How We Study Cells

         Microscopes provide windows to the world of the cell
         Cell biologists can isolate organelles to study their functions

    A Panoramic View of the Cell

         Prokaryotic and eukaryotic cells differ in size and complexity
         Internal membranes compartmentalize the functions of a eukaryotic cell

    The Nucleus and Ribosomes

         The nucleus contains a eukaryotic cell's genetic library
         Ribosomes build a cell's proteins

    The Endomembrane System

         The endoplasmic reticulum manufactures membranes and performs many
         other biosynthetic functions
         The Golgi apparatus finishes, sorts, and ships cell products
         Lysosomes are digestive compartments
         Vacuoles have diverse functions in cell maintenance

    Other Membranous Organelles

         Mitochondria and chloroplasts are the main energy transformers of cells
         Peroxisomes consume oxygen in various metabolic functions

    The Cytoskeleton

        Providing structural support to the cell, the cytoskeleton also functions in
         cell motility and regulation

    Cell Surfaces and Junctions

         Plant cells are encased by cell walls
         The extracellular matrix (ECM) of animal cells functions in support,
         adhesion, movement, and regulation
         Intercellular junctions help integrate cells into higher levels of structure and
         function
         The cell is a living unit greater than the sum of its parts

Chapter  7

light microscope (LM) - An optical instrument with lenses that refract (bend) visible light to magnify images of specimens.

resolving power -  A measure of the clarity of an image; the minimum distance that two points can be separated and still be distinguished as two separate points.

organelle (OR-guh-NEL) - One of several formed bodies with a specialized function, suspended in the cytoplasm and found in eukaryotic cells.

electron microscope (EM) - A microscope that focuses an electron beam through a specimen, resulting in resolving power a thousandfold greater than that of a light microscope. A transmission electron microscope (TEM) is used to study the internal structure of thin sections of cells. A scanning electron microscope (SEM) is used to study the fine details of cell surfaces.

cell fractionation - the disruption of a cell and separation of its organelles by centrifugation.

ultracentrifuges - instrument used to fractionate cells

prokaryotic cell (pro-KAR-ee-OT-ik) - a type of cell lacking a membrane-enclosed nucleus and membrane-enclosed organelles; found only in the kingdom Monera; also called prokaryote.

nucleoid - (NOO-klee-oid) - a dense region of DNA in a prokaryotic cell.

cytoplasm (SY-toh-plaz-um) - the entire contents of the cell, exclusive of the nucleus, and bounded by the plasma membrane.

cytosol (SY-toh-sol) - the semifluid portion of the cytoplasm.

plasma membrane - the membrane at the boundary of every cell that acts as a selective barrier, thereby regulating the cell's chemical composition.

nuclear lamina - a netlike array of protein filaments that maintains the nuclear matrix

chromatin (KRO-muh-tin) - the aggregate mass of dispersed genetic material formed of DNA and protein and observed between periods of cell division in eukaryotic cells.

chromosome (KRO-muh-some) - a long, threadlike association of genes in the nucleus of all eukaryotic cells and most visible during mitosis and meiosis. Chromosomes consist of DNA and protein.

nucleolus (noo-KLEE-oh-lus) (plural, nucleoli) - a specialized structure in the nucleus, formed from various chromosomes and active in the synthesis of ribosomes. ribosomes

endomembrane system - the collection of membranes inside and around a eukaryotic cell, related either through direct physical contact or by the transfer of membranous vesicles.

endoplasmic reticulum (ER) (EN-doh-plaz-mik reh-TIK-yoo-lum) - an extensive membranous network in eukaryotic cells, continuous with the outer nuclear membrane and composed of ribosome-studded (rough) and ribosome-free (smooth) regions.
smooth ER That portion of the endoplasmic reticulum that is free of ribosomes.
rough ER That portion of the endoplasmic reticulum studded with ribosomes.

glycoproteins - proteins that are covalently bonded to carbohydrates.

golgi apparatus (GOAL-jee) - an organelle in eukaryotic cells consisting of stacks of membranes that modify, store, and route products of the endoplasmic reticulum.

lysosome (LY-so-some) - a membrane-enclosed bag of hydrolytic enzymes found in the cytoplasm of eukaryotic cells.

