Human Anatomy & Physiology - Chapter 3: Cells: The Living Units

Vocabulary flashcards covering key terms and concepts from Chapter 3 Cells: The Living Units.

Cell

The structural unit of all living things, with the human body containing $50$ to $100\text{ trillion}$ cells.

Cell Theory

Concept stating that the cell is the smallest unit of life, all organisms are made of one or more cells, and cells arise only from other cells.

Plasma Membrane

Flexible outer boundary separating intracellular fluid (ICF) from extracellular fluid (ECF).

Interstitial Fluid

Extracellular fluid in which body cells are submersed or bathed.

Fluid Mosaic Model

Model depicting the plasma membrane as a moving bilayer of phospholipids containing $20\%$ cholesterol with embedded proteins and surface sugars.

Integral Proteins

Transmembrane proteins inserted into the lipid bilayer that function as transport proteins, enzymes, or cell surface receptors.

Peripheral Proteins

Proteins loosely attached to integral proteins or membrane lipids that function as enzymes, motor proteins, or cell-to-cell connections.

Glycocalyx

Biological sugar coating on the outer cell surface consisting of glycolipids and glycoproteins that acts as specific markers for cell recognition.

Tight Junctions

Impermeable cell junctions formed by fused integral proteins that prevent fluids and most molecules from moving between adjacent cells.

Desmosomes

Anchoring cell junctions formed by interlocking linker proteins (cadherins) anchored to internal membrane plaques and keratin filaments.

Gap Junctions

Communicating cell junctions formed by transmembrane proteins (connexons) that create tunnels allowing ions and small molecules to pass directly between cells.

Passive Transport

Membrane transport processes that require no energy input from the cell as substances move down their concentration gradient.

Simple Diffusion

Unassisted passive diffusion of nonpolar lipid-soluble hydrophobic substances directly through the phospholipid bilayer.

Facilitated Diffusion

Passive transport of hydrophobic or water-soluble molecules across the membrane using carrier or channel proteins down their concentration gradient.

Osmosis

The movement of water through a selectively permeable membrane from an area of low solute concentration to high solute concentration.

Aquaporins (AQPs)

Transmembrane channel proteins specifically designed for the movement of water across plasma membranes.

Osmolarity

Total concentration of all solute particles in a solution, expressed in units of $\text{osmol/L}$.

Hydrostatic Pressure

The back pressure exerted by water against a cell wall or membrane.

Osmotic Pressure

The tendency of water to move into a cell by osmosis based on solute concentration.

Tonicity

The ability of a solution to change the shape or plasma membrane tension of cells by altering internal water volume.

Isotonic Solution

A solution having the same solute concentration as inside the cell, leaving cell volume unchanged.

Hypertonic Solution

A solution having a higher solute concentration than inside the cell, causing water to leave the cell and leading to crenation.

Crenation

The shrinking of cells that occurs when placed in a hypertonic solution.

Hypotonic Solution

A solution having a lower solute concentration than inside the cell, causing water to enter the cell and leading to swelling or lysing.

Primary Active Transport

Active membrane transport process where energy comes directly from ATP hydrolysis by transport pumps to move solutes against concentration gradients.

Sodium-Potassium Pump

A primary active transport enzyme ($\text{Na}^+/\text{K}^+$ ATPase) that ejects $\text{Na}^+$ from the cell and brings $\text{K}^+$ back in.

Secondary Active Transport

Cotransport driven indirectly by energy stored in ion concentration gradients established by primary active transport pumps.

Symporters

Transport proteins that move two different substances across the plasma membrane in the same direction.

Antiporters

Transport proteins that move one substance into the cell while moving a different substance out.

Phagocytosis

A type of endocytosis ("cell eating") where pseudopods engulf solid particles to form an intracellular vesicle called a phagosome.

Pinocytosis

A non-specific type of endocytosis ("cell drinking") where the plasma membrane infolds to bring extracellular fluid and dissolved solutes inside.

Receptor-Mediated Endocytosis

A highly selective endocytosis mechanism where specific extracellular substances bind to unique plasma membrane protein receptors to be ingested.

Resting Membrane Potential (RMP)

Voltage across a resting cell membrane produced by separation of charged ions, typically ranging from $-50\,mV$ to $-100\,mV$.

