Microbiology - Topic 6

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Translation

Back 1

mRNA nucleotide base sequence is used to dictate the amino acid.

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Codon

Back 2

3 mRNA nucleotide bases that make an amino acid.

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Genetic Code

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Refers to the relationship of the nucleotide base sequence of DNA.

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Inteins

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Sequence for self-splicing proteins that remove themselves from proteins and splice 2 exteins together.

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Exteins

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Intervening sequence for self-splicing proteins. 2 exteins are spliced together.

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Constitutive Gene

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Constantly being expressed and continuatively producing enzymes.

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Repression

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Stops the RNA polymerase from starting protein synthesis.

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Repressors

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Blocks RNA polymerase.

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Repressible genes

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Are always on and continue to make mRNA unless instructed otherwise.

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Induction

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Causes gene expression in the presence of inducers.

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Inducers

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Must be present for induction.

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Inducible genes

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Always turned off unless an inducer is present.

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Operon model

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Control of a gene. Applicable to both induction and repression.

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Operon

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Term used to describe a group of coordinately regulated structured genes with related metabolic functions. In bacteria; on DNA.

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Promoter site

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AKA Operator site. Controls transcription of structural genes. Promoter site + Operator site are known control region.

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Lac Operon

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A model for an inducible system.

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Inducible system

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AKA inducible operon. Where a regulatory gene codes for the repressor protein. When the inducer (lactose) is absent and the repressor binds to the operator and no mRNA is synthesized.

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Cyclic amp

Back 18

an alarmone

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Alarmone

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Accumulates when the cell is under stress.

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Mutation

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A change in the nitrogenous base sequence of DNA. Therefore there is a product change that is coded by the mutated gene.

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Mutagen

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Causes mutations.

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Spontaneous

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Absence of mutagen but causes mutation.

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Deliberate

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When microbe is exposed to a mutagen.

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3 Types of Mutation

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Silent – when there is no change in the product coded for. Harmful - microbe dies or is unable to pass on genes. Beneficial - causes it to have a survival advantage.

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Base Substitution

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AKA Point mutation. When 1 base pair in DNA is replaced with another base pair.

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Misense Mutation

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Type of point mutation. Causes amino acid substitution.

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Nonsense Mutation

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Type of point mutation. Causes creation of a stop codon.

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Frame-Shift Mutations

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One or several base pairs are deleted or added to the DNA. Results in stops, mutations, ect.

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Chemical Mutagens

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Includes base-pair mutagens, frame-shift mutagens, nucleotide analogs. Often carcinogenic.

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Ionizing Radiation

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X-Rays and Gamma Rays.
Causes formations of ions and free radicals that react with DNA. A base-substitution or breakage of pentose sugar and phosphate backbone induces mutations.

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Mutation Rate

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Probability that a gene will mutate when a cell divides.

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Positive or Direct Selection

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Detects a mutagen cell because they grow or appear different than a non-mutagen cell

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.

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.

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Replica Plating

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Used for negative selection by detecting mutant cells that will not grow without a particular growth factor.

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Auxotrophs

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Nutritional requirement not found in the parent or non-mutated cells.

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Back Mutations

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AKA Reversion. A mutant can revert to a normal cell when exposed to mutagens

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Carcinogens

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Stronger mutations are more carcinogenic.

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Crossing-over

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Genes from 2 chromosomes are recombined into 1 chromosome. Like a donor that provides new DNA a recipient.

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Vertical Gene Transfer

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When genes are transferred from one organism to its offspring.

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Horizontal Gene Trans.

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In bacteria, one portion of the bacterium’s DNA is transferred to another within the same generation.

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Recombinant

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All recipient cells have successfully integrated into the new DNA.

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Transformation

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A gene transfers from one bacterium to another as naked DNA in solution.

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Conjugation

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Another method of transferring genetic material by contact between living cells, mediated by a circular piece of DNA (plasmid).

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Plasmid

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Self-replicating circular molecule of DNA that carries genes non-essential to cell survival.

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Sex Pilus

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coded by the plasmid in gram negative DNA.

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Mating Bridge

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coded by the plasmid in gram positive DNA.

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F Factors

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A fertility factor. F positive cells from a donor replicates and transfers the plasmid to recipient cells which are transformed from F negative to F positive. (p. 18)

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HFR Cells

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High frequency of recombination. Happens if plasmid becomes incorporated into chromosomes.

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Transduction

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DNA is passed from one bacterium to another in a bacteriophage.

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Bacteriophage

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A virus that infects bacteria AKA phage.

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Generalized

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When any bacterialized gene can be transfered

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Special Transduction

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When only specific genes can be transferred

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Conjugated Plasmids

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Carry genes for sex pili and transfer to plasmid.

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Dissimilation Plasmid

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Encode enzymes for catabolism of unusual compounds.

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Resistance Factors

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Encode for antibiotic resistance. Usually contain 2 types of genes. 1 codes for plasmid replication and conjugation (resistance transfer factor RTF). The second one is enzymes that inactivate medication or toxic substances to the cell (R Determinant)

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Bacteriocins

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Toxic protein that kills other bacteria.

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Transposons

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Small segments of DNA that can move from place to place within the same chromosome to another chromosome or plasmid.

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Simple Transposons

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Called insertion sequences which code for the enzyme transposase and recognition sites.

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Transposase

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Catalyzes the cutting and rejoining (annealing) of DNA.

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Complex Transposons

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Carry the insertion sequences of at least one gene. Including antibiotic resistance genes. Is a natural mechanism of moving genes.