phagocytosis (FAY-goh-sy-TOH-sis) - a type of endocytosis involving large, particulate substances.

vacuoles - a membrane-enclosed sac taking up most of the interior of a mature plant cell and containing a variety of substances important in plant reproduction, growth, and development.

food vacuoles - membrane-bound sacs within the cell, formed by phagocytosis

contractile vacuole - membrane-bound sacs within the cell that pump excess water out of the cell

central vacuole - a large membrane-bound sac within the cells of mature plants

tonoplast - a membrane that encloses the central vacuole in a plant cell, separating the cytosol from the cell sap.

mitochondrion (MY-toh-KON-dree-un) (plural, mitochondria) - an organelle in eukaryotic cells that serves as the site of cellular respiration.

chloroplast (KLOR-oh-plast) - an organelle found only in plants and photosynthetic protists that absorbs sunlight and uses it to drive the synthesis of organic compounds from carbon dioxide and water.

crista (KRIS-tuh) (plural, cristae) - an infolding of the inner membrane of a mitochondrion that houses the electron transport chain and the enzyme catalyzing the synthesis of ATP mitochondrial matrix

plastid - one of a family of closely related plant organelles, including chloroplasts, chromoplasts, and amyloplasts (leucoplasts).

thylakoid (THY-luh-koid) - a flattened membrane sac inside the chloroplast, used to convert light energy to chemical energy.

granum (GRAN-um) (plural, grana) - a stacked portion of the thylakoid membrane in the chloroplast. Grana function in the light reactions of photosynthesis The conversion of light energy to chemical energy that is stored in glucose or other organic compounds; occurs in plants, algae, and certain prokaryotes. stroma The fluid of the chloroplast surrounding the thylakoid membrane; involved in the synthesis of organic molecules from carbon dioxide and water.

peroxisome (pur-OKS-eh-some) - a microbody containing enzymes that transfer hydrogen from various substrates to oxygen, producing and then degrading hydrogen peroxide.

microtubule - a hollow rod of tubulin protein in the cytoplasm of all eukaryotic cells and in cilia, flagella, and the cytoskeleton.

microfilament - a solid rod of actin protein in the cytoplasm of almost all eukaryotic cells, making up part of the cytoskeleton and acting alone or with myosin to cause cell contraction.

intermediate filament - a component of the cytoskeleton that includes all filaments intermediate in size between microtubules and
microfilaments.

centrosome - material present in the cytoplasm of all eukaryotic cells and important during cell division; also called microtubule-organizing center.

centriole (SEN-tree-ole) - one of two structures in the center of animal cells, composed of cylinders of nine triplet microtubules in a ring. Centrioles help organize microtubule assembly during cell division.

flagellum (fluh-JEL-um) (plural, flagella) - a long cellular appendage specialized for locomotion, formed from a core of nine outer doubletmicrotubules and two inner single microtubules, ensheathed in an extension of plasma membrane.

cilium (SILL-ee-um) (plural, cilia) - a short cellular appendage specialized for locomotion, formed from a core of nine outer doublet microtubules and two inner single microtubules ensheathed in an extension of plasma membrane.

basal body - structurally identical to the centriole, it anchors the microtubual assembly of a cilium of flagellum in the cell

dynein (DY-nin) - a large contractile protein forming the sidearms of microtubule doublets in cilia and flagella.

actin (AK-tin) - a globular protein that links into chains, two of which twist helically about each other, forming microfilaments in muscle and other contractile elements in cells.

myosin (MY-uh-sin) - a type of protein filament that interacts with actin filaments to cause cell contraction.

pseudopodium (SOO-doh-POH-dee-um) (plural, pseudopodia) - a cellular extension of amoeboid cells used in moving and feeding.

cytoplasmic streaming - a circular flow of cytoplasm, involving myosin and actin filaments, that speeds the distribution of materials within cells.

primary cell wall - a protective layer external to the plasma membrane in plant cells, bacteria, fungi, and some protists. In the case of plant cells, the wall is formed of cellulose fibers embedded in a polysaccharide-protein matrix. The primary cell wall is thin and flexible, whereas the secondary cell wall is stronger and more rigid, and is the primary constituent of wood.

