Introduction to Cell Biology: Origins, Cellular Organization, and Biomolecules

Comprehensive vocabulary flashcards covering the origin of life, chemical evolution, endosymbiosis, cellular organization, and the chemical structure of macromolecules (carbohydrates, lipids, proteins, and nucleic acids) based on the lecture material.

Chemical Evolution

The prebiotic process on early Earth in which simple inorganic and atmospheric molecules ($H_2$, $H_2O$, $NH_3$, $CH_4$) reacted under energy inputs such as radiation, sunlight, heat, and electrical discharge to form increasingly complex, stable organic molecules.

Urey-Miller Experiment

A landmark 1953 chemical experiment simulating early Earth's primitive atmosphere with electrical spark discharges, providing empirical evidence that biologically important organic monomers (such as amino acids, carboxylic acids, and purine/pyrimidine bases) can synthesize abiotically.

RNA World Hypothesis

The hypothesis, first proposed by Walter Gilbert in 1988, stating that early biological evolution was centered on self-replicating RNA molecules functioning simultaneously as genetic information storage and catalytic enzymes before DNA and proteins evolved.

Ribozyme

A catalytic RNA molecule capable of accelerating specific chemical reactions independently of proteins, examples of which include RNase P (cleaves the $5'$ end of pre-tRNA), self-splicing introns, and the peptidyl transferase center of ribosomal RNA (rRNA).

Protocell

A primitive, non-living cell precursor formed by the spontaneous aggregate of chemically synthesized organic polymers and self-replicating molecules enclosed within a protective, selectively permeable lipid bilayer vesicle.

Phospholipid Bilayer Self-Assembly

The spontaneous and energetically favorable closure of planar phospholipid bilayers into spherical, sealed vesicular compartments to bury their hydrophobic hydrocarbon tails away from surrounding water.

Compartmentalization

The structural division of the interior of eukaryotic cells into distinct membrane-bound organelles, each specialized for distinct biochemical pathways and preventing cross-interference.

Endosymbiosis Theory

The evolutionary framework proposing that eukaryotic organelles, notably mitochondria and chloroplasts, originated from free-living prokaryotes that entered into a permanent, cooperative intracellular relationship inside ancestral host cells.

Lynn Margulis

The evolutionary biologist who championed and formulated the modern Endosymbiosis Theory in 1981, citing evidence such as organelles having double membranes, circular DNA, and their own ribosomes.

Mitochondrion

A double-membraned organelle in eukaryotic cells that evolved from an engulfed ancestral aerobic heterotrophic prokaryote, retaining its own distinct circular DNA, autonomous replication, and bacterial-type ribosomes.

Volvox Colony

A colonial green alga consisting of 8 to 40,000 cells living in close association with defined functional division of labor (vegetative vs. reproductive cells), representing a key evolutionary transition from unicellularity to multicellularity.

Prokaryotic Cell

A unicellular organism lacking a membrane-bound nucleus and complex internal organelles, characterized by naked circular DNA residing in a nucleoid region, ribosomes, a cell membrane, and a cell wall.

Water Polarity

The dipolar property of the $H_2O$ molecule resulting from its bent geometry ($105^\circ$ bond angle) and the electronegativity difference between oxygen ($2\delta^-$) and hydrogen ($\delta^+$), allowing extensive hydrogen-bonding capabilities.

Amphipathic

A chemical characteristic describing molecules that possess both a hydrophilic (water-attracting, polar) region and a hydrophobic (water-repelling, nonpolar) region, fundamental to membrane formation.

Monosaccharide

A simple carbohydrate monomer with the empirical formula $(CH_2O)_n$ containing 3 to 7 carbons; those with 5 or more carbons cyclize into stable ring structures, with glucose ($C_6H_{12}O_6$) acting as the principal cellular energy source.

Glycosidic Bond

A covalent bond formed through a condensation dehydration reaction linking monosaccharide units to form disaccharides, oligosaccharides, or polysaccharides.

Glycogen

The primary storage polysaccharide of animal cells, stored predominantly in the liver and muscle, composed of glucose monomers linked via $\alpha(1\rightarrow 4)$ chains with frequent $\alpha(1\rightarrow 6)$ branch points.

Cellulose

An unbranched structural polysaccharide that constitutes the rigid cell wall of plant cells, consisting of glucose units linked by $\beta(1\rightarrow 4)$ glycosidic bonds.

Fatty Acid

A simple lipid monomer consisting of a long hydrocarbon chain (typically 16 to 18 carbon atoms) with a polar, hydrophilic carboxyl group ($-COOH$) at one end.

Unsaturated Fatty Acid

A fatty acid chain that contains one or more double bonds ($C=C$) between adjacent carbon atoms, introducing kinks in the hydrocarbon chain (e.g., oleic, linoleic, and linolenic acids).

