4 - Microbial Genetics

• Microbial Genetics is the study of the mechanisms of heritable information in microorganisms.
• The Central Dogma of Molecular Biology mainly involves the conversion of DNA-encoded information into RNA, which is then essential to forming proteins.
• The Central Dogma of Molecular Biology is therefore divided into three major events: DNA replication, mRNA Transcription, and protein Translation.
• Mutation is any heritable alteration in the base sequence of the genetic material.
• Nucleotides - structural units of nucleic acids.
• 3 parts of a nucleotide: a nitrogen-containing base, a pentose sugar, and a phosphate group (phosphoric acid).
• Vertical gene transfer - gene transfer in prokaryotes that involves movement of genetic material by descent.
• Horizontal gene transfer - gene transfer of prokaryotes that involve the movement of genes between cells that are not direct descendants of one another.
• Purines: Adenine and Guanine
• Pyrimidine: Cytosine, Thymine, Uracil
• A molecule of DNA consists of two strands that form a double helix structure.
• Each DNA strand is composed of nucleotides.
• The sequences of nitrogenous bases on the two strands of a DNA molecule are complementary.
• The nitrogenous base pairs are joined by hydrogen bonds.
• The two strands of DNA are antiparallel.
• Three main differences between DNA and RNA:

  1. RNA uses the sugar ribose instead of deoxyribose.
  2. RNA is generally single-stranded.
  3. RNA contains uracil in place of thymine.
• mRNA (messenger RNA) – a type of RNA generated from transcribing DNA. Carries information for the translation of a particular protein.
• rRNA (ribosomal RNA) – structural component of ribosomes.
• tRNA (transfer RNA) – carries amino acids to the ribosome during translation to help build an amino acid chain.
• Identify the following:

  A) Nucleobases

  B) Base pair

  C) helix of sugar-phosphates

  D) Ribonucleic Acid

  E) Deoxyribonucleic Acid

  
• DNA contains the complete genetic information that defines the structure and function of an organism.
• Proteins are formed using the genetic code of the DNA.
• Genotype – the organism’s genetic makeup - all its DNA—the information that codes for all the particular characteristics of the organism.
• Phenotype – refers to actual, expressed properties (proteins).
• Genetic information flows from DNA - RNA - Protein
• Semi-conservative mode - resulting daughter molecules each have one parental (old) strand and one newly synthesized strand.
• Watson and Crick's base pairing maintained - 3 bases on each strand are complementary to each other
• DNA is synthesized in the 5' to 3' direction
• A primer is needed for initiation - stretch of DNA or RNA nucleotides that provide 3' OH end
• DNA Replication - The process of making a copy of DNA in a cell.
• Stages of DNA Replication:

  1. Initiation
  2. Elongation
  3. Termination
• Origin of Replication - sequence of DNA at which replication is initiated on a chromosome, plasmid, or virus.
• In prokaryotes and viruses – begins at a defined chromosomal locus (usually unique) ~300 nuc. Example: ori C in E. coli.
• In eukaryotes– begins at various replication origins; faster replication. Example in Drosophila embryos.
• DNA replicates in three minutes.
• DNA gyrase and topoisomerases relaxes supercoiling ahead of the replication fork
• Replication fork - The point at which replication actively occurs.
• Primers signal the starting point of DNA replication. It is synthesized by primase
• Elongation - Both parental strands serve as templates for DNA replication.
• DNA polymerase synthesizes only at the 5’ to 3’ direction.