nucleotides

Question 1

define nucleotide

Answer 1

monomer which makes up nucleic acids

Question 2

describe the structure of a nucleotide

Answer 2

• a pentose sugar (deoxyribose in DNA) - pentagon
• a phosphate group – circle
• nitrogenous organic base – rectangle

Question 3

how do nucleotides join to form nucleic acids?

Answer 3

• condensation reactions
• to form phosphodiester bonds
• phosphate at 5’ joins hydroxyl at 3’
• forms strong sugar phosphate backbone

Question 4

what are the properties of the phosphodiester bond?

Answer 4

• strong
• covalent bond

Question 5

what is a purine?

Answer 5

• double carbon ringed structures
• adenine
• guanine

Question 6

what is a pyrimidine?

Answer 6

• single carbon ringed structure
• thymine
• cytosine

Question 7

what are the base pairing rules?

Answer 7

• A and T bind with two hydrogen bonds
• C and G bind with three hydrogen bonds
• a purine and a pyrimidine must bind together

Question 8

why must a purine and a pyrimidine bind together?

Answer 8

so the arrangement maintains constant distance between the DNA backbone

Question 9

what is the sugar phosphate backbone?

Answer 9

part of the nucleotide which the base attaches to

Question 10

describe the structure of a DNA nucleotide (3 marks)

Answer 10

a DNA nucleotide consists of a phosphate base, deoxyribose sugar and nitrogenous base

Question 11

describe how the two nucleotide chains in DNA are bonded together (4 marks)

Answer 11

the chains are bonded by hydrogen bonds between complementary base pairs. the pairs are adenine and thymine, cytosine and guanine. a purine always binds to a pyrimidine.

Question 12

state three ways in which the structure of DNA differs from RNA (3 marks)

Answer 12

• DNA is double stranded
• DNA has deoxyribose, RNA has ribose
• DNA is A+T but RNA is A+U