Question 1

Which of the following statements best describes the central dogma of molecular biology?

Accepted Answer

Information flows from DNA to RNA to protein.

Question 2

Which of the following bases is a purine found in both DNA and RNA?

Accepted Answer

Adenine

Question 3

What is the main structural difference between DNA and RNA sugars?

Accepted Answer

DNA contains deoxyribose, while RNA contains ribose.

Question 4

Which of the following correctly pairs the DNA base analog with its clinical use?

Accepted Answer

3’-deoxy-3’-azidothymidine (AZT): treatment of HIV

Question 5

Which form of DNA is left-handed and forms under high salt concentrations?

Accepted Answer

Z-form

Question 6

What is the effect of increasing GC content on the melting temperature ($$T_m) of $$DNA?

Accepted Answer

It increases $$T_m.$$

Question 7

Which enzyme is responsible for introducing negative supercoils into DNA ahead of the replication fork?

Accepted Answer

DNA gyrase (Topoisomerase II)

Question 8

A DNA molecule is denatured by heating. Which of the following best explains the increase in absorbance at 260 nm?

Accepted Answer

The bases become more exposed, leading to a hyperchromic shift.

Question 9

Which of the following statements about DNA methylation is correct?

Accepted Answer

Methylation patterns are species-specific and can be inherited.

Question 10

Which of the following best describes the function of restriction endonucleases in bacteria?

Accepted Answer

They cut DNA at specific sequences to protect against foreign DNA.

Question 11

During PCR, what is the purpose of the denaturation step at $$95^\circ C$$?

Accepted Answer

To separate the double-stranded DNA into single strands.

Question 12

Which of the following is a correct statement about the phosphodiester bond in DNA?

Accepted Answer

It links the 5'-carbon of one sugar to the 3'-carbon of the next sugar.

Question 13

A patient is treated with 5-fluorouracil for cancer. What is the mechanism of action of this drug?

Accepted Answer

It is an analog of thymine and irreversibly inhibits thymidylate synthetase.

Question 14

Which of the following best explains why DNA with a high GC content is more stable than DNA with a high AT content?

Accepted Answer

GC pairs form three hydrogen bonds, while AT pairs form two.

Question 15

Which of the following is a function of histone H1 in chromatin structure?

Accepted Answer

It stabilizes the 30 nm chromatin filament by linking nucleosomes.

Question 16

Which of the following is true regarding the reassociation kinetics of DNA?

Accepted Answer

Single-copy DNA sequences reassociate more slowly than highly repetitive sequences.

Question 17

A mutation in the $$eta-$$globin gene causes sickle cell anemia. Which molecular technique is commonly used to detect this mutation?

Accepted Answer

Restriction fragment length polymorphism (RFLP) analysis

Question 18

Which of the following statements about DNA cloning is correct?

Accepted Answer

Cloning allows specific DNA sequences to be separated and amplified in a vector.

Question 19

Which of the following best describes the difference between a nucleoside and a nucleotide?

Accepted Answer

A nucleotide contains a base, a sugar, and a phosphate group.

Question 20

Which of the following is a correct statement about the major and minor grooves of DNA?

Accepted Answer

DNA binding proteins typically recognize base sequences in the major groove.

Structure and Properties of DNA: Biochemistry Study Notes

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