Essay Questions - Past Exams

Question 1

Why do rearrangements and changes in chromosome number sometimes affect gene activity or gene transmission?

Answer 1

It will effect the whole gene activity by changing the gene expression, because a gene is complex and composed of many codons of amino acids. Each codon has a specific function.
There may be 2 types of rearrangements:
balanced and unbalanced.
Balanced: no addition or subtraction of genetic materials - translocations and inversions
Unbalanced: genetic material is added or subtracted from the whole gene - deletions, duplications, and inheritance of unbalanced translocation products

Question 2

Explain the possible effects that a transposable elements may have on a gene

Answer 2

Insertion of a transposable element near or within a gene can affect expression and alter phenotype
The effect of insertion depends on what the element is and where the insertion point is
If it is into a protein coding exon the reading frame may shift or a stop codon may be introduced.
Insertion into an intron may lower the efficiency of splicing, which can result in removal from the transcript and lower production of a normal polypeptide.
A stop signal could also affect genes down stream.
Upstream insertions into a regulatory gene could affect gene function in various ways as well.

Question 3

If DNA replication were conservative or dispersive (instead of semeconservative), what would be the results of the Meselson-Stahl experiment?

Answer 3

If DNA were replicated in a dispersive manner replication would have resulted in exclusively a single band in the new generation, with the height slowly moving up closer to the height of the 14N DNA
If DNA were replicated in a conservative manner replication would produce 2 new DNA helices. Where one has old DNA and the other has new DNBA

Question 4

Describe the process of splicing in eukaryotic RNA molecules

Answer 4

The process of splicing takes place by a mechanism called, sequence-specific splicing, whereby the introns are removed from the sequence and the exons are joined or ligated accurately with the precision of a single nucleotide. The mechanism is as follows:

1. The Spliceosomes are a combination of proteins and RNA that cleave pre-mRNA that is still in the nucleus. Five snRNPs subunits make up spliceosomes. Each snRNPs are made of a complex of protein and a unique RNA that is only found in the nucleus called the snRNA or small nuclear RNA.
2. Spliceosomes detect sequences at the 5’ and 3’ ends of introns as introns usually begin with the nucleotides GU and terminate with the nucleotides AG.
3. At guanine, from where the intron begins, the spliceosomes break the backbone of the pre-mRNA and the guanine is covalently linked to an intrinsic adenine nucleotide into the intron
   4.The spliceosome then joins the 3’ end of the first exon to the 5’ end of the next exon, splitting the intron at the same time.
   5.As a result, the two exons are joined to each other, and the removal of an intron is facilitated by splicing.

Question 5

How is DNA altered by hydrolysis, radiation, UV light and oxidation respectively

Answer 5

DNA hydrolysis of A or G bases results in depurination and the DNA strand has a continuous sugar backbone but an unspecified base where the depurination occurred.
X-irradiation breaks the sugar backbone while UV light induces thymidine dimerization.
Oxygen free radicals oxidize bases into analogs that do not hydrogen bond properly in the DNA double strand. During replication, mismatch pairing ends up creating a base change resulting in mutation.

Question 6

If a thymine dimer is formed in the DNA as a result of UV radiation, what is the repair mechanism involved? (Outline the 3 key enzymes involved in the repair)

Question 7

Briefly describe the role of an initiator protein in DNA replication

Answer 7

An initiator protein plays a crucial role in DNA replication by recognizing and binding to specific DNA sequences called origins of replication. Once bound, the initiator protein recruits other proteins to form a complex that helps to unwind and separate the DNA strands at the origin site, creating a replication bubble.

The initiator protein then facilitates the assembly of the replication machinery, including DNA polymerase and other enzymes, at the replication bubble. These enzymes work together to synthesize new DNA strands by adding nucleotides in a complementary fashion to the separated DNA strands.

Overall, the role of the initiator protein is to initiate the process of DNA replication by recognizing and binding to the origin of replication, and by recruiting other proteins and enzymes to facilitate the unwinding, separation, and synthesis of new DNA strands.