Microbial Genetics

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  • Microbial Genetics - It is the study of the mechanisms of heritable information in microorganisms
  • Microbial Genetics also involves the study of the genotype of microbial species and the expression system in the form of phenotypes
  • Structural units of nucleic acids are the nucleotides
  • Each nucleotide has 3 parts:
    • A nitrogenous base
    • A pentose sugar
    • A phosphate group
    1. Purines: Adenine (A) and Guanine (G)
    2. Pyrimidines: Cytosine (C), Thymine (T), and Uracil (U)
  • RNA - It is also made up of nucleotides consisting of a 5-carbon sugar ribose, a phosphate group, and a nitrogenous base
  • RNA - it uses the sugar ribose instead of deoxyribose
  • RNA - generally single-stranded
  • RNA - contains uracil in place of thymine
  • A molecule of DNA consists of two strands that form a double helix structure.
  • Each DNA strand is composed of nucleotides—units made up of a sugar (deoxyribose), a phosphate group, and a nitrogenous base.
  • 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.
  • mRNA – a type of RNA generated from transcribing DNA. Carries information for the translation of a particular protein.
  • rRNA – structural component of ribosomes
  • tRNA – carries amino acids to the ribosome during translation to help build an amino acid chain.
  • Three types of RNA:
    1. messenger RNA
    2. ribosomal RNA
    3. transfer RNA
  • the genetic information flows from DNA → RNA → Proteins
  • 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)
  • 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
  • Conversion of DNA-encoded information to RNA is essential to form proteins.
  • The Central Dogma of Molecular Biology - It mainly involves the conversion of DNA encoded information into RNA, that is then essential to form proteins
  • It is therefore divided into three major events:
    • DNA replication
    • mRNA Transcription
    • protein Translation.
  • DNA replication - It is the process by which DNA makes a copy of itself during cell division
  • Watson and Crick base pairing maintained
  • Replication - A complex process involving several enzymes and proteins
  • A primer is needed for initiation
  • 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
  • In eukaryotes – begins at various replication origins; faster replication
  • During elongation, a primer sequence is added with complementary RNA nucleotides, which are then replaced by DNA nucleotides.
  • During elongation the leading strand is made continuously, while the lagging strand is made in pieces called Okazaki fragments
  • Both parental strands serve as template for the DNA replication.
  • DNA polymerase synthesizes only at the 5’ to 3’ direction
  • DNA replication is bidirectional.
  • DNA gyrase and topoisomerases relaxes supercoiling ahead of the replication fork
  • Replication fork – the point at which replication actively occurs.