's A site.
Upon correct codon-anticodon pairing, EF-Tu hydrolyzes GTP, releasing tRNA into the ribosome.

Stop Codon Recognition in Eukaryotes

Stop codons are recognized by class I release factors RF1 and RF2 using a peptide anticodon that specifically binds to the codon.
This recognition leads to the termination of protein synthesis by hydrolyzing the bond between the polypeptide and tRNA.

Termination of Translation

Upon stop codon recognition, release factors facilitate polypeptide release and ribosome disassembly through a series of interactions, involving RF3 and RRF.
EF-G helps displace deacylated tRNAs from the ribosome.

Translation Accuracy

The error rate for translation (10^-3 to 10^-4) is higher than that for transcription (10^-4 to 10^-5) and DNA replication (as low as 10^-10).
Higher error rates in translation are acceptable since they only affect individual proteins, unlike transcription which influences multiple proteins from a single mRNA.

Translation Elongation Events

Key events for amino acid addition during elongation include the insertion of the correct aminoacyl-tRNA into the ribosome’s A site, peptidyl bond formation, and translocation of peptidyl-tRNA to the P site.

Differences in Translation between Prokaryotes and Eukaryotes

While the processes are similar, distinct differences exist in translation elongation between prokaryotes and eukaryotes.

Ribosome Structure and Function

Prokaryotic ribosome: 70S total (30S + 50S), Eukaryotic ribosome: 80S total (40S + 60S).
The ribosome has three tRNA binding sites: A (aminoacyl), P (peptidyl), and E (exit).

Understanding tRNA

Charged tRNA is one that has an amino acid attached, crucial for protein synthesis.
tRNA structure features a 3' terminus with a CCA sequence and contains an anticodon that recognizes mRNA codons.

Peptidyl Transferase Reaction

Catalyzed by the 23S rRNA of the large subunit, the reaction facilitates peptidyl bond formation.

Mechanisms Ensuring Accurate tRNA Insertion

Hydrogen bonds between adenine residues in 16S rRNA and the anticodon-codon pair enhance specificity.
Correct pairing allows for EF-Tu interaction with the ribosome, leading to subsequent peptide bond formation through tRNA accommodation.

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Description

Test your knowledge on the roles of 16S rRNA and the Shine-Dalgarno sequence in translation. These flashcards cover key concepts important for understanding protein synthesis in prokaryotes. Ideal for biology students looking to reinforce their learning.