2Section 1: An Introduction to Cells Learning Outcomes3.1 Describe the cell and its organelles, including the composition and function of each.3.2 Describe the chief structural features of the plasma membrane.3.3 Differentiate among the structures and functions of the cytoskeleton.3.4 Describe the ribosome and indicate its specific functions.
3Section 1: An Introduction to Cells Learning Outcomes3.5 Describe the Golgi apparatus and indicate its specific functions.3.6 Describe mitochondria, indicate their functions, and explain their significance to cellular function.
4Section 1: An Introduction to Cells Typical cellSmallest living unit in the body~0.1 mm in diameterCould not be examined until invention of microscope in 17th centuryAnimation: Your Cells
5Section 1: An Introduction to Cells Cell theoryCells are building blocks of all plants and animalsAll new cells come from division of preexisting cellsCells are smallest unit that perform all vital physiological functions
6The differentiation of the four tissue types from a single cell: Cells are the building blocks of allplants and animals.All new cells come from the divisionof pre-existing cells.Cells are the smallest units that performall vital physiological functions.NutrientsO2DivisionWastesCO2CellGrowthNewcellsThe cell theoryEpithelial tissueConnective tissueFigure 3 Section 1 An Introduction to CellsMuscle tissueThe differentiation of the four tissue types from a single cell:the fertilized ovumNeural tissueFigure 3 Section 16
7Section 1: An Introduction to Cells Each cell maintains homeostasisCoordinated activities of cells allow homeostasis at higher organizational levels
8Section 1: An Introduction to Cells Cells vary in structure and function but all descend from a single fertilized ovumFertilized ovum contains genetic potential to become any cellCell divisions occur creating smaller, different parcels of cytoplasmCytoplasmic differences turn off/on specific genes in DNA and daughter cells become specialized= DifferentiationDifferentiated cells are responsible for all body functions
9Section 1: An Introduction to Cells Extracellular fluidWatery medium surrounding cellsCalled interstitial fluid (interstitium, something standing between) in most tissues
10Module 3.1: Smallest living units of life Cell componentsPlasma membrane (cell membrane)Separates cell contents from extracellular fluidCytoplasmMaterial between cell membrane and nuclear membraneColloid containing many proteinsTwo subdivisionsCytosolIntracellular fluidOrganelles (“little organs”)Intracellular structures with specific functions
11Module 3.1: Smallest living units of life OrganellesNonmembranousNot completely enclosed by membranesIn direct contact with cytosolExamples:CytoskeletonMicrovilliCentriolesCiliaRibosomes
12Module 3.1: Smallest living units of life OrganellesMembranousEnclosed in a phospholipid membraneIsolated from cytosolExamples:MitochondriaNucleusEndoplasmic reticulumGolgi apparatusLysosomesPeroxisomes
13Module 3.1: Smallest living units of life OrganellesMicrovilliSTRUCTURE: membrane extensions containing microfilamentsFUNCTION: increase surface area for absorptionCytoskeletonSTRUCTURE: fine protein filaments or tubesCentrosomeOrganizing center containing pair of centriolesFUNCTION:Strength and supportIntracellular movement of structures and materials
14Module 3.1: Smallest living units of life OrganellesRibosomesSTRUCTURE: RNA and proteinsFixed: attached to endoplasmic reticulumFree: scattered in cytoplasm
15Module 3.1: Smallest living units of life OrganellesPeroxisomeSTRUCTURE: vesicles containing degradative enzymesFUNCTION:Catabolism of fats/other organic compoundsNeutralization of toxic compoundsLysosomeSTRUCTURE: vesicles containing digestive enzymesRemoval of damaged organelles or pathogens
16Module 3.1: Smallest living units of life OrganellesGolgi apparatusSTRUCTURE: stacks of flattened membranes (cisternae) containing chambersFUNCTION: storage, alteration, and packaging of synthesized productsMitochondriaSTRUCTURE:Double membraneInner membrane contains metabolic enzymesFUNCTION: production of 95% of cellular ATP
17Module 3.1: Smallest living units of life OrganellesNucleusSTRUCTURE:Fluid nucleoplasm containing enzymes, proteins, DNA, and nucleotidesSurrounded by double membraneFUNCTION:Control of metabolismStorage/processing of genetic informationControl of protein synthesisAnimation: Nucleus
18Module 3.1: Smallest living units of life OrganellesEndoplasmic reticulum (ER)STRUCTURE: membranous sheets and channelsFUNCTION: synthesis of secretory products, storage, and transportSmooth ERNo attached ribosomesSynthesizes lipids and carbohydratesRough ERAttached ribosomesModifies/packages newly synthesized proteins
19Module 3.1 Review a. Distinguish between the cytoplasm and cytosol. b. Describe the functions of the cytoskeleton.c. Identify the membranous organelles and describe their functions.
20Module 3.2: Plasma membrane Selectively permeable membrane that controls:Entry of ions and nutrientsElimination of wastesRelease of secretions
21Module 3.2: Plasma membrane Plasma membrane componentsGlycocalyxSuperficial membrane carbohydratesComponents of complex moleculesProteoglycans (carbohydrates with protein attached)Glycoproteins (protein with carbohydrates attached)Glycolipids (lipids with carbohydrates attached)FunctionsCell recognitionBinding to extracellular structuresLubrication of cell surface
22Module 3.2: Plasma membrane Plasma membrane components (continued)Integral proteinsPart of cell membraneCannot be removed without damaging cellOften span entire cell membrane= Transmembrane proteinsCan transport water or solutesPeripheral proteinsAttached to cell membrane surfaceRemovableFewer than integral proteins
23Integral (transmembrane) proteins Structure of the plasma membraneEXTRACELLULAR FLUIDGlycocalyx(extracellularcarbohydrates)Integral proteinwith channelGlycolipidFigure The plasma membrane isolates the cell from its environment and performs varied functionsIntegralglycoproteins= 2 nmCYTOPLASMIntegral (transmembrane) proteinsPeripheral proteinsCytoskeleton(microfilaments)Figure23
24Module 3.2: Plasma membrane Plasma membrane structureThin (6–10 nm) and delicatePhospholipid bilayerMostly comprised of phospholipid molecules in two layersHydrophilic heads at membrane surfaceHydrophobic tails on the insideIsolates cytoplasm from extracellular fluidAnimation: Cell Membrane Barrier
25The phospholipid bilayer that forms the plasma membrane HydrophilicheadsHydrophobictailsFigure The plasma membrane isolates the cell from its environment and performs varied functionsCholesterolFigure25
26Module 3.2: Plasma membrane Plasma membrane functionsPhysical isolationRegulation of exchange with external environmentSensitivity to environmentStructural supportLipid bilayer provides isolationProteins perform most other functions
27Figure The plasma membrane isolates the cell from its environment and performs varied functionsFigure27
28Figure The plasma membrane isolates the cell from its environment and performs varied functionsFigure28
29Module 3.2 Reviewa. List the general functions of the plasma membrane.b. Which structural component of the plasma membrane is mostly responsible for its ability to isolate a cell from its external environment?c. Which type of integral protein allows water and small ions to pass through the plasma membrane?