middle lamella (luh-MEL-uh) -a thin layer of adhesive extracellular material, primarily pectins, found between the primary walls of adjacent young plant cells.

secondary cell wall - a protective layer external to the plasma membrane in plant cells, bacteria, fungi, and some protists. In the case of plant cells, the wall is formed of cellulose fibers embedded in a polysaccharide-protein matrix. The primary cell wall is thin and flexible, whereas the secondary cell wall is stronger and more rigid, and is the primary constituent of wood.

extracellular matrix (ECM) - ahe nonliving component of connective tissue, consisting of a web of fibers embedded in homogeneous ground substance that may be liquid, jellylike, or solid.

collagen - a glycoprotein in the extracellular matrix of animal cells that forms strong fibers, found extensively in connective tissue and bone; the most abundant protein in the animal kingdom.

proteoglycans (pro-tee-oh-GLY-kanz) - a glycoprotein in the extracellular matrix of animal cells, rich in carbohydrate.

fibronectins - glycoproteins that bind to receptor proteins.

integrins - receptor proteins that are built into the plasma membrane.

plasmodesma (PLAZ-moh-DEZ-muh) (plural, plasmodesmata) - an open channel in the cell wall of plants through which strands of cytoplasm connect from adjacent cells.

tight junction - a type of intercellular junction in animal cells that prevents the leakage of material between cells.

desmosome (DEZ-muh-some) - a type of intercellular junction in animal cells that functions as an anchor.

gap junction  - a type of intercellular junction in animal cells that allows the passage of material or current between cells.
 
 

    Membrane Structure

         Membrane models have evolved to fit new data: science as a process
         A membrane is a fluid mosaic of lipids, proteins, and carbohydrates

    Traffic Across Membranes

         A membrane's molecular organization results in selective permeability
         Passive transport is diffusion across a membrane
         Osmosis is the passive transport of water
         Cell survival depends on balancing water uptake and loss
         Specific proteins facilitate the passive transport of selected solutes
         Active transport is the pumping of solutes against their gradients
         Some ion pumps generate voltage across membranes
         In cotransport, a membrane protein couples the transport of one solute to
         another
         Exocytosis and endocytosis transport large molecules

Chapter  8

amphipathic molecule - a molecule that has both a hydrophilic region and a hydrophobic region.

fluid mosaic model - the currently accepted model of cell membrane structure, which envisions the membrane as a mosaic of individually inserted protein molecules drifting laterally in a fluid bilayer of phospholipids.

integral proteins - transmembrane proteins with hydrophobic regions that completely span the hydrophobic interior of the membrane.

peripheral proteins - proteins not embedded in the lipid bilayer, but rather on the surface.

transport proteins - proteins that span the membrane allowing hydrophilic substances to pass through and avoid the lipid bilayer.

diffusion - the spontaneous tendency of a substance to move down its concentration gradient from a more concentrated to a less concentrated area.

concentration gradient - a regular increase or decrease in the intensity or density of a chemical substance. Cells often maintain concentration gradients of H+ ions across their membranes. When a gradient exists, the ions or other chemical substances involved tend to move from where they are more concentrated to where they are less concentrated.

hypertonic solution - a solution with a greater solute concentration than another, a hypotonic solution

hypotonic solution - a solution with a lesser solute concentration than another, a hypertonic solution.

isotonic solutions - solutions of equal solute concentration.

osmosis (oz-MOH-sis) - the diffusion of water across a selectively permeable membrane.

osmoregulation - adaptations to control the water balance in organisms living in hypertonic, hypotonic, or terrestrial environments.

turgid (TUR-jid) - firm; walled cells become turgid as a result of the entry of water from a hypotonic environment.

flaccid (FLAS-id) - limp; walled cells are flaccid in isotonic surroundings, where there is no tendency for water to enter.

plasmolysis (plaz-MOL-eh-sis) - a phenomenon in walled cells in which the cytoplasm shrivels and the plasma membrane pulls away from the cell wall when the cell loses water to a hypertonic environment
.
facilitated diffusion - the spontaneous passage of molecules and ions, bound to specific carrier proteins, across a biological membrane down their concentration gradients.

