Molecular Genetics: Replication, Transcription, Translation, and Inheritance Patterns

Vocabulary practice flashcards covering DNA replication mechanisms, transcription, translation, Mendelian extensions, non-Mendelian inheritance, and pedigrees.

Central Dogma

The biological framework stating that genetic information flows unidirectionally from nucleic acids to functional proteins via $DNA \rightarrow mRNA \rightarrow \text{Protein}$.

Replisome

The multi-protein molecular complex of enzymes and DNA that coordinates and executes the process of DNA replication.

Helicase

An enzyme in the replisome that unzips and unwinds the double-stranded DNA helix at the replication fork.

Replication Fork

The $Y$-shaped active anatomical region formed where double-stranded parental DNA unwinds into single strands during replication.

Primase

An enzyme that initiates DNA synthesis by building a short RNA primer to provide a necessary landing pad for DNA polymerase.

DNA Polymerase

An enzyme that synthesizes daughter DNA strands by adding complementary nucleotides exclusively to the $3'$ end in a $5' \rightarrow 3'$ direction.

Topoisomerase

An enzyme that relieves torsional strain, overwinding, and stress downstream of the advancing replication fork.

Phosphodiester Bond

The covalent chemical bond linking two adjacent sugar residues via a phosphate group within a nucleic acid backbone.

Leading Strand

The newly synthesized DNA strand that is elongated smoothly and continuously toward the replication fork in the $5' \rightarrow 3'$ direction.

Lagging Strand

The newly synthesized DNA strand that is elongated discontinuously away from the replication fork in multiple short fragments.

DNA Ligase

An enzyme that joins newly synthesized adjacent fragments by creating phosphodiester bonds to seal gaps in the sugar-phosphate backbone.

Exonuclease Activity

The enzymatic proofreading capability of DNA polymerase to excise an incorrect, mispaired terminal nucleotide from the end of a strand in the $3' \rightarrow 5'$ direction.

Thymine Dimer

A DNA lesion caused by ultraviolet ($UV$) radiation wherein two adjacent thymine bases on the same strand form abnormal covalent bonds with each other.

Endonuclease

An enzyme that possesses the activity to cleave phosphodiester bonds and excise damaged nucleotides from within an internal DNA strand.

Transcription

The process by which the genetic instructions encoded on a template DNA strand are copied into a complementary $mRNA$ molecule.

Transcription Bubble

A localized unwound region of the DNA double helix that exposes nucleotide bases so that RNA polymerase can read the template.

Template Strand

The specific strand of DNA that is read and transcribed by RNA polymerase to synthesize complementary $mRNA$.

Coding Strand

The non-template DNA strand that has the same nucleotide sequence and direction as the resulting $mRNA$, except that thymine ($T$) is replaced by uracil ($U$).

Promoter

A specific regulatory DNA sequence recognized and bound by RNA polymerase to designate the start site and orientation of gene transcription.

RNA Polymerase

The enzyme that unwinds DNA, synthesizes complementary $mRNA$ in a $5' \rightarrow 3'$ direction from NTPs, and subsequently rewinds the DNA downstream.

Ribonucleotide Triphosphates (NTPs)

The free nucleotide building blocks containing ribose and three phosphates that RNA polymerase incorporates into growing RNA strands.

Purines

The class of double-ringed nitrogenous bases comprising adenine ($A$) and guanine ($G$).

Pyrimidines

The class of single-ringed nitrogenous bases comprising thymine ($T$), cytosine ($C$), and uracil ($U$).

Translation

The cellular process occurring at ribosomes where the nucleotide code of an $mRNA$ molecule directs the sequential assembly of amino acids into a protein.

Codon

A consecutive sequence of three nucleotides on $mRNA$ (or DNA) that specifies a single amino acid or an instruction to terminate synthesis.

tRNA

Transfer RNA; a folded self-complementary RNA molecule possessing three loops, an anticodon at its base, and an amino acid attachment site at its opposite end.

Anticodon

A three-nucleotide sequence on a tRNA loop that pairs complementarily with a corresponding three-nucleotide codon on $mRNA$.

Start Codon

A three-nucleotide sequence ($AUG$) on $mRNA$ coding for methionine that designates the start of protein synthesis.

Stop Codon

A triplet sequence on $mRNA$ ($UAA$, $UAG$, or $UGA$) that signals termination of translation rather than encoding an amino acid.

Codominance

A non-Mendelian inheritance pattern where heterozygous individuals express both parental alleles simultaneously without blending (e.g., roan cattle possessing both red and white hairs).

Loss-of-Function Mutation

A genetic alteration resulting in a protein that cannot perform its normal physiological function; frequently responsible for recessive disorders.

CFTR Gene

The gene encoding an ion channel regulating salt and water movement across cell membranes, which causes cystic fibrosis when two mutated recessive copies are inherited.

Polygenic Inheritance

The inheritance of a phenotypic trait controlled by the additive contribution of multiple genes, resulting in continuous, bell-shaped distribution across a population.

Linked Genes

Genes residing in close proximity on the same physical chromosome that tend to segregate together during meiosis instead of assorting independently.

Sex Chromosomes

A homologous pair of chromosomes determining biological sex, such as the male-heterogametic $XY$ system in mammals or the female-heterogametic $ZW$ system in birds.

OPN1 Gene

An $X$-linked gene coding for color-detecting retinal pigments; recessive loss-of-function mutations in this gene cause red-green color blindness primarily in males.

Pedigree

A standardized genealogical chart depicting the occurrence and phenotypic expression of specific traits across multiple generations of related individuals.