Nucleic Acids and DNA as Hereditary Material

Vocabulary practice flashcards covering nucleic acid structure, nucleotide chemistry, DNA replication, transcription, translation, Chargaff's rules, chromatin organization, and experimental evidence for DNA as the genetic material.

Genotype

The genetic composition of an individual organism.

Genome

The totality of hereditary information embodied in the linear sequence of nucleotides in the DNA of any cell.

Nucleotide

The monomer of nucleic acids, composed of three components linked by covalent bonds: a pentose sugar, a negatively charged phosphate group, and a nitrogenous base.

Phosphodiester Bond

A covalent linkage formed by a condensation reaction joining the 5' phosphate group of one nucleotide to the 3' carbon (specifically its hydroxyl group) of the adjacent nucleotide's sugar.

Sugar–Phosphate Backbone

The repeating structural strand of alternating sugar and phosphate units in DNA and RNA that provides stability and shields the inward-pointing nitrogenous bases.

Purines

Larger, double-ring nitrogenous bases comprising adenine (A) and guanine (G), which are present in both DNA and RNA.

Pyrimidines

Smaller, single-ring nitrogenous bases comprising cytosine (C, found in both DNA and RNA), thymine (T, found only in DNA), and uracil (U, found only in RNA).

Complementary Base Pairing

The strict hydrogen-bonding rule where adenine pairs with thymine (or uracil in RNA) via 2 hydrogen bonds, and guanine pairs with cytosine via 3 hydrogen bonds.

Antiparallel Strands

Two polymer strands aligned side by side but running in opposite chemical directions, with one oriented $5' \rightarrow 3'$ and the opposite strand oriented $3' \rightarrow 5'$.

Directionality

The chemical polarity of a nucleic acid strand defined by its exposed ends: the 5' terminal features a free phosphate on carbon 5 of the sugar, while the 3' terminal features an exposed carbon 3 hydroxyl group.

Central Dogma

The pathway of genetic information flow consisting of replication, transcription of DNA into RNA, and translation of RNA into functional proteins composed of amino acids.

Transcription

The stage of gene expression where segments of the DNA sequence guide the enzymatic synthesis of RNA molecules.

Translation

The synthesis of proteins by ribosomes reading mRNA in the $5' \rightarrow 3'$ direction to assemble specific sequences of amino acids.

Ribozyme

An RNA molecule capable of functioning as a biological catalyst to accelerate chemical reactions.

Codon

A sequence of three nucleotides in DNA or RNA that corresponds to a specific amino acid, a start signal, or a stop signal during protein synthesis.

Universal Common Ancestry

The hypothesis that all living organisms descend from a shared ancestral population, evidenced by the near-universal conservation of the genetic code across all life forms.

Chargaff's Rules

The biochemical observation that in double-stranded DNA, the percentage of adenine equals thymine ($\%A = \%T$) and guanine equals cytosine ($\%G = \%C$), ensuring the total purines equal total pyrimidines.

Deoxyribose vs. Ribose

Both are five-carbon pentose sugars; ribose possesses a hydroxyl group on carbon 2', whereas deoxyribose lacks this oxygen atom and carries only a hydrogen atom on carbon 2'.

Chromatin

The complex of genomic DNA bound to histone and non-histone proteins found in eukaryotic cells, composed of approximately one-third DNA and two-thirds protein by mass.

Nucleosome

The basic structural repeating unit of eukaryotic chromatin, consisting of approximately 200 nucleotide pairs of DNA wrapped around an octamer core of histone proteins.

Nucleosome Core Particle Dissociation

The breakdown under high salt concentration of an $11\,\text{nm}$ nucleosome core particle into a 147-nucleotide-pair DNA double helix and an octamer composed of two copies each of histones H2A, H2B, H3, and H4.

Mitotic Chromosome Compaction

The multi-stage hierarchical packaging process that condenses a $2\,\text{nm}$ DNA double helix into a fully compact $1400\,\text{nm}$ mitotic chromosome that is $10{,}000\text{-fold}$ shorter than its extended length.

Hershey–Chase Experiment

A 1952 experiment demonstrating that DNA is the genetic material by showing that radioactive phosphorus-32 ($^{32}\text{P}$) in bacteriophage DNA entered bacterial cells upon infection, while sulfur-35 ($^{35}\text{S}$) in protein coats remained outside.