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Antibiotic

A chemical substance from one microorganism that inhibits or kills another microorganism.

Bactericidal

A drug that kills bacteria.

Bacteriostatic

A drug that inhibits bacterial growth but does not kill bacteria.

Selective toxicity

Killing microbial cells but not the host’s own cells (skin, muscle, nerves, etc.).

Broad spectrum antibiotic

A drug that is effective against a wide range of microbes.

Narrow spectrum antibiotic

A drug that is effective against a limited range of microbes.

Beta-lactam antibiotic

Antibiotics that inhibit penicillin binding proteins, thus interfering with peptidoglycan synthesis.

Acquired resistance

Resistance due to mutation or acquisition of new genes.

Penicillin

An antibiotic discovered by Alexander Fleming from Penicillium chrysogenum that interferes with peptidoglycan synthesis.

Minimum inhibitory concentration

The lowest concentration of a drug that will inhibit the microorganism from growing.

Minimum bactericidal concentration

The lowest concentration of a drug that will kill 99.9% of the population of a particular bacterium.

Disc diffusion test

The 'Kirby-Bauer Test', which determines the susceptibility or resistance to antibiotics by observing clear zones around antibiotic discs on a bacterial lawn.

R plasmid

A plasmid carrying one or more genes for antibiotic resistance.

Therapeutic index (TI)

The lowest dose toxic to the patient divided by the dose used to treat the disease; a higher TI indicates less toxicity.

Intrinsic resistance

Resistance due to an inherent characteristic of the microbe.

Site of action

Antibiotic target that includes essential processes in the bacteria such as the cell membrane, cell wall, DNA, mRNA, and proteins.

Vertical gene transfer

The movement of genes, including antibiotic resistant genes, through reproduction; passing the genes to daughter cells.

Horizontal gene transfer

The movement of genes, including antibiotic resistant genes, through conjugation, transduction, and transformation.

DNA

The genetic material that carries heritable information; has a sugar-phosphate chain with nitrogen bases (adenine, thymine, guanine, and cytosine).

mRNA

Messenger RNA, used as a template for translation; a type of RNA translated during protein synthesis.

tRNA

Transfer RNA, involved in interpreting the genetic code; each tRNA carries a specific amino acid.

rRNA

Ribosomal RNA, a type of RNA molecule present in ribosomes.

Nucleotide

Contains a 5-carbon sugar (deoxyribose or ribose), a phosphate group, and one of four nucleobases (A, T/U, G, or C).

Adenine

A nucleobase that pairs with thymine.

Thymine

A nucleobase in DNA that pairs with adenine.

Guanine

A nucleobase that pairs with cytosine.

Cytosine

A nucleobase that pairs with guanine.

Uracil

A nucleobase in RNA that pairs with adenine.

Promoter

Nucleotide sequence to which RNA polymerase binds to start transcription.

RNA polymerase

An enzyme that synthesizes RNA using one strand of DNA as a template.

DNA polymerase

An enzyme that synthesizes DNA, using an existing strand as a template to make a new complementary strand.

DNA replication

The duplication of a DNA molecule.

Template (in transcription)

The DNA strand that serves as the template for transcription; called the minus (-) strand.

Haploid

A single set of unpaired chromosomes.

Diploid

Two complete sets of chromosomes, one from each parent.

Transcription

The process by which the information encoded in DNA is copied into RNA.

Translation

The process by which the information carried by mRNA is used to synthesize the encoded protein.

Codon

A series of three nucleotides that code for a specific amino acid.

Start codon

Codon at which translation is initiated; typically the first AUG after a ribosome-binding site.

Stop codon

Codon that terminates translation, signaling the end of the protein; there are three stop codons.

Intron

Non-coding regions that must be removed from pre-mRNA to create functional mRNA.

Constitutive gene expression

Gene expression that is always active (mRNA transcription always occurs).

Inducible gene expression

Gene expression that occurs only under certain conditions (mRNA transcription only occurs under these conditions).

Repressible gene expression

Gene expression that is usually active but blocked under certain conditions.

Co-repressor

A molecule that attaches to a repressor, allowing the repressor to bind to the operator and block transcription.

Inducer

A molecule that binds to the repressor, changing its shape so it can no longer bind to the operator.

Repressor protein

A regulatory protein that blocks transcription (negative regulation) by binding to an operator.

Operator

A specific DNA sequence located immediately downstream of a promoter.

Lac operon

An operon that mRNA transcribes lacZ, lacY, and lacA when lactose is being utilized by the cell.

Ames test

A test for potential mutagenic chemicals by comparing mutation rates in control and test plates.

Mutant

An organism that bears a mutation and may exhibit an altered phenotype.

Wild-type

An organism that exhibits the normal (non-mutant) phenotype.

Mutation

Any permanent, inheritable change in the genetic information of the cell.

Frameshift

Mutations caused by insertions or deletions that shift the reading frame of mRNA.

Transposon

Transposable elements that can move from one location in the genome to another, containing inverted repeat sequences.

Plasmid

A small circular double-stranded DNA that can carry antibiotic resistance genes.

F plasmid

The fertility plasmid that can form a sex pilus needed for conjugation.

Donor cell

An F+ cell that contains the F plasmid originally.

Recipient cell

An F- cell that receives the F plasmid from the donor through conjugation.

Conjugation

The transfer of the F plasmid using a sex pilus, resulting in the recipient cell becoming F+.

Hfr cell

A high frequency recombination cell where the F plasmid integrates into the bacterial chromosome.

Generalized transduction

A phage mistake where bacterial DNA can mistakenly enter a protein coat during viral particle construction.

Specialized transduction

Transduction where a prophage takes adjacent bacterial DNA during excision, injecting it into a new host.

Transformation

The bacterial uptake of small fragments of DNA from the surrounding environment.

Mitosis

A process in which each daughter cell receives the same number of chromosomes as the parent cell.

Meiosis

A process in which diploid cells give rise to haploid cells, involving two sequential divisions and crossing-over.

Crossing-over

The exchange of chromosome segments between non-sister chromatids during Meiosis I.