30Module 3.3: Cytoskeleton Cytoskeleton (cellular framework) components Microfilaments<6 nm in diameterTypically composed of actinCommonly at periphery of cellMicrovilliFinger-shaped extensions of cell membraneHas core of microfilaments to stiffen and anchorEnhance surface area of cell for absorptionTerminal web (layer inside plasma membrane in cells forming a layer or lining)
31Module 3.3: CytoskeletonCytoskeleton (cellular framework) components (continued)Intermediate filaments7–11 nm in diameterStrongest and most durable cytoskeletal elementsMicrotubules~25 nm in diameterLargest components of cytoskeletonExtend outward from centrosome (near nucleus)
32Structures of the cytoskeleton MicrovilliMicrofilamentsPlasma membraneTerminal webMicrovilliSEM X 30,000Figure The cytoskeleton plays both a structural and a functional roleIntermediate filamentsMicrotubuleSecretory vesicleMitochondrionEndoplasmicreticulumFigure32
33Module 3.3: Cytoskeleton Centrioles Cylindrical structures Composed of microtubules (9 groups of triplets)Two in each centrosomeControl movement of DNA strands during cell divisionCells without centrioles cannot divideRed blood cellsSkeletal muscle cells
34The structure of centrioles Microtubulesin centrioleFigure The cytoskeleton plays both a structural and a functional roleFigure34
35Module 3.3: Cytoskeleton Cilia Long, slender plasma membrane extensionsCommon in respiratory and reproductive tractsAlso composed of microtubulesNine groups of pairs surrounding a central pairAnchored to cell surface with basal bodyBeat rhythmically to move fluids or secretions across cell
36The structure of cilium PlasmamembraneFigure The cytoskeleton plays both a structural and a functional roleMicrotubulesBasalbodyFigure36
37The action of a beating cilium Power strokeFigure The cytoskeleton plays both a structural and a functional roleReturn strokeFigure37
38Module 3.3 Reviewa. List the three basic components of the cytoskeleton.b. Which cytoskeletal component is common to both centrioles and cilia?c. What is the function of cilia?
39Module 3.4: Ribosomes Ribosomes Protein synthesis Two subunits (1 large, 1 small) containing special proteins and ribosomal RNA (rRNA)Must join together before synthesis beginsFree ribosomesThroughout cytoplasmManufactured proteins enter cytosol
40The two subunits of a functional ribosome Small ribosomal subunit Large ribosomalsubunitThe two subunits of afunctional ribosomeFigure Ribosomes are responsible for protein synthesis and are often associated with the endoplasmic reticulumFigure40
41Module 3.4: Ribosomes Endoplasmic reticulum (ER) Network of intracellular membranes attached to nucleusForms hollow tubes, sheets, and chambers (cisternae, singular, cisterna, reservoir for water)
42Module 3.4: Ribosomes Endoplasmic reticulum (ER) Two types Smooth (SER)Lacks ribosomesTubular cisternaeRough (RER)Has attached (fixed) ribosomesModification of newly synthesized proteinsExport to Golgi apparatusProportion of SER to RER depends on the cell and its functions
43The structure of the endoplasmic reticulum (ER) NuclearenvelopeTubularcisternaeCisternaeSmoothendoplasticreticulum (SER)Figure Ribosomes are responsible for protein synthesis and are often associated with the endoplasmic reticulumFigure – 343
44Figure Ribosomes are responsible for protein synthesis and are often associated with the endoplasmic reticulumFigure44
45Module 3.4: Ribosomes Functions of SER Synthesis of phospholipids and cholesterolSynthesis of steroid hormonesSynthesis and storage of glycerides in liver and fat cellsSynthesis and storage of glycogen in skeletal and liver cells
46The structure and function of rough endoplasmicreticulum (RER)FixedribosomesmRNA strandRibosomeTransport vesiclesEnzymeFigure Ribosomes are responsible for protein synthesis and are often associated with the endoplasmic reticulumGrowingpolypeptideProteinGlycoproteinAs a polypeptide issynthesized on aribosome, the growingchain enters thecisterna of the RER.The polypeptideassumes itssecondary andtertiary structure.The complete proteinmay become anenzyme or aglycoprotein.Glycoproteins,proteins, and enzymesare packaged intransport vesicles.Transport vesiclesdeliver proteins,enzymes, andglycoproteins to theGolgi apparatus.Figure46
47Module 3.4: Ribosomes Function of RER Polypeptide synthesized on attached ribosomeGrowing chain enters cisternaPolypeptide assumes secondary/tertiary structuresCompleted protein may become enzyme or glycoproteinProducts not destined for RER are packaged into transport vesiclesDeliver products to Golgi apparatus
48Module 3.4 Reviewa. Describe the immediate cellular destinations of newly synthesized proteins from free ribosomes and fixed ribosomes.b. Describe the structure of smooth endoplasmic reticulum.c. Why do certain cells in the ovaries and testes contain large amounts of smooth endoplasmic reticulum (SER)?
