Cells, Membranes, and The Molecules of Life

Vocabulary flashcards covering cell biology, cell membrane transport, organelles, biochemistry basics, functional groups, and biological macromolecules.

Cell Theory

The foundational biological theory stating that all organisms are made up of cells, the cell is the fundamental unit of life, and all cells come from pre-existing cells.

Prokaryotic Cell

A type of cell that lacks a nucleus and membrane-bound organelles, characteristic of bacteria and archaea.

Eukaryotic Cell

A cell containing a membrane-bound nucleus and internal membrane-bound organelles, characteristic of animal, plant, fungal, and protist cells.

Phospholipid

An amphipathic lipid composed of a polar, hydrophilic head and two nonpolar, hydrophobic fatty acid tails, serving as the main structural component of cell membranes.

Micelle

A spherical lipid structure formed in water by phospholipids possessing large, bulky polar head groups and a single hydrophobic fatty acid tail.

Liposome

A spherical vesicle enclosed by a lipid bilayer that spontaneously forms when phospholipids with two hydrophobic tails are placed in an aqueous environment.

Fluid Mosaic Model

A model of cell membrane structure describing lipids and proteins as dynamic components capable of moving laterally within the membrane layer.

Integral Membrane Protein

A protein permanently associated with the lipid bilayer that typically spans the entire membrane.

Peripheral Membrane Protein

A protein temporarily associated with either the extracellular or cytoplasmic face of the cell membrane.

Osmosis

The net diffusion of water across a selectively permeable membrane from a region of lower solute concentration (hypotonic) to a region of higher solute concentration (hypertonic).

Hypertonic Solution

A solution with a higher solute concentration compared to the cell cytoplasm, causing water to leave the cell and leading to cell shrinkage.

Hypotonic Solution

A solution with a lower solute concentration compared to the cell cytoplasm, causing water to enter the cell and leading to swelling or lysis.

Isotonic Solution

A solution having an equal solute concentration relative to the cell cytoplasm, resulting in no net water movement.

Simple Diffusion

The passive movement of solute particles down a concentration gradient from an area of higher concentration to lower concentration without transport proteins.

Facilitated Diffusion

The passive transport of molecules across a membrane down their concentration gradient mediated by channel or carrier proteins.

Primary Active Transport

The movement of solutes against their concentration gradient across a membrane, directly requiring energy supplied by ATP hydrolysis.

Sodium-Potassium Pump

A primary active transport protein that moves three sodium ions ($\text{Na}^+$) out of the cell and two potassium ions ($\text{K}^+$) into the cell per ATP consumed, maintaining cellular electrochemical gradients.

Secondary Active Transport

The transport of a solute against its concentration gradient driven by an electrochemical gradient previously established by primary active transport.

Endomembrane System

An interconnected eukaryotic network of internal membranes that includes the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vesicles, and cell membrane.

Phagocytosis

A mechanism of endocytosis where a cell engulfs large particles or debris within a food vacuole, which subsequently merges with a lysosome for degradation.

Pinocytosis

A non-specific endocytic process in which a cell engulfs fluid droplets and dissolved extracellular solutes into small vesicles.

Receptor-Mediated Endocytosis

A selective form of endocytosis triggered when specific extracellular ligands bind to cell-surface receptors, inducing coat protein-assisted vesicle formation.

Exocytosis

The process where intracellular transport vesicles fuse with the plasma membrane to secrete their contents into the extracellular space.

Nuclear Envelope

A double-membrane barrier enclosing the cell nucleus perforated by nuclear pores that regulate transport between the nucleoplasm and cytoplasm.

Rough Endoplasmic Reticulum

A region of the endoplasmic reticulum studded with ribosomes, responsible for synthesizing and folding proteins destined for secretion, organelles, or the cell membrane.

Smooth Endoplasmic Reticulum

A region of the endoplasmic reticulum lacking ribosomes, serving as the site for lipid synthesis, carbohydrate metabolism, calcium storage, and chemical detoxification.

Golgi Apparatus

An organelle composed of flattened sacs (cisternae) that receives proteins and lipids at its cis-face, modifies and sorts them, and ships them from its trans-face.

Lysosome

A specialized vesicle containing hydrolytic enzymes maintained at a low pH ($\approx 5$) that degrades worn-out cell parts, macromolecules, and ingested materials.

Peroxisome

An organelle containing enzymes that metabolize long-chain fatty acids and neutralize toxic hydrogen peroxide ($\text{H}_2\text{O}_2$) into water and oxygen.

Endosymbiosis

The theory that mitochondria and chloroplasts originated as free-living prokaryotes that were engulfed by ancestral eukaryotic cells and maintained symbiotic relationships.

Mitochondria

Double-membraned organelles that carry out cellular respiration to produce ATP, possessing their own circular DNA genomes.

Chloroplast

An organelle present in plants and algae surrounded by a double membrane with an internal thylakoid membrane, responsible for capturing light energy to synthesize sugars.

Atomic Number

The number of protons contained within the nucleus of an atom, defining its chemical identity.

Atomic Mass

The combined mass of protons and neutrons in an atom, where each proton and neutron weighs approximately $1\,\text{Da}$.

Isotope

Atoms belonging to the same element that share the same atomic number of protons but differ in neutron count.

Radioactive Isotope

An unstable isotope whose nucleus undergoes spontaneous decay, releasing energetic subatomic particles.

