Microbial Genetics
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| Genetics | Study of what genes are, how they carry information, how information is expressed, and how genes are replicated.
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| Gene | A segment of DNA that encodes a functional product, usually a protein.
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| Chromosome | Structures containing DNA.
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| Genome | All of the genetic material in a cell.
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| Genomics | Molecular study/characterization of genomes.
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| Genotype | Genes of an organism.
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| Phenotype | Expression of the genes.
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| Bacteria | Typically have single circular chromosomes consisting of a single circular molecule of DNA with associated proteins.
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| Flow of Genetic information | Information contained in the DNA is transcribed into RNA and translated into proteins.
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| DNA | Consists of Polymer nucleotides; Adenine, Thymine, Cytosine, Guanine. Double helix associated with proteins. Strands held together by hydrogen bonds between A-T and C-G.
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| DNA replication | Result is two new strands of DNA, each having base sequence complementary to original strands. Because each double-strand molecule contains one original and one new strand it's known as semi-conservative.
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| Transcription | DNA is transcribed to make RNA (mRNA, tRNA, and rRNA). Begins when the RNA polymerase binds to a promoter sequence. Proceeds in the 5' to 3' direction. Stops when it reaches a terminator sequence.
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| Translation | mRNA is translated in codons (3 nucleotides). Begins at the start codon: AUG. Ends ate a stop codon: UAA, UAG, or UGA.
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| Regulation of bacterial gene expression | Constitutive enzymes are expressed at a fixed rate, others are expressed only as needed.
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| Inducible enzymes (Induction) | In the presence of certain chemicals (inducers), cells synthesize more enzymes. Inducer is a chemical or environmental stimulus that causes (induces) the transcription of specific genes.
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| Example of Induction | Lactose induces the transcription of genes to make enzymes for consuming lactose.
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| Repessible enzymes | Control the synthesis of one or several (repressible) enzymes. when cells are exposed to particular a end-product, the synthesis of enzymes related to that product decreases.
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| Repression | Is the process by which a repressor protein can stop the synthesis of another protein by binding the operator site and thus preventing transcription. Many genes are transcribed until they are "turned off" by a repressor.
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| Example of Repression | The genes for making tryptophan are "turned off" when excess tryptophan is present.
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| Mutation: Change in genetic material | Are a change in genetic material. Mutations may be neutral, beneficial, or harmful. Change in one base results in change in amino acid added to sequence.
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| Mutagen | Agents in the environment that cause permanent changes in DNA (mutations). Examples are radiation, and toxic chemicals.
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| Spontaneous mutations | Occur without the presence of any mutagen.
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| UV radiation | Is non-ionizing; it causes bonding between adjacent thymine's (causes thymine dimers).
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| Light-repair | Enzymes that repair thymine dimers in the presence of visible light.
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| Frequency of Mutations | Not very many "mistakes" per gene copied.
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| Vertical gene transfer (genetic transfer) | Occurs during reproduction, when genes are passed from one organism to its offspring.
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| Horizontal gene transfer (genetic transfer) | Transfer of genes between bacterial cells of the same generation. (involves portion of the cell's DNA being transferred from donor to recipient).
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| Genetic recombination | The rearrangement of genes from separate groups of genes, usually involves DNA from different organisms; it contributes to genetic diversity. When some of the donor's DNA has been integrated into the recipient's DNA the resultant cell is recombinant.
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| Transformation in bacteria | During this process, genes are transferred from one bacterium to another as "naked" DNA in a solution. this process occurs naturally among a few genera of bacteria.
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| Conjugation in bacteria (via cell to cell contact) | This process requires contact between living cells. Example when an F factor (a plasmid) is transferred from a donor (F+) to a recipient (F-), the F- cell is converted into an F+ cell.
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| Transduction in bacteria (via a bacteriophage-virus) | In this process, DNA is passed from one bacterium to another in a bacteriophage (virus) and is then incorporated into the recipient's DNA. In generalized transduction, any bacterial genes can be transferred.
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| Plasmids | Self-replicating small circular molecules of DNA carrying genes that are not usually essential for the cell's survival.
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| Transposons | Are small segments of DNA that can move from one region to another region of the same chromosome or to a different chromosome or plasmid.
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| Types of Plasmids | Conjucative plasmids, dissimilation plasmids and plasmids carrying genes for toxins or bacteriocins, and resistance factors.
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