49Module 3.5: Golgi apparatus FunctionsRenews or modifies plasma membraneModifies or packages secretions for release from cell (exocytosis)Packages special enzymes within vesicles for use in cytosolTypically consist of 5–6 flattened discs (cisternae)May be more than one in a cellSituated near nucleusAnimation: Golgi Apparatus
50Module 3.5: Golgi apparatus Steps of functionProducts from RER arrive at the forming face in transport vesiclesTransport vesicles fuse with Golgi apparatus and empty contents into cisternaeEnzymes modify productsNew vesicles move material between cisternaeProduct arrives at maturing face
51Module 3.5: Golgi apparatus ProductsMembrane renewal vesiclesAdd to plasma membraneSecretory vesiclesContain products to be discharged from the cellFuse with plasma membrane and release contents into extracellular environmentEnzymes for cytosolContained within lysosomes (lyso-, a loosening + soma, body)Isolate damaging chemical reactions
52Module 3.5: Golgi apparatus LysosomesIsolated intracellular location for toxic chemicals involved in breakdown and recycling of large organic moleculesThree basic functionsMay fuse with another organelle to activate digestive enzymesMay fuse with another vesicle containing fluid or solid extracellular materialsMay break down with cell injury or death causing autolysis (enzymes destroy cytoplasm)“Suicide packets”
53Figure 3.5.2 The Golgi apparatus is a packaging center The three basic functions of lysosomesWaste products and debris are ejected from the cellwhen the vesicle fuses with the plasma membrane.Vesicles containing fluids or solids mayform at the surface of the cell.Extracellularsolid or fluidLysosomal enzymesare activated byfusion withanother vesicleor organelleAs the materialsor pathogens arebroken down bylysosomal enzymes,released nutrientsare absorbed.Lysosomesinitially containinactiveenzymes.As digestionoccurs, nutrientsare reabsorbedfor recycling.GolgiapparatusFigure The Golgi apparatus is a packaging centerFunction 1: A lysosomemay fuse with the mem-brane of anotherorganelle, such as amitochondrion. Thisactivates the enzymesand begins thedigestion of thelysosomal contents.Function 2: A lysosomemay also fuse with avesicle containing fluid orsolid materials fromoutside the cell.Function 3: The lysosomal membranemay break down following injury to, ordeath of, the cell. The digestiveenzymes become active and thenattack the cytoplasm in a destructiveprocess known as autolysis. For thisreason, lysosomes are sometimescalled “suicide packets.”Figure53
54Module 3.5: Golgi apparatus Membrane flowContinuous movement and exchange of materials between organelles using vesiclesCan replace parts of cell membrane to allow cell to grow, mature, or respond to changing environment
55Module 3.5 Reviewa. List the three major functions of the Golgi apparatus.b. The Golgi apparatus produces lysosomes. What do these lysosomes contain?c. Describe three functions of lysosomes.
56Animation: Mitochondria Module 3.6: MitochondriaMitochondria (mitos, thread + chondrion, granule)Produce energy (ATP) for cells through the breakdown of carbohydrates (glucose)Vary widely in shape and numberRed blood cells have noneCardiac muscle cells are 30% mitochondria by volumeAnimation: Mitochondria
57Figure 3.6.2 Mitochondria are the powerhouses of the cell The role of mitochondria in the production of the high-energy compound ATPAlthough most ATP productionoccurs inside mitochodria,the first steps take place in thecytosol. In this reactionsequence, called glycolysis(glycos, sugar + -lysis, aloosening), each glucosemolecule is broken down intotwo molecules of pyruvate. Thepyruvate molecules are thenabsorbed by mitochondria.GlucoseCYTOPLASMThe energy releasedduring a series of stepsperforms the enzymaticconversion of ADP toATP, which leaves themitochondrion.2 PyruvateMITOCHONDRIONADP +phosphateEnzymes andcoenzymesof cristaeCitric acidcycleFigure Mitochondria are the powerhouses of the cellMATRIXIn the mitochondrial matrix, aCO2 molecule is removedfrom each absorbed pyruvatemolecule; the remainderenters the citric acid cycle,of TCA (tricarboxylic acid)cycle, an enzymatic pathwaythat systematically breaksdown the absorbed pyruvateremnant into carbon dioxideand hydrogen atoms.The hydrogen atoms aredelivered to enzymes andcoenzymes of the cristaewhich catalyze thesynthesis of ATP fromADP and phosphate. Atthe end of this process,oxygen combines with thehydrogen atoms to formwater molecules.Figure57
58Module 3.6: Mitochondria Mitochondria Double membrane Outer (surrounds organelle)Inner (contains numerous folds called cristae)Encloses liquid (matrix)Cristae increase surface area for energetic reactions
59Cytoplasm of cell Matrix Cristae A colorized TEM of a mitochondrion Figure Mitochondria are the powerhouses of the cellA colorized TEM of a mitochondrionTEM x 50,000Figure59
60Module 3.6: Mitochondria Steps of ATP production Glycolysis (glycos, sugar + -lysis, a loosening)Occurs in cytosol1 glucose 2 pyruvatePyruvate absorbed into mitochondriaIn mitochondrial matrixCO2 removed from pyruvateEnters citric acid (or TCA, tricarboxylic acid) cycleSystematically removes CO2 and hydrogen atoms
61Module 3.6: Mitochondria Steps of ATP production (continued) Enzymes and coenzymes use hydrogen atoms to catalyze ATP from ADPAlso forms H2OATP leaves mitochondrion
62Module 3.6 Review a. Describe the structure of a mitochondrion. b. Most of a cell’s ATP is produced within its mitochondria. What gas do mitochondria require to produce ATP?c. What does the presence of many mitochondria imply about a cell’s energy requirements?
63Section 2: Nucleus Learning Outcomes Explain the functions of the cell nucleus, and discuss the nature and importance of the genetic code.Summarize the process of protein synthesis.Summarize the process of transcription.3.10 Summarize the process of translation.
