nucleotides basics

Question 1

define ‘nucleotide’

Answer 1

monomer which makes up nucleic acids

Question 2

describe the structure of a nucleotide

Answer 2

phosphate (circle)
pentose sugar (pentagon)
nitrogenous base (rectangle)

Question 3

how do nucleotides join to form nucleic acids?

Answer 3

• hydroxyl on 3’ of one nucleotide pentose
• joins 5’ of another nucleotide pentose
• condensation reaction
• forms a phosphodiester bond
• strong sugar phosphate backbone

Question 4

what are the properties of the phosphodiester bond?

Answer 4

• strong
• covalent

Question 5

what is a purine?

Answer 5

• A or G base
• 2 carbon rings

Question 6

what is a pyrimidine?

Answer 6

• T or C or U base
• 1 carbon ring

Question 7

describe complementary base pairing

Answer 7

• purine must bind with pyrimidine
• so strands are equal length
• DNA has a regular structure

Question 8

what is the sugar phosphate backbone?

Answer 8

part of the nucleotide which the base attaches to

Question 9

describe the structure of a DNA nucleotide (3 marks)

Answer 9

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

Question 10

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

Answer 10

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 11

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

Answer 11

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