gated ion channel - a specific ion channel that opens and closes to allow the cell to alter its membrane potential.

active transport - the movement of a substance across a biological membrane against its concentration or electrochemical gradient, with the help of energy input and specific transport proteins.

sodium-potassium pump - a special transport protein in the plasma membrane of animal cells that transports sodium out of and potassium into the cell against their concentration gradients.

membrane potential - the charge difference between the cytoplasm and extracellular fluid in all cells, due to the differential distribution of ions. Membrane potential affects the activity of excitable cells and the transmembrane movement of all charged substances.

electrochemical gradient - the diffusion gradient of an ion, representing a type of potential energy that accounts for both the concentration difference of the ion across a membrane and its tendency to move relative to the membrane potential.

electrogenic pump - an ion transport protein generating voltage across the membrane.

proton pump (PRO-tahn) - an active transport mechanism in cell membranes that consumes ATP to force hydrogen ions out of a cell and, in the process, generates a membrane potential.

cotransport - the coupling of the "downhill" diffusion of one substance to the "uphill" transport of another against its own concentration gradient.

exocytosis (EKS-oh-sy-TOH-sis) - the cellular secretion of macromolecules by the fusion of vesicles with the plasma membrane.

endocytosis (EN-doh-sy-TOH-sis) - the cellular uptake of macromolecules and particulate substances by localized regions of the plasma membrane that surround the substance and pinch off to form an intracellular vesicle.

phagocytosis (FAY-goh-sy-TOH-sis) - a type of endocytosis involving large, particulate substances.

pinocytosis (PY-noh-sy-TOH-sis) - a type of endocytosis in which the cell ingests extracellular fluid and its dissolved solutes.

receptor-mediated endocytosis (EN-doh-sy-TOH-sis) - the movement of specific molecules into a cell by the inward budding of membranous vesicles containing proteins with receptor sites specific to the molecules being taken in; enables a cell to acquire bulk quantities of specific substances.

ligand (LIG-und) - a molecule that binds specifically to a receptor site of another molecule.
 
 

    Principles of Energy Harvest

         Cellular respiration and fermentation are catabolic (energy-yielding)
         pathways
         Cells recycle the ATP they use for work
         Redox reactions release energy when electrons move closer to
         electronegative atoms
         Electrons "fall" from organic molecules to oxygen during cellular respiration
         The "fall" of electrons during respiration is stepwise, via NAD+ and an
         electron transport chain

    The Process of Cellular Respiration

         Respiration involves glycolysis, the Krebs cycle, and electron transport: an
         overview
         Glycolysis harvests chemical energy by oxidizing glucose to pyruvate: a
         closer look
         The Krebs cycle completes the energy-yielding oxidation of organic
         molecules: a closer look
         The inner mitochondrial membrane couples electron transport to ATP
         synthesis: a closer look
         Cellular respiration generates many ATP molecules for each sugar molecule
         it oxidizes: a review

    Related Metabolic Processes

         Fermentation enables some cells to produce ATP without the help of
         oxygen
         Glycolysis and the Krebs cycle connect to many other metabolic pathways
         Feedback mechanisms control cellular respiration
 

Chapter  9

fermentation - a catabolic process that makes a limited amount of ATP from glucose without an electron transport chain and that produces a characteristic end-product, such as ethyl alcohol or lactic acid.

cellular respiration - the most prevalent and efficient catabolic pathway for the production of ATP, in which oxygen is consumed as a reactant along with the organic fuel.

redox reaction (REE-doks) - a chemical reaction involving the transfer of one or more electrons from one reactant to another; also called oxidation-reduction reaction.

reduction - the gaining of electrons by a substance involved in a redox reaction.

oxidation - the loss of electrons from a substance involved in a redox reaction.

reducing agent - the electron donor in a redox reaction.

oxidizing agent - the electron acceptor in a redox reaction.

NAD+ (nicotinamide adenine dinucleotide) - A coenzyme present in all cells that helps enzymes transfer electrons during the redox reactions of metabolism.

electron transport chain - a group of molecules in the inner membrane of a mitochondrion that synthesize ATP by means of an exergonic slide of electrons. Thylakoid membranes of chloroplasts are also equipped with electron transport chains.

glycolysis (gly-KOL-eh-sis) - the splitting of glucose into pyruvate. Glycolysis is the one metabolic pathway that occurs in all living cells, serving as the starting point for fermentation or aerobic respiration.

Krebs cycle - a chemical cycle involving eight steps that completes the metabolic breakdown of glucose molecules to carbon dioxide; occurs within the mitochondrion; the second major stage in cellular respiration.

oxidative phosphorylation (FOS-for-eh-LAY-shun) - the production of ATP using energy derived from the redox reactions of the electron transport chain.

substrate-level phosphorylation - the formation of ATP by directly transferring a phosphate group to ADP from an intermediate substrate in catabolism.

acetyl CoA - the entry compound for the Krebs cycle in cellular respiration; formed from a fragment of pyruvate attached to a coenzyme.

cytochrome (SY-toh-krome) - an iron-containing protein, a component of electron transport chains in mitochondria and chloroplasts.

ATP synthase - a protein complex that produces ATP.

chemiosmosis (KEE-mee-os-MOH-sis) - the ability of certain membranes to use chemical energy to pump hydrogen ions and then harness the energy stored in the H+ gradient to drive cellular work, including ATP synthesis.

proton-motive force - the potential energy stored in the form of an electrochemical gradient, generated by the pumping of hydrogen ions across biological membranes during chemiosmosis.

aerobic (air-OH-bik) - containing oxygen; referring to an organism, environment, or cellular process that requires oxygen.

anaerobic (an-air-OH-bik) - lacking oxygen; referring to an organism, environment, or cellular process that lacks oxygen and may be poisoned by it.

alcohol fermentation - fermentation resulting in the formation of ethanol.

lactic acid fermentation - fermentation resulting in the formation of lactic acid.

facultative anaerobe (FAK-ul-tay-tiv AN-uh-robe) - an organism that makes ATP by aerobic respiration if oxygen is present but that switches to fermentation under anaerobic conditions.
 
 

    Photosynthesis in Nature

         Plants and other autotrophs are the producers of the biosphere
         Chloroplasts are the sites of photosynthesis in plants

    The Pathways of Photosynthesis

         Evidence that chloroplasts split water molecules enabled researchers to
         track atoms through photosynthesis: science as a process
         The light reactions and the Calvin cycle cooperate in converting light energy
         to the chemical energy of food: an overview
         The light reactions convert solar energy to the chemical energy of ATP and
         NADPH: a closer look
         The Calvin cycle uses ATP and NADPH to convert CO2 to sugar: a closer
         look
         Alternative mechanisms of carbon fixation have evolved in hot, arid climates
         Photosynthesis is the biosphere's metabolic foundation: a review

Chapter  10

autotroph (AW-toh-TROHF) - an organism that obtains organic food molecules without eating other organisms. Autotrophs use energy from the sun or from the oxidation of inorganic substances to make organic molecules from inorganic ones.

chlorophyll - a green pigment located within the chloroplasts of plants; chlorophyll a can participate directly in the light reactions, which convert solar energy to chemical energy.

mesophyll (MEZ-oh-fil) - the ground tissue of a leaf, sandwiched between the upper and lower epidermis and specialized for photosynthesis.

stoma (plural, stomata) - a microscopic pore surrounded by guard cells in the epidermis of leaves and stems that allows gas exchange between  the environment and the interior of the plant.

light reactions - the steps in photosynthesis that occur on the thylakoid membranes of the chloroplast and convert solar energy to the chemical energy of ATP and NADPH, evolving oxygen in the process.

Calvin cycle - the second of two major stages in photosynthesis (following the light reactions), involving atmospheric CO2 fixation and reduction of the fixed carbon into carbohydrate.

