IB BIO TOPIC 3.3 : DNA STRUCTURE

Question 1

Outline the 3 structures of a nucleotide

Answer 1

• sugar = deoxyribose
• nitrogenous base
• phosphate group

Question 2

State the 4 nitrogenous bases in DNA

Answer 2

• adenine
• guanine
• thymine
• cytosine

Question 3

Outline how the DNA nucleotides are linked together by covalent bonds into a single strand

Answer 3

• backbone: deoxyribose - phosphate - deoxyribose - phosphate
• nitrogenous base attached to deoxyribose

Question 4

Explain how a DNA double helix is formed using:

complementary base paring:

Answer 4

• A = T: adenine forms two hydrogen bonds with its complementary base, thymine
• G ≡ C: guanine forms three hydrogen bonds with its complementary base, cytosine

Question 5

Explain: how a DNA double helix is formed using hydrogen bonds:

Answer 5

• the combination of hydrogen bonds between A = T and G ≡ C hold the two strands of DNA together
• each strand forms a helix, the two strands together form a double helix