64Section 2: Nucleus Nucleus Usually largest cellular structure Control center for cellular operationsCan direct synthesis of >100,000 different proteinsCoded in sequence of nucleotidesDetermines cell structure/functionUsually only one per cellExceptions:Multiple: skeletal muscle cellNone: mature red blood cells
65Section 2: NucleusThe nucleus directs cellular responses to environmental (ECF) changesShort-term adjustmentsEnzyme activity changesLong-term adjustmentsChanges in enzymes producedChanges in cell structure from changes in structural proteinsOften occur as part of growth, development, and aging
66EXTRACELLULAR FLUID (ECF) The role of the nucleus in preservinghomeostasis at the cellular levelPlasma membraneBinding tomembranereceptorsSHORT-TERMADJUSTMENTSChangesin thecompositionof theECFEnzymeactivation orinactivationDiffusionthroughmembranechannelsLONG-TERMADJUSTMENTSChanges in the bio-chemical processesunder way in the cellresulting from thesynthesis of additionalenzymes, fewerenzymes, or differentenzymesBinding to nuclearreceptors that altergenetic activityFigure 3 Section 2 Structure and Function of the NucleusChanges in thephysical structure ofthe cell due to altera-tions in the rates ortypes of structuralproteins synthesizedDNA innucleusCYTOPLASMFigure 3 Section 266
67Module 3.7: Nuclear structure Nuclear structures and functionsNuclear envelopeSeparates nucleus from cytoplasmDouble membranePerinuclear space (peri-, around)Space between layersNuclear poresAllow passage of small molecules and ions
68Module 3.7: Nuclear structure Nuclear structures and functions (continued)NucleoplasmFluid contents of nucleusFine filamentsIonsEnzymesRNA and DNA nucleotidesSmall amounts of RNADNA
69Module 3.7: Nuclear structure Nuclear structures and functions (continued)Nucleoli (singular, nucleolus)Transient, clear nuclear organellesComposed of:RNAEnzymesProteins (histones)Form around DNA instructions for forming proteins/RNAAssemble RNA subunitsMany found in large, protein-producing cellsLiverNerveMuscle
70The structure of the nucleus PerinuclearspaceNuclear envelopeNuclear poresFigure The nucleus contains DNA, RNA, organizing proteins, and enzymesNucleoplasmNucleolusFigure70
71Module 3.7: Nuclear structure DNAInstructions for protein synthesisStrands coiledWrap around histone molecules forming nucleosomesLoosely coiled (chromatin) in nondividing cellsTightly coiled (chromosomes) in dividing cellsTo begin, two copies of each chromosome held together at centromere23 paired chromosomes in somatic (general body) cellsOne each from mother/fatherCarry instructions for proteins and RNAAlso some regulatory and unknown functions
72The coiled structure of DNA in the nucleus of a nondividing cell ChromatinNucelosomeHistonesDNA doublehelixNucleus of nondividing cellFigure The nucleus contains DNA, RNA, organizing proteins, and enzymesFigure72
73The tighter coiling of DNA to form chromosomes in dividing cells CentromereSupercoiledregionFigure The nucleus contains DNA, RNA, organizing proteins, and enzymesDividing cellVisible chromosomeFigure73
74Module 3.7 Reviewa. What molecule in the nucleus contains instructions for making proteins?b. Describe the contents and the structure of the nucleus.c. How many chromosomes are contained within a typical somatic cell?
75Module 3.8: Protein synthesis DNALong parallel chains of nucleotidesChains held by hydrogen bondsFour nitrogenous basesAdenine (A)Thymine (T)Cytosine (C)Guanine (G)Genetic code (sequence of nucleotides)Triplet code (three nucleotides specify single amino acid)
76Figure 3.8.2 Protein synthesis involves DNA, enzymes, and three types of RNA 76
77Module 3.8: Protein synthesis DNA (continued)GeneFunctional unit of heredityAll the DNA nucleotides needed to produce a specific proteinSize varies (~3003000 nucleotides)
78Module 3.8: Protein synthesis Gene activationRemoval of histones and DNA uncoilingMessenger RNA (mRNA)Assembled by enzymesConnecting complementary RNA nucleotides(A, G, C, U)Contains information in triplets (codons)Leaves nucleus through poresTransfer RNA (tRNA)Contains triplets (anticodons) that bind to mRNA codonsEach type carries a specific amino acid linked to form a polypeptide
79Module 3.8: Protein synthesis Animation: Protein Synthesis: RNA PolymeraseAnimation: Protein Synthesis: Transcription and Translation
80methionine-proline-serine-leucine The key events of protein synthesisUncoiling of the portion of DNA moleculecontaining an activated geneDNA triplets are exposed to the nucleoplasmsPaired DNA strandsEnzymeAssembly of an mRNA strand by enzymesThe mRNA strand containingthe complementary codonspasses through a nuclear poreand enters the cytoplasm.Codon on mRNABinding of transfer RNA (tRNA) moleculescarrying a specific amino acidAmino acidFigure Protein synthesis involves DNA, enzymes, and three types of RNAtRNA attachesto mRNAAnticodonmRNA strandCodonLinking of amino acids to forma polypeptidePolypeptidemethionine-proline-serine-leucineFigure – 680
81acids in the polypeptide A summary of how DNA codes for a proteinThe DNAtripletsdetermine thesequence ofmRNA codons.The mRNAcodonsdeterminethe sequenceof tRNAs.The sequence of tRNAsdetermines thesequence of aminoacids in the polypeptideor protein.Figure Protein synthesis involves DNA, enzymes, and three types of RNAFigure81
82Module 3.8 Reviewa. List the three types of RNA involved in protein synthesis.b. What is a gene?c. Why is the genetic code described as a triplet code?
