Biology

Molecular Biology and Genetics

985 Questions

Molecular biology and genetics explore the structure and function of DNA, RNA, genetic mutations, and heredity. Understanding these building blocks of life is essential for most biology examinations. Review these practice questions to test your molecular genetics knowledge.

DNA structure and basesGenetic mutationsNucleic acids compositionDNA sequencing and replication

Molecular Biology and Genetics Questions

Multiple choice

What is the function of lac repressor?

  1. It binds to the CAP site and prevents transcription.

  2. Lac repressor binds to the CAP site and facilitates transcription.

  3. Lac repressor binds to the operator and prevents transcription.

  4. Lac repressor binds to the operator and facilitates transcription.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

When lac repressor binds to the operator, transcription is blocked.

Multiple choice

In lac operon, RNA polymerase binds to

  1. operator

  2. promoter

  3. activator

  4. structural proteins
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In lac operon, RNA polymerase binds to the promoter and carries out transcription.

Multiple choice

Repressor proteins are encoded by

  1. promoter genes

  2. operator genes

  3. regulatory genes

  4. structural genes
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Repressor proteins are encoded by regulatory genes. 

Multiple choice

Lac operon is an example of

  1. negative repressible operons

  2. negative inducible operons

  3. positive inducible operons

  4. positive repressible operons
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The lac operon is a negatively-controlled inducible operon, where the inducer molecule is allolactose.

Multiple choice

Which of the following statements is true?

  1. The lac repressor binds with lactose and transcription occurs when both glucose and lactose are present in the cell.

  2. When both glucose and lactose are absent, transcription occurs.

  3. In the absence of glucose, when lactose is present, it combines with the repressor, allowing RNA polymerase to carry on transcription.

  4. When glucose is present, cyclic AMP is high, CAP does not bind to the activator binding site and transcription of lactose is turned on.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

This is a true statement.

Multiple choice

The lac operator is located

  1. adjacent to activator

  2. partially within the promoter

  3. within the structural genes

  4. just before terminator
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The lac operator lies partially within the promoter and interacts with a regulatory protein that controls the transcription of the operon.

Multiple choice

Which of the following characteristics differentiates DNA from RNA?

  1. Occurence of 3' deoxyribose in DNA, ribose in RNA.

  2. Occurence of uracil in RNA instead of thymidine in DNA.

  3. Existence of base pairing in DNA but not RNA.

  4. Existence of 5' phosphate in DNA but not RNA.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

It is the only correct statement. In RNA, uracil is present instead of thymidine in DNA.

Multiple choice

Pick out the CORRECT statement regarding genomic imprinting.

  1. It is a characteristic of all genes.

  2. It is associated with methylation of cytosine bases adjacent to guanosines.

  3. It occurs in females but not in males.

  4. It is reversible in somatic cells.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

It is the correct statement that it is associated with methylation of cytosines 5' to guanosines.

Multiple choice

The activity of DNA gyrase is interrupted by

  1. puromycin

  2. streptomycin

  3. nalidixic acid

  4. chloramphenicol

  5. none of the above
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

It inhibits the subunit of DNA gyrase and induces formation of relaxation complex analogue.