NADP - an acceptor which temporarily stores the energized electrons

carbon fixation - the incorporation of carbon from atmospheric CO2 into the carbon in organic compounds. During photosynthesis in a CO3 plant, carbon is fixed into a three-carbon sugar as it enters the Calvin cycle. In CO4 and CAM plants, carbon is fixed into a four-carbon sugar.

wavelength - the distance between crests of waves, such as those of the electromagnetic spectrum.

electromagnetic spectrum - the entire spectrum of radiation; ranges in wavelength from less than a nanometer to more than a kilometer.

visible light - that portion of the electromagnetic spectrum detected as various colors by the human eye, ranging in wavelength from about 400 nm to about 700 nm.

photon (FOH-tahn) - a quantum, or discrete amount, of light energy.

spectrophotometer - an instrument that measures the proportions of light of different wavelengths absorbed and transmitted by a pigment solution.

absorption spectrum - the range of a pigment's ability to absorb various wavelengths of light.

Chorophyll a  - a pigment in the chloroplast.

Action spectrum  - profiles the relative performancesof the differnet wavelengths more accurately than an absorption spectrum.

Chlorophyll b  - a pigment in the chloroplast.

carotenoids (keh-ROT-en-oydz) - accessory pigments, yellow and orange, in the chloroplasts of plants; by absorbing wavelengths of light that chlorophyll cannot, they broaden the spectrum of colors that can drive photosynthesis.

photosystem - the light-harvesting unit in photosynthesis, located on the thylakoid membrane of the chloroplast and consisting of the  antenna complex, the reaction-center chlorophyll a, and the primary electron acceptor. There are two types of photosystems, I and II; they absorb light best at different wavelengths.

reaction center - the location of one or a pair of specialized chlorophyll a molecules in the pigment assembly system of the light reactions of photosynthesis.

Primary electron acceptor - a specialized molecule of the reaction center.

Photosystem I - a photosystem that cooperates in the light reactions of photosynthesis.

Photosystem II - a photosystem that cooperates in the light reactions of photosynthesis.

Noncyclic electron flow - a route of electron flow during the light reactions of photosynthesis that involves both photosystems and produces ATP, NADPH, and oxygen; the net electron flow is from water to NADP+.

Noncyclic photophosphorylation (FO-toh-fos-FOR-eh-LAY-shun) - the production of ATP by noncyclic electron flow.
Cyclic electron flow A route of electron flow during the light reactions of photosynthesis that involves only photosystem I and produces ATP but not NADPH or oxygen.

photophosphorylation (FOH-toh-fos-for-uh-LAY-shun) - the process of generating ATP from ADP and phosphate by means of a proton-motive force generated by the thylakoid membrane of the chloroplast during the light reactions of photosynthesis.

Glyceraldehyde 3-phosphate - the carbonate directly produced from the Calvin cycle.

rubisco Ribulose carboxylase - the enzyme that catalyzes the first step (the addition of CO2 to RuBP, or ribulose bisphosphate) of the Calvin cycle.

C3 plant - a plant that uses the Calvin cycle for the initial steps that incorporate CO2 into organic material, forming a three-carbon compound as the first stable intermediate.

photorespiration - a metabolic pathway that consumes oxygen, releases carbon dioxide, generates no ATP, and decreases photosynthetic output; generally occurs on hot, dry, bright days, when stomata close and the oxygen concentration in the leaf exceeds that of carbon dioxide.

C4 plant - a plant that prefaces the Calvin cycle with reactions that incorporate CO2 into four-carbon compounds, the end-product of which supplies CO2 for the Calvin cycle.

Bundle sheath cells - photosynthetic cells that arranged into tightly packed sheaths around the veins of a leaf.

Mesophyll cells (MEZ-oh-fil) - the ground tissue of a leaf, sandwiched between the upper and lower epidermis and specialized for photosynthesis.

PEP-carboxylase Enzyme that adds CO2 to PEP.

Crassulacean acid metabolism (CAM)

CAM plant - a plant that uses crassulacean acid metabolism, an adaptation for photosynthesis in arid conditions, first discovered in the family Crassulaceae. Carbon dioxide entering open stomata during the night is converted into organic acids, which release CO2 for the Calvin cycle during the day, when stomata are closed.
 
