Chapter 9: An Introduction to Microbial Genetics

Comprehensive vocabulary flashcards covering microbial genetics, DNA structure, replication, protein synthesis, gene regulation, and genetic recombination.

Genetics

The study of heredity, exploring the transmission, expression, variation, and structure/function of genetic material.

Genome

The sum total of genetic material ($DNA$) in a cell, including chromosomes, mitochondria, chloroplasts, and plasmids.

Chromosome

A discrete cellular structure composed of a neatly packaged $DNA$ molecule.

Bacterial Chromosome

A single circular loop of $DNA$.

Eukaryotic Chromosomes

Multiple and linear $DNA$ molecules located in the nucleus.

Gene

The fundamental unit of heredity; a segment of $DNA$ that contains the code to make a protein or $RNA$ molecule.

Structural Genes

Genes that code for the primary structure of proteins.

Regulatory Genes

Genes that control gene expression.

Genotype

The genetic makeup of an organism constituted by all types of its genes.

Phenotype

The observable traits created by the expression of the genotype.

DNA Gyrase

An enzyme in prokaryotes that coils the chromosome into a tight bundle by introducing twists into the $DNA$ molecule.

Nucleosomes

The first level of coiling in eukaryotic $DNA$ packaging, consisting of $DNA$ wrapped around histone proteins.

Nucleotide

The basic unit of $DNA$ structure, consisting of a deoxyribose sugar, a phosphate group, and a nitrogenous base.

Nitrogenous Bases in DNA

Adenine ($A$), Guanine ($G$), Thymine ($T$), and Cytosine ($C$).

Complementary Base Pairing

Adenine pairs with thymine via $2$ hydrogen bonds; guanine pairs with cytosine via $3$ hydrogen bonds.

Antiparallel Arrangement

The orientation of the $DNA$ double helix where one strand runs $5'$ to $3'$ and the other runs $3'$ to $5'$.

Semiconservative Replication

The process where each new $DNA$ molecule consists of one original parent strand and one newly synthesized strand.

Origin of Replication

A specific sequence that is $AT$-rich, where $DNA$ replication is initiated because less energy is required to separate the strands.

Helicase

The enzyme responsible for unzipping the $DNA$ helix by breaking hydrogen bonds at the origin of replication.

Primase

The enzyme that synthesizes an $RNA$ primer to provide a starting point for $DNA$ synthesis.

DNA Polymerase III

An enzyme that adds bases to the new $DNA$ chain and proofreads the chain for mistakes; it builds in the $5'$ to $3'$ direction.

DNA Polymerase I

An enzyme that removes $RNA$ primers, replaces gaps with correct nucleotides, and repairs mismatched bases.

Ligase

The enzyme that performs the final binding of nicks in the $DNA$ backbone during synthesis and repair.

Okazaki Fragment

Short segments of $DNA$ synthesized discontinuously on the lagging strand.

Transcription

The process where genetic information in $DNA$ is conveyed to $RNA$ molecules.

Translation

The process where information in $RNA$ is used to produce proteins.

Messenger RNA (mRNA)

A transcribed version of a structural gene that carries the $DNA$ master code to the ribosome in triplets called codons.

Transfer RNA (tRNA)

A molecule with a cloverleaf structure that carries specific amino acids to the ribosome; contains an anticodon.

Ribose

The five-carbon sugar found in $RNA$, replacing the deoxyribose found in $DNA$.

Uracil (U)

The nitrogenous base in $RNA$ that replaces thymine and pairs with adenine.

Stop Codons

Codons for which there is no corresponding $tRNA$, resulting in the termination of translation ($UAA$, $UAG$, and $UGA$).

Introns

Intervening sequences of noncoding $DNA$ in eukaryotes that must be spliced out of the final $mRNA$ transcript.

Operon

A set of genes in prokaryotes that are regulated as a single unit.

Inducible Operon

An operon turned on by a substrate, usually involving catabolic enzymes, such as the Lac operon.

Repressible Operon

An operon turned off by its product, usually involving anabolic enzymes, such as the Arginine operon.

Mutation

A change in the phenotype due to a change in the nitrogen base sequence of $DNA$.

Wild Type

The natural, nonmutated characteristic of an organism.

Point Mutation

The addition, deletion, or substitution of a few bases in the genetic code.

Nonsense Mutation

A mutation that changes a normal codon into a stop codon, almost always resulting in a nonfunctional protein.

Frameshift Mutation

A mutation occurring when the reading frame of $mRNA$ is altered by the insertion or deletion of nucleotides.

Ames Test

A procedure using a mutant strain of Salmonella enterica to screen agricultural, industrial, and medicinal compounds for mutagenicity.

Conjugation

Genetic recombination requiring direct contact between a donor and recipient cell via a pilus.

Transformation

A process where a recipient cell accepts small fragments of $DNA$ from the surrounding environment, often from a lysed donor cell.

Transduction

Genetic transfer where a bacteriophage serves as a carrier of $DNA$ from a donor cell to a recipient cell.

Transposons

Special $DNA$ segments, also called 'jumping genes', that can move from one location in the genome to another.