Molecular Basis of Inheritance

Comprehensive vocabulary flashcards covering the molecular basis of inheritance, including DNA structure, replication, transcription, translation, genetic code, gene regulation (lac operon), the Human Genome Project, and DNA fingerprinting.

DNA (Deoxyribonucleic Acid)

A long polymer of deoxyribonucleotides that acts as the genetic material in the majority of living organisms.

Nucleotide

The basic monomer unit of nucleic acids, consisting of three components: a nitrogenous base, a pentose sugar (ribose in RNA, deoxyribose in DNA), and a phosphate group.

Purines

A class of two-carbon nitrogen ring nitrogenous bases found in nucleic acids, specifically Adenine (A) and Guanine (G).

Pyrimidines

A class of single-ring nitrogenous bases found in nucleic acids, consisting of Cytosine (C), Uracil (U), and Thymine (T).

$N$-glycosidic Linkage

The covalent bond linking a nitrogenous base to the $1'\text{-OH}$ group of a pentose sugar to form a nucleoside.

Phosphodiester Linkage

The $3'\text{--}5'$ chemical linkage formed between the phosphate group of one nucleotide and the $3'\text{-OH}$ of the adjacent pentose sugar, joining nucleotides into a polynucleotide chain.

Nuclein

The name given by Friedrich Miescher in 1869 to the acidic substance he first identified inside the cell nucleus, later known as DNA.

Chargaff's Rule

The biochemical observation that for double-stranded DNA, the ratios between Adenine and Thymine, and Guanine and Cytosine, are constant and equal to one ($A=T$ and $G=C$).

DNA Double Helix

The structural model proposed by James Watson and Francis Crick in 1953, featuring two antiparallel polynucleotide chains coiled in a right-handed fashion with a sugar-phosphate backbone on the outside and complementary bases paired via hydrogen bonds on the inside.

Pitch of the Helix

The length of one complete turn of the DNA double helix, which is $3.4\,\text{nm}$ and contains roughly $10\,\text{bp}$, resulting in a distance of approximately $0.34\,\text{nm}$ between consecutive base pairs.

Central Dogma

The principle formulated by Francis Crick stating that genetic information flows unidirectionally from DNA $\rightarrow$ RNA $\rightarrow$ Protein.

Nucleoid

The distinct, non-membrane-bound region in prokaryotes like \textit{E. coli} where the negatively charged DNA is held in large loops by positively charged proteins.

Histones

A set of positively charged, basic proteins rich in the basic amino acid residues lysine and arginine that organize and package eukaryotic DNA.

Histone Octamer

A core unit of eight histone molecules around which negatively charged DNA is wrapped to form a nucleosome.

Nucleosome

The fundamental repeating structural unit of chromatin, consisting of approximately $200\,\text{bp}$ of DNA helix wrapped around a positively charged histone octamer.

Beads-on-String Structure

The microscopic appearance of nucleosomes repeating along a DNA strand within chromatin when observed under an electron microscope (EM).

Non-histone Chromosomal (NHC) Proteins

An additional set of non-histone proteins required for the higher-level packaging and condensation of chromatin fibers into chromosomes.

Euchromatin

Loosely packed regions of chromatin in a typical nucleus that stain lightly and represent transcriptionally active chromatin.

Heterochromatin

Densely packed regions of chromatin that stain dark and represent transcriptionally inactive chromatin.

Transforming Principle

The substance identified by Frederick Griffith in 1928 that was transferred from heat-killed virulent S strain \textit{Streptococcus pneumoniae} to live R strain bacteria, transforming them into virulent S strain bacteria.

Avery, MacLeod, and McCarty Experiment

The 1933–44 study that purified biochemicals from heat-killed S cells and established that only DNA-digesting enzyme (DNase) inhibited transformation, proving DNA is the genetic material.

Hershey-Chase Experiment

The 1952 experiment using bacteriophages labeled with radioactive phosphorus ($^{32}\text{P}$) and radioactive sulfur ($^{35}\text{S}$) that provided unequivocal proof that DNA, not protein, enters bacteria to act as genetic material.

RNA World Hypothesis

The concept that RNA was the first genetic material and catalyst on Earth, around which essential life processes like metabolism, translation, and splicing evolved.

Semiconservative DNA Replication

The replication scheme where the two parental DNA strands separate and each serves as a template, producing daughter DNA molecules composed of one conserved parental strand and one newly synthesized strand.

Meselson and Stahl's Experiment

The 1958 experiment using \textit{E. coli} grown in $^{15}\text{NH}_4\text{Cl}$ followed by $^{14}\text{NH}_4\text{Cl}$ medium and separated via CsCl density gradient centrifugation, experimentally proving semiconservative replication.

DNA-dependent DNA Polymerase

The primary replication enzyme that uses a DNA template to catalyze the polymerisation of deoxynucleotides exclusively in the $5' \rightarrow 3'$ direction at high speed and accuracy.

Deoxyribonucleoside Triphosphates (dNTPs)

Molecules that serve a dual role during DNA replication: acting as substrate monomers and providing energy for the polymerisation reaction through their two terminal high-energy phosphate bonds.

Replication Fork

The small Y-shaped opening of the unwound DNA helix where replication actively takes place.

DNA Ligase

The enzyme responsible for covalently joining the discontinuously synthesized DNA fragments on the lagging strand during replication.

Origin of Replication

The specific DNA sequence where the process of DNA replication originates and initiates.

Transcription

The biological process of copying genetic information from one strand of the DNA into a complementary single-stranded RNA molecule.

Transcription Unit

A functional region of DNA comprising three essential elements: a promoter, the structural gene, and a terminator.

Template Strand

The strand of DNA in a transcription unit with $3' \rightarrow 5'$ polarity that serves as the guide for RNA synthesis by RNA polymerase.

