Chapter 17

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Questions and Answers

During transcription, what is the function of RNA polymerase?

Synthesize an RNA version of the instructions stored in DNA (correct)

Match complementary bases to both strands of DNA

Promote the synthesis of DNA from an RNA template

Serve as a structural component of the ribosome

Which strand of DNA is used as the template during transcription?

The non-template, or coding strand

One strand of DNA, known as the template strand (correct)

The strand with the highest GC content

Both strands of DNA simultaneously

What type of nucleotides does RNA polymerase use during transcription?

Deoxyribonucleoside monophosphates (dNMPs)

Ribonucleoside triphosphates (NTPs) (correct)

Ribonucleoside monophosphates (NMPs)

Deoxyribonucleoside triphosphates (dNTPs)

What is the role of the non-template (coding) strand during transcription?

It matches the sequence of the mRNA (except U for T) (C) Signup and view all the answers

In bacteria, how many RNA polymerases are involved in transcription?

One (B) Signup and view all the answers

What is a characteristic feature of eukaryotic transcription start sites?

Presence of a TATA box (A) Signup and view all the answers

Which organism's RNA processing is more extensive?

Eukaryotes (A) Signup and view all the answers

How does translation initiation and termination complexity compare between bacteria and eukaryotes?

More complex in eukaryotes (D) Signup and view all the answers

What did Crick propose regarding the interaction between mRNA codons and amino acids?

An adapter molecule holding the amino acid in place while interacting with a codon (A) Signup and view all the answers

How are amino acids transferred from tRNAs to polypeptides?

Through the interaction of tRNAs with mRNA codons (D) Signup and view all the answers

In eukaryotes, how many general transcription factors are involved in transcription?

Many (C) Signup and view all the answers

What is a characteristic feature of bacterial promoter structure?

Proteins that associate with promoter (B) Signup and view all the answers

What is the role of the Shine–Dalgarno sequence in translation initiation in bacteria?

It is the binding site for the small ribosomal subunit (A) Signup and view all the answers

What does the initiator tRNA carry in bacteria during translation initiation?

Modified methionine (f-Met) (A) Signup and view all the answers

What occurs at the start of elongation in translation?

The initiator tRNA is in the P site and the E and A sites are empty (D) Signup and view all the answers

What is the composition of the ribosome's active site where peptide bond formation occurs?

Consists of ribosomal RNA (A) Signup and view all the answers

When does translocation occur in the ribosome?

When it slides one codon toward the 3′ end of the mRNA (B) Signup and view all the answers

What happens during translocation in the ribosome?

Movement of tRNAs and exposes a new codon for aminoacyl tRNA binding (D) Signup and view all the answers

What triggers the termination of translation?

When the A site encounters a stop codon (B) Signup and view all the answers

What is the next step after the arrival of aminoacyl tRNA during translocation?

Peptide bond formation (B) Signup and view all the answers

What occurs at the start of translation initiation in bacteria?

mRNA binding (B) Signup and view all the answers

What happens to most proteins before they become functional?

Undergo post-translational modification and extensive processing steps (D) Signup and view all the answers

What is crucial for determining a protein's function?

Protein folding (A) Signup and view all the answers

Where does the ribosome move during translocation in translation?

One codon toward the 3′ end of the mRNA (A) Signup and view all the answers

Which direction does RNA polymerase perform template-directed synthesis?

5' → 3' (B) Signup and view all the answers

What is the length of bacterial promoters?

40–50 base pairs (B) Signup and view all the answers

What is the function of sigma protein in bacterial transcription initiation?

Binds to the −35 and −10 boxes (B) Signup and view all the answers

How does termination occur in bacterial transcription?

RNA polymerase transcribes a termination signal (C) Signup and view all the answers

What distinguishes eukaryotic transcription from bacterial transcription?

Promoters (A) Signup and view all the answers

What is the role of spliceosomes in eukaryotic transcription?

Catalyze RNA splicing (B) Signup and view all the answers

How many distinct types of RNA polymerases do eukaryotes have?

