DNA

Question 1

Adenosine triphosphate (ATP) is a nucleotide derivative.

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

Answer 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 always adenine and in DNA nucleotide base can be different / varies;

Question 2

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

Answer 2

Weak / easily broken hydrogen bonds between bases allow two strands to separate / unzip;

may appear in the same feature

2. Two strands, so both can act as templates;

may appear in the same feature

3. Complementary base pairing allows accurate replication;

Allow description of complementary base pairing and accurate replication.

Question 3

Name two enzymes involved in the semi-conservative replication of DNA.

Answer 3

(DNA) helicase;

2. (DNA) polymerase;

Question 4

The enzyme-catalysed reactions activated by ATR only occur if the substrates have been phosphorylated.

Use your knowledge of energy changes in enzyme-catalysed reactions to suggest why.

Answer 4

Phosphorylation / phosphate) makes substrates more reactive / raises their energy level(s) / lowers activation energy for the reaction;

Question 5

Describe the role of DNA polymerase in DNA replication.

Answer 5

Joins nucleotides (to form new strand).

Accept: joins sugar and phosphate / forms sugar-phosphate

Question 6

In a further investigation, the DNA of the bacterium was isolated and separated into single strands. The percentage of each nitrogenous base in each strand was found. The table shows some of the results.

Percentage of base present

DNA sample

Adenine

Cytosine

Guanine

Thymine

Strand 1

26

28

14

Strand 2

14

DO QU 14C

Question 7

Explain why the replication of DNA is described as semi-conservative

Answer 7

each strand copied / acts as a template;
(daughter) DNA one new strand and one original / parent strand;

Question 8

Explain how DNA replicates.

Answer 8

hydrogen bonds broken;
semi-conservative replication / both strands used (as templates);
nucleotides line up complementary / specific base pairing / A and T / C and G;
DNA polymerase;

Question 9

The sequence of bases on one strand of DNA is important for protein synthesis. What is its role?

____________

Answer 9

determines (sequence of) amino acids / specific protein
produced / mRNA formation;

Question 10

Give one advantage of DNA molecules having two strands.

Answer 10

stability / protects bases / replication;

Question 11

Describe how, after the parent DNA strands separated, the second strand of DNA in region Y was formed.

Answer 11

Semi-conservative replication;
Complementary pairing;
Hydrogen bonding (of bases/nucleotides);
Condensation/described of nucleotides;
DNA polymerase involved;