U8: Microbial Genetics

Genome

The entire genetic complement (all of the DNA) contained within an organism or cell.

Chromosome

Structurally organized structures within a cell that carry hereditary information containing the genes.

Prokaryotic Chromosomes

Typically a single, circular loop of double-stranded DNA localized in the nucleoid region.

Eukaryotic Chromosomes

Linear DNA molecules located inside a membrane-bound nucleus.

Plasmid

Tiny, self-replicating, extra-chromosomal circular pieces of double-stranded DNA.

Gene

A specific sequence of nucleotides in DNA that codes for a functional product, usually a protein.

Genetics

The science and study of heredity and how traits are passed down.

Genomics

The molecular study and sequencing of genomes.

Genotype

The precise genetic makeup or collection of genes within an organism.

Phenotype

The actual, expressed physical traits or manifest structural/functional properties of an organism.

Bacterial Phenotypes

Structural traits like having a capsule, flagella arrangement, or metabolic traits like the ability to ferment a specific sugar.

Directional (5' → 3')

Phosphodiester backbones are highly directional; the 5' end terminates with a phosphate group, while the 3' end terminates with a hydroxyl group.

Complementary

Nitrogenous bases interact selectively via hydrogen bonding: A=T (2 hydrogen bonds), G≡C (3 hydrogen bonds).

Antiparallel

The two opposing strands run parallel to each other but point in opposite structural directions.

Semiconservative replication

When a double helix replicates, each of the original parental strands serves as a template to build a new daughter strand.

Nucleoside Triphosphates

Building blocks (dATP, dTTP, dCTP, dGTP) that provide energy for DNA synthesis.

DNA Gyrase

Enzyme that relaxes supercoiled DNA and neutralizes structural tension ahead of the replication fork.

Helicase

Enzyme that unwinds the double-stranded DNA helix by breaking hydrogen bonds.

RNA Primase

Synthesizes a temporary, short RNA primer sequence required for DNA Polymerase to initiate DNA synthesis.

DNA Polymerase III

Main enzyme that synthesizes the new complementary DNA strand in the 5' → 3' direction.

DNA Polymerase I

Enzyme that removes RNA primers and replaces them with DNA nucleotides.

DNA Ligase

Enzyme that covalently patches up structural nicks in the sugar-phosphate backbone.

Leading Strand

Synthesized continuously moving into the replication fork, requiring only one RNA primer.

Lagging Strand

Synthesized discontinuously away from the replication fork in Okazaki fragments requiring multiple RNA primers.

Prokaryotes

DNA replication takes place in the cytoplasm, specifically the nucleoid region.

Eukaryotes

DNA replication takes place inside the nucleus.

mRNA

Messenger RNA that carries the temporary copy of the genetic recipe from DNA to the ribosome.

tRNA

Transfer RNA that carries specific amino acids and matches its anticodon sequence to the mRNA codon.

rRNA

Ribosomal RNA that makes up the core physical components of the ribosome.

Transcription

The process of copying a sequence of DNA nucleotides into a complementary sequence of RNA nucleotides.

RNA Polymerase

Enzyme that synthesizes RNA from a DNA template by creating a complementary strand.

Sense Strand

The strand of DNA that matches the exact sequence of the newly synthesized mRNA transcript.

Antisense Strand

The actual template strand of DNA that RNA Polymerase reads to create mRNA.

Codon

A sequence of three nucleotides on mRNA that corresponds to a specific amino acid.

A Site

Aminoacyl site in the ribosome where incoming tRNA molecules carrying amino acids dock.

P Site

Peptidyl site in the ribosome where the growing peptide chain is held.

E Site

Exit site in the ribosome where uncharged tRNAs leave after donating their amino acids.

Genetic Code

The set of rules by which information encoded in genetic material is translated into proteins.

Inducible Operon

Operon that is usually off and needs an inducer to turn it on.

Repressible Operon

Operon that is usually on and can be turned off by the presence of a corepressor.

Corepressor

Molecule that binds to a repressor protein, activating it and preventing transcription.

Mutations

Permanent structural changes in the nitrogenous base sequence of a DNA molecule.

Silent Mutation

A point mutation where a single base change results in no change in amino acid sequence.

Missense Mutation

A point mutation that results in a different amino acid being incorporated into a protein.

Nonsense Mutation

A mutation that converts a codon into a premature stop codon.

Frameshift Mutation

Insertion or deletion of nucleotide bases that alters the reading frame.