83Module 3.9: Transcription Transcription (“to copy” or “rewrite”)Production of RNA from DNA templateAll three types of RNA are formedExample:mRNA (information for synthesizing proteins)
84Module 3.9: Transcription Steps of transcriptionGene activationOccurs at control segment (1st segment of gene)Template strand (One DNA strand used to synthesize RNA)2. RNA polymerase (enzyme)Binds to promoterAssembles mRNA strandComplementary to DNAExample: (DNA triplet TAC = mRNA AUG)Hydrogen bonds between nucleotides
85Events in the process of transcription of mRNA The templatestrand is theDNA strand thatwill be used tosynthesize RNA.The enzymeRNA polymerasebinds to theexposed controlsegment and, usingthe triplets as aguide, assembles astrand of mRNA.The segmentat the start of thegene is known asthe controlsegment.Triplet 111GeneTriplet 22Complementarytriplets23Triplet 334Figure Transcription encodes genetic instructions on a strand of RNATriplet 44Gene activation, which results in temporarydisruption of the hydrogen bonds between thenitrogenous bases of the two DNA strandsAdenineDNAGuanineCytosineUracil (RNA)Thymine (DNA)Figure85
86Module 3.9: Transcription Steps of transcription (continued)Transcription endsStop codon reachedmRNA detachesComplementary DNA strands reassociate (hydrogen bonding between complementary base pairs)
87Immature mRNAEvents in the process of transcription of mRNA (continued)RNA polymerase works onlyon RNA nucleotides—it canattach adenine, guanine,cytosine, or uracil, but neverthymine. If the DNA triplet isTAC, the correspondingmRNA codon will be AUG.IntronsremovedExons spliced togetherto from mature mRNAThe production of functional mRNAfrom immature mRNAmRNA strandCodon 1Codon2Codon1Codon3Codon 4(stop codon)RNAnucleotideFigure Transcription encodes genetic instructions on a strand of RNARNApolymeraseRNApolymeraseHydrogen bonding betweenthe nitrogenous bases ofthe template strand andcomplementary nucleotidesin the nucleoplasmConclusion of transcriptionwhen stop codon is reachedAdenineGuanineCytosineUracil (RNA)Thymine (DNA)Figure – 387
88Module 3.9: Transcription Immature RNAContains triplets not needed for protein synthesis“Edited” before leaving nucleus through poresIntrons (removed nonsense regions)Exons (remaining coding segments)Creates shorter, functional mRNAChanging “edits” can produce mRNAs for different proteins
89Exons spliced together The production of functional mRNA Immature mRNAIntronsremovedExons spliced togetherto form mature mRNAFigure Transcription encodes genetic instructions on a strand of RNAThe production of functional mRNAfrom immature mRNAFigure89
90Module 3.9 Review a. Define DNA template strand. b. What is transcription?c. What process would be affected if a cell could not synthesize the enzyme RNA polymerase?
91Module 3.10: TranslationTranslation (translate nucleic acids to proteins)Uses mRNA created in nucleusLeaves via nuclear poresOccurs in cytoplasmAnimation: Protein Synthesis: Translation Initiation
92Module 3.10: Translation Steps of translation mRNA binds to small ribosomal subunitBinding between mRNA and tRNAmRNA codons with tRNA anticodonsSmall and large ribosomal subunits assemble around mRNA strandAdditional tRNAs arriveMore than 20 kindsAt least one for each amino acid
93The process of translation NUCLEUSAmino acidtRNAAnticodontRNA binding sitesEntry of mRNA into cytoplasmStart codonmRNA strandSmallribosomalsubunitLargeribosomalsubunitBinding of mRNA strand to a smallribosomal subunit and arrival of thefirst tRNAJoining of small and largeribosomal subunits around themRNA strand and arrival ofadditional tRNAsFigure Translation builds polypeptides as directed by an mRNA strandAdenineGuanineCytosineUracilFigure – 293
94Module 3.10: Translation Steps of translation (continued) Ribosome attaches to next complementary tRNARibosome links amino acids forming dipeptideMore tRNAs arrive and continue forming polypeptideStops once stop codon is reached on mRNARibosomal subunits detachLeaves intact mRNA and new polypeptideAnimation: Protein Synthesis: Sequence of Amino Acids in the Newly Synthesized Polypeptide
95The process of translation (continued) Small ribosomalsubunitPeptidebondLargeribosomalsubunitCompletedpolypeptideStopcodonAttachment of tRNA withanticodon that is complementaryto codon on RNA strandFormation of a depeptide,release of first tRNA, andarrival of another tRNACompletion of polypeptide anddetachment of ribosomalsubunitsFigure Translation builds polypeptides as directed by an mRNA strandAdenineGuanineCytosineUracilFigure – 595
96Animation: Transcription Translation Module 3.10: TranslationTranslationProduces a typical protein in ~20 secondsmRNA can interact with other ribosomes and produce more proteinsMultiple ribosomes can attached to a single mRNA strand to quickly produce many proteinsAnimation: Transcription Translation
97Module 3.10 Review a. What is translation? b. The nucleotide sequence of three mRNA codons is AUU-GCA-CUA. What is the complementary anticodon sequence for the second codon?c. During the process of transcription, a nucleotide was deleted from an mRNA sequence that coded for a protein. What effect would this deletion have on the amino acid sequence of the protein?
98Section 3: Membrane Transport Learning Outcomes3.11 Explain the process of diffusion, and identify its significance to the body.3.12 Explain the process of osmosis, and identify its significance to the body.3.13 Describe carrier-mediated transport and its role in the absorption and removal of specific substances.3.14 Describe vesicular transport as a mechanism for facilitating the absorption or removal of specific substances from cells.
