Chapter 3: Cellular Level

Cell Theory

A theory developed by Schleiden, Schwann, and Virchow stating that cells are the building blocks of plants and animals, all new cells come from pre-existing cells, and cells are the smallest units that perform vital physiological functions.

Complementarity of Form and Function

The concept that cellular functions are dictated by which subcellular structures are present in the cell.

Cytology

The study of cells.

Differentiation

The gradual specialization of cells into cells with specific structural and functional characteristics.

Extracellular fluid

The watery medium surrounding body cells.

Interstitial fluid

The extracellular fluid surrounding most tissues.

Plasma membrane

The membrane that separates the cell contents, or cytoplasm, from the extracellular fluid.

Cytoplasm

The material located between the plasma membrane and the membrane surrounding the nucleus.

Cytosol

The fluid component of the cytoplasm, also called intracellular fluid.

Organelles

Intracellular structures that have specific functions.

Membranous organelles

Organelles isolated from the cytosol by a phospholipid membrane.

Non-membranous organelles

Organelles that are not completely enclosed by a membrane, so their components are in direct contact with the cytosol.

Phospholipid bilayer

The primary structural component of the plasma membrane, consisting of two layers of phospholipids.

Hydrophilic heads

The water-attracting heads of phospholipids that face outward toward watery environments.

Hydrophobic tails

The water-repelling tails of phospholipids that face inward and are sandwiched between the hydrophilic heads.

Integral proteins

Proteins that are part of the membrane structure and cannot be removed without damaging or destroying the membrane.

Transmembrane proteins

Integral proteins that pass all the way through the plasma membrane one or more times.

Peripheral proteins

Proteins bound to the inner or outer surface of the plasma membrane that can be easily separated from it.

Anchoring proteins

Membrane proteins that attach the plasma membrane to other structures and stabilize its position.

Recognition proteins

Membrane proteins detected by cells of the immune system.

Receptor proteins

Membrane proteins that bind to specific extracellular molecules called ligands.

Ligand

A molecule that binds to a receptor protein; it can range from a small ion to a large hormone.

Carrier proteins

Membrane proteins that bind solutes and transport them across the plasma membrane.

Channels

Integral membrane proteins containing a central pore that forms a passageway across the plasma membrane.

Glycocalyx

A layer of superficial membrane carbohydrates important in cell recognition, binding to extracellular structures, and lubrication of the cell surface.

Cholesterol

A lipid in the plasma membrane that helps stabilize the relatively weak membrane.

Selectively permeable barrier

A plasma membrane that controls what enters and leaves the cell, including ions, nutrients, wastes, and secretions.

Permeability

The ability of a membrane to allow substances to pass through it.

Freely permeable membrane

A membrane that allows any substance to pass through without difficulty.

Selectively permeable membrane

A membrane that permits some materials to pass while preventing others.

Impermeable membrane

A membrane through which nothing can pass.

Passive transport

Transport processes that do not require energy because particles move down their concentration gradient.

Concentration gradient

A difference in the concentration of a substance between two areas that influences the direction of particle movement.

Simple diffusion

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

Solute

A dissolved particle in a solution.

Solvent

The substance in which solutes dissolve.

Facilitated diffusion

A passive transport process in which molecules cross the membrane using carrier proteins without requiring ATP.

Osmosis

The diffusion of water through a selectively permeable membrane from an area of higher water concentration to an area of lower water concentration.

Osmotic pressure

An indication of the force with which pure water moves into a solution as a result of its solute concentration.

Osmolarity

The solute concentration of a solution.

Tonicity

The effect of a solution's osmolarity on a cell.

Isotonic

A solution with the same solute concentration as the cell; there is no net movement of water and the animal cell maintains its normal shape.

Hypertonic

A solution with a higher solute concentration than the cell; water moves out of the cell, causing animal cells to crenate.

Hypotonic

A solution with a lower solute concentration than the cell; water moves into the cell, causing animal cells to lyse.

Crenation

The shrinking of an animal cell caused by water moving out of the cell in a hypertonic solution.

Lysis

The bursting of an animal cell caused by water moving into the cell in a hypotonic solution.

Filtration

The bulk flow movement of substances caused by a pressure gradient.

Active processes

Transport processes that require energy.

Active transport

A transport process that uses carrier proteins and ATP to move substances across the membrane regardless of concentration gradients.

Sodium-potassium pump

A common example of active transport that moves sodium and potassium across the plasma membrane.

Secondary active transport

A transport process in which the movement of sodium across the membrane stores energy that can be used to pump glucose against its concentration gradient.

Vesicular transport

The transport of large particles, macromolecules, and fluids across plasma and intracellular membranes.

Exocytosis

The movement of substances out of the cell.

Endocytosis

The movement of substances into the cell.

