Molecular Biology: RNA and Genome Basics

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Questions and Answers

What role does allolactose play in the lac operon system?

It acts as a repressor directly preventing transcription.
It binds to the repressor, preventing it from binding to the operator. (correct)
It inhibits the activity of beta-galactosidase.
It functions as a corepressor, halting lactose metabolism.

In the absence of tryptophan, what happens to the trp operon?

The repressor binds to the operator, halting transcription.
The operon is permanently inactive regardless of other conditions.
RNA polymerase binds to the operator and transcription begins. (correct)
Tryptophan is synthesized at a slow rate.

Which statement about catabolite repression is true?

Lactose is used preferentially over glucose at all times.
Lactose metabolism is fully induced in the presence of glucose.
Glucose serves as a less preferred carbon source compared to lactose.
Bacteria will grow faster when glucose is present rather than when it is depleted. (correct)

What occurs when tryptophan is in excess within the trp operon?

Tryptophan binds to the repressor, allowing it to bind to the operator. (A) Signup and view all the answers

What is the impact of glucose depletion on bacterial growth when lactose is present?

Bacterial growth slows down but continues after glucose is gone. (B) Signup and view all the answers

What type of mutation is characterized by the addition of one or more bases?

Insertion mutation (D) Signup and view all the answers

What is the primary consequence of a nonsense mutation?

Shorter, non-functional proteins (A) Signup and view all the answers

What type of mutation has no effect on the protein's structure?

Silent mutation (A) Signup and view all the answers

Which event can lead to frameshift mutations due to distortion of DNA?

Intercalating agents (C) Signup and view all the answers

What is a characteristic of chemical mutagens?

Modify normal DNA bases (A) Signup and view all the answers

How does a missense mutation typically affect protein function?

May provide a beneficial change (D) Signup and view all the answers

What is the mutation rate for an average gene during cell division?

One in a million replicated genes (A), One in a billion replicated base pairs (D) Signup and view all the answers

What type of radiation can lead to the formation of thymine dimers?

Non-ionizing radiation (A) Signup and view all the answers

What distinguishes the initiator tRNA in prokaryotes from that in eukaryotes?

Prokaryotes use fMet, while eukaryotes use Met. (C) Signup and view all the answers

Which site on the ribosome is primarily responsible for the formation of peptide bonds?

P site (B) Signup and view all the answers

During translation termination, what event occurs at the A site?

Alignment with nonsense codons. (D) Signup and view all the answers

What is the role of mutagens in mutation?

They are agents that cause mutations. (D) Signup and view all the answers

What is the primary role of histone-like proteins in microbial genetics?

To package and stabilize DNA (B) Signup and view all the answers

What characterizes frameshift mutations?

They involve insertions or deletions of nucleotides. (C) Signup and view all the answers

What is the significance of plasmids in bacterial cells?

They carry genes that can provide advantageous traits through horizontal gene transfer. (A) Signup and view all the answers

Which structural feature is absent in eukaryotic mRNA compared to prokaryotic mRNA?

Shine-Dalgarno sequence (A) Signup and view all the answers

During DNA replication, which enzyme is responsible for synthesizing the new complementary DNA strand?

DNA polymerase III (A) Signup and view all the answers

What role does the E site on the ribosome play during translation?

It releases dissociated tRNAs for recharging. (C) Signup and view all the answers

In the semiconservative model of DNA replication, what does each newly formed double-stranded DNA consist of?

One conserved strand and one newly synthesized strand (C) Signup and view all the answers

How do ribosome sizes differ between bacteria and eukaryotes?

Bacterial ribosomes (70S) are smaller than eukaryotic ribosomes (80S). (D) Signup and view all the answers

What occurs at the origin of replication in prokaryotes?

Topoisomerase II initiates DNA unwinding (A) Signup and view all the answers

Which statement about transcription is accurate?

It produces mRNA by directly copying DNA. (D) Signup and view all the answers

What is the primary function of topoisomerase during DNA replication?

To relax supercoiled DNA strands (C) Signup and view all the answers

What is the primary purpose of the central dogma in molecular biology?

To describe the flow of genetic information within a cell (C) Signup and view all the answers

What is the primary function of mRNA in cellular processes?

To carry the message from DNA to make a protein (D) Signup and view all the answers

What is the characteristic shape of tRNA during protein synthesis?

Clover shape in 2D and L shape in 3D (D) Signup and view all the answers

What is a key characteristic of rRNA?

Makes up 60% of a ribosome and has a stable structure (A) Signup and view all the answers

Which of the following correctly describes the role of genes?

Segments of DNA that encode functional products, usually proteins (C) Signup and view all the answers

How do eukaryotic chromosomes differ from prokaryotic chromosomes?

Eukaryotic chromosomes are linear, diploid, and consist of multiple distinct chromosomes (D) Signup and view all the answers

What is the function of topoisomerases in relation to DNA?

They prevent DNA supercoiling during replication (D) Signup and view all the answers

Which of the following statements about RNA is NOT true?

All types of RNA are stable and long-lived (A) Signup and view all the answers

What best defines the term 'genotype'?

The full collection of genes within an organism's genome (B) Signup and view all the answers

What initiates the transcription process in bacteria?

The binding of sigma factor to the promoter (B) Signup and view all the answers

What is one of the key differences between eukaryotic and prokaryotic mRNAs?

Eukaryotic mRNAs undergo processing before translation (D) Signup and view all the answers

How does RNA polymerase add nucleotides during transcription?

To the 3'-OH group of the growing RNA strand (B) Signup and view all the answers

Which statement describes the process of termination in prokaryotic transcription?

Termination can be Rho-independent or influenced by Rho protein (B) Signup and view all the answers

What role does the 5' cap play in eukaryotic mRNA processing?

It provides a binding site for ribosomes (D) Signup and view all the answers

What is the role of the sigma factor in bacterial transcription?

Directs RNA polymerase binding to the specific promoter (D) Signup and view all the answers

Which of the following accurately describes the transcription speed of RNA polymerase during elongation?

40 nucleotides per second (A) Signup and view all the answers

What happens to the DNA double helix during the transcription process?

It is only partially unwound to form a transcription bubble (B) Signup and view all the answers

Flashcards

Eukaryotic Translation Initiation

In eukaryotes, translation initiation does not use a Shine-Dalgarno sequence but instead utilizes a 5' cap and a 3' poly-A tail.

Ribosome Binding Sites

The ribosome has three sites (A, P, E) to hold tRNAs during protein synthesis.

Peptide Bond Formation

A peptide bond forms between the amino group of the amino acid in the A site and the carboxyl group of the amino acid in the P site.