99Section 3: Membrane Transport Plasma membraneActs as a barrier separating cytosol and ECFMust still coordinate cellular activity with extracellular environmentPermeability (determines which substances can cross membrane)Freely permeable (any substances)Selectively permeable (some substances cross)Impermeable (none can pass)No living cell is impermeable
100Permeability characteristics of membranes Freely permeable membranesSelectively permeable membranesImpermeable membranesIonsCarbohydratesIonsCarbohydratesIonsCarbohydratesProtein—Protein—Protein—WaterWaterWaterLipidsLipidsLipidsFreely permeable membranesallow any substance to pass withoutdifficulty.Selectively permeable membranes,such as plasma membranes, permit thepassage of some materials and preventthe passage of others.Nothing can pass through impermeablemembranes. Cells may be impermeableto specific substances, but no living cellhas an impermeable membrane.Figure 3 Section 3.1 How Things Enter and Leave the CellFigure 3 Section100
101Section 3: Membrane Transport Selectively permeable membranesSelective based on:Characteristics of material to passSizeElectrical chargeMolecular shapeLipid solubilityOther factorsCharacteristics of membraneWhat lipids and proteins presentHow components are arranged
102Section 3: Membrane Transport Selectively permeable membranesTypes of membrane transportPassive (do not require ATP)DiffusionCarrier-mediated transportActive (require ATP)Vesicular transport
103Characteristics of selectively permeable membranes EXTRACELLULARFLUIDMaterials may crossthe plasma membranethrough active orpassive mechanisms.PlasmamembranePassive mechanismsdo not require ATP.Active mechanismsrequire ATP.Diffusion ismovement drivenby concentrationdifferences.Carrier-mediatedtransport involvescarrier proteins, andthe movement maybe passive or active.Vesicular transportinvolves theformation ofintracellularvesicles; this is anactive process.Figure 3 Section 3.2 How Things Enter and Leave the CellCYTOPLASMFigure 3 Section103
104Module 3.11: Diffusion Diffusion Continuous random movement of ions or molecules in a liquid or gas resulting in even distributionGradientConcentration difference or when molecules are not evenly distributedAt an even distribution, molecular motion continues but no net movementSlow in air and water but important over small distancesAnimation: Membrane Transport: Diffusion
105Figure 3.11.1 Diffusion is movement driven by concentration differences 105
106Module 3.11: Diffusion In ECF Water and solutes diffuse freely Across plasma membraneSelectively restricted diffusionMovement across lipid portion of membraneExamples: lipids, lipid-soluble molecules, soluble gasesMovement through membrane channelExamples: water, small water-soluble molecules, ionsMovement using carrier moleculesExample: large molecules
107The effects of the plasma membrane, a selectively permeable membrane, on the diffusion of various substancesLipids, lipid-soluble molecules,and soluble gases (O2 and CO2)can diffuse across the lipid bilayerof the plasma membrane.Water, small water-soluble molecules,and ions diffuse through membrane channelsthat vary in shape, size, and specificity.EXTRACELLULAR FLUIDChannelproteinPlasma membraneFigure Diffusion is movement driven by concentration differencesLarge molecules that cannot fitthrough the membrane channelsand cannot diffuse through themembrane lipids can only crossthe plasma membrane whentransported by a carrier mechanism.CYTOPLASMFigure107
108Module 3.11: Diffusion Factors that influence diffusion rates: Distance (inversely related)Molecule size (inversely related)Temperature (directly related)Gradient size (directly related)Electrical forcesAttraction of opposite charges (+,–)Repulsion of like charges (+,+ or –,–)
109Module 3.11 Review a. Define diffusion. b. Identify factors that influence diffusion rates.c. How would a decrease in the oxygen concentration in the lungs affect the diffusion of oxygen into the blood?
110Module 3.12: Osmosis Osmosis (osmos, a push) Net diffusion of water across a membraneMaintains similar overall solute concentrations between the cytosol and extracellular fluidOsmotic flowMovement of water driven by osmosisOsmotic pressureIndication of force of pure water moving into a solution with higher solute concentrationHydrostatic pressureFluid forceCan be estimate of osmotic pressure when applied to stop osmotic flow
111Osmotic flow, the movement of water driven by osmosis VolumeincreasedAppliedforceVolumedecreasedOriginallevelVolumesequalWatermoleculesSolutemoleculesSelectively permeable membraneFigure Osmosis is the passive movement of waterA selectively permeable membraneseparates these two solutions,which have different soluteconcentrations. Water molecules(small blue dots) begin to crossthe membrane toward solution B,the solution with the higherconcentration of solutes (largerpink circles).At equilibrium, the soluteconcentrations on the twosides of the membrane areequal. Note that the volumeof solution B has increasedat the expense of that ofsolution A.Pushing against a fluid generateshydrostatic pressure. Theosmotic pressure of solution Bis equal to the amount ofhydrostatic pressure, indicatedby the weight, required to stopthe osmotic flow.Figure111
112Module 3.12: Osmosis Osmolarity (osmotic concentration) Tonicity Total solute concentration in an aqueous solutionTonicityEffect of osmotic solutions on cell volumeThree effectsIsotonic (iso-, same + tonos, tension)Solution that does not cause osmotic flow across membrane
113Module 3.12: Osmosis Tonicity Three effects (continued) 2. Hypotonic Causes osmotic flow into cellExample: hemolysis (hemo-, blood + lysis, loosening)3. HypertonicCauses osmotic flow out of cellExample: crenation of RBCs
114Module 3.12: Osmosis Importance of tonicity vs. osmolarity: Example Administering large fluid volumes to patients with blood loss or dehydrationAdministered solution has same osmolarity as ICF but higher concentrations of individual ions/moleculesDiffusion of solutes may occur across cell membraneWater will follow through osmosisCell volume increasesNormal saline0.9 percent or 0.9 g/dL of NaClIsotonic with blood
115Module 3.12 Review a. Describe osmosis. b. Contrast the effects of a hypotonic solution and a hypertonic solution on a red blood cell.c. Some pediatricians recommend using a 10 percent salt solution to relieve nasal congestion in infants. Explain the effects this treatment would have on the cells lining the nasal cavity. Would it be effective?
