Cell Physiology & Homeostasis

Cell theory

The cell is the smallest structural and functional unit capable of life; all new life arises only from preexisting cells; cells are the building blocks of all multicellular organisms; organism structure/function depend on cellular properties.

Plasma membrane

The boundary of the cell, a phospholipid bilayer that regulates movement of material between the intracellular fluid (ICF) and extracellular fluid (ECF).

Nucleus

Cell structure that houses DNA and controls cellular activities; contains the nuclear envelope, nucleolus, and nuclear pores.

DNA

Deoxyribonucleic acid; genetic material organized into 46 chromosomes in humans; blueprint for protein synthesis.

Genome

All genetic information contained in an organism’s DNA.

Proteome

The complete set of proteins expressed by the genome in a cell or organism.

Epigenetics

Environmentally induced changes in gene expression without changes to the underlying DNA sequence.

Lipidome

The full complement of lipids within a cell or organism.

RNA

Ribonucleic acid; acts as the intermediary in transcription and as a component of ribosomes during translation.

Cytoplasm

The interior of the cell excluding the nucleus; contains organelles, cytosol, and cytoskeleton.

Cytosol

The semi-fluid portion of the cytoplasm where metabolic processes occur.

Endoplasmic reticulum (ER)

Elaborate network of membranous tubules; site of protein and lipid synthesis; rough ER has ribosomes; smooth ER lacks ribosomes and handles lipid synthesis.

Rough ER

Endoplasmic reticulum studded with ribosomes; synthesizes proteins for secretion and membrane construction.

Smooth ER

Endoplasmic reticulum without ribosomes; synthesizes lipids and packages proteins in transport vesicles.

Golgi complex

Stack of flattened sacs that modifies, sorts, and packages proteins for secretion or delivery to other organelles.

Vesicle

Membrane-bound carrier that transports substances between organelles and to the plasma membrane.

Lysosome

Membrane-bound organelle containing hydrolytic enzymes for digestion of macromolecules and worn-out organelles.

Peroxisome

Organelle with oxidative enzymes that detoxify substances and produce/detoxify hydrogen peroxide (H2O2).

Mitochondrion

Energy-producing organelle; generates ATP via glycolysis (cytosol), citric acid cycle, and oxidative phosphorylation; enclosed by two membranes with cristae.

ATP synthase

Enzyme in the inner mitochondrial membrane that uses the proton (H+) gradient to synthesize ATP from ADP and Pi.

Electron transport chain (ETC)

A series of proteins in the inner mitochondrial membrane that transfer electrons from NADH/FADH2 to O2, pumping protons to create a gradient.

Oxidative phosphorylation

Process by which ATP is produced using the proton gradient created by the ETC and ATP synthase.

Glycolysis

Glucose breakdown in the cytosol to pyruvate, yielding net 2 ATP and 2 NADH per glucose.

Pyruvate to Acetyl-CoA

Conversion of pyruvate to acetyl-CoA by pyruvate dehydrogenase; feeds the citric acid cycle.

Citric acid cycle (Krebs cycle)

Oxidizes acetyl-CoA to CO2 in the mitochondrial matrix, producing NADH, FADH2, and GTP/ATP.

NADH

Reduced nicotinamide adenine dinucleotide; electron carrier that donates electrons to the ETC.

FADH2

Flavin adenine dinucleotide in its reduced form; electron carrier for the ETC.

Coenzyme Q (CoQ / ubiquinone)

Lipid-soluble electron carrier in the ETC that shuttles electrons between complexes.

Cytochrome c

Small heme protein in the ETC that transfers electrons between complexes III and IV.

H+ gradient

Proton concentration difference across the inner mitochondrial membrane that drives ATP synthesis via chemiosmosis.

Chemiosmosis

Movement of protons through ATP synthase to synthesize ATP from ADP and Pi.

Vaults

Nonmembranous cytoplasmic granules thought to function in transport of molecules within the cell and possibly in drug resistance.

Cytoskeleton

Network of protein filaments (microtubules, microfilaments, intermediate filaments) providing shape, support, and movement.

Microtubules

Hollow tubes made of tubulin that maintain shape, serve as tracks for vesicle transport, and form cilia/flagella and the mitotic spindle.

Microfilaments

Actin-based filaments essential for contractility and movement; support microvilli and cytoplasmic movement.

Intermediate filaments

Rope-like proteins providing mechanical strength to cells and resisting stress.

Cilia

Hairlike cell surface projections with a 9+2 microtubule arrangement that move fluid or track particles; bendable via dynein motors.

Flagella

Long, whip-like projections used for cell propulsion; share the 9+2 microtubule structure with cilia.

Basal body

Centriole-derived structure that organizes the microtubules of cilia and flagella.

Pseudopods

Temporary cytoplasmic extensions used for locomotion and phagocytosis (cell eating).

Endocytosis

Process of taking material into the cell via vesicle formation and plasma membrane invagination.

