A Tour of the Cell

Chapter 6: A Tour of the CellEssential Knowledge2.a.2 Organisms capture and store free energy for use in biological processes (6.2).2.b.3 Eukaryotic cells maintain internal membranes that partition the cell into specialized regions (6.2-6.5).4.a.2 The structure and function of subcellular components, and their interactions, provide essential cellular processes (6.2-6.5).4.b.2 Cooperative interactions within organisms promote efficiency in the use of energy and matter (6.4). Light Microscope - LMUses visible light to illuminate the objectRelatively inexpensive type of microscopeCan examine live or dead objectsLight passes through specimen and then through various lensesLenses refract/bend light to magnifyLight Microscope

Occular LensObjective LensStage with specimenLight SourceLimitations - LMMiss many cell structures that are beyond the magnification of the light microscopeEx: lysosomes, centriolesNeed other ways to make the observations

Electron MicroscopesUse beams of electrons instead of lightInvented in 1939, but not used much until after WWIIAdvantages:Much higher magnificationsMagnifications of 50,000X or higher are possible. Can get down to atomic level in some casesDisadvantages of EMNeed a vacuumSpecimen must stop the electronsHigh cost of equipmentSpecimen preparationOther Types of MicroscopesTransmission Electron Microscope - TEMSends electrons through thinly sliced and stained specimensGives high magnification of interior views. Many cells structures are now visibleScanning Electron Microscopes SEMExcellent views of surfacesProduces 3-D viewsLive specimens possibleLimitations to EMTEM: Specimen dead; specimen prep is difficultSEM: Lower magnifications than the TEM; only see surface of specimen

TEM - interiorSEM - surface

Cell Biology or CytologyCyto = cell - ology = study ofShould use observations from several types of microscopes to make a total picture of how a cell is put togetherDirectly related to biochemistryTools for CytologyCell FractionationChromatographyElectrophoresisCell FractionationDisrupt cellsSeparate parts (organelles and membrane) by centrifugation at different speedsSeparates by size and density of the various structuresResult - pure samples of cell structures for studyCell Fractionation

ChromatographyTechnique for separating mixtures of chemicalsSeparates chemicals by size or degree of attraction to the materials in the mediumEx - paper, gas, column, thin-layer

ElectrophoresisSeparates mixtures of chemicals by their movement in an electrical fieldUsed for proteins and DNA

Cell HistorySee alternate PptHistory of CellsRobert Hooke - Observed cells in corkCoined the term "cells in 1665Came from jail cells and/or monastery cellsCells:Al life is made of cells!!!Cells are the simplest form of lifeHistory of Cells1833 - Robert Brown, discovered the nucleus1838 - M.J. Schleiden, all plants are made of cells1839 - T. Schwann, all animals are made of cells.1840 - J.E. Purkinje, coined the term protoplasmLate 1800s Rudolf Virchow (Omnis cellula e cellula - All cells are from other cells)

Cell Theory: 3 PartsAll living matter is composed of one or more cells.The cell is the structural and functional unit of life.Cells come only from existing cells. Two Types of Cells1) Prokaryotic - lack a nucleus and other membrane-bound structures.2) Eukaryotic - have a nucleus and other membrane-bound structures.ExamplesNucleusOrganellesProkBacteria, blue-green algae, ArchaebacteriaNoSome (ribosomes, cell mem, cytoplasm)EukAnimal, plants, fungiYesMost (depends on whether plant/animal)DNAComplexity# of cellsProkCircular, single-stranded, in cytoplasmLessOne/Uni, smaller in sizeEukHelical, double-stranded, in nucleusMoreSeveral/Multi, larger in size

ProkaryoticEukaryoticCell diversityMost cells are between 5-50 micrometersMycoplasmas - bacteria that are .1 to 1.0 mm. (1/10 the size of regular bacteria)# of cells: uni- and multicellularWhy Are Cells So Small?Cell volume to surface area ratios favor small sizeNucleus to cytoplasm consideration (control)Metabolic requirementsSurface area v. VolumeVol and SA are proportionate (if one increases, the other increases)Vol increases more than surface area (as cell grows)Smaller objects have a greater ratio of sa to volStructure/Function:Villi in intestinal cells inc sa so cells can absorb more materials from food

Basic Cell OrganizationMembrane*NucleusCytoplasm*OrganellesDNA/RNA*

*EVERY cell has these 3 parts

Animal Cell

Plant CellCell MembraneSeparates the cell from the environmentBoundary layer for regulating the movement of materials in/out of a cellOften called plasma membraneBilayer of phospholipidsAllows oxygen, nutrients, wastes to pass through a series of processes:DiffusionOsmosisActive transport

CytoplasmCell substance between the cell membrane and the nucleusThe fluid part of a cell. Neutral pH (serves as a natural buffer)Exists in two forms: gel - thick sol - fluidOrganellesTerm means "small organ Formed body in a cell with a specialized functionImportant in organizational structure of cellsMore prominent/numerous in eukaryotic cellsEx: Mitochondria, Endoplasmic reticulum, lysosomesNucleusMost obvious organelleUsually spherical, but can be lobed or irregular in shapeContains genetic infoFound ONLY in euk cellsFunction/s:Control center for the cellContains the genetic instructionsControls protein synthesis by making mRNA and rRNA (from DNA)

