Molecular Biology Quiz

Which of the following best defines recombinant DNA?

• DNA extracted from a donor organism

• DNA that has been artificially combined from different sources

• DNA that has undergone natural mutation

• DNA isolated from RNA

Answer explanation

Recombinant DNA refers to DNA that has been artificially combined from different sources, allowing for the creation of new genetic combinations. This distinguishes it from naturally occurring DNA or DNA isolated from RNA.

Why is genetic engineering important in biotechnology?

• It allows the random mutation of genes

• It is used to manipulate genetic material to modify traits

• It prevents gene expression

• It deactivates enzymes in bacteria

Answer explanation

Genetic engineering is crucial in biotechnology because it allows scientists to manipulate genetic material to modify traits, enhancing organisms for agriculture, medicine, and research.

A gene of interest can be obtained by:

• Extracting it from donor DNA

• Synthesizing it from mRNA using reverse transcriptase

• Chemically synthesizing it from nucleotides

• All of the above

Answer explanation

A gene of interest can be obtained through various methods: extracting from donor DNA, synthesizing from mRNA using reverse transcriptase, or chemically synthesizing from nucleotides. Therefore, the correct answer is 'All of the above'.

Which of the following is **not** a function of restriction enzymes?

• Cutting DNA at specific sequences

• Recognizing palindromic sequences

• Joining DNA fragments together

• Producing sticky or blunt ends

Answer explanation

Restriction enzymes cut DNA at specific sequences, recognize palindromic sequences, and produce sticky or blunt ends. However, they do not join DNA fragments together; that function is performed by ligases.

What is the role of **DNA ligase** in recombinant DNA technology?

• Cutting DNA into fragments

• Synthesizing new DNA strands

• Joining DNA fragments by forming phosphodiester bonds

• Copying RNA into DNA

Answer explanation

DNA ligase plays a crucial role in recombinant DNA technology by joining DNA fragments together. It forms phosphodiester bonds between the sugar and phosphate groups of the DNA backbone, effectively sealing the fragments.

What is the **main purpose of PCR** in molecular biology?

• To amplify specific DNA sequences

• To cut DNA into fragments

• To join DNA fragments together

• To separate DNA by size

Answer explanation

The main purpose of PCR (Polymerase Chain Reaction) is to amplify specific DNA sequences, making millions of copies of a targeted segment. This is essential for various applications in molecular biology, such as cloning and analysis.

Which enzyme is essential for PCR?

• DNA ligase

• Restriction enzyme

• Taq polymerase

• Reverse transcriptase

Answer explanation

Taq polymerase is essential for PCR as it synthesizes new DNA strands by adding nucleotides to a template strand at high temperatures, making it crucial for the amplification process.

What is the correct order of the PCR cycle?

• Extension → Denaturation → Annealing

• Denaturation → Annealing → Extension

• Annealing → Extension → Denaturation

• Denaturation → Extension → Annealing

Answer explanation

The correct order of the PCR cycle is Denaturation → Annealing → Extension. Denaturation separates the DNA strands, Annealing allows primers to bind, and Extension synthesizes new DNA strands.

Why is **Taq polymerase** used in PCR instead of regular DNA polymerase?

• It works only on single-stranded DNA

• It can withstand high temperatures

• It produces sticky ends in DNA

• It is slower than other polymerases

Answer explanation

Taq polymerase is used in PCR because it can withstand high temperatures, which is essential for the denaturation step of the process. Regular DNA polymerases would denature and lose activity at these temperatures.

What is the role of **primers** in PCR?

• Cutting DNA into fragments

• Providing a starting point for DNA synthesis

• Binding to RNA molecules

• Breaking hydrogen bonds in DNA

Answer explanation

Primers are short sequences of nucleotides that provide a starting point for DNA synthesis in PCR. They bind to the target DNA, allowing DNA polymerase to extend the new DNA strand from the primer.