Ch 09_An Introduction to Microbial Genetics

Chapter 9: An Introduction to Microbial Genetics

Genomes: Total genetic material present in a cell.
Prokaryotic Cells: Circular DNA, located in the nucleoid.
Eukaryotic Cells: Linear DNA organized into chromosomes housed in the nucleus.
Extrachromosomal DNA: Present in organelles such as mitochondria and chloroplasts; may also include plasmids.

DNA (Deoxyribonucleic Acid) vs. RNA (Ribonucleic Acid):
- Sugars: DNA contains deoxyribose; RNA contains ribose.
- Bases: DNA has thymine (T); RNA has uracil (U).
- Nucleotide Structure:
  - Nucleotides = phosphate + deoxyribose/ribose + nitrogenous base.
  - Nucleosides = sugar + base (no phosphate).

Double Helix:
- Two polynucleotide strands coiled around each other, anti-parallel.
- Sugar-phosphate backbone exterior; nitrogenous bases interior.
- Hydrogen Bonds: Between complementary bases (A-T, G-C).

Central Dogma of Molecular Biology:
- Transcription: DNA → RNA (mRNA).
- Translation: RNA → Protein.
Replication: Process by which DNA duplicates itself.
- Semiconservative process resulting in two new double helices.

Semiconservative: Each new DNA molecule consists of one old strand and one newly synthesized strand.
Replication Forks: Two forks moving in opposite directions during DNA replication.
Key Enzymes:
- DNA Polymerase: Synthesizes new DNA strands.
- Primase: Synthesizes RNA primers for lagging strand synthesis.
- Ligase: Joins Okazaki fragments.

Leading Strand: Synthesized continuously towards the replication fork.
Lagging Strand: Synthesized discontinuously away from the replication fork using Okazaki fragments.

Initiation:
- RNA polymerase binds to the promoter region of the DNA.
- DNA unwound to expose template strand.
Elongation: RNA polymerase adds nucleotides complementary to the DNA template, forming mRNA.
Termination: RNA polymerase stops transcribing at termination sites.

5′ Untranslated Region (5' UTR): Section upstream of the coding sequence.
Protein-coding Sequence: Encodes the amino acid sequence of the protein.
3′ Untranslated Region (3' UTR): Section downstream from the coding sequence.

Ribosomes: Facilitate the translation of mRNA into proteins.
- tRNA (Transfer RNA): Transports amino acids to the ribosome; matches anticodon with mRNA codon.
Start Codon: AUG (methionine); marks the beginning of translation.
Stop Codons: UAG, UAA, UGA; signal the termination of protein synthesis.

Operon: A cluster of genes under the control of a single promoter, allowing for coordinated regulation.
- Lac Operon: Inducible operon involved in lactose metabolism.
- Trp Operon: Repressible operon controlling tryptophan synthesis.

Conjugation: Direct transfer of DNA between bacteria via cell-to-cell contact.
Transformation: Uptake of naked DNA from the environment.
Transduction: Transfer of DNA via bacteriophages.

Substitution Mutations: Change one base pair; can lead to missense or nonsense mutations.
Frameshift Mutations: Caused by insertions or deletions; shifts reading frame, altering all downstream amino acids.
Inversion Mutations: Sections of DNA are flipped, which can affect protein function.

Understand the differences between DNA and RNA at both the structural and functional levels.
Mastery of the processes of replication, transcription, and translation is essential.
Familiarize yourself with operon functions, particularly lac and trp operons in bacterial gene regulation.
Recognize the significance of horizontal gene transfer in microbial evolution.
Be able to identify and explain various types of mutations and their potential impacts on protein synthesis.