Three (B) Signup and view all the answers

What is the function of the holoenzyme in bacterial transcription initiation?

Binds to the −35 and −10 boxes (D) Signup and view all the answers

What is the sequence of the −10 box in bacterial promoters?

TATAAT (A) Signup and view all the answers

What is the sequence of the −35 box in bacterial promoters?

TTGACA (A) Signup and view all the answers

What occurs during elongation in bacterial transcription?

RNA polymerase reads the DNA template and adds nucleotides to the 3’ end of the RNA (C) Signup and view all the answers

What was revealed by the discovery of split eukaryotic genes in 1977?

Presence of noncoding DNA (introns) and coding DNA (exons) (D) Signup and view all the answers

What is the function of adding a 5' cap and a poly(A) tail to pre-mRNAs?

To prevent degradation and enable translation (D) Signup and view all the answers

Where are untranslated regions (UTRs) found in mature mRNAs?

At both ends (D) Signup and view all the answers

What is the role of transfer RNA (tRNA) in translation?

To link amino acids to the growing polypeptide (D) Signup and view all the answers

How are amino acids attached to tRNA?

With the help of aminoacyl-tRNA synthetases (C) Signup and view all the answers

What allows tRNAs to read the 61 different codons?

Wobble pairing in the anticodon's third position (B) Signup and view all the answers

Where do tRNAs fit into during translation in the ribosome?

A site (acceptor or aminoacyl), P site (peptidyl), and E site (exit) (B) Signup and view all the answers

What is the site of protein synthesis according to the pulse-chase experiment by Britten and colleagues?

Ribosomes (D) Signup and view all the answers

In bacteria, when can ribosomes begin translating an mRNA?

Before transcription is complete (D) Signup and view all the answers

How are transcription and translation related in eukaryotes?

They are separated, with mature mRNAs being transported to the cytoplasm for translation (D) Signup and view all the answers

What is the role of the small subunit of ribosomes during translation?

It holds mRNA (D) Signup and view all the answers

How many tRNAs are there in most cells?

About 40 (C) Signup and view all the answers

What is the length of transfer RNA (tRNA)?

75-95 nucleotides (B) Signup and view all the answers

Study Notes

Overview of Transcription and Translation Processes

Pre-mRNAs undergo processing which includes adding a 5' cap and a poly(A) tail to protect against degradation and enable translation.
Mature mRNAs contain untranslated regions (UTRs) at both ends.
Translation is a complex process involving ribosomes, mRNA, and tRNAs.
A pulse-chase experiment by Britten and colleagues showed that ribosomes are the site of protein synthesis, where proteins are synthesized and then released.
In bacteria, ribosomes can begin translating an mRNA before transcription is complete, forming a polyribosome and producing many copies of a protein from one mRNA.
In eukaryotes, transcription and translation are separated, with mature mRNAs being transported to the cytoplasm for translation by ribosomes and polyribosomes.
Transfer RNA (tRNA) is used as the adapter molecule in translation, linking amino acids to the growing polypeptide.
tRNAs are relatively short, 75-95 nucleotides long, and contain a CCA sequence at the 3' end as the amino acid binding site and an anticodon for mRNA codon binding.
Amino acids are attached to tRNA with the help of aminoacyl-tRNA synthetases, with each amino acid having a specific synthetase.
There are about 40 tRNAs in most cells, which can read the 61 different codons through wobble pairing in the anticodon's third position.
Ribosomes, containing proteins and ribosomal RNA (rRNA), have a small subunit that holds mRNA and a large subunit where peptide bonds form during translation.
During translation, tRNAs fit into three sites in the ribosome: A site (acceptor or aminoacyl), P site (peptidyl), and E site (exit) where tRNAs without amino acids exit the ribosome.

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Test your knowledge of transcription and translation processes with this quiz. Explore key concepts such as mRNA processing, ribosome function, tRNA structure, and the intricacies of translation in both prokaryotes and eukaryotes.