Nucleic acids

What is the function of DNA?

Storing genetic information.

What is the function of RNA?

Transferring genetic information from DNA to ribosomes.

Which two substances make up ribosomes?

• Ribosomal RNA (rRNA).

• Protein.

What do you call a polymer of nucleotides?

A polynucleotide.

Why are the phosphodiester bonds between adjacent nucleotides in DNA important?

Phosphodiester bonds are strong covalent bonds that ensure that the genetic code is not broken down.

How many hydrogen bonds do adenine and thymine form together?

Two.

How many hydrogen bonds to cytosine and guanine form together?

Three.

Why is complementary base pairing important?

It helps maintain the sequence of the genetic code when DNA replicates and when mRNA is being created (identical copies of DNA can be made).

Why is DNA stable?

Due to the strong phosphodiester bonds and the double helix structure.

Why are the two DNA strands in a DNA molecule easily broken?

They are held together by weak hydrogen bonds with complementary base pairs that are easily broken to form two template strands.

Why is DNA a large molecule?

Because it carries lots of information.

True or false? DNA replication is semi-conservative.

True.

What does semi-conservative mean in terms of DNA replication?

The daughter DNA contains one strand from the original DNA molecule and one newly synthesised strand.

Name the two enzymes involved in DNA replication.

• DNA helicase.

• DNA polymerase.

Talk me through the process of DNA replication.

1) DNA helicase breaks the hydrogen bonds between complementary base pairs in the parental DNA, forming two template strands of DNA.

2) Complementary base pairing takes place with free nucleotides and the template strand of DNA.

3) DNA polymerase joins adjacent nucleotides with phosphodiester bonds in multiple condensation reactions, forming the daughter DNA.

True or false? Hydrogen bonding exists between water molecules.

True.

Give and explain the five key properties of water.

• Metabolite in many metabolic reactions, like in hydrolysis and condensation reactions.

• Solvent in which some metabolic reactions occur.

• Buffers temperature changes due to it’s high heat capacity.

• Cooling effect when it evaporates and is lost due to it’s large latent heat of vaporisation.

• Cohesion between water molecules due to hydrogen bonding, supports water columns and provides surface tension when water meets air.

Talk me through how an experiment proved that DNA is replicated semi-conservatively.

1) Two bacterial cultures are grown separately, each in one isotope of nitrogen (one heavier (15) and one lighter (14)).

2) The bacteria take up the nitrogen when they grow to make nucleotides for DNA replication.

3) DNA of each bacterial culture was spun in a centrifuge to separate the heavier and lighter DNA.