cell level of organizationedit

Chapter 3: The Cellular Chapter 3: The Cellular Level of OrganizationLevel of Organization

What is cell theory?What is cell theory?The Cell - Performs all life functions The Cell - Performs all life functions - -

2 Types of Cells2 Types of Cells

Sex cellsSex cells ( (germ cellsgerm cells):):– reproductive cells reproductive cells – male male spermsperm– female female oocytesoocytes (eggs) (eggs)

Sex CellsSex Cells

Somatic CellsSomatic CellsSomatic cellsSomatic cells ( (somasoma

= body):= body):– all body cells except all body cells except

sex cellssex cells

OrganellesOrganelles

Organelle FunctionsOrganelle Functions

Organelle FunctionsOrganelle Functions

What are the structures and What are the structures and functions of the cell membrane?functions of the cell membrane?

Components of the Cell MembraneComponents of the Cell MembraneContains lipids, carbohydrates, and functional proteinsContains lipids, carbohydrates, and functional proteins

Phospholipid BilayerPhospholipid BilayerDouble layer of phospholipid molecules:Double layer of phospholipid molecules:– hydrophilic heads—toward watery environment, hydrophilic heads—toward watery environment,

both sidesboth sides– hydrophobic fatty-acid tails—inside membrane hydrophobic fatty-acid tails—inside membrane – barrier to ions and water soluble compoundsbarrier to ions and water soluble compounds

Membrane ProteinsMembrane ProteinsIntegral proteinsIntegral proteins::– within the membrane within the membrane

Peripheral proteinsPeripheral proteins::– inner or outer surface of the membraneinner or outer surface of the membrane

6 Functions of Membrane Proteins6 Functions of Membrane Proteins1.1. Anchoring proteinsAnchoring proteins (stabilizers): (stabilizers):– attach to inside or outside structures attach to inside or outside structures

2.2. Recognition proteinsRecognition proteins (identifiers): (identifiers): – label cells normal or abnormal label cells normal or abnormal

3.3. EnzymesEnzymes: : – catalyze reactions catalyze reactions

4.4. