Introductory Microbiology Exam II Review: Molecular Genetics, Viruses, and Prions

Comprehensive vocabulary flashcards covering DNA replication, gene expression, types of mutations, horizontal gene transfer, viral cycles, and prions from the Introductory Microbiology Exam II Review.

Helicase

An enzyme that unwinds the DNA double helix at the replication fork, separating the two DNA strands so they can be copied.

Topoisomerase and Gyrase

Enzymes that relieve torsional strain and coil tension ahead of the replication fork during DNA replication.

Single-Strand Binding Proteins

Proteins that bind to and stabilize single-stranded DNA after unwinding to prevent the strands from reannealing.

Primase

An enzyme that synthesizes short RNA primers on DNA templates to provide the starting point required for DNA synthesis.

RNA Primer

A short sequence of RNA necessary for initiating DNA replication because DNA polymerase III cannot begin synthesizing a new strand from scratch.

DNA Polymerase III

The primary enzyme responsible for synthesizing the new daughter DNA strand by adding nucleotides exclusively in the $5' \rightarrow 3'$ direction.

Leading Strand

The daughter DNA strand synthesized continuously in the $5' \rightarrow 3'$ direction toward the replication fork, requiring only one RNA primer.

Lagging Strand

The daughter DNA strand synthesized discontinuously away from the replication fork in short segments called Okazaki fragments.

Okazaki Fragments

Short sections of newly synthesized DNA built on the lagging strand, each synthesized in the $5' \rightarrow 3'$ direction from multiple RNA primers.

Semiconservative Replication

The mechanism of DNA replication in which each newly formed daughter DNA molecule consists of one parental (original) template strand and one newly synthesized strand.

Central Dogma

The fundamental framework describing the flow of genetic information in cells: $\text{DNA} \rightarrow \text{RNA} \rightarrow \text{Protein}$, mediated by transcription and translation.

RNA Polymerase

An enzyme that binds to a promoter sequence on DNA to synthesize RNA from a DNA template during transcription.

Promoter

A specific sequence of DNA located upstream of a gene where RNA polymerase binds to initiate transcription.

TATA Box

A stretch of consensus nucleotides in eukaryotic DNA that serves as the promoter sequence for RNA polymerase binding.

-10/-35 Consensus Nucleotides

Consensus promoter sequences located at the $-10$ and $-35$ regions upstream in prokaryotic DNA that direct transcription initiation.

Codon

A sequence of three consecutive nucleotides on mRNA that encodes a specific amino acid or a stop signal.

Anticodon

A sequence of three nucleotides on a tRNA molecule that is complementary to a corresponding codon on mRNA.

Messenger RNA (mRNA)

The RNA molecule that carries genetic instructions and codon sequences transcribed from DNA to the ribosome.

Transfer RNA (tRNA)

The adaptor RNA molecule that carries a specific amino acid at its $3'$ attachment site and pairs with mRNA codons via its anticodon.

Ribosomal RNA (rRNA)

The structural and catalytic RNA component of the ribosome that participates in translating mRNA into protein.

AUG Codon

The universal start codon on mRNA that specifies the amino acid methionine and marks the beginning of translation.

Substitution Mutation

A point mutation in DNA wherein one nucleotide is replaced by a different nucleotide.

Insertion Mutation

A type of mutation in which one or more extra nucleotides are added into a DNA sequence.

Deletion Mutation

A type of mutation in which one or more nucleotides are removed from a DNA sequence.

Frameshift Mutation

A mutation resulting from nucleotide insertions or deletions not in multiples of three, which shifts the triplet reading frame for all downstream codons.

Silent Mutation

A base substitution that causes no change in the resulting amino acid due to the degeneracy (redundancy) of the genetic code.

Missense Mutation

A base substitution that changes a single codon so that it codes for a different amino acid in the protein sequence.

Nonsense Mutation

A base substitution that changes an amino-acid-coding codon into one of the three premature stop codons.

Conjugation

A mechanism of horizontal gene transfer in bacteria involving direct cell-to-cell transfer of DNA (such as an F plasmid) via a pilus.

Transformation

A mechanism of horizontal gene transfer in which a bacterial cell takes up naked exogenous DNA directly from the surrounding environment.

Transduction

A mechanism of horizontal gene transfer where bacterial DNA is transferred from one host cell to another by a bacteriophage.

Obligate Intracellular Pathogen

An infectious agent, such as a virus, that cannot replicate independently and can only reproduce inside a host cell by using the host's cellular machinery.

Lytic Cycle

A viral replication cycle consisting of attachment, penetration, replication, assembly, and release, culminating in the lysis and destruction of the host cell.

Lysogenic Cycle

A viral life cycle in which phage DNA integrates into the host bacterial chromosome as a dormant prophage and replicates alongside the host genome without immediately lysing the cell.

Prion

An infectious, misfolded protein that lacks any viral genome or nucleic acid and causes progressive neurological disease.