Question 1

Which of the following best explains why DNA is described as 'antiparallel'?

Accepted Answer

The two DNA strands run in opposite directions, with one strand running 5' to 3' and the other 3' to 5'.

Question 2

Which of the following base pairings is correct in DNA, and how many hydrogen bonds connect them?

Accepted Answer

Adenine pairs with Thymine via 2 hydrogen bonds.

Question 3

A DNA molecule has the following sequence on one strand: 5'-ATCGGGTTGTGC-3'. What is the complementary sequence on the other strand?

Accepted Answer

3'-TAGCCCAACACG-5'

Question 4

Why is it advantageous for DNA base pairs to be connected by hydrogen bonds rather than covalent bonds?

Accepted Answer

Hydrogen bonds are weak, allowing the strands to separate easily during replication and transcription.

Question 5

Which enzyme is responsible for unwinding the DNA double helix at the replication fork?

Accepted Answer

Helicase

Question 6

During DNA replication, which enzyme synthesizes the RNA primer required for DNA polymerase to begin synthesis?

Accepted Answer

Primase

Question 7

What is the main difference between the synthesis of the leading and lagging strands during DNA replication?

Accepted Answer

The leading strand is synthesized continuously, while the lagging strand is synthesized in short fragments called Okazaki fragments.

Question 8

Which enzyme removes RNA primers and replaces them with DNA nucleotides during replication?

Accepted Answer

DNA polymerase I

Question 9

What is the function of DNA ligase during DNA replication?

Accepted Answer

It joins Okazaki fragments on the lagging strand by forming phosphodiester bonds.

Question 10

Why is DNA replication described as 'semiconservative'?

Accepted Answer

Each new DNA molecule consists of one parental (old) strand and one newly synthesized strand.

Question 11

Which of the following best describes the chemical structure of the DNA backbone?

Accepted Answer

A repeating pattern of sugar and phosphate groups connected by phosphodiester bonds.

Question 12

If a DNA molecule contains 20% adenine, what percentage of guanine would you expect to find?

Accepted Answer

$$30\%$$

Question 13

What is the role of single-strand binding proteins during DNA replication?

Accepted Answer

They bind to and stabilize single-stranded DNA to prevent it from re-annealing.

Question 14

Which of the following best explains why DNA is negatively charged?

Accepted Answer

The phosphate groups in the DNA backbone carry negative charges.

Question 15

A mutation changes a guanine to an adenine in a DNA sequence. Which of the following is a possible consequence at the molecular level?

Accepted Answer

The hydrogen bonding pattern will change from three bonds (G-C) to two bonds (A-T), potentially affecting DNA stability.

Question 16

Which of the following statements about Okazaki fragments is correct?

Accepted Answer

They are short DNA fragments synthesized on the lagging strand during DNA replication.

Question 17

Which of the following best describes DNA supercoiling and its biological significance?

Accepted Answer

Supercoiling compacts DNA to fit inside the cell and helps regulate access to genetic information.

Question 18

During DNA replication in E. coli, what is the function of DNA gyrase (a type of topoisomerase)?

Accepted Answer

It relieves strain ahead of the replication fork by cutting and rejoining DNA.

Question 19

A scientist is studying a bacterial cell with a mutation that prevents the formation of RNA primers. Which step of DNA replication will be directly affected?

Accepted Answer

Initiation of DNA synthesis by DNA polymerase will be blocked.

DNA Structure and Replication: Microbiology Study Notes

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