Topic 1: Nucleic acids

Question 1

Draw and label the general structure of a nucleotide

Question 2

What are the two differences between the DNA and RNA nucleotides?

Answer 2

1. DNA contains the pentose sugar deoxyribose whereas RNA contains the pentose sugar ribose
2. DNA has the base thymine, whereas RNA has uracil

Question 3

Name the reaction that joins the nucleotides together to form both the DNA and RNA polymers

Answer 3

Reaction- condensation
Name the bond that forms- phosphodiester

Question 4

Between which molecules in the nucleotide does the bond form?

Answer 4

The phosphate group and the pentose sugar

Question 5

Describe basic structure of DNA molecule

Answer 5

A DNA molecule is a double helix with two polynucleotide chains held together by hydrogen bonds between specific complementary base pairs. The two chains align antiparallel to each other.

Question 6

Name the three RNA polymers and describe the function

Answer 6

1 Name: mRNA
Function:
RNA transfers genetic information from the DNA in the nucleus to the ribosomes in the cytoplasm.

2 Name: tRNA
Function:
Carries specific amino acids to the mRNA on the ribosome.

3 Name: rRNA
Function:
Combines with proteins to form a ribosome.

Question 7

Which polymer is shorter? (RNA or DNA)

Answer 7

RNA

Question 8

Before cells divide (by mitosis or meiosis), all the DNA must replicate to provide a copy for the new cell. DNA replication is described as being semi-conservative.
What does this mean? (2 marks)

Answer 8

When DNA replicates, one strand of the original DNA is conserved and one strand is newly synthesised.

Question 8

Why did scientists doubt that DNA carried the genetic code?

Answer 8

Due to the relative simplicity of the DNA molecule

Question 9

Describe the process of DNA replication ( 5 marks)

Answer 9

1. The double helix unwinds
2. Hydrogen bonds between the complementary bases of the two strands break so the strands separate and act as templates
3. DNA helicase is responsible for the unwinding of the double helix and breaking of hydrogen bonds
4. DNA nucleotides within the nucleus are attracted to the complementary exposed bases on the template strands.
5. DNA polymerase catalyses the condensation reactions to join adjacent nucleotides together and form phosphodiester bonds.