Molecular Genetics, Bacterial Pathogens, and Virology

Comprehensive vocabulary flashcards reviewing molecular genetics, DNA mutations, cancer mechanisms, bacterial biology, pathogenic mechanisms, and viral replication cycles.

Gene Expression

The cellular process wherein genetic information stored in DNA is transcribed and translated into a functional gene product, such as a polypeptide or functional RNA.

Purines

Double-ring nitrogenous bases found in nucleic acids; specifically adenine (A) and guanine (G).

Pyrimidines

Single-ring nitrogenous bases found in nucleic acids; specifically cytosine (C) and thymine (T) in DNA, and cytosine (C) and uracil (U) in RNA.

Central Dogma of Molecular Biology

The fundamental framework describing the flow of genetic information inside a biological system: DNA is copied into RNA via transcription, and mRNA is translated into functional proteins.

Promoter

A specific sequence motif in DNA where RNA polymerase binds to initiate the transcription of a gene.

Codon

A three-nucleotide sequence in mRNA that codes for a specific amino acid or a termination signal during protein translation.

Point Mutation

A genetic mutation resulting from a change in a single nucleotide base pair or a small number of bases within a DNA sequence.

Frameshift Mutation

A genetic mutation caused by the insertion or deletion of a number of nucleotides that is not a multiple of three, altering the entire downstream triplet reading frame.

Germ-Line Mutation

A heritable mutation occurring in reproductive cells (sperm or egg) that can be passed down to an organism's offspring.

Somatic Mutation

A non-heritable mutation occurring in non-germline body cells (such as skin or lung cells) that affects the individual during their lifetime but is not transmitted to progeny.

Thymine Dimer

A lesion caused by nonionizing ultraviolet (UV) radiation in which two adjacent thymine bases become covalently linked, forming a kink in the DNA backbone that can stall replication.

Nucleotide Excision Repair

A DNA repair pathway where damage-detecting proteins recognize helical distortions, endonuclease complexes nick both sides of the lesion, helicase removes the excised segment, DNA polymerase resynthesizes the missing strand in the $5' \rightarrow 3'$ direction, and DNA ligase seals the nick.

Proto-Oncogene

A normal cellular gene encoding proteins that stimulate cell division and survival, which can trigger abnormal, unregulated cell cycle progression when mutated or overly active (becoming an oncogene).

Tumor-Suppressor Gene

A normal gene whose protein products negatively regulate the cell cycle, promote DNA repair, control cell adhesion, or trigger programmed cell death to prevent malignant transformation.

p53

A critical tumor-suppressor protein dubbed the 'guardian of the genome' that arrests the cell cycle upon sensing DNA damage, directs DNA repair pathways, and initiates apoptosis if damage is unrepairable; lost or mutated in approximately $50\%$ of human cancers.

Pathogen

Any biological agent capable of causing disease—including bacteria, viruses, eukaryotic parasites, and prions—by entering a host, evading immune defenses, replicating, and inflicting tissue damage.

Bacterial Cell Anatomy

Prokaryotic structural arrangement typically containing a protective capsule, cell wall, plasma membrane, cytoplasm, $70\text{S}$ ribosomes, a non-membrane-bound nucleoid region containing circular DNA, flagella for motility, and pili for adhesion or conjugation.

Binary Fission

The asexual reproductive mechanism in prokaryotes where the circular chromosome replicates, the cell elongates, and a septum/cell wall forms down the middle to yield two identical daughter cells.

Bacterial Conjugation

A mechanism of horizontal gene transfer in bacteria requiring direct cell-to-cell contact through which genetic elements, typically plasmids, are transferred from a donor to a recipient cell.

Bacterial Transformation

The uptake and stable incorporation of naked environmental DNA fragments released from lysed cells into a recipient bacterial cell's genome.

Transduction

The transfer of bacterial host DNA from one cell to another mediated by an infecting bacteriophage vector.

Chemolithotroph

An autotrophic or mixotrophic bacterium that generates ATP by oxidizing inorganic compounds with high potential energy, such as hydrogen gas ($H_2$), hydrogen sulfide ($H_2S$), or elemental sulfur ($S^0$).

Virulence

The degree or intensity of pathogenicity of an infectious organism, functioning as a heritable, variable trait often governed by virulence genes or toxin-producing capabilities.

Bacterial Endospore

A dehydrated, thick-walled, highly resilient dormant structure produced by certain Gram-positive bacteria during environmental stress, resistant to desiccation, extreme heat, UV radiation, and antibiotics.

Leprosy

A chronic infectious disease caused by Mycobacterium leprae characterized by skin lesions, peripheral nerve damage, loss of tactile and pain sensation, and localized tissue deterioration.

Virus

An obligate, intracellular parasite consisting of a nucleic acid genome (DNA or RNA) enclosed by a protective protein capsid (and sometimes a lipid envelope), lacking its own metabolic capabilities, cytoplasm, and ribosomes.

Capsid

The protective shell composed of repeating protein subunits (capsomeres) that surrounds and encapsidates the viral genome.

Lysogeny

A dormant viral life cycle exhibited by temperate bacteriophages where the viral genome integrates directly into the host bacterial chromosome, replicating with each host division without killing the cell or assembling active virions.

Episome

A viral genetic element that can replicate independently within the host nucleus or cytoplasm during latency and may occasionally integrate into host DNA, as observed in Herpes simplex viruses.

Reverse Transcriptase

A retroviral RNA-dependent DNA polymerase enzyme that uses single-stranded viral RNA as a template to synthesize a complementary DNA molecule.

Provirus

A double-stranded DNA copy of a retroviral genome (such as HIV) integrated stably into the host cell's nuclear chromosome by the viral enzyme integrase.

Antigenic Reassortment

The mixing and exchange of segmented genomic RNA strands that occurs when two distinct viral strains (such as influenza) co-infect the same host cell, resulting in novel progeny strains with altered virulence.

Pandemic

An epidemic of an infectious disease that spreads widely across national boundaries, multiple continents, or globally, causing substantial morbidity and mortality.

Rabies Virus

A neurotropic rhabdovirus that enters peripheral nerves and migrates retrogradely to the central nervous system, inducing encephalitis, aggression, altered behavior, difficulty swallowing, and excessive salivation.