Question

1.Human cells can produce perhaps as many as 100,000 different proteins, yet the human genome has only about 25,000 genes. How can you explain this? Name 4 responsible mechanisms.

2.True or false (provide explanation)
a)The consequence of transcription errors is less severe than that of an error in replication.

b) The loss of the p53 protein in certain cancers makes them more resistant to irradiation therapies and to several chemotherapies, which would normally kill cancer cells by inducing apoptosis or stopping the cyclecellular cell.

Answer 1

Q1)

Several mechanisms can explain the differences in the number of genes are the number of proteins in a human cell. Examples of possible mechanisms are:

1. Alternate splicing: Alternate splicing is a process by which alternate exons are utilized by the cell for making mRNA. This 'pick and choose' means of variation leads to several proteins from the same gene.
2. Posttranslational Cleavage: Some proteins are modified by cleavage to achieve their active form. This modification can also to the variability of protein products.
3. Somatic recombination of genes: Several proteins, especially those involved in the immune system, are the result of genetic recombination in somatic cells. This recombination produces novel proteins from pre-existing genes.
4. RNA editing: RNA editing is a tool that allows organisms to alter the mRNA sequence depending on growth conditions. These small alterations often have a significant impact on cellular response to changing conditions.

Q2)

a) True

Since transcription produces mRNA that is used to produce a few protein molecules while transcription produces mRNA, which inturn is responsible for all the proteins from that locus, a mutation during replication is more severe since all the proteins of that gene would be affected. With a mutation in Transcription, only those protein molecules resulting from that particular mRNA would be mutated.

b) True

p53 protein plays an important part in RNA surveillance of the cell. Cancer cells that have a mutation in p53 would not respond to radiation therapy as much since they have a defetive DNA repair pathway, and since p53 is mutated, these cells would not attempt to repair their DNA.