Structure of NucleusNuclear membraneNuclear poresNucleolusChromatin

Nuclear MembraneOtherwise known as Nuclear EnvelopeDouble membrane (lipid bilayer) separated by a 20-40 nm spaceInner membrane supported by a protein matrix (nuclear lamina) which gives the shape to the nucleusSeparates nuclear contents from cytoplasmDissolves during cell divisionNuclear PoresRegular holes through both membranes100 nm in diameterProtein complex gives shapeLines every nuclear poreAllows materials, such as macromolecules, in/out of nucleusNucleolusDark staining area in the nucleus0 - 4 per nucleusStorage area for ribosomesrRNA made here (from DNA)No membrane encloses it??? (Research about nucleolus continues!!!)ChromatinChrom: colored - tin: threadsDNA and protein in a loose formatWill form the chromosomes during Interphase of cell division (Chromosomes more condensed)Each eukary cell has specific #

RibosomesStructure: 2 subunits made of protein and rRNANo membraneFunction: protein synthesisThe more occurrences of protein synthesis, the more ribosomesEx: Pancreatic cells have over 1.2 million ribosomes

Ribosome structure2 Subunits:1) Large45 proteins, 3 rRNA molecules2) Small23 proteins, 1 rRNA molecule2 Locations:1) Free in the cytoplasm - make proteins for use in cytosol2) Membrane bound - make proteins that are exported from the cell (Attached to rough ER)

Endomembrane SystemSeries of membranes connected by direct physical continuity or by transfer of membrane segments called vesiclesIncludes: ER, Golgi, vesiclesFunction: protein synthesis, transport of proteins, move lipids, detoxify proteinsWorks closely with: nucleus, lysosomes, ribosomes, plasma membraneEndomembrane System

Endoplasmic ReticulumOften referred to as ERMakes up to 1/2 of the total membrane in cellsOften continuous with the nuclear membrane/poresAll cisternae (inner portion) are connectedStructure:Folded sheets or tubes of membranesVery fluid in structure with the membranes constantly changing size and shape.

2 Types of ER1) Smooth ER: no ribosomesUsed for lipid synthesis, carbohydrate storage, detoxification of poisonsEx: store calcium ions, sex hormones contain LOADS of these (lipid synthesis)2) Rough ER: with ribosomesMakes secretory protein and lipid parts of cell membraneEx: liver cells (add water to detoxify proteins to secrete), insulin (secretory protein)Most proteins are called glycoproteins (contain protein and carb parts)Golgi Apparatus or DictyosomesStructure: parallel array of flattened cisternae (looks like a stack of Pita bread)3 to 20 per cellLikely an outgrowth of the ER systemThink of the UPS man

2 Faces of Golgi1) Cis face - side toward the nucleus Receiving sideLocated near ER2) Trans face - side away from the nucleus. Shipping sideGives rise to vesiclesBoth contain varying polarityFunction of GolgiProcessing - modification of ER productsDistribution - packaging of ER products for transportSorting and ShippingUPS man/organelle!!!Found in large #s in secretory cellsEver-changing organelle

Transport VesiclesSecretory proteins in transit from one organelle to anotherTwo kinds:1) From ER to Golgi2) From Golgi to ?Otherwise known as Golgi vesiclesGolgi VesiclesSmall sacs of membranes that bud off the Golgi BodyTransportation vehicle for the modified ER productsMay become polypeptide chains or amino acidsContain identifiers to help determine where destination isLysosomeSingle membrane made by rough ER Made from the Trans face of the Golgi apparatusFunctions:Breakdown and degradation of cellular materialsCarry out intracellular digestionDigest cells own materials Called autophagyDigest old, non-repairable itemsContains hydrolytic enzymes to breakdown fats, proteins, polysaccs, and nucleic acids

Lysosome Function, cont.Important in cell death (apoptosis)Missing enzymes may cause various genetic enzyme diseasesExamples: Tay-Sachs, Pompes DiseaseTay-Sachs: Cant break down lipid in brain (accumulates and causes nervous system disorders)VacuolesStructure - single membrane, usually larger than the Golgi vesiclesFunction - depends on the organism (most control hydrolysis and store materials)Types - Food, contractile, centralFunction:Water regulation - hydrolysisStorage of ionsStorage of hydrophilic pigments (e.g. red and blues in flower petals)Helps attract pollinators

Protist vacuolesContractile vacuoles - pump out excess water.Food vacuoles - store newly ingested food until the lysosomes can digest itPlant vacuolesLarge single vacuole in mature (making up to 90% of the cell's volume)Tonoplast - vacuole membraneRegulatory (Semi-permeable)Function:Used to enlarge cells and create turgor pressureAbsorb waterStore enzymes (various types)Store toxinsColoration (may contain pigment)

