GEN2MHG Topic 2: Nucleic Acid and Higher order DNA

Comprehensive vocabulary flashcards covering Mendel's laws, DNA/RNA biochemistry, packaging, cell division, and replication mechanisms.

Law of Segregation

Gregor Mendel's principle of inheritance stating that alleles segregate so that each gamete carries only one allele for each gene.

Law of Independent Assortment

Gregor Mendel's principle of inheritance stating that different traits (such as seed shape and seed colour) are inherited independently of one another.

Avery, MacLeod, and McCarty Experiment (1944)

The landmark experiment demonstrating that DNA (not protein) encodes and transmits genetic information, as only DNA-containing bacterial extracts could transform avirulent bacteria into virulent bacteria.

Transformation

The biological process in which avirulent living R bacterial cells take up DNA from heat-killed virulent S bacteria and acquire the virulent phenotype.

Chargaff's Rules

The rule based on chemical analysis of hydrolysed DNA showing that the base composition has equal proportions of adenine to thymine ($\%A = \%T$) and guanine to cytosine ($\%G = \%C$).

Rosalind Franklin's X-ray Crystallography Data

X-ray diffraction data demonstrating that DNA forms a double helix with the nitrogenous bases located on the inside of the structure.

Nucleoside

A chemical subunit composed strictly of a five-carbon pentose sugar bound to a nitrogenous base, lacking a phosphate group ($\text{Nucleoside} = \text{sugar} + \text{base}$).

Nucleotide

The repeating structural unit of DNA and RNA, composed of a pentose sugar, a phosphate group, and a nitrogenous base.

Phosphodiester Bond

The covalent linkage that connects carbon #$5'$ of one nucleotide sugar to carbon #$3'$ of an adjacent nucleotide sugar to create the nucleic acid backbone.

Anti-parallel

The structural arrangement of the DNA double helix where the two complementary strands run in opposite orientations from $C5'$ to $C3'$.

Purines

A class of nitrogenous bases characterized by a two-ring chemical structure, comprising adenine (A) and guanine (G).

Pyrimidines

A class of nitrogenous bases characterized by a single-ring chemical structure, comprising thymine (T), cytosine (C), and uracil (U).

Adenine-Thymine (A-T) Base Pair

A complementary base pair held together by $2$ hydrogen bonds, making it thermally weaker and easier to denature than a G-C pair.

Guanine-Cytosine (G-C) Base Pair

A complementary base pair held together by $3$ hydrogen bonds, making it stronger and requiring higher temperatures to denature compared to A-T pairs.

Uracil

A pyrimidine base present in RNA instead of thymine that forms $2$ hydrogen bonds with adenine.

DNA Denaturation ("Melting")

The separation of the two strands of the DNA duplex into single strands by disrupting hydrogen bonds using heat, chemicals, or enzymes.

Transfer RNA (tRNA)

A single-stranded RNA molecule folded into a cloverleaf structure containing an amino acid attachment site, an anticodon loop, a D-stem/loop, and a T-stem/loop.

Plasmids

Small, extra-chromosomal circular pieces of DNA (~$5\,\text{kb}$) originally isolated from bacteria that replicate independently from host chromosomes and often contain antibiotic resistance genes.

Bacterial Chromosome

A single circular, double-stranded DNA molecule ($1.2\,\text{mm}$ long and $4.6\,\text{million bp}$ in E. coli) that is not compacted by histones and is always accessible for replication and transcription.

Nucleoid

The intracellular region within a prokaryotic cell where the uncompacted circular chromosome resides without a surrounding nuclear membrane.

Histones

A family of positively charged eukaryotic proteins around which negatively charged DNA coils to condense into chromatin.

Nucleosome

The fundamental packaging unit of chromatin, composed of eukaryotic DNA wound around core histone proteins.

Chromatin

The chromosomal material of eukaryotes consisting of genomic DNA tightly bound to and associated with histone proteins.

Centromere

A specialized non-coding region of repetitive eukaryotic DNA where sister chromatids join and spindle fibres attach during cell division.

Telomeres

Repetitive non-coding sequences containing repeated $\text{TTAGGG}$ motifs at chromosome ends that act as a dispensable buffer to postpone gene damage during division.

Variable Number Tandem Repeats (VNTRs)

Minisatellite DNA sequences of $15\text{--}100\,\text{bp}$ repeated tandemly up to hundreds of times, used in forensic and evolutionary investigations (DNA fingerprinting).

Short Tandem Repeats (STRs)

Microsatellite DNA sequences composed of $2\text{--}5\,\text{nucleotides}$ repeated $5\text{--}50\,\text{times}$, utilized for DNA fingerprinting and relatedness testing.

Transposable Elements ("Jumping Genes")

Mobile DNA sequences containing repetitive parts at each end that can spontaneously excise from one genomic location and integrate into another.

Endosymbiotic Theory

The evolutionary model stating that mitochondria and chloroplasts arose ~$2\,\text{billion years}$ ago from free-living protobacteria capable of aerobic respiration and photosynthesis engulfed by ancestral host cells.

Mitochondrial DNA (mtDNA)

Circular, maternally inherited chromosomes present in mitochondria encoding rRNAs, tRNAs, and mRNAs for oxidative phosphorylation (OXPHOS).

S Phase

The interphase stage of the cell cycle where DNA replication occurs, doubling the cellular genetic complement from diploid ($2n$) to tetraploid ($4n$).

Disjunction

The anaphase separation event where centromeres of sister chromatids dissociate and chromatids are pulled toward opposite cell poles.

Reductional Division

The first division of meiosis (Meiosis I) that separates homologous chromosome pairs, reducing chromosome number and restoring the genetic complement to diploid ($2n$).

Equational Division

The second division of meiosis (Meiosis II) where sister chromatids separate into haploid ($1n$) gametes, resulting in an equal distribution of chromosome number.

Origin of Replication (oriC)

The single defined sequence on a bacterial chromosome where DNA synthesis initiates and proceeds bidirectionally toward the termination point (ter).

Helicase (DnaB/DnaC)

Enzymes that unwind the DNA double helix at the replication fork ahead of DNA synthesis.

DNA Gyrase

A topoisomerase enzyme that relieves torsional strain by creating cuts in the DNA and re-joining it after undoing kinks and supercoiling knots ahead of the replication fork.

RNA Primer

A short RNA sequence synthesized de novo (without requiring a free $3'$ end) to furnish the free $3'\text{-OH}$ group required by DNA polymerase to extend DNA.

Okazaki Fragments

Short DNA segments synthesized discontinuously along the lagging strand, each initiated by an individual RNA primer.

Telomerase

An enzyme active in stem cells and germ cells that replaces repetitive sequences at chromosome ends to maintain chromosome length and solve the end-replication problem.