nucleic acids

Question 1

describe the structure of DNA (5)

Answer 1

•polymer of nucleotides
•each nucleotide formed from deoxyribose, phosphate, nitrogenous base
•phosphodiester bonds between nucleotides
•double helix strand held by H bonds
•between A,T,C,G

Question 2

describe how a phosphodiester bond is formed between two nucleotides within a DNA molecule (3)

Answer 2

•condensation
•between phosphate and deoxyribose
•catalysed by DNA polymerase

Question 3

describe how the separation of strands occurs (2)

Answer 3

•DNA helicase
•breaks hydrogen bonds between pairs

Question 4

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

Answer 4

•joins nucleotides
•catalyses condensation reactions
•catalyses formation of phosphodiester bonds

Question 5

the role of the single stranded DNA fragments (2)

Answer 5

•template
•determines the order of nucleotides

Question 6

the role of the DNA nucleotides (2)

Answer 6

•forms complementary pairs
•forms complementary strands

Question 7

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

Answer 7

•weak hydrogen bonds between bases allow two strands to separate
•two strands so both can act as a template

Question 8

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

Answer 8

•DNA helicase- causes breaking of H bonds
•DNA polymerase- joins nucleotides forming phosphodiester bonds

Question 9

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

Answer 9

•ATP has ribose and DNA nucleotides has deoxyribose
•ATP has 3phosphate groups whereas DNA has 1 group

Question 10

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

Answer 10

•DNA polymerase
•which is specific
•only complementary with 5’ ends
•shapes of 5’ and 3’ are different