EXP Biology ~ AS genetic info/ variation + relationship 3.4.1 (DNA and genes and chromosomes

The scientists used units of μg g-1 for the concentration of ammonia in soil. Suggest why, in this investigation, the scientists used these units. μg g-1

μg = Very small mass of ammonia g-1 = Allows for comparison

Compare and contrast the DNA in eukaryotic cells with the DNA in prokaryotic cells

1. DNA in Eukaryotic cells are linear, DNA in prokaryotic cells are circular 2.DNA is associated with histone proteins in Eukaryotic cells , DNA not associated with histone proteins in prokaryotic cells 3. The DNA nucleotides in both are the same , and have phosphodiester bonds 4. Eukaryotic DNA contain introns, prokaryotic DNA does not.

DNA is a polymer of nucleotides. Each nucleotide contains an organic base. Explain how the organic bases help to stabilise the structure of DNA

1. Hydrogen bonds between the base pairs holds two strands together 2. Many hydrogen bonds provides strength Reject strong hydrogen bonds.

Haemoglobins are chemically similar molecules found in many different species. Differences in the primary structure of haemoglobin molecules can provide evidence of phylogenetic (evolutionary) relationships between species. Explain how

1. Mutations change base / nucleotide (sequence); Reject if mutation in amino acid 2. (Causing) change in amino acid sequence; 3. Mutations build up over time; 4. More mutations / more differences (in amino acid / base / nucleotide sequence / primary structure) between distantly related species;

Suggest the role of the mRNA base triplets UGA, UAG and UAA. ( stop codons )

1. Stop translation; 2. Result in detachment of polypeptide chain from ribosome

Give two differences between the structure of mRNA and the structure of tRNA.

2. mRNA is a straight molecule but tRNA is a folded molecule / clover-leaf shaped molecule; 3. mRNA contains no paired bases / hydrogen bonds but tRNA has some paired bases / hydrogen bonds.

A change from Glu to Lys at amino acid 300 had no effect on the rate of reaction catalysed by the enzyme. The same change at amino acid 279 significantly reduced the rate of reaction catalysed by the enzyme. Use all the information and your knowledge of protein structure to suggest reasons for the differences between the effects of these two changes.

Change at amino acid 300 does not change the shape of the active site Amino acid 279 may have been involved in a (ionic, disulfide or hydrogen) bond and so the shape of the active site changes OR Amino acid 279 may have been involved in a (ionic, disulfide or hydrogen) bond and so the tertiary structure changed; OR Amino acid 279 may be in the active site and be required for binding the substrate;

Give the two types of molecule from which a ribosome is made.

One of RNA and One of protein

The genetic code is described as degenerate. What is meant by this? Use an example from Table 1 to illustrate your answer.

More than one codon codes for a single amino acid