Module 2

Question 1

Compare and contrast the structure of ATP, RNA and DNA nucleotides (6)

Answer 1

All three are forms of nucleotide
They all consist of a pentose sugar, phosphate group and nitrogen base
The pentose sugar is attached to the phosphate by phosphodiester bonds
The pentose sugar is attached to the nitrogen base by glyosidic bond
ATP has 3 phosphate groups whereas DNA and RNA have 1
ATP can only have the base adenine, whereas DNA can have A/T/C/G and RNA can have A/U/C/G
ATP and RNA have ribose sugar whereas DNA has deoxyribose

Question 2

Name the enzymes involved in DNA replication and their role (4)

Answer 2

2. DNA helicase – breaks the hydrogen bond between bases in DNA, DNA polymerase – synthesises the new DNA molecule by forming phosphodiester bonds between nucleotides

Question 3

Explain what is meant by semi conservative DNA replication (3)

Answer 3

3. During DNA replication, the strands of DNA are separated, and free/new nucleotides base pair with the exposed bases on both strands, making two new double stranded molecules. In each one, one strand is from the original strand and one is the newly synthesised strand.

Question 4

Explain why it is necessary for transcription to occur

Answer 4

As thecode/instructions for makingproteinsis within the DNA, however the DNA is too large to leave the nucleus. Transcription is needed so that the small, single strandof RNAcan be made which can leave the nucleus through the nuclearpore

Question 5

Write out the stages of transcription
(including name and function of enzymes)

Answer 5

DNA helicase attaches to DNA andhydrogen bonds betweenbases are broken. FreeRNA nucleotidespair with the exposed, complimentary DNA nucleotides of the antisense strand. Phosphodiesterbonds formbetween the RNA nucleotides due to RNA polymerase

Question 6

What is meant by the following:
Template strand
Coding strand
Sense strand
Antisense strand

Answer 6

Template strand -the strand whichRNA is madealong
Coding strand – the strand which has the same sequence of bases as the mRNA made
Sense strand – the same as the coding strand
Antisense strand – the same as thetemplate strand

Question 7

What is meant by the following:
Triplet code
Codon
Anticodon

Answer 7

Triplet code – sequence of 3 bases on DNA
Codon – sequence of 3 bases on mRNA
Anticodon – sequence of 3 bases on tRNA