nucleic acids

Question 1

describe the structure of DNA (5)

Answer 1

1. polymer of nucleotides
2. each nucleotide contains deoxyribose, phosphate, nitrogenous base
3. phosphodiester bonds between nucleotides
4. double helix- 2 strands held together by hydrogen bonds
5. hydrogen bonds between complementary base pairs, A-T and C-G

Question 2

describe how a phosphodiester bond forms between two nucleotides in DNA (2)

Answer 2

1. condensation reaction between phosphate and deoxyribose
2. by DNA polymerase

Question 3

describe the role of DNA polymerase in the semi-conservative replication of DNA (3)

Answer 3

1. joins adjacent DNA nucleotides
2. forms phosphodiester bonds between them
3. condensation reaction

Question 4

name the 2 scientists who made models of structure of DNA and DNA replication (1)

Answer 4

Watson and Crick

Question 5

what is the role of these in semi-conservative replication
- single-stranded DNA fragments
- DNA nucleotides

Answer 5

role of fragments:
1. act as templates
2. determine order of nucleotides
role of nucleotides:
3. forms complementary base pairs to form complementary DNA strand

Question 6

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

Answer 6

1. double stranded- both act as templates
2. weak hydrogen bonds between bases allow the two strands to separate

Question 7

describe the role of 2 named enzymes in semi-conservative replication (3)

Answer 7

1. DNA helicase breaks hydrogen bonds between DNA strands
2. DNA polymerase joins DNA nucleotides
3. forming phosphodiester bonds

Question 8

contrast the structures of ATP and a DNA nucleotide (3)

Answer 8

1. ATP has ribose, DNA has deoxyribose
2. ATP has 3 phosphate groups, DNA has 1 phosphate group
3. ATP base is always adenine, DNA bases can be different

Question 9

why does DNA polymerase run in opposite directions on different strands? (4)

Answer 9

1. DNA strands are antiparallel
2. nucleotides aligned differently
3. enzymes have active sites with specific shapes
4. only substrate with complementary shape can bind to active site

Question 10

nucleotides can only be added in 5’ to 3’ direction, explain why. (4)

Answer 10

1. DNA polymerase joins adjacent nucleotides
2. DNA polymerase is specific
3. is only complementary with 5’ end of strand
4. shapes of 5’ and 3’ ends are different

Question 11

contrast the structures of DNA and RNA (4)

Answer 11

1. DNA uses deoxyribose, RNA uses ribose
2. DNA uses thymine, RNA uses uracil
3. DNA is long, RNA is short
4. DNA is double stranded, RNA is single stranded