Microbial Genetics: Translation, Gene Regulation, Mutation, and Recombinant DNA Technology

Comprehensive practice flashcards defining core vocabulary terms from Chapter 8 on translation, operon regulation, horizontal gene transfer, DNA repair, and recombinant DNA technology.

Translation

The cellular process in which a cell reads the genetic code carried in messenger RNA (mRNA) and builds a specific chain of amino acids to synthesize proteins.

Codon

A specific sequence of three nucleotides in DNA or RNA (triplet) that serves as a fundamental unit of genetic information, dictating which amino acid is added to a polypeptide chain or signaling the start or termination of protein synthesis.

Redundancy (Degeneracy)

The property of the genetic code that allows a single amino acid to be specified by several different codons (for example, Leucine and Serine are each encoded by 6 different codons), buffering against DNA sequence errors.

Wobble Theory

A model stating that only the first two nucleotides in a codon are strictly required to specify the correct amino acid, while the third nucleotide can vary without altering the amino acid specified.

Prokaryotic Ribosome (70S)

A protein synthesis macromolecule found in bacteria, mitochondria, and chloroplasts that has a total sedimentation rate of $70\text{S}$, composed of a $50\text{S}$ large subunit (containing $5\text{S}$ and $23\text{S}$ rRNA) and a $30\text{S}$ small subunit (containing $16\text{S}$ rRNA).

Transfer RNA (tRNA)

A 75 to 95 nucleotide RNA molecule containing complementary base-paired hairpin loops that form a cloverleaf structure folding into a 3D helix; features a bottom anticodon triplet that complements an mRNA codon and an opposite binding site that carries the corresponding amino acid.

Anticodon

A specialized three-nucleotide sequence situated on the bottom hairpin loop of a tRNA molecule that base-pairs complementarily with a specific codon on an mRNA strand.

A Site (Aminoacyl Site)

The ribosomal binding site that receives an incoming tRNA molecule carrying the next appropriate amino acid to be incorporated into the growing polypeptide chain.

P Site (Peptidyl Transferase Site)

The ribosomal site that holds the initiator tRNA or the tRNA attached to the growing peptide chain and where peptide bond formation is enzymatically catalyzed.

E Site (Exit Site)

The ribosomal site that briefly holds a discharged, uncharged tRNA that has transferred its amino acid before it is released into the cytoplasm.

Start Codon

The specific mRNA triplet $AUG$ (coding for formyl-methionine in bacteria) that establishes the reading frame and initiates the translation process.

Nonsense Codons (Stop Codons)

The three mRNA codons—$UAA$, $UAG$, and $UGA$—that do not correspond to any tRNA or amino acid and dictate the termination of translation, causing the ribosome to dissociate and release the finished polypeptide.

Polyribosomal Complex

A structure formed when multiple ribosomes attach sequentially to a single mRNA transcript to translate multiple identical proteins simultaneously, allowing bacteria to couple translation directly to ongoing transcription.

Antisense RNA

Single-stranded RNA (ssRNA) that is complementary to an mRNA strand transcribed inside a cell, acting post-transcriptionally to bind the mRNA and inhibit its translation.

MicroRNAs (miRNAs)

Small non-coding RNA molecules approximately $22$ nucleotides long present in plants, animals, and certain viruses that function in RNA silencing and the negative regulation of gene expression.

Riboswitch

A regulatory segment within an mRNA molecule that directly binds a specific small metabolite or ligand, causing a conformational change that alters translation or production of the encoded protein.

Operon

A coordinated genetic regulatory system found exclusively in bacteria that comprises a set of structural genes transcribed together as a single polycistronic unit along with contiguous control elements.

Catabolic (Inducible) Operon

An operon, exemplified by the lac operon, that is normally in an 'off' state and is stimulated into transcription when the specific substrate of the catabolic enzymes it encodes is present in the environment.

Repressible Operon

An operon, such as the tryptophan operon, that codes for anabolic enzymes and remains normally active until turned off by the accumulated end-product synthesized by those enzymes.

Operator

A non-coding DNA locus positioned between the promoter and structural genes of an operon that functions as an on/off molecular switch by serving as the binding site for the repressor protein.

Allosteric Repressor (lac Operon)

A regulatory protein encoded constitutively by the upstream regulator gene that possesses two active binding sites—one for the DNA operator locus and one for lactose—blocking RNA polymerase progression when unbound to lactose.

Recombination

An event in which one bacterium donates genetic material to another bacterium, generating a novel recombinant strain distinct from both the donor and recipient cells.

Plasmid

Small, circular, extrachromosomal double-stranded DNA capable of autonomous replication that is not essential for bacterial viability but carries advantageous adaptive traits such as antibiotic resistance.

Horizontal Gene Transfer (HGT)

Any process in which an organism acquires genetic material from another organism without being its direct offspring, mediated in bacteria via conjugation, transformation, or transduction.