 

    An Overview of Cell Signaling

         Cell signaling evolved early in the history of life
         Communicating cells may be close together or far apart
         The three stages of cell signaling are reception, transduction, and response

    Signal Reception and the Initiation of Transduction

         A signal molecule binds to a receptor protein, causing the protein to change
         shape
         Most signal receptors are plasma-membrane proteins

    Signal-Transduction Pathways

         Pathways relay signals from receptors to cellular responses
         Protein phosphorylation, a common mode of regulation in cells, is a major
         mechanism of signal transduction
         Certain small molecules and ions are key components of signaling
         pathways (second messengers)

    Cellular Responses to Signals

         In response to a signal, a cell may regulate activities in the cytoplasm or
         transcription in the nucleus
         Elaborate pathways amplify and specify the cell's response to signals
 

Chapter  11

Signal transduction pathway - a mechanism linking a mechanical or chemical stimulus to a cellular response.

Local regulator - a substance that influences cells in the vicinity.

hormone - one of many types of circulating chemical signals in all multicellular organisms that are formed in specialized cells, travel in body fluids, and coordinate the various parts of the organism by interacting with target cells.

ligand (LIG-und) - a molecule that binds specifically to a receptor site of another molecule.

G protein linked receptor - a plasma-membrane receptor that works with the help of a protein called G protein.

G protein - a membrane protein that relays signals from the plasma membrane signal receptor, known as a G-protein linked receptor, to other signal-transduction proteins inside the cell.

Tyrosine kinase - catalyzes the transfer of phosphate groups from ATP to the amino acid tyrosine on a substrate protein.

Tyrosine kinase receptors - membrane receptors that attach phosphates to protein tyrosines.

Ligand-gated ion channel receptor - a signal receptor protein in a cell membrane that can act as a channel for the passage of a specific ion across the membrane.

protein kinase - an enzyme that regulates the activity of another protein by adding a phosphate group (phosphorylation).

Protein phosphatases - enzymes that remove phosphate groups from proteins.

Second messengers - small nonprotein, water-soluble molecules or ions, such as a calcium ion or cyclic AMP, that relays a signal to the cell's interior in response to a signal received by a signal receptor protein.

adenyl cyclase - an enzyme that converts ATP to cyclic AMP in response to a chemical signal; a membrane protein that is the effector in a signal-transduction pathway.

inositol trisphosphate (IP3) (in-NOS-i-tahl) - the second messenger, which functions as an intermediate between certain nonsteroid hormones and the third messenger, a rise in cytoplasmic Ca2+ concentration.

calmodulin (kal-MOD-yoo-lin) - an intracellular protein to which calcium binds in its function as a second messenger in hormone action.
 

    The Key Roles of Cell Division

         Cell division functions in reproduction, growth, and repair
         Cell division distributes identical sets of chromosomes to daughter cells

    The Mitotic Cell Cycle

         The mitotic phase alternates with interphase in the cell cycle: an overview
         The mitotic spindle distributes chromosomes to daughter cells: a closer
         look
         Cytokinesis divides the cytoplasm: a closer look
         Mitosis in eukaryotes may have evolved from binary fission in bacteria

    Regulation of the Cell Cycle

         A molecular control system drives the cell cycle
         Internal and external cues help regulate the cell cycle
         Cancer cells have escaped from cell-cycle controls

Chapter  12

Cell division - reproduction of cells.

genome (JEE-nome) - the complete complement of an organism's genes; an organism's genetic material.

somatic cell (soh-MAT-ik) - any cell in a multicellular organism except a sperm or egg cell.

gamete (GAM-eet) - a haploid egg or sperm cell; gametes unite during sexual reproduction to produce a diploid zygote.

chromatin (KRO-muh-tin) - the aggregate mass of dispersed genetic material formed of DNA and protein and observed between periods of cell division in eukaryotic cells.

sister chromatids (KROH-muh-tidz) - replicated forms of a chromosome joined together by the centromere and eventually separated during mitosis or meiosis II.

centromere (SEN-troh-mere) - the centralized region joining two sister chromatids.

mitosis (my-TOH-sis) - a process of cell division in eukaryotic cells conventionally divided into the growth period (interphase) and four stages: prophase, metaphase, anaphase, and telophase. The stages conserve chromosome number by equally allocating replicated chromosomes to each of the daughter cells.

cytokinesis (SY-toh-kin-EE-sis) - the division of the cytoplasm to form two separate daughter cells immediately after mitosis.

meiosis (my-OH-sis) A two-stage type of cell division in sexually reproducing organisms that results in gametes with half the chromosome number of the original cell.

