Foundations of Biology: Cellular Organization, Biomolecules, and the Tree of Life

Vocabulary flashcards covering cellular organization, the three domains of life, molecular biology, criteria of life, and foundational atomic chemistry.

Domains of Life

The three great, evolutionarily grounded primary branches of the Tree of Life: Bacteria, Archaea, and Eukarya.

Prokaryotes

A collective term for bacteria and archaea, characterized as tiny, exclusively single-celled organisms that lack internal membranes or a membrane-bound nucleus.

Eukaryote

An organism composed of cells whose DNA is enclosed within a double-membrane-bound nucleus; named from the Greek eu (true) and karyon (kernel or nucleus).

Nucleoid

The non-membrane-bound region in a prokaryotic cell where the circular DNA chromosome is located (oid meaning resembling a nucleus).

Organelle

A specialized subcellular structure that performs a specific function within a cell; eukaryotic cells contain many membrane-bound organelles, whereas prokaryotes lack them.

Histones

Special proteins around which linear DNA molecules are wrapped in eukaryotic chromosomes; they are absent in prokaryotes.

Binary Fission

The simple mode of cell division in prokaryotes whereby a single cell splits into two (binary meaning two, and fission meaning split).

Mitosis and Meiosis

The two complex modes of cell division utilized by eukaryotes to ensure accurate segregation and distribution of multiple linear chromosomes into daughter cells.

Protists

A collective term for diverse, typically smaller eukaryotic lineages that do not belong to the animal, plant, or fungal groups.

Plasmodium

A single-celled eukaryotic parasite that causes malaria and is estimated to have killed approximately $5\%$ of all humans in history.

Methanogens

Archaea that produce methane ($\text{CH}_4$), the second most important greenhouse gas after carbon dioxide; they inhabit cow rumens and significantly influence global climate.

Bacterium and Archaeon

The grammatically correct singular forms of the plural domain and organism names bacteria and archaea.

Central Dogma of Molecular Biology

The core biological framework describing information flow from DNA to mRNA via transcription, and from mRNA to functional proteins via translation.

Transcription

The molecular process wherein a specific segment of DNA is copied into an mRNA molecule.

Translation

The molecular process wherein ribosomes read the sequence of an mRNA molecule to assemble a specific chain of amino acids into a protein.

DNA Replication

The biological copying of an entire DNA molecule before cell division to ensure both daughter cells receive an exact copy of genetic material.

Ribosome

A macromolecular cellular machine present in thousands of copies per cell that reads mRNA instructions to synthesize proteins.

Gene

A distinct segment of DNA that encodes instructions for synthesizing a specific type of protein.

Homeostasis

The ability of a living organism to regulate and sustain a relatively stable internal environment (such as maintaining human core body temperature near $37\,^\circ\text{C}$) despite fluctuating external conditions.

Cellular Organization

The universal property of life stating that all living organisms are composed of one or more membrane-enclosed cells and the products of cells.

Metabolism

The biochemical transformation of energy acquired from food or sunlight used to drive cellular maintenance, movement, growth, and reproduction.

HOMA

An acronym representing the fundamental characteristics of life: Homeostasis, Organization (cellular), Metabolism, and Adaptation/Ancestry through biological evolution.

Element

A substance that cannot be broken down or chemically converted into other substances; of $118$ defined elements, $92$ occur naturally, and fewer than $30$ are found in living cells.

Atom

The smallest component of an element that retains its distinct chemical properties, consisting of a nucleus containing protons and neutrons surrounded by orbiting electrons.

Proton

A positively charged subatomic particle residing within the atomic nucleus that possesses a relative mass of $1$ and a charge of $+1$.

Neutron

An uncharged subatomic particle residing within the atomic nucleus that has a relative mass of $1$ and an electric charge of $0$.

Electron

A negatively charged subatomic particle traveling in energy levels outside the nucleus that has negligible mass and a charge of $-1$.

Atomic Number

A value equal to the total number of protons present in the nucleus of an atom of a given element.

Mass Number

The total number of protons plus neutrons contained within an atom's nucleus.

Isotopes

Different forms of the same chemical element that possess identical numbers of protons but varying numbers of neutrons, such as carbon-$12$ and carbon-$14$.

Radioisotopes

Unstable isotopes that decay by emitting subatomic particles, protons, or energy to reach a more stable atomic state.

Octet Rule

The principle that low atomic number elements (up to calcium, atomic number $20$) attain maximum chemical stability when their outermost electron shell contains $8$ electrons.

Cation

A positively charged ion formed when a neutral atom loses or donates one or more valence electrons.

Anion

A negatively charged ion formed when a neutral atom gains or accepts one or more valence electrons.

Ionic Bond

A strong chemical interaction formed by electrostatic attraction between oppositely charged cations and anions following an electron transfer.

Covalent Bond

The strongest and most common chemical bond in biological systems, formed when two atoms share pairs of electrons without dissociating in water.

Nonpolar Covalent Bond

A covalent bond formed between atoms that share electrons equally, resulting in no regional electric charge across the molecule (e.g., $\text{O}_2$, $\text{CH}_4$).

Polar Covalent Bond

A covalent bond where electrons are shared unequally between atoms of different electronegativities, generating slight partial positive ($\delta^+$) and partial negative ($\delta^-$) charges.

Hydrogen Bond

A weak intermolecular attraction formed between a slightly positive ($\delta^+$) hydrogen atom in a polar covalent bond and an adjacent slightly negative ($\delta^-$) atom.

van der Waals Interactions

Weak, transient attractions between polar covalently bound atoms in different molecules resulting from fleeting partial charges as electrons orbit nuclei.

Hydrophilic

Describing polar or charged substances ("water-loving") that readily form hydrogen bonds with water molecules and dissolve in aqueous solution.

Hydrophobic

Describing nonpolar substances ("water-fearing"), such as lipids and oils, that cannot form hydrogen bonds with water and do not dissolve in it.

Sphere of Hydration

A surrounding cluster of oriented water molecules that surrounds and isolates dissolved ions in solution, also termed a hydration shell.

pH Scale

A scale ranging from $0$ to $14$ measuring the concentration of free hydrogen ions ($\text{H}^+$) in solution, where each single unit represents a $10$-fold change in $\text{H}^+$ concentration.

Buffer

A chemical system that absorbs excess $\text{H}^+$ or $\text{OH}^-$ ions to maintain physiological pH within a narrow homeostatic range (typically $7.2$ to $7.6$ in human tissues), such as the carbonic acid-bicarbonate buffer system ($\text{H}_2\text{CO}_3$ / $\text{HCO}_3^-$).