Conjugation

A direct mode of horizontal gene transfer where a living donor bacterium ($\text{F}^+$) forms a pilus-mediated bridge to transfer a copy of a plasmid to a living recipient bacterium ($\text{F}^-$) in a conservative manner.

Hfr (High-Frequency Recombination) Donor

A bacterial donor cell in which the fertility plasmid (F factor) has integrated into the chromosome, causing partial or full chromosomal genes to be copied and transferred through a conjugation bridge.

Resistance (R) Plasmid

A plasmid transferred among bacteria that bears genes conferring resistance to multiple antibiotics, heavy metals, or directing the synthesis of virulence factors like toxins and adhesins.

Transformation

An indirect genetic transfer mechanism whereby a competent bacterial cell takes up naked, free donor DNA fragments from its surrounding solution and incorporates them into its own chromosome.

Competence

The physiological capability of a bacterial recipient cell to bind and transport free environmental DNA fragments across its cell wall and membrane.

Generalized Transduction

A bacteriophage-mediated transfer mechanism occurring during the lytic cycle, where random fragments of degraded host DNA are accidentally packaged into a defective phage capsid and injected into a recipient cell.

Specialized Transduction

A bacteriophage-mediated transfer mechanism involving a temperate prophage that excises imperfectly from a fixed bacterial chromosomal site, carrying specific adjacent host genes into new viral particles.

Transposon

A discrete DNA element ('jumping gene') that can excise or replicate itself to shift locations from one genomic locus to another, between chromosomes and plasmids, or between different cells.

Wild Type

A natural, non-mutated microorganism exhibiting standard baseline phenotypic characteristics found in characteristic natural populations.

Point Mutation

A mutation that involves the substitution, addition, or deletion of a single nucleotide base pair within a DNA gene sequence.

Silent Mutation

A base substitution mutation that alters an mRNA codon but, due to code redundancy, encodes the identical amino acid, resulting in zero alteration to protein structure or function.

Missense Mutation

A point mutation that replaces a single nucleotide, thereby altering the triplet codon to specify a different amino acid, potentially creating a faulty, nonfunctional, or altered protein.

Nonsense Mutation

A point mutation that substitutes a normal sense codon with a premature stop (nonsense) codon, causing early termination of translation and producing a truncated protein.

Frameshift Mutation

A genetic mutation caused by the insertion or deletion of one or more base pairs (in numbers not divisible by three), altering the entire downstream triplet reading frame and almost always yielding an inactive protein.

Excision Repair

A multi-step enzymatic repair system where restriction endonucleases cut out incorrect or damaged bases, DNA polymerase I fills the gap with complementary nucleotides, and ligase seals the phosphodiester backbone.

Photoactivation (Light Repair)

A cellular DNA repair mechanism mediated by the enzyme photolyase, which uses visible light energy to directly cleave and repair pyrimidine dimers induced by ultraviolet (UV) radiation.

Restriction Endonuclease

A bacterial bacterial-defense enzyme that recognizes specific symmetrical palindromic sequences of DNA and hydrolyzes the phosphodiester bonds on both strands, producing sticky or blunt fragments.

Sticky Ends

Staggered, single-stranded complementary overhang tails left on DNA ends following cleavage by certain restriction endonucleases, allowing cohesive base-pairing during molecular splicing.

Reverse Transcriptase

A viral enzyme utilized in genetic engineering to synthesize double-stranded complementary DNA (cDNA) copies from extracted, mature mRNA transcripts.

Complementary DNA (cDNA)

DNA synthesized in vitro from processed eukaryotic mRNA transcripts using reverse transcriptase, thereby omitting all non-coding intervening sequences (introns).

Polymerase Chain Reaction (PCR)

A cyclic in vitro molecular technique that rapidly amplifies target DNA segments into billions of copies via automated thermal cycling through denaturation ($94^\ne\circ\text{C}$), priming/annealing ($50^\ne\circ\text{C}-65^\ne\circ\text{C}$), and extension ($72^\ne\circ\text{C}$).

Taq Polymerase

A heat-stable DNA polymerase isolated from the thermophile Thermus aquaticus that remains active and stable at the elevated temperatures ($94^\ne\circ\text{C}$) utilized in PCR denaturation.

Gel Electrophoresis

An analytical laboratory method that separates charged nucleic acid fragments through an agarose gel under an electric field, migrating negatively charged DNA toward the positive electrode at rates inversely related to molecular size.

Cloning Vector

A self-replicating genetic vehicle (usually a plasmid or bacteriophage) designed to carry foreign DNA fragments into a cloning host such as Escherichia coli or yeast for propagation and protein expression.

Genomic Library

A comprehensive repository of cloned recombinant DNA fragments maintained within host cells that represents the entire genomic sequence of a particular organism.