Nucleic Acids

Question 1

DNA

Answer 1

Deoxyribonucleic acid, holds genetic information

Question 2

RNA

Answer 2

Ribonucleic acid, transfers genetic information from DNA to ribosomes

Question 3

Nucleotide structure

Answer 3

1 phosphate, 1 pentose sugar and 1 nitrogenous base

Question 4

4 bases

Answer 4

Adenine=Thymine/Uracil

Guanine =-Cytosine

Question 5

What bond is used between 2 nucleotides?

Answer 5

Phosphodiester bond produced by a condensation reaction

Question 6

Polynucleotides in DNA/RNA

Answer 6

Condensation of many nucleotides
DNA - two polynucleotide chains in a double helix
RNA - one short polynucleotide chain in a single helix

Question 7

Semi-conservative DNA replication principle

Answer 7

• 1 DNA strand comes from the original DNA, the other from a newly synthesised strand
• Ensure genetic continuity between generations of cells

Question 8

Semi-conservative DNA replication process

Answer 8

1. DNA helicase unzip the double helix by breaking the hydrogen bonds between complementary bases in the polynucleotide strand
2. New DNA nucleotides are attracted to their complementary ashes on template strands and base pairing occurs
3. DNA polymerase joins adjacent nucleotides from 5’ to 3’ to form phosphodiester bonds

Question 9

Meselson - Stahl experiment idea

Answer 9

To give evidence for semi-conservative replication by using nitrogen isotopes

Question 10

Meselson - Stahl experiment process

Answer 10

• two nitrogen isotopes (14N and 15N) added to separate test tubes containing e.coli and let them replicate for a generation
• then a sample was taken of each a they replicated together for a generation
• they then took all 3 test tubes and spun them in a centrifuge

Question 11

Meselson - Stahl experiment results

Answer 11

14N (light isotope) -> band near the top
15N (heavy isotope) -> band near the bottom
14N + 15N -> band near the middle
- could only happen due to semi-conservative replication