1. One way in which eukaryotic DNA differs from prokaryotic DNA is that it is associated with proteins. Explain what this means.
Answer
In eukaryotes, DNA is wrapped around histone proteins, forming a complex that helps organize and package the DNA.
2. List the two functions of a gene.
Answer
To code for the amino acid sequence of a polypeptide and to code for functional RNA.
3. The genetic code is described as being universal, non-overlapping and degenerate. Explain what these three terms mean.
Answer
Universal = the same triplet code codes for the same amino acid in all living organisms.
Non-overlapping = each base in a sequence is only "read" once and contributes to only one triplet code.
Degenerate = there is more than one triplet code for some amino acids.
4. Much of the DNA in a eukaryote is non-coding. Some of this DNA is in the form of introns. What is an intron ?
Answer
Introns are non-coding sections within a gene that are removed from pre-mRNA before protein synthesis.
5. What name is given to the position of a particular gene on a chromosome ?
Answer
A locus.
6. Complete the table below.
Answer
7. Name one other organelle that has its own DNA.
Answer
Chloroplasts.
8. Describe two ways in which an ATP molecule differs from a nucleotide in a DNA molecule.
Answer
ATP has three phosphates and DNA nucleotide only has one. ATP only has adenine as a base but DNA nucleotide can have either adenine, thymine, cytosine and guanine
9. Scientists were investigating a gene that consisted of 3.9 × 105 base pairs. Calculate the maximum number of amino acids that this gene codes for.
Answer
390000 ÷ 3 = 130000
10. The actual number of amino acids is much lower than the value calculated above. Give two possible reasons why.
Answer
Non-coding sections (introns) have been removed. A stop codon does not code for an amino acid.
11. The number of amino acids that make up the polypeptide chain that a gene codes for can never be more than the maximum number of amino acids that this gene codes for. Explain why.
Answer
The genetic code is non-overlapping. Every base only contributes to one triplet within the code.