Question

This is a Microbiology essay question. Please provide detailed answers.

Viral genomes have a higher rate of mutation than most living organisms.
a. Describe two ways that any genome (not necessarily a virus) might gain mutations.
b. How might viruses cause mutations in their hosts?
c. Why might a virus particle end up with a huge number of mutations or an entirely different piece of genetic information?

Answer 1

a. Although the haploid human genome consists of 3 billion nucleotides, changes in even a single base pair can result in dramatic physiological malfunctions. These changes can be caused by environmental factors such as ultraviolet radiation from the sun, or can occur if an error is made as DNA copies itself during cell division.

A mutation occurs at a single base on a polynucleotide DNA chain is called point mutation.  In this case, fragments of chromosomes can be deleted, duplicated, inverted, translocated to different chromosomes, or otherwise rearranged, resulting in changes such as modification of gene dosage, the complete absence of genes, or the alteration of the gene sequence. the types are -

Substitution -One base is incorrectly added during replication and replaces the pair in the corresponding position on the complementary strand

Insertion -One or more extra nucleotides are inserted into replicating DNA, often resulting in a frameshift

Deletion -One or more nucleotides is "skipped" during replication or otherwise excised, often resulting in a frameshift

Mutations can result from a number of events, including unequal crossing-over during meiosis. In addition, some areas of the genome simply seem to be more prone to mutation than others. These "hot spots" are often a result of the DNA sequence itself being more accessible to mutagens. Hot spots include areas of the genome with highly repetitive sequences, such as trinucleotide repeats, in which a sequence of three nucleotides is repeated many times. During DNA replication, these repeat regions are often altered because the polymerase can "slip" as it disassociates and reassociates with the DNA strand.

b. Both DNA and RNA viruses have been shown to reprogram various aspects of host central carbon metabolism, including increased glycolysis, elevated pentose phosphate activity to support generation of nucleotides, amino acid generation, and lipid synthesis . While several viruses upregulate consumption of key nutrients like glucose and glutamine and converge on similar metabolic pathways for anabolism, the precise metabolic changes induced by specific viruses are often context-dependent and can vary even within the same family of viruses or depend on the host cell type that is infected.

The replication mechanism depends on the viral genome. DNA viruses usually use host cell proteins and enzymes to make additional DNA that is transcribed to messenger RNA (mRNA), which is then used to direct protein synthesis. RNA viruses usually use the RNA core as a template for the synthesis of viral genomic RNA and mRNA. The viral mRNA directs the host cell to synthesize viral enzymes and capsid proteins, and assemble new virions.

To convert RNA into DNA, retroviruses must contain genes that encode the virus-specific enzyme reverse transcriptase that transcribes an RNA template to DNA. Reverse transcription never occurs in uninfected host cells—the needed enzyme reverse transcriptase is only derived from the expression of viral genes within the infected host cells.

c.  

• Viruses undergo evolution and natural selection, just like cell-based life, and most of them evolve rapidly.Some viruses have very high mutation rates, but this is not universally the case. In general, RNA viruses tend to have high mutation rates, while DNA viruses tend to have low mutation rates.

• Viral mutation rates are determined by multiple processes, including polymerase intrinsic fidelity, replication mode, 3′ exonuclease activity, spontaneous nucleic acid damage, etc

• mutation rates are not static and can evolve in response to selective pressures, as exemplified by fidelity variants selected under mutagenic conditions in a variety of viruses. In addition to polymerase fidelity, other mutation rate-determinants such as access to DNA repair may have also changed in response to selective pressures during viral evolution.

• genetic diversity depends on multiple factors, the mutation rate is of particular interest because it constitutes the ultimate source of genetic variation. Similarly, mutation rates should not be confused with molecular evolutionary rates. The neutral theory of molecular evolution posits a linear relationship between these two rates, but whereas mutation is a biochemical/genetic process, molecular evolution refers to the fixation of new alleles in populations.