3.1.5 - DNA and RNA

Question 1

describe the structure of DNA (5)

Answer 1

1. polymer of nucleotides (polynucleotide)
2. each nucleotide formed from deoxyribose, a phosphate group and a nitrogenous base
3. phosphodiester bonds between the nucleotides
4. double helix (two strands held together by hydrogen bonds)
5. hydrogen bonds/pairing between adenine, thymine and cytosine, guanine

Question 2

describe how a phosphodiester bond is formed between two nucleotides within a DNA molecule (2)

Answer 2

1. condensation reaction/loss of water
2. between phosphate and deoxyribose
3. catalysed by DNA polymerase

Question 3

name the protein associated with DNA in a chromosome (1)

Answer 3

histone

Question 4

in the process of semi-conservative DNA replication, the two strands within a DNA molecule are separated.

describe how the separation of strands occurs (2)

Answer 4

1. DNA helicase
2. breaks hydrogen bonds between complementary base pairs

Question 5

describe the role of DNA polymerase in the semi-conservative replication of DNA (2)

Answer 5

1. joins adjacent DNA nucleotides
2. DNA polymerase catalyses condensation reaction
3. catalyses formation of phosphodiester bonds between adjacent nucleotides

Question 6

name the two scientists who proposed models of the chemical structure of DNA and of DNA replication (1)

Answer 6

Watson and Crick

Question 7

give two features of DNA and explain how each one is important in the semi-conservative replication of DNA (2)

Answer 7

1. weak hydrogen bonds between bases allow two strands to easily separate
2. two strands, so both can act as templates
3. complementary base pairing allows accurate replication

Question 8

describe the role of two named enzymes in the process of semi-conservative replication of DNA (3)

Answer 8

1. DNA helicase catalyses breaking of hydrogen bonds between DNA strands, unwinding the helix
2. DNA polymerase joins the DNA nucleotides
3. forming phosphodiester bonds (forms sugar-phosphate backbone)

Question 9

ATP is a nucleotide derivative.

contrast the structures of ATP and a nucleotide found in DNA to give two differences (2)

Answer 9

1. ATP has ribose and DNA nucleotide has deoxyribose
2. ATP has 3 phosphate groups and DNA nucleotide has 1 phosphate group
3. ATP base is always adenine and in DNA the nitrogenous base can vary