Micropara Quiz 2 (Genetics)

• Microbial Genetics


  The study of the mechanisms of heritable information in microorganisms (bacteria, archaea, viruses and some protozoa and fungi)

  
• 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)
• Central Dogma of Molecular Biology

  1. DNA replication

  2. mRNA Transcription

  3. Protein Translation

  
• Mutation


  Any heritable alteration in the base sequence of the genetic material
• Gene transfer mechanisms in prokaryotes

  • Vertical gene transfer (movement of genetic material by descent)
  • Horizontal gene transfer (movement of genes between cells that are not direct descendants of one another)
• Nucleic acids


  • Structural units are nucleotides
  • Each nucleotide has a nitrogen-containing base, a pentose (five-carbon) sugar, and a phosphate group
• Purines


  Adenine (A) and Guanine (G)
• Pyrimidines


  Cytosine (C), Thymine (T), and Uracil (U)
• DNA


  • A molecule consisting 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 are complementary
  • The nitrogenous base pairs are joined by hydrogen bonds
  • The two strands are antiparallel

  
• RNA


  • Made up of nucleotides consisting of a 5-carbon sugar ribose, a phosphate group, and a nitrogenous base
  • RNA is generally single-stranded
  • RNA contains uracil in place of thymine
• Types of RNA


  • mRNA (messenger RNA)
  • rRNA (ribosomal RNA)
  • tRNA (transfer RNA)
• DNA contains the complete genetic information


  Proteins are formed using the genetic code of the DNA

  
• Conversion of DNA encoded information to RNA


  Essential to form proteins

  
• Semi-conservative mode of DNA replication


  Resulting daughter molecules each have one parental (old) strand and one newly synthesized strand

  
• DNA Replication


  1. Initiation

  2. Elongation

  3. Termination

  
• Transcription


  The synthesis of a complementary strand of RNA from a DNA template

  
• Transcription


  1. RNA polymerase binds to the DNA at the promoter

  2. RNA polymerase synthesizes mRNA in the 5' - 3' direction

  3. RNA synthesis continues until RNA polymerase reaches the terminator

  
• Translation


  • From mRNA to protein
  • The language of mRNA is in the form of codons (groups of 3 nucleotides)
  • The sequence of codons on an mRNA molecule determines the sequence of amino acids that will be in the protein being synthesized

  
• Third Base Degeneracy / Wobble Hypothesis

  Codons for the same amino acid usually differ in the 3rd position only
• Translation


  1. The ribosome binds to mRNA at a specific area

  2. The ribosome starts matching tRNA anticodon sequences to the mRNA codon sequence

  3. Each time a new tRNA comes into the ribosome, the amino acid that it was carrying gets added to the elongating polypeptide chain

  4. The ribosome continues until it hits a stop sequence, then it releases the polypeptide and the mRNA

  5. The polypeptide forms into its native shape and starts acting as a functional protein in the cell

  
• Mutation


  • Any heritable alteration in the base sequence of the genetic material
  • Can either be spontaneous or induced
• Spontaneous mutation


  Occur without external intervention, and most result from occasional errors in the pairing of bases by DNA polymerase during DNA replication
• Induced mutation


  • Caused by agents in the environment and include mutations made deliberately by humans
  • Result from exposure to natural radiation that alters the structure of bases in the DNA, or from a variety of chemicals that chemically modify DNA
• Types of Mutation


  • Base Substitution / Point Mutation
  • Transition
  • Transversion
• Induced mutation


  Caused by agents in the environment and include mutations made deliberately by humans
• Induced mutations result from exposure to natural radiation that alters the structure of bases in the DNA, or from a variety of chemicals that chemically modify DNA
• Base Substitution / Point Mutation

  A single base at one point in the DNA sequence is replaced with a different base during replication
• Types of Base Substitution / Point Mutation

  • Transition (Purine to purine or pyrimidine to pyrimidine)
  • Transversion (Purine to pyrimidine or vice versa)
• Missense mutation


  Changes a codon for one amino acid to a codon for another amino acid, resulting in an amino acid substitution in the protein product
• Nonsense mutation


  Changes a codon for an amino acid with a codon for chain termination (UAG, UAA, UGA)
• Silent mutation


  A change in codon composition that has no effect on the resulting polypeptide
• Frameshift Mutation


  Adds or deletes one or two bases (or any non-multiple of 3) from a coding sequence in a DNA, so that the genetic code is read out-of-phase
• Consequence of Frameshift Mutation


  Incorrect amino acid or premature termination, severe phenotypic effects
• Deletion


  Mutation in which a region of the DNA has been eliminated
• Insertion


  Occurs when new bases are added to the DNA
• Physical Mutagens


  High energy radiations that penetrate living cells
• Types of Physical Mutagens

  • Electromagnetic radiations (Gamma rays, X-rays, Ultraviolet rays)
  • Particulate radiations (Alpha particles, Beta particles, Neutrons)
• Consequence of Gamma Rays and X-rays (ionizing radiation)

  Direct effect: single or double stranded breaks in the DNA molecules. Indirect effect: free radicals created that form compounds, hydrogen peroxide - initiate harmful chemical reactions within the cells. Can lead to cell death
• Consequence of Ultraviolet rays (non-ionizing radiation)

  Formation of pyrimidine dimers, most are immediately repaired, but some escape repair and inhibit replication and transcription