Horizontal Gene Transfer

The transfer of genetic material between independent organisms of the same generation.

Vertical Gene Transfer

The transfer of genetic material from a parent organism to its offspring.

Transformation

A process where a recipient bacterial cell imports naked DNA from its surrounding environment.

Conjugation

The direct transfer of genetic material between bacterial cells through physical contact.

Transduction

Transfer of bacterial genes by a bacteriophage from a donor cell to a recipient cell.

Catalytic subunits

Core physical components of the ribosome instrumental in protein synthesis.

Diauxic Growth

Growth pattern in bacteria observed when two sugars (like glucose and lactose) are present.

Cyclic AMP

A molecule that serves as a signaling agent indicating energy levels in cells.

Catabolite Activator Protein (CAP)

Protein that enhances transcription by binding to the cAMP signal and promoting RNA Polymerase activity.

Glucose Repression

Mechanism by which the presence of glucose represses the expression of alternative sugar operons.

Photoreactivation

Repair mechanism that uses visible light to repair thymine dimers.

Excision Repair

Dark repair mechanism involving endonucleases, DNA polymerase, and DNA ligase.

Mutagens

External agents that increase the mutation rate in DNA.

Spontaneous Mutation Rate

The natural rate at which mutations occur in the absence of external influences.

Thymine Dimer

A type of DNA damage caused by UV radiation, where two thymine bases bond incorrectly.

Operon Anatomy

The structural components (regulatory gene, promoter, operator, structural genes) that govern a gene cluster in prokaryotes.

Gene Regulation

Processes that control the timing and amount of gene expression in cells.

Constitutive Genes

Genes that are continuously expressed at a constant rate.

Mutation Repair Mechanisms

Processes through which cells repair mutations that occur in DNA.

Adenine

Nitrogenous base that pairs with Thymine in DNA and Uracil in RNA.

Thymine

Nitrogenous base that pairs with Adenine in DNA.

Cytosine

Nitrogenous base that pairs with Guanine in DNA.

Guanine

Nitrogenous base that pairs with Cytosine in DNA.

RNA Processing

Modifications made to the mRNA transcript before it is translated.

Start Codon

The codon AUG, which signals the start of translation.

Stop Codon

Codons that signal the termination of translation.

Genetic Diversity

The variability of the genetic makeup within a population.

Anticodon

A sequence of three bases in tRNA that pairs with a corresponding codon in mRNA.

Template Strand

The strand of DNA that is used as a guide to synthesize RNA during transcription.

Saturation Binding

Condition in which all ribosome sites are occupied with tRNA during translation.

Nuclear Envelope

Membrane that encloses the nucleus in eukaryotic cells.

Ribosomal Subunits

The two components (large and small) that make up ribosomes; vital for protein synthesis.

Peptide Bond

The bond formed between amino acids during protein synthesis.

Proteins

Macromolecules composed of amino acids that perform a wide variety of functions in organisms.

Signal Transduction

The process by which a cell responds to signals from its environment.

Metabolic Pathways

Series of chemical reactions occurring within a cell.

Self-Replicating DNA

DNA that can make copies of itself independently.

Antibiotic Resistance Genes

Genes that confer resistance to antibiotics in bacteria.

Bacterial Conjugation

A process of genetic exchange between bacteria through direct physical contact.

Virulence Factors

Molecules produced by pathogens that contribute to the pathogenicity.

Covalent Bond

A type of strong bond that involves the sharing of electron pairs between atoms.

Intron

Non-coding sequence in a gene that is removed during RNA processing.

Exon

The coding sequences of a gene that remain in the mRNA after processing.

Ribosomal RNA (rRNA)

Types of RNA that are incorporated into the ribosome.

Messenger RNA (mRNA)

RNA molecule that conveys genetic information from DNA to the ribosome.

Transfer RNA (tRNA)

Adapter molecule that brings amino acids to the ribosome during translation.

Peptide Chain

A sequence of amino acids linked by peptide bonds.

Gene Expression

The process by which information from a gene is used to synthesize functional gene products.

RNA Splicing

The process by which introns are removed from the RNA transcript.

Amino Acid

Building blocks of proteins, coded for by mRNA codons.

Mutation Effect

Impact of a mutation on the function or expression of a gene.

Repressor Protein

Protein that binds to an operator to inhibit transcription.

Inducer Molecule

Substance that triggers the expression of a gene by inactivating a repressor.

Operon Model

A model describing the function of operons in regulating gene expression.