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Geosciences LibreTexts

3: Mechanisms of Microbial Genetics

  • Page ID
    6183
    • DNA, RNA, Genes and Chromosomes
      Nucleic acids (DNA and RNA) carry the genetic blueprint of a cell and instructions for its function. DNA is the genetic material responsible for inheritance, and it also codes for the construction of the proteins necessary to a cell for growth and reproduction in a particular cellular environment. DNA is packaged into chromosomes, and their geometry strongly influences gene expression. A cell's genotype consists of all the genes it contains whereas its phenotype is determined by gene expression.
    • DNA Replication
      The DNA replication process results in two DNA molecules, each having one parental strand of DNA and one newly synthesized strand. DNA replication starts at the origin of replication with enzymes uncoiling the DNA. The new DNA molecules are elongated with enzymes adding appropriate complementary base pairs. Organisms replicate the DNA in their chromosomes as well as in organelles (for Eukarya), plasmids, and viruses if present.
    • How Asexual Prokaryotes Achieve Genetic Diversity
      How then do organisms whose dominant reproductive mode is asexual create genetic diversity? In prokaryotes, horizontal gene transfer (HGT), the introduction of genetic material from one organism to another organism within the same generation, is an important way to introduce genetic diversity. HGT allows even distantly related species to share genes, influencing their phenotypes.
    • Mutations
      A mutation is a heritable change in the DNA sequence of an organism. The resulting organism, called a mutant, may have a recognizable change in phenotype compared to the wild type, which is the phenotype most commonly observed in nature. A change in the DNA sequence is conferred to mRNA through transcription, and may lead to an altered amino acid sequence in a protein on translation.
    • Operon Theory
      Genomic DNA contains both structural genes, which encode products that serve as cellular structures or enzymes, and regulatory genes, which encode products that regulate gene expression. The expression of a gene is a highly regulated process. Whereas regulating gene expression in multicellular organisms allows for cellular differentiation, in single-celled organisms like prokaryotes, it ensures that a cell’s resources are not wasted making proteins that the cell does not need at that time.
    • Protein Synthesis (Translation)
      The synthesis of proteins consumes more of a cell’s energy than any other metabolic process. In turn, proteins account for more mass than any other macromolecule of living organisms. They perform virtually every function of a cell, serving as both functional (e.g., enzymes) and structural elements. The process of translation, or protein synthesis, the second part of gene expression, involves the decoding by a ribosome of an mRNA message into a polypeptide product.
    • RNA Transcription
      During the process of transcription, the information encoded within the DNA sequence of one or more genes is transcribed into a strand of RNA, also called an RNA transcript. The resulting single-stranded RNA molecule, composed of ribonucleotides containing the bases adenine, cytosine, guanine, and uracil, acts as a mobile molecular copy of the original DNA sequence. Transcription in prokaryotes and in eukaryotes requires the DNA double helix to partially unwind in the region of RNA synthesis.
    • What Are Genes?
      A gene is composed of DNA that is “read” or transcribed to produce an RNA molecule during the process of transcription. One major type of RNA molecule, called messenger RNA (mRNA), provides the information for the ribosome to catalyze protein synthesis in a process called translation. The processes of transcription and translation are collectively referred to as gene expression.

    Thumbnail: DNA Double Helix. Image used with permission (Public Domain; Apers0n).