Biology: The Molecules of Life, Cells, Membranes, and Homeostasis

Vocabulary practice flashcards generated from Chapters 2 and 3 slide notes covering chemical foundations of life, macromolecules, cell structure, membrane transport, and organelles.

Atomic Number

The number of protons in an atom, which uniquely specifies the element.

Atomic Mass

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

Isotopes

Atoms of the same element that have the same number of protons but different numbers of neutrons.

Valence Electrons

Electrons located in an atom's outermost shell that determine its ability to form chemical bonds.

Covalent Bond

A chemical bond formed when two atoms share electrons in a shared molecular orbital.

Polar Covalent Bond

A covalent bond formed by the unequal sharing of electrons between atoms with different electronegativities, resulting in partial positive and partial negative charges.

Nonpolar Covalent Bond

A covalent bond formed when atoms with identical or similar electronegativities share electrons equally.

Ionic Bond

A chemical bond formed when a highly electronegative atom completely steals an electron from another atom, creating oppositely charged ions that attract each other.

Hydrogen Bond

A weak interaction formed between a hydrogen atom carrying a partial positive charge and an electronegative atom (such as oxygen) carrying a partial negative charge.

Isomers

Molecules that share the same chemical formula but have different structural arrangements of atoms, often conferring different functions.

Amino Acid

The monomer subunit of proteins, consisting of a central $\alpha$ carbon bonded to an amino group, a carboxyl group, a hydrogen atom, and a variable R group.

Peptide Bond

The covalent bond joining the carboxyl group of one amino acid to the amino group of another, formed with the release of a water molecule.

Nucleotide

The monomer building block of nucleic acids, composed of a 5-carbon sugar, a nitrogen-containing base, and one or more phosphate groups.

Phosphodiester Bond

The covalent bond that joins adjacent nucleotides together by linking the phosphate group of one nucleotide to the 3'-OH group of the next.

Pyrimidines

Single-ring nitrogenous bases found in nucleic acids, consisting of cytosine (C), thymine (T), and uracil (U).

Purines

Double-ring nitrogenous bases found in nucleic acids, consisting of guanine (G) and adenine (A).

Saturated Fatty Acid

A fatty acid chain that lacks carbon-carbon double bonds, resulting in a straight hydrocarbon structure that favors tight packing.

Unsaturated Fatty Acid

A fatty acid chain containing one or more carbon-carbon double bonds, which introduce kinks in the structure and reduce packing tightness.

Van der Waals Forces

Weak electrostatic attractions between nonpolar molecules caused by temporary, short-lived fluctuations in electron distribution.

Steroids

A class of lipids containing a core ring structure, such as cholesterol, which serves as a membrane component and precursor for hormones like estrogen and progesterone.

Cell Theory

The foundational biological principle stating that all organisms are composed of cells, the cell is the fundamental unit of life, and cells come from preexisting cells.

Prokaryotes

Single-celled organisms ranging from $1\text{--}2_\mu m$ in size that lack a nucleus and internal membrane-bound organelles.

Eukaryotes

Organisms ranging from $10\text{--}20_\mu m$ in size whose cells contain a distinct nucleus and internal membrane-bound organelles.

Phospholipid

An amphipathic lipid made of a hydrophilic polar head group and two hydrophobic nonpolar fatty acid tails, forming the primary component of cell membranes.

Micelle

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

Liposome

A spherical vesicle enclosed by a lipid bilayer, formed spontaneously when phospholipids with small heads and two hydrophobic tails are placed in water.

Fluid Mosaic Model

A model describing the cell membrane as a dynamic mixture of lipids and embedded proteins that are capable of moving laterally within the bilayer.

Homeostasis

The active process by which a cell or organism maintains a constant, stable internal environment despite external variations.

Simple Diffusion

The passive net movement of solute particles from an area of higher solute concentration to an area of lower solute concentration.

Osmosis

The passive movement of water across a selectively permeable membrane from a region of lower solute concentration to a region of higher solute concentration.

Facilitated Diffusion

The passive movement of molecules down their concentration gradient through embedded membrane channel or carrier proteins.

Primary Active Transport

The movement of ions or molecules against their concentration gradient directly powered by ATP hydrolysis, such as the $Na^+/K^+$ pump moving $3_Na^+$ out and $2_K^+$ into the cell.

Secondary Active Transport

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

Hypertonic Solution

An extracellular environment with a higher solute concentration than the cytoplasm, causing water to leave the cell and the cell to shrink.

Hypotonic Solution

An extracellular environment with a lower solute concentration than the cytoplasm, causing water to enter the cell and potentially lyse it.

Contractile Vacuole

An organelle in single-celled organisms that absorbs excess intracellular water and expels it to prevent cell lysis.

Turgor Pressure

The force exerted against the plant cell wall by water entering the cell via osmosis, providing structural rigidity.

Rough Endoplasmic Reticulum

An internal membrane network studded with ribosomes that synthesizes transmembrane and secreted proteins.

Smooth Endoplasmic Reticulum

A network of membrane-bound tubules lacking ribosomes that serves as the primary site for lipid and steroid synthesis.

Golgi Apparatus

An organelle consisting of flattened sacs called cisternae that modifies, sorts, and routes proteins and lipids from the ER to their destinations.

Lysosomes

Specialized Golgi-derived vesicles containing enzymes that break down damaged or unneeded macromolecules at an acidic $\text{pH } 5$.

Mitochondria

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

Chloroplasts

Double-membraned plant organelles containing an internal thylakoid membrane system that capture sunlight energy to synthesize sugars.

FRAP (Fluorescence Recovery After Photobleaching)

An experimental method demonstrating protein mobility in the cell membrane by photobleaching a fluorescently labeled region and monitoring the return of fluorescence.