Chapter 8 Study Guide: Bacterial Genetics, Mutations, and Gene Transfer

Vocabulary practice flashcards covering terms, definitions, repair mechanisms, and gene transfer processes from the Chapter 8 Study Guide.

Mutation

Any change in a nucleotide or nucleotide sequence.

Wild-type

The most common, standard, non-mutated gene form.

Genotype

What genes are present in an organism.

Phenotype

The genes that are physically visible or presented.

Silent mutation

A DNA base change that does not result in a change in the amino acid sequence.

Auxotroph

An organism that is nutritionally deficient because of a genetic mutation.

Prototroph

An organism having no mutations in its genes.

Spontaneous mutation

Mutations that occur naturally in the absence of mutagens, such as replication errors occurring at a rate of $1\text{ in }10,000$.

Frameshift mutation

The addition or subtraction of $1$ or $2$ nucleotides during DNA replication, causing every amino acid after the insertion point to be completely changed.

Point mutation

A genetic mutation involving a change in a single base ($1$ nucleotide).

Base substitution

A mutation in which a single nucleotide or base pair is replaced with a different one.

Missense mutation

A base substitution that results in a codon coding for a different amino acid.

Nonsense mutation

A base change that results in a codon for an amino acid changing to a stop codon, potentially causing a very severe reaction.

Transposable elements

Mobile genetic elements ('jumping genes') that move between organisms and within a single chromosome, often causing knockout or insertion mutations.

Base analogs

Structural analogs and chemical compounds, such as AZT, that mimic the structure of DNA bases and are wrongly incorporated into a growing DNA strand.

Intercalating agents

Mutagenic chemicals, such as ethidium bromide, that insert between base pairs, tricking enzymes into adding or deleting base pairs and causing frameshift mutations.

Proofreading by DNA polymerase

A DNA repair mechanism where DNA polymerase removes a mispaired nucleotide and replaces it with the correct one.

Mismatch repair

A repair mechanism where a protein binds to the site of the mismatch, cuts the unmethylated strand, degrades a short stretch of that strand, and DNA polymerase synthesizes a replacement.

Dark repair

An enzyme-driven repair mechanism for UV damage where the damaged section is removed by cutting the DNA backbone on either side of a thymine dimer, followed by DNA polymerase and DNA ligase filling and sealing the gap.

Eroderma pigmentosum

A human disease resulting from defects in dark repair where individuals cannot repair UV damage and get skin cancer when exposed to the sun.

Light repair (photoreactivation)

A repair mechanism in prokaryotes and eukaryotes where the energy of light is used to break the covalent bond between thymine nucleobases, restoring the original DNA molecule.

Photolayse

The specific enzyme responsible for executing light repair through photoreactivation to break thymine dimer bonds.

Vertical gene transfer

The transmission of genetic material from parent to daughter cells via binary fission.

Horizontal gene transfer

The transmission of genetic material from one cell to another cell, which prokaryotes require to acquire new traits.

DNA mediated transformation

A form of horizontal gene transfer involving the uptake of exogenous ('naked') DNA from the environment by a competent bacterial cell.

Competent cell

A bacterial cell capable of undergoing transformation, possessing required binding proteins and a membrane permeable to transferable DNA.

Transduction

The transfer of bacterial DNA from one cell to another mediated by a bacteriophage.

Transducing particle

A defective viral particle formed when bacterial DNA mistakenly enters a phage protein coat instead of phage DNA during viral assembly.

Generalized transduction

A type of transduction in which any bacterial gene can be transferred from a donor to a recipient cell.

Specialized transduction

A type of transduction in which only specific bacterial genes can be transferred.

Conjugation

The transfer of DNA from one bacterial cell to another requiring direct cell-to-cell contact.

Sex pilus (F pilus)

A specialized bacterial structure produced by $F^+$ cells that makes direct contact with an $F^-$ recipient cell and retracts to draw the cells together for conjugation.

Hfr cell

A bacterial cell formed when the F plasmid integrates into the bacterial chromosome by homologous recombination, capable of transferring chromosomal DNA.

Plasmids

Small, circular, double-stranded DNA molecules that replicate independently from chromosomal DNA using their own origin of replication.

R plasmids

Plasmids that carry resistance genes (such as carbenicillin, chloramphenicol, and tetracycline resistance) and pilus synthesis genes.

CRISPR system

A bacterial adaptive immune system against bacteriophages that captures invading DNA fragments into a CRISPR array, expresses crRNA, and degrades invading DNA.