Molecular Genetics: DNA Replication, Transcription, Translation, and Mutations

A complete set of 54 vocabulary flashcards covering the fundamentals of microbial genetics, DNA replication machinery, transcription, eukaryotic RNA processing, operon regulation, translation, and genetic mutations.

Genome

The complete set of genetic information in a cell, including chromosomes and plasmids.

Gene

A functional segment of DNA that encodes a specific gene product, usually a protein.

Genomics

The study and analysis of the complete nucleotide sequence of DNA.

Genotype

The specific genetic makeup or nucleotide sequence of an organism.

Phenotype

The observable physical characteristics or functional properties of an organism, which are determined by the genotype and influenced by the environment.

Antiparallel Strands

The orientation of double-stranded DNA where the two complementary strands run in opposite directions, with one running 5' to 3' and the other running 3' to 5'.

Sugar-Phosphate Backbone

The structural side-chains of DNA formed by covalent bonds linking the 5' phosphate group of one pentose sugar to the 3' hydroxyl (OH) group of the adjacent sugar.

Complementary Base Pairing

Specific hydrogen bonding between nitrogenous bases: Adenine (A) pairs with Thymine (T) via two hydrogen bonds, and Cytosine (C) pairs with Guanine (G) via three hydrogen bonds.

Central Dogma

The principle describing the directional flow of genetic information inside a cell: DNA → RNA → Protein.

Origin of Replication

A specific nucleotide sequence on a chromosome where DNA replication begins.

Bidirectional Replication

Replication that proceeds simultaneously in opposite directions away from the origin of replication via two advancing replication forks until meeting at a terminating site.

Replication Fork

The Y-shaped region where the double helix is unwound and active DNA synthesis occurs.

Helicase

The enzyme that unzips double-stranded DNA by breaking hydrogen bonds between complementary nucleobases to expose single-stranded templates.

DNA Gyrase (Topoisomerase)

The enzyme that relaxes torsional strain and supercoiling in the DNA double helix ahead of the advancing replication fork.

RNA Primase

An enzyme that synthesizes short RNA fragments called primers to provide the 3'-OH starting group required by DNA polymerase.

DNA Polymerase III

The main replicative enzyme that synthesizes new DNA strands in the 5' to 3' direction and performs proofreading.

DNA Polymerase I

DNA polymerase that removes RNA primers from Okazaki fragments and replaces them with deoxynucleotides (DNA).

Leading Strand

The newly synthesized DNA strand that is constructed continuously toward the advancing replication fork in the 5' to 3' direction.

Lagging Strand

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

Okazaki Fragments

Short, discontinuous segments of DNA synthesized on the lagging strand, each requiring an RNA primer.

DNA Ligase

The enzyme that joins adjacent Okazaki fragments by forming covalent sugar-phosphate bonds to seal backbone nicks.

Semiconservative Replication

The mechanism of DNA replication where each daughter DNA molecule consists of one original parental template strand paired with one newly synthesized strand.

Transcription

The process of copying the genetic information from a DNA template into a single-stranded RNA molecule.

RNA Polymerase

The enzyme that synthesizes single-stranded RNA in the 5' to 3' direction using the minus (−) DNA strand as a template.

Promoter

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

Sigma (σ) Factor

A component of bacterial RNA polymerase that recognizes specific promoter sequences to orient transcription.

Minus (−) Template Strand

The DNA strand used as the template for RNA synthesis.

Plus (+) Strand

The complement of the minus DNA strand, which matches the RNA transcript sequence except that uracil (U) replaces thymine (T).

Terminator

A distinct DNA sequence that signals RNA polymerase to detach from the template and release the newly synthesized RNA transcript.

Messenger RNA (mRNA)

Single-stranded RNA that carries protein-coding instructions from DNA to the ribosome.

Pre-mRNA Processing

Post-transcriptional modifications occurring in eukaryotes: 5' capping (methylated guanine), 3' polyadenylation (poly-A tail), and splicing.

Introns

Non-coding intervening sequences removed during eukaryotic splicing.

Exons

Coding regions joined together during eukaryotic splicing to form functional mRNA.

Operon

A cluster of regulated bacterial genes transcribed together as a single polycistronic mRNA along with its control elements (promoter and operator).

Inducible Operon

An operon routinely turned OFF that is switched ON in the presence of a specific inducer substrate, such as the lac operon.

Repressible Operon

An operon routinely turned ON that is switched OFF when an end product accumulates.

Repressor & Operator

A repressor is a regulatory protein that binds to an operator DNA sequence to physically block RNA polymerase progression.

Translation

The decoding of an mRNA nucleotide sequence into a linear chain of amino acids to construct a functional protein.

Genetic Code

The set of rules dictating how 3-nucleotide codons translate into amino acid sequences.

Codon

A triplet of three consecutive nucleotides on mRNA that specifies a particular amino acid or stop signal.

Start Codon (AUG)

The codon that establishes the starting point of translation, encoding formyl-methionine (f-Met) in prokaryotes.

Stop Codons

Three specific codons (UAA, UAG, UGA) that terminate translation because no tRNA molecules recognize them.

Degenerate Code

The property of the genetic code where multiple distinct codons specify the same amino acid.

Reading Frame

One of three possible ways nucleotide triplets can be grouped during translation.

Ribosome (70S vs. 80S)

The cellular structure composed of rRNA and protein that translates mRNA; prokaryotes possess 70S ribosomes (30S + 50S subunits), while eukaryotes possess 80S ribosomes (40S + 60S subunits).

Ribosome-Binding Site (Shine-Dalgarno)

A sequence on bacterial mRNA upstream of the start codon where the 30S subunit attaches.

Transfer RNA (tRNA)

The adapter RNA molecule carrying a specific amino acid and featuring an anticodon loop that base-pairs with complementary mRNA codons.

Ribosomal Binding Sites (A, P, E Sites)

Functional sites within the ribosome: the A site (aminoacyl) accepts incoming tRNAs, the P site (peptidyl) holds tRNA with the growing peptide chain, and the E site (exit) releases uncharged tRNAs.

Polyribosome (Polysome)

Multiple ribosomes simultaneously translating a single mRNA transcript in prokaryotes.

Point Mutation / Base-Pair Substitution

A change in a single base pair in DNA.

Silent Mutation

A mutation that alters a codon but still codes for the same amino acid, resulting in no change to the protein.

Missense Mutation

A mutation that changes a codon to specify a different amino acid, often altering protein function.

Nonsense Mutation

A mutation that converts an amino acid codon into a premature stop codon, yielding a shortened protein.

Frameshift Mutation

The insertion or deletion of 1 or 2 base pairs, altering the reading frame for all downstream codons and usually introducing a premature stop codon.