Coding Strand

The strand of DNA in a transcription unit with $5' \rightarrow 3'$ polarity whose nucleotide sequence matches the newly transcribed RNA (except thymine replaces uracil) and serves as the reference point for structural coordinates.

Promoter

A regulatory DNA sequence located towards the $5'\text{-end}$ (upstream) of the coding strand that provides the binding site for RNA polymerase and initiates transcription.

Terminator

A DNA sequence located towards the $3'\text{-end}$ (downstream) of the coding strand that defines the termination point of transcription.

Cistron

A segment of DNA that specifically codes for a single polypeptide.

Exons

The coding or expressed sequences in split eukaryotic genes that appear in mature or processed RNA molecules.

Introns

The non-coding intervening sequences in eukaryotic split genes that interrupt exons and are removed during processing.

Splicing

The post-transcriptional process in eukaryotes where non-functional introns are excised and exons are joined together in a defined order.

Capping

The addition of an unusual nucleotide, methyl guanosine triphosphate, to the $5'\text{-end}$ of heterogeneous nuclear RNA (hnRNA).

Tailing

The addition of $200\text{--}300$ adenylate residues at the $3'\text{-end}$ of hnRNA in a template-independent manner to form a poly-A tail.

RNA Polymerase II

The eukaryotic enzyme responsible for transcribing the precursor of mRNA, known as heterogeneous nuclear RNA (hnRNA).

Sigma Factor ($\sigma$)

The transient initiation factor that associates with bacterial RNA polymerase to confer promoter recognition and facilitate the initiation of transcription.

Rho Factor ($\rho$)

The termination factor that transiently binds to bacterial RNA polymerase to terminate the transcription process.

Genetic Code

The set of nucleotide base triplets (codons) in mRNA that dictate the precise sequence of amino acids in a synthesized protein.

Degenerate Code

The property of the genetic code wherein a single amino acid can be specified by more than one distinct codon.

AUG Codon

A dual-function triplet codon that specifies the amino acid Methionine (Met) and acts as the universal initiator codon for translation.

Stop Codons

The three codons—UAA, UAG, and UGA—that do not code for any amino acids and signal the termination of translation.

Frameshift Mutation

A mutation caused by the insertion or deletion of one or two bases, altering the contiguous reading frame of codons from that point onward.

tRNA (Transfer RNA)

An adapter molecule possessing an anticodon loop complementary to mRNA codons and an amino acid acceptor stem that links codons to specific amino acids.

Aminoacylation of tRNA

The ATP-dependent first step of translation, also known as charging of tRNA, in which an amino acid is activated and attached to its cognate tRNA.

Ribozyme

A catalytic RNA molecule, exemplified by the 23S rRNA in bacteria which catalyzes peptide bond formation during translation.

Untranslated Regions (UTRs)

Sequences of an mRNA molecule located at both the $5'\text{-end}$ (before the start codon) and the $3'\text{-end}$ (after the stop codon) that are not translated into protein but are required for efficient translation.

Operon

A coordinated unit of bacterial gene expression wherein a polycistronic structural gene is regulated by a shared promoter, an operator, and regulatory genes.

Lac Operon

A transcriptionally regulated bacterial operon elucidated by François Jacob and Jacques Monod that controls the transport and metabolism of lactose.

$i$ Gene

The regulatory gene of the lac operon that constitutively synthesizes the lac repressor protein; the letter $i$ stands for inhibitor.

Beta-galactosidase ($\beta$-gal)

The enzyme encoded by the $z$ gene of the lac operon that hydrolyzes the disaccharide lactose into its monosaccharide units, glucose and galactose.

Permease

The membrane protein encoded by the $y$ gene of the lac operon that enhances the bacterial cell's permeability to $\beta$-galactosides like lactose.

Transacetylase

The enzyme encoded by the $a$ gene of the lac operon that participates in lactose metabolism.

Inducer

A substrate molecule such as lactose or allolactose that binds to and inactivates the repressor protein, allowing RNA polymerase access to transcribe the lac operon.

Human Genome Project (HGP)

A mega project launched in 1990 and completed in 2003 to decipher the complete nucleotide sequence of all $3 \times 10^9\,\text{bp}$ of human DNA.

Expressed Sequence Tags (ESTs)

A genome sequencing approach focused exclusively on identifying and sequencing all the genes that are expressed as functional RNA.

Sequence Annotation

The blind whole-genome sequencing approach of sequencing both coding and non-coding regions and subsequently assigning functional regions to sequences.

BAC and YAC

Bacterial Artificial Chromosomes and Yeast Artificial Chromosomes; specialized cloning vectors utilized to amplify large human DNA fragments during the Human Genome Project.

Single Nucleotide Polymorphisms (SNPs)

Single-base DNA sequence differences occurring at roughly $1.4\,\text{million}$ locations in the human genome, valuable for locating disease-associated sequences and tracing human history.

Satellite DNA

Repetitive, non-coding fractions of genomic DNA that separate into minor peaks distinct from bulk genomic DNA during density gradient centrifugation.

Variable Number of Tandem Repeats (VNTR)

A class of mini-satellite DNA sequences varying from $0.1\,\text{to }20\,\text{kb}$ arranged in varying tandem copy numbers among individuals, utilized by Alec Jeffreys as a probe for DNA fingerprinting.

DNA Polymorphism

An inheritable sequence variation arising from mutations that persists in a population at an allelic frequency greater than $0.01$, forming the basis of genetic mapping and DNA fingerprinting.

DNA Fingerprinting

A forensic and identification technique developed by Alec Jeffreys that identifies individual-specific differences in polymorphic repetitive DNA sequences via restriction digestion, electrophoresis, Southern blotting, and VNTR probe hybridisation.