Q: Which of the following is a correct representation of a phosphodiester bond in DNA?

$$\mathrm{3'\text{-}OH\text{-}Sugar\text{-}Phosphate\text{-}5'}$$

Question 1

Which of the following best describes the structure of a nucleotide found in DNA?

Accepted Answer

A phosphate group, a deoxyribose sugar, and a nitrogenous base

Question 2

In a DNA double helix, which type of bond holds the two complementary strands together?

Accepted Answer

Hydrogen bonds

Question 3

Which carbon of the deoxyribose sugar in DNA is attached to the phosphate group of the next nucleotide in the chain?

Accepted Answer

3' (three prime) carbon

Question 4

If a segment of DNA has the sequence 5'-ATCG-3', what is the complementary sequence on the opposite strand (written 3' to 5')?

Accepted Answer

3'-TAGC-5'

Question 5

Which of the following statements about DNA directionality is correct?

Accepted Answer

The two strands of DNA run antiparallel, meaning one runs 5' to 3' and the other 3' to 5'

Question 6

Which of the following base pairs is found in DNA but not in RNA?

Accepted Answer

Adenine–Thymine

Question 7

What is the main difference between the sugars found in DNA and RNA?

Accepted Answer

DNA contains deoxyribose, which lacks an oxygen atom at the 2' carbon compared to ribose in RNA

Question 8

Which of the following best explains why purines always pair with pyrimidines in DNA?

Accepted Answer

Pairing a purine with a pyrimidine maintains a uniform width of the DNA double helix

Question 9

Which type of bond forms the backbone of the DNA molecule, connecting the sugar of one nucleotide to the phosphate of the next?

Accepted Answer

Phosphodiester bond

Question 10

A mutation causes a cytosine (C) in DNA to be replaced by a thymine (T). Which of the following is a likely consequence for base pairing at this site?

Accepted Answer

The new thymine will pair with adenine instead of guanine, potentially altering the genetic code

Question 11

Which of the following correctly matches a pyrimidine with its complementary purine in DNA?

Accepted Answer

Cytosine pairs with guanine

Question 12

During DNA replication, which end of the new strand are nucleotides added to?

Accepted Answer

3' (three prime) end

Question 13

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

Accepted Answer

$$\mathrm{3'	ext{-}OH	ext{-}Sugar	ext{-}Phosphate	ext{-}5'}$$

Question 14

A scientist is analyzing a DNA sample and finds that 30% of the bases are adenine. According to Chargaff's rules, what percentage of the bases should be guanine?

Accepted Answer

20%

Question 15

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

Accepted Answer

The two strands run in opposite directions: one 5' to 3', the other 3' to 5'

Question 16

Which of the following is a pyrimidine found only in RNA and not in DNA?

Accepted Answer

Uracil

Question 17

A DNA molecule is subjected to high heat, causing the two strands to separate. Which bonds are primarily broken during this process?

Accepted Answer

Hydrogen bonds between nitrogenous bases

Question 18

Which of the following best describes the difference in base pairing between DNA and RNA?

Accepted Answer

DNA uses thymine (T) while RNA uses uracil (U) to pair with adenine (A)

Question 19

A mutation disrupts the formation of phosphodiester bonds in a cell. Which of the following processes would be most directly affected?

Accepted Answer

The formation of the DNA backbone during DNA replication

Question 20

Which of the following best explains why the 5' and 3' ends of DNA are important in molecular biology techniques such as PCR?

Accepted Answer

DNA polymerases can only add nucleotides to the 3' end, so primers must be designed accordingly

Structure and Properties of Nucleic Acids (DNA & RNA)

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