1. The human papillomavirus (HPV) is commonly known as a cancer-causing virus. A
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Question
1. The human papillomavirus (HPV) is commonly known as a cancer-causing virus. A dormant form of the virus can survive in the body by integrating into host cell DNA. The location in the genome where the virus integrates often alters the expression of certain genes, which may lead to cancer.
(i) Form one hypothesis in which HPV genome integration results in increased expression of a gene; and
(ii) form a second hypothesis in which HPV genome integration results in decreased expression of a gene.
2. The genetic code is considered universal in that across all forms of like, all 64 codons either code for a specific amino acid or a stop. If this is true, how can amino acids, like selenocysteine and pyrrolysine, be added to the genetic code?
Explanation / Answer
Please find the answers below:
Answer 1: The human papilloma virus can add the viral genome to the host DNA even in a dormant stage. When the host DNA undergoes replication, the viral genome also gets activated and thus promotes disease progression. In this regard, the following can take place:
1. Increase in gene expression: The human papilloma virus might get integrated in the human genome at a region inside the promoter or close to it. When the conditions are favorable and the human genome undergoes replication, it will also upregulate the replication of the viral genome and thus increase the overall rate of gene expression of human as well as the viral genome.
2. Decrease in gene expression: The human papilloma virus genome might get integrated in the heterochromatin region of the human genome and hence it will not undergo gene expression. Further, integration of viral genome downstream the cistron itself or exactly inside the promoter region will prevent gene expression due to faulty gene expression termination and initiation respectively.
Answer 2: The genetic code is universal across all the living forms of life. However, certain deviations from the genetic code do exist. For example, cystein is normally genetic codes UGU or UGC. In some cases, a variant of cystein might occur as selenocystein in living organisms. Genetically it has been shown that this proteinaceous amino acid selenocystein arises from codon UGA unlike cystein. This occurs due to presence of a specific selenium insertion sequence in the mRNA of the UGA encoding RNA in the genome. Some organisms genetically carry this sequence and thus can synthesize a different amino acid than usual.
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