Micro F Bacterial Gene Expression, Mutagenesis, and Genetic Transfer

Vocabulary flashcards covering bacterial gene expression, operon regulation, regulatory RNAs, mutation classifications, DNA repair methods, mutant screening techniques, and mechanisms of horizontal gene transfer.

Constitutive Genes

Genes in bacteria that are expressed all the time and remain continuously active.

Operon

A functional genetic unit in prokaryotes consisting of a promoter, an operator, and a contiguous set of genes that perform a related function.

Promoter

The specific DNA site where RNA polymerase binds to initiate the transcription of mRNA.

Operator

The regulatory DNA sequence in an operon that dictates whether RNA polymerase can bind to the promoter.

Inducible Operon

An operon that is normally turned off and requires an inducer to become activated; typically involved in catabolic pathways, with the lactose (lac) operon serving as the classic example.

Repressible Operon

An operon that is constitutively active and must be deactivated or shut down by a repressor; typically involved in anabolic pathways, such as the tryptophan operon.

Lac Operon

An inducible operon with three genes encoding lactose-metabolizing enzymes; active transcription occurs when lactose binds to and pulls the repressor off the operator.

Tryptophan Operon

A repressible operon containing five genes required to synthesize tryptophan; it is shut off when accumulated high concentrations of tryptophan activate an inactive repressor.

MicroRNAs (miRNAs)

Small regulatory RNA molecules complementary to mRNA that bind to single-stranded mRNA (covering regions like the AUG start codon) to block ribosomal binding and inhibit translation.

Small Interfering RNAs (siRNAs)

Regulatory RNAs that bind to mRNA, tRNA, or DNA to render them ineffective; heavily researched for biotechnology and stopping viral infections.

Riboswitch

An RNA element that alters its secondary shape to regulate and turn off transcription.

Point Mutation

A genetic mutation in which a single base pair in the DNA sequence is altered through substitution, addition, or deletion.

Frameshift Mutation

A mutation caused by the insertion or deletion of a nucleotide base, offsetting the three-base reading frame of mRNA and altering every downstream amino acid.

Silent Mutation

A base substitution that still codes for the exact same amino acid, resulting in no downstream change to the translated protein structure.

Missense Mutation

A point mutation that changes a single codon to code for a different amino acid, altering R-group interactions and potentially altering protein shape or function.

Nonsense Mutation

A point mutation that substitutes an amino acid codon with an early stop codon, causing premature termination of translation and resulting in a truncated, nonfunctional protein.

Mutagen

A physical or chemical agent, such as radiation or certain chemicals, that induces mutations in DNA.

Photolyase

An enzyme used during light repair that utilizes visible light to cut and repair thymine dimers formed by nonionizing UV radiation.

Nucleotide Excision Repair

A single-strand DNA repair mechanism where an enzyme cuts out the damaged sequence (such as a thymine dimer) along with flanking bases, allowing DNA polymerase and ligase to rebuild the strand.

Error-Prone Repair

A category of DNA repair mechanisms specialized in repairing double-stranded DNA breaks.

Positive Selection (Direct Selection)

A technique to identify mutants by plating bacteria on selective media (such as penicillin-containing media) where only the mutant phenotype can survive and grow.

Negative Selection (Indirect Selection)

A screening technique that uses replica plating with velvet to detect auxotrophic mutants by observing colonies that grow on complete medium but fail to grow on media lacking an essential nutrient.

Auxotroph

A mutant organism that requires an additional nutritional growth factor (such as tryptophan) because it has lost the ability to synthesize it.

Ames Test

A rapid and inexpensive microbiological screening procedure using bacteria and liver extract to determine whether a suspected chemical is mutagenic.

Vertical Gene Transfer

The transmission of an entire duplicated genome from a parent organism to its subsequent descendant cells via binary fission.

Horizontal Gene Transfer

The lateral transmission of small portions of chromosomal DNA or plasmids from a donor cell directly to a recipient cell without transferring the full genome.

Competent Cell

A bacterial cell with modified cell walls and membranes that has open pores capable of taking up exogenous DNA from its environment.

Transformation

A form of horizontal gene transfer in which a competent bacterial cell takes up naked DNA directly from the surrounding environment.

Transduction

The process of horizontal gene transfer in which a bacteriophage (phage) transfers host DNA sequences from an original host cell into a new host cell.

Conjugation

A mechanism of horizontal gene transfer mediated by a conjugation pilus that pulls two bacterial cells together to transfer plasmid DNA, such as fertility (F) or resistance plasmids, from donor to recipient.