Phagocytosis

"Cell eating"; a type of endocytosis involving the intake of large particles.

Pinocytosis

"Cell drinking"; a type of endocytosis involving the intake of fluids.

Endoplasmic reticulum (ER)

A network of intracellular membranes connected to the nuclear envelope.

Rough endoplasmic reticulum (RER)

Endoplasmic reticulum covered with ribosomes; it modifies and packages newly constructed proteins for export to the Golgi apparatus.

Smooth endoplasmic reticulum (SER)

Endoplasmic reticulum without ribosomes that synthesizes phospholipids, cholesterol, steroid hormones, glycerides, and glycogen.

Golgi apparatus

A stack of flattened discs that modifies and packages secretions, renews or modifies the plasma membrane, and packages enzymes into vesicles.

Lysosomes

Vesicles containing digestive enzymes that provide an isolated environment for potentially dangerous chemical reactions.

Peroxisomes

Vesicles containing degradative enzymes that break down organic compounds and neutralize toxic compounds.

Mitochondria

The powerhouses of the cell responsible for ATP synthesis.

Cristae

The folded internal membrane of a mitochondrion that increases the internal surface area available for reactions.

Matrix

The liquid enclosed by the inner membrane of a mitochondrion.

Aerobic respiration

A multi-step process in mitochondria that produces ATP.

Glycolysis

The first step of aerobic respiration in which glucose is broken down into two pyruvate molecules; it occurs in the cytoplasm and produces two ATP.

Citric acid cycle

The second step of aerobic respiration that occurs in the mitochondrial matrix and breaks down pyruvate remnants into carbon dioxide and hydrogen atoms while producing two ATP.

Electron transport system

The third step of aerobic respiration in which hydrogen atoms are delivered to enzymes and coenzymes of the cristae, producing additional ATP; oxygen combines with hydrogen to form water.

Cytoskeleton

The cell's internal framework made of proteins that gives the cytoplasm strength and flexibility.

Microfilaments

The smallest cytoskeleton elements, generally less than 6 nm in diameter and typically composed of actin.

Actin

The protein that typically composes microfilaments.

Intermediate filaments

Cytoskeleton elements 7–11 nm in diameter that are the strongest and most durable of the cytoskeleton elements.

Microtubules

The largest cytoskeleton components, about 25 nm in diameter, that extend outward from the centrosome.

Centrosome

A region near the nucleus from which microtubules extend into the cell periphery.

Centrioles

Cylindrical structures made of short microtubules arranged into nine triplets; they help form spindle fibers during cell division.

Spindle fibers

Fibers associated with cell division that move DNA strands toward opposite poles of the cell.

Cilia

Long, slender microtubule extensions from the cell surface that propel fluids or solids.

Microvilli

Finger-shaped extensions of the plasma membrane that increase surface area and enhance nutrient absorption.

Ribosomes

Structures responsible for protein synthesis; each functional ribosome consists of a small and a large subunit.

Nucleus

The control center of the cell that stores genetic information and directs cellular operations.

Nuclear envelope

The double membrane surrounding the nucleus that separates it from the cytoplasm.

Nuclear pores

Passageways through the nuclear envelope that permit chemical communication between the nucleus and cytosol.

Nucleoplasm

The fluid contents of the nucleus containing the nuclear matrix, ions, enzymes, nucleotides, and small amounts of RNA and DNA.

Nuclear matrix

A network of fine filaments within the nucleoplasm that provides structural support and may help regulate genetic activity.

Nucleoli

Transient nuclear organelles that synthesize ribosomal RNA and assemble ribosomal subunits.

DNA

The molecule that stores instructions for protein synthesis.

Histones

Proteins around which DNA strands are loosely coiled in nondividing cells.

Nucleosome

A complex formed when DNA strands coil around histones.

Chromatin

Filaments formed when nucleosomes twist together.

Chromosome

A tightly coiled DNA structure formed from chromatin at the beginning of cell division.

Centromere

The constricted region in the middle of a chromosome.

Gene

A functional unit of heredity containing the nucleotides needed to produce a specific protein.

RNA

A nucleic acid necessary for protein synthesis because it carries information from DNA in the nucleus to the cytoplasm.

Ribosomal RNA (rRNA)

RNA that combines with proteins to form ribosomes where polypeptides are synthesized.

Messenger RNA (mRNA)

RNA that carries the coded message from DNA to the cytoplasm and ribosomes for construction of polypeptides.

Codon

A triplet of nucleotides in mRNA that represents coded information for protein synthesis.

Transfer RNA (tRNA)

RNA that transfers amino acids to the ribosome for addition to the growing polypeptide chain.

Anticodon

A sequence on tRNA that matches a codon on mRNA.

Transcription

The process in which DNA serves as a template for formation of mRNA.