Topic 3 - Genetics in Prokaryotes - micro unit 2.1

Vocabulary flashcards covering major terms from the lecture on microbial genetics, DNA structure, replication, gene regulation, quorum sensing, gene transfer, and mutations.

DNA Double Helix

Two antiparallel strands of nucleotides held together by hydrogen bonds between complementary bases.

Sugar-Phosphate Backbone

Alternating deoxyribose sugars and phosphate groups that form the structural framework of DNA.

Antiparallel Strands

Orientation of the two DNA strands running 5′→3′ and 3′→5′ relative to each other.

5′ End

DNA or RNA strand terminus bearing a free phosphate group on carbon 5 of the sugar.

3′ End

Strand terminus bearing a free hydroxyl group on carbon 3 of the sugar.

Nucleoside

A nitrogenous base linked to a five-carbon sugar without the phosphate group.

Gene

A DNA segment that contains specific information to produce an RNA or protein product.

Nucleoid

Irregularly shaped region in a bacterium containing its chromosomal DNA.

Plasmid

Small, circular, independently replicating DNA molecule carrying non-essential but useful genes.

Fertility Plasmid

Plasmid that encodes genes for sex pilus formation and DNA transfer during conjugation.

Resistance Plasmid

Plasmid carrying genes that provide resistance to antibiotics or heavy metals.

Catabolic Plasmid

Plasmid containing genes that encode enzymes for degradation of unusual organic compounds (e.g., toluene).

Bacteriocin Plasmid

Plasmid encoding proteins that kill closely related bacterial species.

Virulence Plasmid

Plasmid whose genes enable a bacterium to infect or damage a host.

Tumor-Inducing (Ti) Plasmid

Plasmid of Agrobacterium tumefaciens that transfers genes causing plant gall formation; tool for plant cloning.

Cryptic Plasmid

Plasmid with no known function.

Origin of Replication

Specific DNA sequence where replication begins.

Bidirectional Replication

Process where two replication forks move in opposite directions from a single origin.

Leading Strand

DNA strand synthesized continuously in the 5′→3′ direction toward the replication fork.

Lagging Strand

DNA strand synthesized discontinuously as Okazaki fragments away from the fork.

Okazaki Fragment

Short DNA segment produced on the lagging strand during replication.

Semi-Conservative Replication

Each daughter DNA molecule contains one parental and one newly synthesized strand.

RNA Primase

Enzyme that synthesizes short RNA primers needed to start DNA synthesis.

DNA Polymerase III

Major bacterial enzyme that elongates new DNA strands during replication.

Helicase

Enzyme that unwinds the DNA double helix at the replication fork.

DNA Polymerase I

Enzyme that removes RNA primers and fills gaps with DNA.

DNA Ligase

Enzyme that seals nicks by joining adjacent DNA fragments.

DNA Gyrase

Topoisomerase that relieves supercoiling ahead of the replication fork.

DNA Methylation

Addition of –CH₃ groups to bases (often cytosine) to protect DNA from restriction enzymes and regulate functions.

Restriction Endonuclease

Bacterial enzyme that recognizes specific DNA sequences and cleaves foreign DNA.

Ribose

Five-carbon sugar found in RNA.

Uracil

RNA base that pairs with adenine and replaces thymine.

mRNA

Messenger RNA; transcript that carries genetic code to ribosomes for translation.

tRNA

Transfer RNA; small RNA that decodes codons and delivers amino acids to the ribosome.

rRNA

Ribosomal RNA; structural and catalytic component of ribosomes.

Codon

Sequence of three RNA bases specifying one amino acid or a stop signal.

Start Codon

AUG; signals initiation of translation and codes for methionine.

Stop Codon

UAA, UAG, or UGA; signals termination of translation.

Degenerate Code

Genetic code property in which multiple codons can specify the same amino acid.

Unambiguous Code

Each codon specifies only one amino acid.

Operon

Cluster of functionally related genes transcribed together under a single promoter and operator.

Induction

Regulatory pattern where genes are turned on only when their products are needed.

Repression

Regulatory pattern where genes are turned off when their products are unnecessary.

lac Operon

E. coli operon encoding proteins for lactose uptake and catabolism; classic inducible system.

Promoter (lac P)

DNA site where RNA polymerase binds to begin transcription of the lac operon.

Operator (lac O)

DNA region bound by the lac repressor to block transcription.

lacZ

Gene encoding β-galactosidase, which hydrolyzes lactose.

lacY

Gene encoding lactose permease, a membrane transporter.

lacA

Gene encoding transacetylase of uncertain role in lactose metabolism.

lacI

Separate gene encoding the lac repressor protein.

Allolactose

Inducer molecule that binds lac repressor, preventing it from blocking the operator.

Quorum Sensing

Cell-density–dependent communication system that regulates collective bacterial behavior.

Autoinducer

Small diffusible signal molecule produced and sensed during quorum sensing.

Biofilm

Structured community of microorganisms attached to a surface and embedded in a self-produced matrix.

Acyl Homoserine Lactone (AHL)

Common autoinducer used by many Gram-negative bacteria.

AI-2

Furanosyl borate diester autoinducer enabling interspecies quorum-sensing communication.

Quorum Quenching

Disruption or inhibition of quorum sensing, often to reduce bacterial virulence.

Transformation

Uptake of naked DNA from the environment by a bacterial cell.

Transduction

Transfer of bacterial DNA from one cell to another via a bacteriophage.

Conjugation

Direct transfer of DNA between bacteria through cell-to-cell contact (e.g., sex pilus).

Point Mutation

Change of a single nucleotide base pair in DNA.

Silent Mutation

Point mutation that does not alter the amino-acid sequence of a protein.

Frameshift Mutation

Insertion or deletion that alters the reading frame of codons downstream.

Transposon

Mobile DNA element that can move within a genome, potentially disrupting genes.

Ionizing Radiation

High-energy radiation that breaks DNA strands, leading to lethal damage.

Thymine Dimer

Covalent linkage of adjacent thymines caused by UV light, distorting DNA.

Base Analog

Chemical resembling a DNA base that can be incorporated and cause mispairing.

Intercalating Agent

Flat molecule (e.g., ethidium bromide) that inserts between DNA bases, causing frameshifts.

Genotype

Complete genetic composition of an organism.

Phenotype

Observable characteristics resulting from gene expression and environmental influence.

Diauxic Growth

Two-phase bacterial growth pattern where glucose is consumed before secondary sugars.

70S Ribosome

Prokaryotic ribosome composed of 50S and 30S subunits.

Svedberg Unit (S)

Sedimentation coefficient reflecting size and shape of particles during centrifugation.

Simultaneous Transcription-Translation

Coupled process in bacteria where ribosomes begin translating mRNA while it is still being transcribed.

Sense Strand

DNA strand with the same sequence as the mRNA (except T for U); non-template strand.

Antisense Strand

DNA template strand used by RNA polymerase to synthesize mRNA.

Rho Factor

Bacterial protein that terminates transcription by dislodging RNA polymerase.