Electronegativity

The relative measure of an atom's attraction for shared electrons within a chemical bond.

Covalent Bond

A strong chemical interaction formed when two atoms share one or more pairs of valence electrons to achieve stable outer shells.

Polar Covalent Bond

A covalent bond formed between two atoms with differing electronegativities, leading to unequal electron distribution and partial charges.

Nonpolar Covalent Bond

A covalent bond formed between two atoms of similar electronegativity that share valence electrons equally.

Ionic Bond

A chemical attraction resulting from the complete transfer of valence electrons, yielding oppositely charged ions (cations and anions).

Hydrogen Bond

A weak interaction between a hydrogen atom covalently bound to an electronegative atom and a second electronegative atom in another molecule.

Van der Waals Forces

Weak, transient electrostatic attractions arising between nonpolar molecules due to localized, temporary fluctuations in electron density.

Cohesion

The tendency of water molecules to stick to one another due to intermolecular hydrogen bonding.

Adhesion

The tendency of water molecules to adhere to other polar or charged molecules and surfaces.

Specific Heat

The amount of thermal energy required to raise the temperature of $1\,\text{g}$ of a substance by $1\,^\circ\text{C}$.

pH Scale

A logarithmic measure of hydrogen ion concentration in solution defined by $\text{pH} = -\log[\text{H}^+]$, where each single unit step reflects a $10\times$ change in $[\text{H}^+]$.

Buffer

A solution consisting of a weak acid and its conjugate base that resists shifts in pH by neutralizing added $[\text{H}^+]$ or $[\text{OH}^-]$ ions.

Tetravalent

The property of possessing four valence electrons, permitting carbon to establish four covalent bonds in flexible geometry.

Isomer

Compounds that share the exact same chemical formula but feature different structural arrangements of constituent atoms.

Structural Isomer

Isomers that differ in the fundamental covalent arrangement and sequence of their bonded atoms.

Cis-Trans Isomer

Isomers differing in spatial placement across a non-rotatable carbon-carbon double bond, where cis refers to same-side positioning and trans to opposite-side placement.

Enantiomer

Isomers that form non-superimposable mirror images around an asymmetric or chiral carbon atom.

Functional Group

A characteristic grouping of atoms attached to an organic carbon backbone that imparts predictable chemical behavior and reactivity.

Hydroxyl Group

A polar functional group ($-\text{OH}$) present in alcohols that readily forms hydrogen bonds with water.

Carbonyl Group

A functional group consisting of a carbon double-bonded to an oxygen ($-\text{C}=\text{O}$), classified as a ketone when internal to a chain or an aldehyde when terminal.

Carboxyl Group

An acidic functional group ($-\text{COOH}$) that donates a proton ($\text{H}^+$) in aqueous solutions to form a negatively charged carboxylate ion ($-\text{COO}^-$).

Amino Group

A basic functional group ($-\text{NH}_2$) that accepts a proton ($\text{H}^+$) in aqueous solutions to form a positively charged ion ($-\text{NH}_3^+$).

Sulfhydryl Group

A functional group ($-\text{SH}$) found in thiols that forms covalent disulfide bonds to stabilize protein tertiary structure.

Phosphate Group

An acidic, negatively charged functional group ($-\text{PO}_4^{2-}$) involved in energy transfers and structural linkages in nucleic acids.

Methyl Group

A nonpolar functional group ($-\text{CH}_3$) whose covalent attachment to DNA modifies gene expression.

Dehydration Reaction

A condensation reaction that covalently joins monomer units into polymers through the removal of a water molecule.

Hydrolysis

A reaction that cleaves covalent bonds within polymers to regenerate individual monomers by adding a water molecule.

Peptide Bond

The covalent bond joining two amino acids formed via a dehydration reaction between a carboxyl group and an amino group.

Purine

A double-ring nitrogenous base category consisting of adenine (A) and guanine (G).

Pyrimidine

A single-ring nitrogenous base category consisting of cytosine (C), thymine (T), and uracil (U).

Phosphodiester Bond

The covalent linkage connecting the $5'$ phosphate group of one nucleotide to the $3'$ hydroxyl group of an adjacent nucleotide in a nucleic acid polymer.

Central Dogma

The directional pathway describing genetic information flow in biological systems: $\text{DNA} \rightarrow \text{mRNA} \rightarrow \text{Protein}$.

Glycosidic Bond

The covalent bond uniting two monosaccharides via a dehydration reaction to construct disaccharides or polysaccharides.

Saturated Fatty Acid

A fatty acid hydrocarbon chain devoid of carbon-carbon double bonds, yielding a straight configuration that packs tightly into solid fats at room temperature.

Unsaturated Fatty Acid

A fatty acid hydrocarbon chain containing one or more double bonds that introduce structural kinks, preventing tight packing and maintaining liquid state at room temperature.

Triacylglycerol

A lipid formed by esterifying three fatty acid chains to a single glycerol molecule, serving as energy storage.

Steroid

A class of lipids characterized by a core carbon framework of four fused rings, represented by molecules like cholesterol.

Miller-Urey Experiment

An experiment demonstrating that organic molecules, including amino acids, could form spontaneously under simulated early Earth conditions using water vapor, methane ($\text{CH}_4$), ammonia ($\text{NH}_3$), hydrogen gas ($\text{H}_2$), and electrical sparks.