Molecular Genetics: DNA Structure, Replication, Gene Expression, and Biotechnology

Comprehensive vocabulary flashcards covering the structure of DNA, semiconservative replication, transcription, RNA processing, translation, bacterial operon gene regulation, and key molecular biotechnology techniques.

Double Helix

The ladder-like, twisted structure of DNA composed of two complementary molecular strands.

Nucleotide

The basic repeating subunit of a DNA molecule, composed of a phosphate group, a pentose sugar, and a nitrogenous base.

Complementary Base Pairing

The specific chemical bonding between nitrogenous bases in DNA, where Adenine ($\text{A}$) pairs with Thymine ($\text{T}$) and Cytosine ($\text{C}$) pairs with Guanine ($\text{G}$).

Codon

A triplet sequence of nucleotide bases in DNA or mRNA that represents a specific amino acid or stop signal.

Gene

A unique sequence of DNA bases that codes for the production of a specific protein, ultimately contributing to an organism's phenotype.

Semiconservative Replication

The mechanism of DNA replication in which each parental strand serves as a template, producing two daughter DNA molecules that each contain one original strand and one newly synthesized strand.

DNA Helicase

The enzyme responsible for unwinding and separating the double-stranded DNA helix at the replication fork.

Single-Stranded Binding Proteins

Proteins that bind to and stabilize single-stranded parental DNA during replication to prevent the strands from re-annealing.

Primase

An enzyme that synthesizes a short RNA primer to provide a free $3'$ end necessary for DNA polymerase to initiate strand elongation.

Leading Strand

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

Lagging Strand

The new DNA strand that is synthesized discontinuously away from the replication fork in short segments called Okazaki fragments.

Okazaki Fragments

Short stretches of DNA synthesized discontinuously on the lagging strand during DNA replication.

DNA Polymerase III

The primary enzyme responsible for synthesizing new DNA strands by adding nucleotides to the $3'$ end in the $5' \rightarrow 3'$ direction, as well as proofreading for errors.

DNA Polymerase I

The enzyme that removes RNA primers from the newly synthesized strand, replaces them with DNA nucleotides, and participates in proofreading.

DNA Ligase

The enzyme that joins Okazaki fragments on the lagging strand by catalyzing the formation of phosphodiester bonds in the sugar-phosphate backbone.

Central Dogma of Molecular Biology

The framework describing the directional flow of genetic information: $\text{DNA} \rightarrow \text{RNA} \rightarrow \text{Protein}$.

Messenger RNA (mRNA)

A complementary RNA copy of a gene that carries genetic instructions from the nucleus to ribosomes in the cytoplasm for protein synthesis.

Promoter

A specific DNA sequence upstream of a gene that serves as the binding site for RNA polymerase and regulatory proteins to direct the start of transcription.

TATA Box

An Adenine- and Thymine-rich DNA sequence located within the promoter region where transcription factors bind to recruit RNA polymerase.

Introns

Non-coding intervening sequences of pre-mRNA that are excised during posttranscriptional RNA processing in eukaryotic cells.

Exons

Coding sequences of pre-mRNA that remain after splicing and are expressed into a mature mRNA transcript and translated into protein.

Spliceosome

A large complex composed of snRNA and protein complexes (snRNPs) that loops and removes introns from pre-mRNA and splices exons together.

Alternative Splicing

A eukaryotic regulatory mechanism where different combinations of exons are spliced together, enabling a single gene to code for multiple distinct polypeptides.

$5'$ Cap

A modified guanine residue added to the $5'$ end of eukaryotic pre-mRNA that serves as an attachment site for the ribosome.

Poly-A Tail

A sequence of adenine nucleotides added to the $3'$ end of eukaryotic pre-mRNA to protect the transcript from degradation by cytoplasmic enzymes.

Transfer RNA (tRNA)

A folded, cloverleaf-shaped RNA molecule containing an anticodon loop that delivers its specific attached amino acid to the ribosome during translation.

Aminoacyl-tRNA (aa-tRNA)

A transfer RNA molecule covalently bound to its corresponding amino acid, activated for protein synthesis.

A Site (Aminoacyl Site)

The ribosomal binding site that receives an incoming aminoacyl-tRNA carrying the next amino acid to be added to the growing polypeptide.

P Site (Peptidyl Site)

The ribosomal binding site that holds the tRNA carrying the growing polypeptide chain.

E Site (Exit Site)

The ribosomal binding site that temporarily holds the deacylated, empty tRNA before it is released back into the cytoplasm.

Translocation

The process during translation elongation where the ribosome advances three nucleotides (one codon) along the mRNA, shifting tRNAs from the A and P sites to the P and E sites.

Release Factor

A protein that binds to a stop codon at the ribosomal A site, triggering the cleavage and release of the completed polypeptide chain and the disassembly of the ribosome.

Polysome

A structure formed when multiple ribosomes simultaneously translate a single mRNA molecule in a single file.

Operon

A functional unit of genomic DNA found in bacteria consisting of a cluster of genes regulated under the control of a single promoter and an operator.

lac Operon

An inducible bacterial operon in E. coli containing genes for $\beta\text{-galactosidase}$ metabolism that are activated when lactose binds and inactivates the LacI repressor.

LacI Protein

The repressor protein in E. coli that binds to the lac operator to block RNA polymerase transcription when lactose is absent.

trp Operon

A repressible bacterial operon in E. coli encoding enzymes for tryptophan synthesis, which is shut down when intracellular tryptophan levels are sufficient.

Corepressor

A small molecule (such as tryptophan in the trp operon) that binds to an inactive repressor protein, altering its conformation so it can bind the operator and block transcription.

Polymerase Chain Reaction (PCR)

An in vitro laboratory technique used to rapidly amplify a specific DNA sequence into billions of copies through thermal cycles of denaturation, primer annealing, and extension.

Restriction Enzymes

Bacterial endonuclease enzymes that recognize specific, palindromic nucleotide sequences and cleave double-stranded DNA at restriction sites.

Sticky Ends

Single-stranded overhanging ends of a DNA fragment produced when a restriction enzyme cuts the phosphodiester backbone in a staggered fashion.

Cloning Vector

A DNA molecule, commonly a bacterial plasmid or virus, used as a carrier to transport foreign genetic material into a host cell for replication.

Restriction Fragment Length Polymorphism (RFLP)

Variations in DNA fragment lengths produced by restriction enzyme digestion due to sequence differences across individuals, commonly used as genetic markers and forensic fingerprints.

CRISPR/Cas9

A targeted gene-editing technology consisting of a customizable guide RNA that directs the Cas9 endonuclease to cut specific double-stranded DNA targets for genetic modification.

Gel Electrophoresis

A laboratory method used to separate charged nucleic acid or protein molecules across a porous gel matrix by applying an electric current, separating fragments inversely proportional to their length.