Triacylglycerol

The nonpolar storage form of fatty acids consisting of three fatty acid tails esterified to the three carbon positions of a single glycerol backbone.

Glycerophospholipid

The main amphipathic lipid class forming cellular membranes, consisting of two fatty acids esterified to glycerol carbons, with the third carbon bound to a phosphate group linked to a polar head group (e.g., choline, serine, or inositol).

Sphingomyelin

A structural membrane phospholipid that incorporates a serine/sphingosine amino alcohol backbone instead of a glycerol backbone.

Membrane Lipid Asymmetry

The unequal, functional partitioning of lipid types between the outer and inner leaflets of a plasma membrane, where phosphatidylcholine, sphingomyelin, and glycolipids face extracellularly, while phosphatidylserine and phosphatidylethanolamine reside predominantly on the cytosolic face.

Non-standard Amino Acids

The two rare amino acids found in living cells that are not part of the standard 20 universally encoded amino acids: selenocysteine (found in prokaryotes and eukaryotes) and pyrrolysine (found in certain archaea and bacteria).

Peptide Bond

A covalent amide bond formed between the $\alpha$-amino group ($-NH_3^+$) of one amino acid and the $\alpha$-carboxyl group ($-COO^-$) of an adjacent amino acid, synthesizing polypeptides unidirectionally from the N-terminus to the C-terminus.

Primary Protein Structure

The linear, covalently linked sequence of amino acids in a polypeptide chain encoded by the genetic information.

Secondary Protein Structure

Periodic spatial arrangements of the polypeptide backbone, predominantly the $\alpha$-helix and $\beta$-sheet, stabilized by regular hydrogen bonds between backbone carbonyl and amino groups.

Tertiary Protein Structure

The complete three-dimensional folding conformation of a single polypeptide chain driven by interactions between amino acid side chains ($R$ groups), including hydrogen bonds, ionic bonds, hydrophobic interactions, and covalent disulfide bridges.

Quaternary Protein Structure

The spatial organization and physical association of multiple distinct polypeptide subunits into a unified, functional multimeric protein complex (e.g., hemoglobin formed of 4 subunits).

Protein Domain

A distinct, compact, modular unit of tertiary structure within a protein that folds independently and is responsible for a specific chemical activity or binding interaction (e.g., catalytic, SH2, or SH3 domains).

Fibrous Protein

An insoluble structural protein forming elongated rod- or wire-like filaments (such as keratins, collagens, and elastins) that provide mechanical resistance and elasticity to connective tissues.

Globular Protein

A water-soluble, compactly folded spherical protein containing an internal hydrophobic core and external hydrophilic residues, typically performing dynamic biochemical activities such as enzymatic catalysis or molecular transport.

Protein Family

A collection of evolutionarily related proteins that descend from a common ancestor, exhibiting significant amino acid sequence similarity, homologous three-dimensional structures, and related physiological functions.

Nucleoside

A biomolecular unit composed exclusively of a five-carbon pentose sugar (ribose or deoxyribose) covalently joined to a purine or pyrimidine nitrogenous base, lacking any phosphate groups.

Nucleotide

The repeating monomeric unit of nucleic acids consisting of a five-carbon sugar, a nitrogenous base, and one or more covalently bound phosphate groups.

Phosphodiester Bond

The covalent linkage formed between the $3'$ hydroxyl group of one nucleotide's sugar and the $5'$ phosphate group of the next nucleotide, forming the sugar-phosphate backbone of nucleic acids extended in the $5' \rightarrow 3'$ direction.

Purines

Double-ringed heterocyclic nitrogenous bases found in DNA and RNA, specifically adenine (A) and guanine (G).

Pyrimidines

Single-ringed heterocyclic nitrogenous bases found in nucleic acids, specifically cytosine (C), thymine (T, present in DNA), and uracil (U, present in RNA).

Deoxyribonucleic Acid (DNA)

The double-stranded, antiparallel helical polymer encoding cellular genetic instructions, characterized by a deoxyribose sugar-phosphate backbone and complementary base pairing ($A=T$ with 2 hydrogen bonds, and $G\equiv C$ with 3 hydrogen bonds).

Bacterial Cell Chemical Composition

The molecular distribution of a typical bacterium, comprising $70\%$ water and $30\%$ chemicals ($15\%$ proteins, $6\%$ RNA, $2\%$ phospholipids, $2\%$ polysaccharides, $1\%$ DNA, and $4\%$ small molecules and ions).

Katalin Karikó and Drew Weissman

Biochemists awarded the 2023 Nobel Prize in Physiology or Medicine for discoveries concerning nucleoside base modifications that averted immune activation and enabled the successful production of modified mRNA vaccines against COVID-19.