Cell Adhesion Molecules (CAMs)

Thousands of surface proteins on cells that anchor cells to the ECM, assist cell movement, attract WBCs, and transmit intracellular signals.

Ligands

Chemical messengers (such as neurotransmitters, hormones, and paracrines) that bind specifically to cell membrane receptors.

Cytosol

The gel-like fluid of cytoplasm composed of water and dissolved solutes such as proteins, salts, and sugars.

Mitochondria

Double-membraned organelles with inner folds called cristae that act as cellular "power plants" by generating ATP via aerobic cellular respiration.

Ribosomes

Nonmembranous organelles composed of protein and ribosomal RNA (rRNA) that serve as the site of protein synthesis.

Rough Endoplasmic Reticulum

Membrane network studded with ribosomes involved in synthesizing secreted proteins, plasma membrane proteins, and phospholipids.

Smooth Endoplasmic Reticulum

Tubule network continuous with rough ER that functions in lipid metabolism, steroid synthesis, drug detoxification, and calcium storage.

Golgi Apparatus

Organelle of stacked membranous cisterns that modifies, concentrates, and packages proteins and lipids synthesized in the rough ER.

Lysosomes

Spherical membranous bags containing acid hydrolases that digest ingested bacteria, viruses, toxins, and degraded organelles.

Tay-Sachs Disease

A rare genetic neurodegenerative disease where lysosomes lack an enzyme needed to break down a specific glycolipid in nerve membranes.

Peroxisomes

Membranous sacs containing oxidases and catalases that neutralize toxic free radicals and hydrogen peroxide.

Microfilaments

Thinnest cytoskeletal strands made of actin that support cell shape, form the terminal web, and participate in cell motility.

Intermediate Filaments

Tough, insoluble ropelike protein fibers composed of tetramer fibrils that help cells resist pulling forces.

Microtubules

Hollow cytoskeletal tubes composed of tubulin subunits radiating from the centrosome that determine cell shape and move organelles.

Centrosome

Cell center located near the nucleus containing a granular matrix and a pair of centrioles; acts as the microtubule organizing center.

Centrioles

Barrel-shaped organelles in a pinwheel array of nine microtubule triplets that organize the mitotic spindle and form bases of cilia and flagella.

Cilia

Whiplike cellular extensions with a "9 + 2" microtubule array that move substances in a sweeping motion across cell surfaces.

Microvilli

Fingerlike extensions of the plasma membrane with an actin microfilament core that increase surface area for absorption.

Chromatin

Nuclear structure composed of $30\%$ DNA, $60\%$ histone proteins, and $10\%$ RNA, organized into nucleosomes.

Semiconservative Replication

DNA replication mechanism in which each new double-stranded DNA molecule is composed of one old parental strand and one new strand.

Mitosis

Division of the cell nucleus consisting of four phases: prophase, metaphase, anaphase, and telophase.

Cytokinesis

Division of the cytoplasm via a contractile ring of actin microfilaments that forms a cleavage furrow to pinch cells apart.

Gene

A segment of DNA that holds the genetic code for one polypeptide.

Exons

Amino acid-coding regions of a gene that remain after pre-mRNA editing.

Introns

Noncoding segments of a gene interspersed among exons that are spliced out prior to translation.

Transcription

The transfer of genetic information from a DNA template strand to complementary mRNA in the nucleus.

Translation

The decoding of an mRNA base sequence into an amino acid sequence at a ribosome.

Codon

A three-base sequence on mRNA that specifies a particular amino acid or stop signal.

Anticodon

A specific triplet base code on tRNA that complementary base-pairs with an mRNA codon.

Autophagy

Process of disposing of unneeded organelles and cytoplasmic bits by forming autophagosomes that are degraded by lysosomes.

Apoptosis

Programmed cell death triggered by caspases, leading to cell shrinkage, DNA degradation, and phagocytosis by macrophages.

Hyperplasia

Accelerated growth that increases cell numbers in tissues when needed.

Atrophy

A decrease in cell or organ size resulting from loss of stimulation or use.

Telomeres

Nucleotide strings at the ends of chromosomes that shorten with each cell division to regulate cellular lifespan.

Progeria

A rare disease mimicking premature aging caused by a defective progerin protein in the nuclear lamina.