116Module 3.13: Carrier-mediated transport Hydrophilic or large molecules transported across cell membrane by carrier proteinsMany move specific molecules through the plasma membrane in only one directionCotransport (>1 substance same direction)Countertransport (2 substances in opposite directions)Carrier called exchange pump
117Module 3.13: Carrier-mediated transport Three typesFacilitated diffusionRequires no ATP (= passive)Movement limited by number of available carrier proteins (= can become saturated)Active transportRequires energy molecule or ATP (= active)Independent of concentration gradientExamples:Ion pumps (Na+, K+, Ca2+, and Mg2+)Sodium–potassium ATPase
118Module 3.13: Carrier-mediated transport Animation: Membrane Transport: Active TransportAnimation: Membrane Transport: Facilitated Diffusion
119Facilitated diffusion EXTRACELLULARFLUIDGlucosemoleculeReceptor siteGlucose releasedinto cytoplasmCarrierproteinThe shape of the protein then changes, movingthe molecule across the plasma membrane. Thecarrier protein then releases the transportedmolecule into the cytoplasm. Note that this wasaccomplished without ever creating a continuousopen channel between the extracellular fluid andthe cytoplasm.CYTOPLASMFigure In carrier-mediated transport, integral proteins facilitate membrane passageFacilitated diffusion begins when a specificmolecule, such as glucose, binds to a receptorsite on the integral protein.Figure119
120Active transport Sodium ion concentrations are high in the extracellular fluids,but low in the cytoplasm. Thedistribution of potassium in thebody is just the opposite: low inthe extracellular fluids and highin the cytoplasm. As a result,sodium ions slowly diffuse intothe cell, and potassium ionsdiffuse out through leakchannels. Homeostasis withinthe cell depends on the ejectionof sodium ions and the recaptureof lost potassium ions. Thesodium–potassium exchangepump is a carrier protein calledsodium–potassium ATPase. Itexchanges intracellular sodiumfor extracellular potassium.EXTRACELLULARFLUIDSodium–potassiumexchangepumpFigure In carrier-mediated transport, integral proteins facilitate membrane passageCYTOPLASMOn average, for each ATP molecule consumed, three sodium ions are ejected and thecell reclaims two potassium ions. The energy demands are impressive: Sodium-potassium ATPase may use up to 40 percent of the ATP produced by a resting cell!Figure120
121Module 3.13: Carrier-mediated transport Carrier-mediated transport (continued)Three types (continued)Secondary active transportTransport mechanism does not require ATPCell often needs ATP to maintain homeostasis associated with transport
122Secondary active transport GlucosemoleculeSodiumion+Na+–K+pumpTo preserve homeostasis, thecell must then expend ATP topump the arriving sodium ionsout of the cell by using thesodium–potassium exchangepump. It thus “costs” the cellone ATP for every threeglucose molecules ittransports into the cell.CYTOPLASM+Figure In carrier-mediated transport, integral proteins facilitate membrane passageThe carrier protein then changes shape,opening a path to the cytoplasm andreleasing the transported materials. Itthen reassumes its original shape and isready to repeat the process.A sodium ion and a glucosemolecule bind to receptorsites on the carrier protein.Figure122
123Module 3.13 Reviewa. Describe the process of carrier-mediated transport.b. What do the transport processes of facilitated diffusion and active transport have in common?c. During digestion, the concentration of hydrogen ions (H+) in the stomach contents increases to many times that in cells lining the stomach. Which transport process could be responsible?
124Module 3.14: Vesicular transport Materials move across cell membrane in small membranous sacsSacs form at or fuse with plasma membraneTwo major types (both require ATP)EndocytosisExocytosis
125Module 3.14: Vesicular transport Vesicular transport (continued)Two major types (both require ATP)Endocytosis (into cell using endosomes)Receptor-mediated endocytosisLigand binds to receptorPlasma membrane folds around receptors bound to ligandsCoated vesicle formsVesicle fuses with lysosomesLigands freed and enter cytosolLysosome detaches from vesicleVesicle fuses with plasma membrane again
126Receptor-mediated endocytosis Receptor-mediated endocytosis begins when materials in theextracellular fluid bind to receptors on the membrane surface. Mostreceptor molecules are glycoproteins, and each binds to a specifictarget molecule, or ligand, such as a transport protein or a hormone.Receptors bound toligands cluster together.Once an area of theplasma membrane hasbecome covered withligands, it formsgrooves or pockets thatmove to one area of thecell and then pinch offto form an endosome.After the vesiclemembranedetaches, itreturns to thecell surface,where its recep-tors becomeavailable to bindmore ligands.EXTRACELLULAR FLUIDLigandsLigands bindingto receptorsExocytosisEndocytosisLigandreceptorsThe endosomesproduced in this wayare called coatedvesicles, becausethey are “coated” by aprotein-fiber networkon the inner membranesurface.The vesiclemembranedetaches fromthe secondarylysosome.CoatedvesicleCYTOPLASMFigure In vesicular transport, vesicles perform selective membrane passageThe lysosomalenzymes thenfree the ligandsfrom theirreceptors, andthe ligands enterthe cytosol bydiffusion oractive transport.DetachmentFusionThe coated vesiclesfuse with lysosomesfilled with digestiveenzymes.LysosomeLigandsremovedFigure126
127Module 3.14: Vesicular transport Vesicular transport (continued)Two major types (both require ATP)Endocytosis (into cell using endosomes) (continued)Pinocytosis (“cell drinking”)Formation of endosomes with ECFNo receptor proteins involvedPhagocytosis (“cell eating”)Produces phagosomes containing solidsPhagocytes or macrophages perform phagocytosisExocytosisVesicle discharges materials into ECF
128Pinocytosis begins with the formation of deep grooves BloodstreamPinocytosis begins with theformation of deep groovesor pockets that then pinchoff and enter the cytoplasm.The steps are similar tothose of receptor-mediatedendocytosis, but they occurin the absence of ligandbinding.CytoplasmEndosomeFigure In vesicular transport, vesicles perform selective membrane passagePlasma membraneSurrounding tissuePinocytosisTEM 20,000Figure128
129Phagocytosis Exocytosis The vesicular events linking BacteriumPseudopodiumPhagocytosis begins when cytoplas-mic extensions called pseudopodia(soo-dō-PŌ-dē-ah; pseduo-, falsepodon, foot; singular pseudopodium)surround the object.The vesicular events linkingphagocytosis and exocytosisPhagocytosisThe pseudopodia then fuse at theirtips to form a phagosome containingthe targeted material.LysosomeThis vesicle then fuses with manylysosomes, whereupon its contentsare digested by lysosomal enzymes.Figure In vesicular transport, vesicles perform selective membrane passageReleased nutrients diffuse into thesurrounding cytoplasm.GolgiapparatusExocytosisThe residue is then ejected from thecell through exocytosis.Figure129
130Module 3.14 Review a. Describe endocytosis. b. Describe exocytosis. c. When they encounter bacteria, certain types of white blood cells engulf the bacteria and bring them into the cell. What is this process called?
131Section 4: Cell Life Cycle Learning Outcomes3.15 Describe interphase, and explain its significance.3.16 Describe the process of mitosis, and the cell life cycle.3.17 Discuss the relationship between cell division and cancer.
