Microbial Genetics

Question Answer
Genetics Study of what genes are, how they carry information, how information is expressed, and how genes are replicated.
Gene A segment of DNA that encodes a functional product, usually a protein.
Chromosome Structures containing DNA.
Genome All of the genetic material in a cell.
Genomics Molecular study/characterization of genomes.
Genotype Genes of an organism.
Phenotype Expression of the genes.
Bacteria Typically have single circular chromosomes consisting of a single circular molecule of DNA with associated proteins.
Flow of Genetic information Information contained in the DNA is transcribed into RNA and translated into proteins.
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.
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.
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.
Translation mRNA is translated in codons (3 nucleotides). Begins at the start codon: AUG. Ends ate a stop codon: UAA, UAG, or UGA.
Regulation of bacterial gene expression Constitutive enzymes are expressed at a fixed rate, others are expressed only as needed.
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.
Example of Induction Lactose induces the transcription of genes to make enzymes for consuming lactose.
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.
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.
Example of Repression The genes for making tryptophan are "turned off" when excess tryptophan is present.
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.
Mutagen Agents in the environment that cause permanent changes in DNA (mutations). Examples are radiation, and toxic chemicals.
Spontaneous mutations Occur without the presence of any mutagen.
UV radiation Is non-ionizing; it causes bonding between adjacent thymine's (causes thymine dimers).
Light-repair Enzymes that repair thymine dimers in the presence of visible light.
Frequency of Mutations Not very many "mistakes" per gene copied.
Vertical gene transfer (genetic transfer) Occurs during reproduction, when genes are passed from one organism to its offspring.
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).
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.
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.
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.
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.
Plasmids Self-replicating small circular molecules of DNA carrying genes that are not usually essential for the cell's survival.
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.
Types of Plasmids Conjucative plasmids, dissimilation plasmids and plasmids carrying genes for toxins or bacteriocins, and resistance factors.

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