Mutations, Viruses, Bacteria [The Central Dogma of Biology]

• Mutations

  Although the molecular process of gene expression is rigorous, complex, and highly regulated, it is not infallible. Any change to the genetic information of a cell is called a mutation and there are several types of mutations
• A nucleotide substitution occurs when one nucleotide in mRNA gets replaced. This result in three scenarios:

  1. When the substituted nucleotide still encodes for the same amino acid, this will have no effect at all leading to a silent mutation.
  2. The substituted nucleotide causes a change in the amino acid sequence. This is a missense mutation.
  3. When the substitution causes the codon to be one of the stop codons, it is called nonsense mutation which results in a prematurely terminated protein that may not function properly.
• the + or - of nucleotides may alter the resulting sequence of proteins. This is called a frameshift mutation and occurs whenever the mRNA gets inserted or deleted by a nucleotide that is not a multiple of three, resulting in the nucleotide sequences regrouping into different codons.

  “The cat ate the rat” --> “The ata tet her at.” Frameshift mutations will most likely produce nonfunctional polypeptides and have disastrous effects. Mutations are from errors during DNA replication or recombination; or due to effects of physical or chemical agents called mutagens.

  
• The Genetics of Viruses and Bacteria

  Bacteria and viruses served as models in uncovering the molecular mechanisms behind heredity. The latter is still debated by biologists whether it should be considered a living organism or not. In a sense, viruses are infectious particles consisting of nucleic acids wrapped in a protein coat called a capsid and in some, a membranous envelope. Unlike other organisms, viral genomes can be DNA or RNA and usually consist of a single molecule of nucleic acid, which may be linear or circular
• The Genetics of Viruses and Bacteria

  Viruses are parasites that reproduce once they are inside cells. Viruses take two routes to make use of host cells: the lytic cycle and the lysogenic cycle. Both cycles begin when the phage enters the bacterium and forms a loop.
• The Genetics of Viruses and Bacteria

  In the lytic cycle, the virus turns the cell into a virus-producing factory and the cell soon lyses (or bursts) as it releases the viral products which proceed to infect other cells. In the lysogenic cycle, after the viral DNA gets inserted into the bacterial chromosome (referred to as a prophage), every time the bacterial cell divides, it replicates the viral DNA and passes copies of it onto daughter cells.
• The Genetics of Viruses and Bacteria

  the lysogenic cycle allows the virus to spread without killing the host cells they depend on. The virus which causes the Covid-19 disease is a lytic virus targeting the alveoli in the lungs hence the symptoms associated with the respiratory system
• The Genetics of Viruses and Bacteria

  Bacteria are also valuable in genetics research, being representatives for prokaryotes. Most of a bacterium’s DNA is found in a single chromosome, a closed loop of DNA with associated proteins. Bacterial cells reproduce by replication of the bacterial chromosome followed by binary fission
• The Genetics of Viruses and Bacteria

  Bacteria produce new combinations of genes:

  • In transformation, the bacteria take foreign DNA directly from the surrounding environment.
  • Using bacteriophages in a process called transduction
• The Genetics of Viruses and Bacteria

  Bacteria produce new combinations of genes:

  • Swapping genes between bacterial cells, whether they are the same or of different species, through the physical process called conjugation. The donor cell has hollow appendages called sex pili which attaches to the recipient cell and pulls the 2 cells together, like a grappling hook. The donor cell replicates its DNA so the recipient cell doesn’t end up lacking any genes. The ability of a donor cell to carry out conjugation is based on a specific piece of DNA called the F factor (F for fertility).