Exam 3 Homework Flashcards-Microbiology

Positive Selection

A method for identifying microbial mutants whereby cells are plated on a medium without drugs, allowing all to grow, followed by replica plating to identify colonies that grow in the presence of a drug.

Negative Selection

A method for identifying auxotrophic mutants by growing cells on a medium with all essential nutrients followed by shifting to a medium lacking specific nutrients and observing which colonies do not grow.

Conjugation

The process by which a donor cell transfers a plasmid to a recipient cell through a structure called a sex pilus.

Hfr Cells

High-frequency recombination cells that have a plasmid integrated into their genome; can transfer chromosomal DNA to a recipient cell.

F Plasmid

A plasmid that allows for conjugation and is capable of directing the synthesis of the sex pilus.

Competency

The ability of a cell to take up extracellular DNA from its environment, allowing for genetic transformation.

Generalized Transduction

A process where a bacteriophage injects random segments of DNA from one bacterium to another during the infection cycle.

Specialized Transduction

A specific form of transduction where a bacteriophage transfers specific portions of DNA adjacent to its integration site to a new host.

Transcription

The process of synthesizing RNA from a DNA template.

Prokaryotic Transcription Stages

1. Initiation, 2. Elongation, 3. Termination.

Rho-independent termination

Termination of transcription where RNA forms a hairpin structure that displaces RNA polymerase.

Rho-dependent termination

Termination of transcription that involves the Rho protein chasing RNA polymerase to detach it from the DNA.

Eukaryotic transcription

Involves chromatin remodeling, monocistronic messages, and the presence of exons and introns.

Monocistronic

A type of mRNA that encodes for a single protein.

Shine-Dalgarno sequence

A ribosomal binding site in bacterial mRNA that helps in the initiation of translation.

Initiation of Translation

The stage where the small ribosomal subunit binds to mRNA and the initiator tRNA binds to the start codon.

Formyl-Methionine (fMet)

The modified form of methionine that is the first amino acid in bacterial protein synthesis.

Peptidyl transferase

An enzyme that catalyzes the formation of peptide bonds between amino acids during translation.

Lac operon

A group of genes involved in the metabolism of lactose, regulated by the presence of glucose and lactose.

Trp operon

A group of genes responsible for tryptophan synthesis, regulated by a repressor protein that binds to the operator.

Corepression

A mechanism by which the binding of a small molecule to a repressor protein enables it to bind to the operator, thereby inhibiting gene expression.

Initiation Phase

The phase where DNA replication begins at the origin of replication, involving initiator proteins like DnaA and DnaB.

Origin of Replication (OriC)

The specific site in E. coli where DNA replication initiates.

DnaA

The primary replication initiator protein that signals the start of DNA replication.

DnaB

The helicase enzyme that unwinds the DNA strands at the replication fork.

DnaC

A protein that helps guide DnaB helicase in loading onto DNA.

Elongation Phase

The phase of DNA replication where nucleotides are added to the new DNA strand by DNA polymerase.

Leading Strand

The continuously synthesized DNA strand during replication, where DNA polymerase III adds nucleotides.

Lagging Strand

The discontinuously synthesized DNA strand consisting of short RNA Okazaki fragments.

Beta Clamp

A protein that clamps DNA polymerase to the DNA, facilitating continuous synthesis.

DNA Polymerase I

The enzyme that replaces RNA primers with DNA during replication.

Termination Phase

The phase of DNA replication in E. coli where replication stops at specific termination sites.

Tus Protein

The protein that binds to termination sites in E. coli and halts the progression of replication forks.

Topoisomerase

An enzyme that alleviates supercoiling in the DNA ahead of the replication fork by breaking and rejoining DNA strands.

Eukaryotic Replication

Involves multiple origins of replication on each chromosome, unique initiation proteins, and elongation by different polymerases.

DNA Polymerase Alpha

The enzyme in eukaryotes responsible for creating primers during replication.

End-Replication Problem

A phenomenon where DNA polymerase cannot fully replicate the ends of linear chromosomes, leading to DNA loss over time.

Archaeal Replication

Similar to eukaryotic replication but features unique initiation mechanisms and often polyploid chromosomes.

Polymerase Epsilon

A DNA polymerase in archaea that elongates primers on the leading strand.

Polymerase Delta

A DNA polymerase in archaea that elongates primers on the lagging strand.