Microbody Contain specialized enzymes for specific reactionsPeroxisomes: use up H peroxideSome break down fatty acids, detoxify poisonsGlyoxysomes: lipid digestionFound in plant seeds (used for energy storage)

Enzymes in a crystalEnergy Transforming Organelles1) MitochondriaFound in ALL cells (plant, animal, etc)2) ChloroplastsFound only in plant, plant-like cellsConsidered to be energy transforming organellesMitochondria food ATPChloroplast sun/water/CO2 foodMitochondria2 membranes: Inner and outer (each is phospholipid bilayer)The inner membrane has more surface area than the outer membrane.Matrix: inner spaceIntermembrane space: area between the membranesMitochondriaHave ribosomesHave their own DNACan reproduce themselvesMay have been independent cellsFound in nearly ALL eukaryotic cellsFunction:Site for cell respiration - the release of energy from food.Major location of ATP generationPowerhouse of the cell

Inner Membrane of Mito Folded into cristaeAmount of folding depends on the level of cell activityContains many enzymesServe as catalysts for cellular respirationATP generated hereChloroplastsFunction: performs photosynthesisStructure Two outer membranes Complex internal membraneFluid-like stroma is around the internal membranes3 components/parts:1) Stroma2) Thylakoid OR Grana3) Intermembrane space

ChloroplastsContain ribosomesContain DNACan reproduce themselvesOften contain starchMay have been independent cells at one time

Inner/Thylakoid Membranes of ChloroplastArranged into flattened sacs called thylakoidsSome regions stacked into layers called granaContain the green pigment chlorophyll78CytoskeletonNetwork of rods and filaments in the cytoplasmComponents:1) Microtubules2) Microfilaments3) Intermediate Filaments

Cytoskeleton FunctionsCell structure and shapeCell movementMovement of organellesCell division - helps build cell walls and move the chromosomes apartVERY important to animal cells Why? Because animal cells lack the extra support of cell wallMicrotubulesStructure - small hollow tubes made of repeating units of a protein dimerSize - 25 nm diameter with a 15 nm lumen; can be 200 nm to 25 mm in lengthThickest of three componentsContains protein called tubulinMicrotubulesRegulate cell shape Coordinate direction of cellulose fibers in cell wall formationTracks for motor moleculesEx: Guide vesicles from GolgiForm cilia and flagellaInternal cellular movementMake up centrioles, basal bodies and spindle fibers

Cilia and FlagellaCilia - short, but numerousHair-likeFlagella - long, but fewTail-likeFunctions Flight/Movement/Locomotion, reproductive processes, filter waterStructure - arrangement of microtubules, covered by the cell membraneDynein - motor protein that connects the tubules

Dynein ProteinA contractile/motor proteinUses ATPCreates a twisting motion between the microtubules causing the structure to bend or moveMade of several polypeptide chainsQuaternary structured proteinCentriolesUsually one pair per cell, located close to the nucleusFound in animal cells9 sets of triplet microtubulesHelp in cell divisionMicrofilaments5 to 7 nm in diameterStructure - two intertwined strands of actin proteinSolid rods of linear filaments

Functions of MicrofilamentsMuscle contractionCytoplasmic streamingPseudopodia (ex: amoeba)Cleavage furrow formation (ex: cell division)Maintenance and changes in cell shapeIntermediate FilamentsFibrous proteins that are super coiled into thicker cables and filaments 8 - 12 nm in diameterMade from several different types of proteinFunctions:Maintenance of cell shapeHold organelles in place

Cell WallNonliving jacket that surrounds some cellsFunction as the cell's exoskeleton for support and protectionFound in:PlantsProkaryotesFungiSome ProtistsPlant: Primary Cell Wall Thin and flexibleCellulose fibers placed at right angles to expansionPlacement of fibers guided by microtubulesPlant: Secondary Cell Wall Thick and rigidAdded between the cell membrane and the primary cell wall in laminated layersMay cover only part of the cell; giving spiralsMakes up "woodCell wall: Middle LamellaThin layer rich in pectin found between adjacent plant cellsGlues cells together

The Inner Life of the Cell - Harvard University

Intercellular JunctionsPlants - PlasmodesmataChannels between cells through adjacent cell wallsAllows communication between cellsAlso allows viruses to travel rapidly between cells

Intercellular JunctionsAnimals:Tight junctionsDesmosomesGap junctions

Tight JunctionsVery tight fusion of the membranes of adjacent cellsSeals off areas between the cellsPrevents movement of materials around cellsDesmosomesBundles of filaments which anchor junctions between cellsDoes not close off the area between adjacent cellsCoordination of movement between groups of cellsGap JunctionsOpen channels between cells, similar to plasmodesmataAllows communication between cells

SummaryRecognize the types and uses of microscopes in the study of cells.Recognize the limitations on cell size.Recognize why cells must have internal compartmentalization.Identify the structures and functions of cell organelles.Identify the structures and functions of the cytoskeleton.Recognize the surface features and inter-cellular connections of plant and animal cells.