Pinocytosis

Non-specific form of endocytosis taking up fluids and dissolved solutes via vesicles.

Receptor-mediated endocytosis

Targeted endocytosis triggered when ligands bind to specific cell-surface receptors and are internalized via clathrin-coated pits.

Phagocytosis

Engulfment of large particles or organisms by the cell, forming a phagosome that fuses with a lysosome.

Exocytosis

Secretion of vesicle contents to the extracellular space; vesicle membrane integrates into the plasma membrane.

Nucleolus

Nuclear region where ribosomal RNA (rRNA) is synthesized and ribosomal subunits assemble.

Nuclear envelope

Double-membrane barrier surrounding the nucleus that contains nuclear pores for transport.

Nuclear pores

Protein channels in the nuclear envelope that regulate transport between the nucleus and cytoplasm.

Ribosome

Ribonucleoprotein complex that carries out protein synthesis; can be free in cytosol or attached to rough ER.

Transcription

Process of copying DNA into messenger RNA (mRNA) in the nucleus.

Translation

Process of assembling amino acids into proteins at ribosomes using mRNA as a template.

9+2 system

Structural arrangement of microtubules in motile cilia and flagella: nine outer doublets and two central microtubules.

Mitochondrial matrix

Innermost compartment of the mitochondrion where the citric acid cycle occurs.

Intermembrane space

Space between the inner and outer mitochondrial membranes, where proton pumping creates the gradient.

Cristae

Folded inner mitochondrial membrane surfaces that increase area for the electron transport chain and ATP synthesis.

Physiology

The study of the functions of living things, focusing on the mechanisms that underlie body processes; closely related to anatomy.

Anatomy

The study of the structure of the body; structure and function are inseparable.

Levels of Organization

Hierarchical organization from atoms to the whole organism: atoms, molecules, cells, tissues, organs, organ systems, organism.

Atoms

The basic units of matter; in the body, mainly oxygen, carbon, hydrogen, and nitrogen.

Molecules

Groups of two or more atoms; include carbohydrates, proteins, fats, and nucleic acids.

Carbohydrates

Biomolecules that store energy and provide structure; include monosaccharides, disaccharides, and polysaccharides.

Monosaccharides

Simple sugars such as glucose; the basic units of carbohydrates.

Disaccharides

Double sugars such as sucrose and lactose.

Polysaccharides

Complex carbohydrates such as glycogen.

Proteins

Macromolecules made of amino acids; perform structural and functional roles.

Amino Acids

The building blocks of proteins; there are 20 standard amino acids.

Fats

Lipids including steroids and phospholipids; provide energy and cell membrane components.

Nucleic Acids

Genetic material in cells; DNA and RNA.

DNA

Deoxyribonucleic acid; stores genetic information.

RNA

Ribonucleic acid; involved in protein synthesis and regulation.

The Cellular Level

The level of organization focusing on cells as the basic units of life and their functions.

Cell

The basic unit of life; carries out fundamental cellular processes.

Basic Cellular Functions

Obtaining food and O2; energy generation; eliminating wastes; synthesizing proteins and cell components; moving materials; responding to the environment; reproducing.

Specialized Cell Functions

Distinct roles of different cell types, such as secretion of enzymes, selective transport, intracellular movement, electrical signaling, and differentiation.

Tissues

Groups of cells with a similar structure and specialization.

Muscle Tissue

Tissue type enabling movement; skeletal, cardiac, and smooth muscle.

Nervous Tissue

Tissue that initiates and transmits electrical impulses for communication and control.

Epithelial Tissue

Tissue that lines surfaces and exchanges materials; forms sheets or glands.

Connective Tissue

Tissue that connects, supports, and anchors various body parts.

The Tissue Level

The level of organization composed of tissues formed by similar cells.

Organ

A body structure made up of two or more tissue types that performs a specific function.

Organ System

A group of organs that interact to perform related functions essential for survival.

Organism Level

The entire living being; all body systems function together as a whole.

Internal Environment

Fluid surrounding cells that enables life-sustaining exchanges.

Homeostasis

A dynamic, relatively stable state of the internal environment maintained by regulatory mechanisms.

Detect, Integrate, Adjust

The three steps of homeostatic control: detect deviations, integrate information, and adjust to restore normal conditions.

Control System Components

Sensor (detects changes), Integrator (processes information), Effector (carries out the response).

Negative Feedback

A control mechanism in which the response opposes the initial change, stabilizing the system.

Positive Feedback

A control mechanism in which the response amplifies the initial change; less common.

Shivering

A negative-feedback response that increases heat production to raise body temperature.

Feedforward Mechanisms

Anticipatory responses that prepare the body for upcoming changes before they occur.

Disruptions in Homeostasis

Severe disturbances in the internal environment that can threaten survival.

Glands

Organs composed of epithelial tissue that secrete substances.

Epithelial Tissue Functions

Protection, secretion, and absorption; can form sheets or glands.

The Four Primary Tissue Types

Epithelial, connective, muscle, and nervous tissues.