132Section 4: Cell Life Cycle Cell divisionProduction of daughter cells from single cellImportant in organism development and survivalCells have varying life spans and abilities to divideOften genetically controlled death occurs (apoptosis)Two typesMitosis (2 daughter cells, each with 46 chromosomes)Meiosis (sex cells, each with only 23 chromosomes)Animation: Cell Life Cycle
133Section 4: Cell Life Cycle MitosisPair of daughter cells half the size of parent cellGrow to size of original cell before dividingIdentical copies of chromosomes in eachEnds at complete cell separation (= cytokinesis)Followed by nondividing period (= interphase)Cell performs normal activities ORPrepares to divide againChromosomes duplicatedAssociated proteins synthesized
134Original cell Cell division Daughter cells The production of a pair of daughtercells from a single cell divisionOriginalcellCelldivisionFigure 3 Section 4.1 The Cell Life CycleDaughtercellsFigure 3 Section134
135Module 3.15: Interphase Phases G0 (performing normal cell functions) Examples:Skeletal muscle cells (stay in this phase forever)Stem cells (never enter G0; divide repeatedly)G1 (normal cell function plus growth and duplication of organelles)S (duplication of chromosomes)G2 (last minute protein synthesis and centriole replication)
136Module 3.15: Interphase DNA replication Strands unwind DNA polymerase bindsAssembles new DNA strand covalently linking nucleotidesWorks only in one directionOne polymerase works continuously along one strand toward “zipper”One polymerase works away from “zipper”As “unzipping” occurs, another polymerase binds closer point of unzippingTwo new DNA segments bound with ligasesTwo identical DNA strands formed
137Figure 3.15.2 During interphase, the cell prepares for cell division The events in DNAreplication, whichoccurs during theS phase of interphaseDNA replication beings when enzymes unwind thestrands and disrupt the hydrogen bonds between thebases. As the strands unwind, molecules of DNApolymerase bind to the exposed nitrogenous bases. Thisenzyme (1) promotes bonding between the nitrogenousbases of the DNA strand and complementary DNAnucleotides dissolved in the nucleoplasm and (2) links thenucleotides by covalent bonds.As the two original stands graduallyseparate, DNA polymerase binds to thestrands. DNA polymerase can work inonly one direction along a strand of DNA,but the two strands in a DNA moleculeare oriented in opposite directions. TheDNA polymerase bound to the upperstrand shown here adds nucleotides tomake a single, continuous complementarycopy that grows toward the “zipper.”Segment 2DNA nucleotideSegment 1DNA polymerase on the lower strand canwork only away from the zipper. So thefirst DNA polymerase to bind to thisstrand must add nucleotides and build acomplementary DNA strand moving fromleft to right. As the two original strandscontinue to unzip, additional nucleotidesare continuously being exposed to thenucleoplasm. The first DNA polymeraseon this strand cannot go into reverse; itcan only continue to elongate the strandit already started.Figure During interphase, the cell prepares for cell divisionAdenineThus, a second DNA polymerase must bind closerto the point of unzipping and assemble a comple-mentary copy (segment 2) that grows until it“bumps into” segment 1 created by the first DNApolymerase. The two segments are then splicedtogether by enzymes called ligases (LĪ-gās-ez;liga, to tie).GuanineCytosineThymineFigure137
138Duplicated DNA double helices Figure During interphase, the cell prepares for cell divisionFigure138
139Module 3.15 Review a. Describe interphase, and identify its stages. b. What enzymes must be present for DNA replication to proceed normally?c. A cell is actively manufacturing enough organelles to serve two functional cells. This cell is probably in what phase of interphase?
140Module 3.16: Mitosis Mitosis Division and duplication of cell’s nucleusPhasesProphase (pro-, before)Paired chromosomes tightly coiledChromatid (each copy)Connected at centromere with raised area (kinetochore)Replicated centrioles move to polesAstral rays (extend from centrioles)Spindle fibers (interconnect centriole pairs)
141The events in mitosisChromatidsThe centrioleshave replicated,and the pairsnow move toopposite sidesof the nucleus.Microtubules extend outwardfrom each pair of centrioles:astral rays extend into thecytoplasm, whereas spindlefibers interconnect thecentriole pairs.KinetochoreThe kinetochore ofeach chromatidbecomes attachedto a spindle fiber.The nuclearmembranedisintegratesduring this period.Centrioles incentrosomeNucleusFigure Mitosis distributes chromosomes before cytokinesis separates the daughter cellsInterphase, whichprecedes mitosisProphase, the first phase of mitosisFigure – 2141
142Module 3.16: Mitosis Mitosis (continued) Phases (continued) Metaphase (meta, after)Chromosomes align at metaphase plateAnaphase (ana-, apart)Chromatids separateDrawn along spindle apparatusTelophase (telo-, end)Cells prepare to enter interphaseCytoplasm constricts along metaphase plate (= cleavage furrow)Nuclear membranes re-formChromosomes uncoil
143The events in mitosis (continued) The two chromatids are now pulledapart and drawn to opposite ends ofthe cell along the spindleapparatus (the complex of spindlefibers). Anaphase ends when thechromatids arrive near the centriolesat opposite ends of the cell.As the chromatids approachthe ends of the spindleapparatus, the cytoplasmconstricts along the plane ofthe metaphase plate, forminga cleavage furrow.DaughtercellsCYTOKINESISMetaphase plateFigure Mitosis distributes chromosomes before cytokinesis separates the daughter cellsMetaphaseAnaphaseTelophase, the finalphase of mitosisCytokinesisFigure – 6143
144Module 3.16: Mitosis Cytokinesis (cyto-, cell + kinesis, motion) Begins with formation of cleavage furrowContinues through telophaseCompletion marks end of cell division
145Module 3.16 Review a. Define mitosis, and list its four stages. b. What is a chromatid, and how many would be present during normal mitosis in a human cell?c. What would happen if spindle fibers failed to form in a cell during mitosis?
146Module 3.17: Tumors and cancer Illness that disrupts normal rates of cell divisionCharacterized by permanent DNA sequence changes (= mutations)Most common in tissues with actively dividing cellsExamples: skin, intestinal liningCompete with normal cells for resources
147Module 3.17: Tumors and cancer Cancerous tumor (neoplasm; mass of cells) typesBenignRemain in original tissueMalignantAccelerated growth due to blood vessel growth and supply to the areaInvasion (cells migrating into surrounding tissues)Metastasis (formation of secondary tumors)
148Module 3.17 Review a. Define metastasis. b. What is a benign tumor? c. Define cancer.