Molecular microbiology

• Molecular Biology


  The study of the structure and functions of macromolecules in the cell
• Macromolecules


  • Protein
  • Nucleic acids
  • Carbohydrates
  • Lipids
• Genetics


  The study of how traits are passed from one organism to another
• Molecular biology and genetics help us to understand the molecular mechanisms (at the level of the molecule) of cell function
• Many recent advances in agriculture, medicine and industry are dependent on molecular biology and genetics
• Gene


  The functional unit of genetic information, a segment of DNA specifying a protein, rRNA or tRNA
• Protein


  The cell's functional molecules, the work horses
• Flow of Genetic Information

  1. Replication: DNA makes copies of itself

  2. Transcription: DNA -> mRNA (rRNA, tRNA)

  3. Translation: mRNA (rRNA, tRNA) -> protein
• DNA Replication


  • DNA exists as a double helix, during replication 2 double helices are formed from 1
• Transcription


  • The transfer of information from DNA to mRNA (rRNA, tRNA)
• Translation


  • The sequence of amino acids in a protein is specified by the sequence of bases in the mRNA
• Codon


  A sequence of 3 bases that encodes a single amino acid
• Differences between eukaryotes and prokaryotes

  • In eukaryotes, DNA replication and transcription occurs in the nucleus, mRNA is transported to the cytoplasm where translation takes place
  • In prokaryotes, DNA replication, transcription and translation takes place in the cytoplasm
• Bacterial chromosome


  • Usually circular, some are linear, DNA is supercoiled to fit into the small cell
• Eukaryotic chromosome


  • Linear, DNA is wrapped around histones to form nucleosomes and chromatin
• The human genome has 3 billion base pairs and is about 1 metre long
• Most prokaryotic genes occur as a single copy, some eukaryotic genes are present in multiple copies
• What is the name of the DNA sequencer at Dept Microb UHWI?
• When was the structure of the DNA elucidated?
• When was the first sequencing of the human genome?
• What is the name of the DNA sequencer at Dept Microb UHWI
• Eukaryotic chromosome


  • The length of the individual eukaryotic chromosome is shorter than the single prokaryotic chromosome
  • The linear chromosome of eukaryotes have special ends called telomeres
• Prokaryotic chromosome do not have telomeres
• Eukaryotic chromosome


  • Genes are divided into coding regions (exons) and noncoding regions (introns)
  • After transcription the introns are removed before the mRNA is translated to a protein
• There are also repetitive (satellite) DNA in humans (20-30%) which does not seem to code for any protein, rRNA or tRNA ("junk DNA???")
• Prokaryotes have small genetic elements called plasmids which replicate independently of the chromosome
• Plasmids are only present in a few eukaryotes
• Extra- or Non-Chromosomal Elements

  • Viruses
  • Plasmids
  • Chromosomes of mitochondria and chloroplast
  • Transposable elements
• Viruses


  Genetic elements that replicate independently of the cell chromosome but not independently of the cell
• Viruses need a host cell to replicate (reproduce)
• Viruses also have an infectious extracellular form (the virion)
• The replication of the virus is destructive to the cell and this is why many viruses are disease causing agents e.g. influenza virus and SARS-CoV-2
• In the extracellular form the virus consist of nucleic acid (DNA or RNA) surrounded by a protein coat
• The extra cellular form of the virus is metabolically inert
• Once inside a host cell the intracellular form is initiated and virus replication occurs
• Where new copies of the viral genome is produced and the viral coat synthesized
• When the virus is introduced into a cell and replication occurs this is called infection
• Viruses are described as


  • naked
  • enveloped
• Envelop


  A complex membranous structure surrounding the nucleocapsid
• Envelop


  Consists of a lipid bilayer with embedded proteins such as glycoproteins