Mitotic (M) phase - shortest part of the cell cycle, including mitosis and cytokinesis.

interphase - the period in the cell cycle when the cell is not dividing. During interphase, cellular metabolic activity is high, chromosomes and organelles are duplicated, and cell size may increase. Interphase accounts for 90% of the time of each cell cycle.

G1 phase - the first growth phase of the cell cycle, consisting of the portion of interphase beforefree energy of activation The initial investment of energy necessary to start a chemical reaction; also called activation energy.

S phase - the synthesis phase of the cell cycle, constituting the portion of interphase during which DNA is replicated.

G2 phase - the second growth phase of the cell cycle, consisting of the portion of interphase after DNA synthesis occurs.

prophase - the first stage of mitosis, during which duplicated chromosomes condense from chromatin, and the mitotic spindle forms and begins moving the chromosomes toward the center of the cell.

prometaphase - the phase of mitosis in which the nuclear envelope breaks into fragments. Some of the spindle fibers reach the chromosomes and attach to protein structures at the centromeres, called kinetochores, while others make contact with microtubules coming from the opposite pole. The opposing spindle fibers move the chromosomes toward the metaphase plate, an imaginary plane equidistant from the poles.

metaphase - the second stage of mitosis. During metaphase, all the cell's duplicated chromosomes are lined up at an imaginary plane equidistant between the poles of the mitotic spindle.

anaphase - the third stage of mitosis, beginning when the centromeres of duplicated chromosomes divide and sister chromotids separate from each other, and ending when a complete set of daughter chromosomes are located at each of the two poles of the cell.

telophase - the fourth and final stage of mitosis, during which daughter nuclei form at the two poles of a cell. Telophase usually occurs together with cytokinesis.

spindle - an assemblage of microtubules that orchestrates chromosome movement during eukaryotic cell division.

kinetochore (kih-NET-oh-kor) - a specialized region on the centromere that links each sister chromatid to the mitotic spindle.

Metaphase plate - a plane midway between two poles.

cleavage - the process of cytokinesis in animal cells, characterized by pinching of the plasma membrane; also, the succession of rapid cell divisions without growth during early embryonic development that converts the zygote into a ball of cells.

cell plate - a double membrane across the midline of a dividing plant cell, between which the new cell wall forms during cytokinesis.

binary fission - the type of cell division by which prokaryotes reproduce; each dividing daughter cell receives a copy of the single parental chromosome.

cell-cycle control system - a cyclically operating set of proteins that triggers and coordinates events in the eukaryotic cell cycle.

Checkpoint Critical - point where stop and go-ahead signals can regulate the cycles.

G0 phase - non-dividing state in the cell cycle.

cyclin (SY-klin) - a regulatory protein whose concentration fluctuates cyclically.

cyclin-dependent kinase (Cdk) - a protein kinase that is active only when attached to a particular cyclin.

MPF (M-phase promoting factor) - a protein complex required for a cell to progress from late interphase to mitosis; the active form consists of cyclin and cdc2, a protein kinase.

Growth factor - a protein that must be present in the extracellular environment (culture medium or animal body) for the growth and normal development of certain types of cells.

Density dependant inhibitor The phenomenon observed in normal animal cells that causes them to stop dividing when they come into contact with one another.

Anchorage dependence - most animal cells must be attached to a substratum, such as the inside of a culture jar or the extracellular matrix of a tissue inorder to divide.
 
transformation - (1) The conversion of a normal animal cell to a cancerous cell. (2) A phenomenon in which external genetic material is assimilated by a cell.

tumor - A mass that forms within otherwise normal tissue, caused by the uncontrolled growth of a transformed cell.

Benign tumor - abnormal cells remain at their original site.

Malignant tumor - abnornal cells spread beyond their original site and impair the functions of one or more organs.  An individual with a malignant tumor is said to have cancer.

metastasis (meh-TAS-teh-sis) - the spread of cancer cells beyond their original site.