Nucleotides and DNA

Question 1

What are nucleotides

Answer 1

Monomers of nucleic acids

Question 2

What makes up a nucleotide

Answer 2

Contains a:
- Nitrogenous base
- Phosphate group
- Pentose sugar

Question 3

What bond forms between nucleotides

Answer 3

A phosphodiester bond

Question 4

What are the 5 nitrogenous bases

Answer 4

Adenine
guanine
Thymine
Cytosine
Uracil

Question 5

What is the difference between a purine and a pyrimidine

Answer 5

Purines have a double ring structure whilst pyrimidines have a single ringed structure

Question 6

Which bases are purines

Answer 6

Adenine
Guanine

Question 7

Which bases are pyrimidines

Answer 7

Thymine
Cytosine
Uracil

Question 8

How many hydrogen bonds do A and T make

Answer 8

Two hydrogen bonds

Question 9

How many hydrogen bonds do C and G make

Answer 9

Three hydrogen bonds

Question 10

What does anti-parallel mean

Answer 10

The 2nd strand must be upside down in order for base pairs to join

Question 11

Explain how DNA is replicated

Answer 11

1) The double helix is untwisted by the enzyme gyrase
2) the hydrogen bonds are broken down by helicase
3) Each strand acts as a template
4) Free DNA nucleotides in the nucleus start to align with exposed nucleotides
5) Complementary base pairing occurs
6) Hydrogen bonds reform
7) Phosphodiester bonds are formed between the phosphate of one nucleotide and the sugar of another using the DNA polymerase
8) This creates two identical strands with half the original DNA

Question 12

Describe three differences between RNA and DNA

Answer 12

RNA’s sugar molecule is ribose whereas DNA has deoxyribose

RNA has uracil instead of thymine

RNA nucleotide is single stranded where as DNA is double stranded

Question 13

What is messenger RNA

Answer 13

A copy of the template strand of DNA

Has codons

Involved in transcription and translation

Question 14

What is Ribosomal RNA

Answer 14

Complex molecule and accounts for half the mass of a ribosome

Question 15

What is transfer RNA

Answer 15

Small, single stranded
Clover leaf shape
Has binding site for specific amino acids
Has an anticodon

Question 16

Describe transcription

Answer 16

1) Gene to be transcribed unwinds and helicase breaks the hydrogen bonds
2) RNA nucleotides bind to complementary bases on the template strand
3) RNA polymerase catalyses formation of phosphodiester bond between RNA nucleotides
4) mRNA is complementary to the template strand and a copy of the coding strand
5) mRNA released from DNA , leaves nucleus, through nuclear pore to ribosome

Question 17

Describe Translation

Answer 17

6) mRNA binds to a ribosome
7) tRNA attaches and its anticodon binds to the first codon
8) Second tRNA binds to the exposed codon via its anticodon
9) Peptide bonds form between the 2 amino acids
10) Ribosomes moves along the mRNA
11) A 3rd tRNA brings another amino acid
12) 1st tRNA leaves and is able to collect another amino acid
13)The polypeptide chain grows until a stop codon is reached
14) There are no corresponding tRNA’s so translation stops

Question 18

What does universal mean

Answer 18

All living organisms use the same code

Question 19

What does degenerate mean

Answer 19

for most amino acids there is more than one
base triplet

Question 20

What does non-overlapping mean

Answer 20

it is read starting from a fixed point in
groups of three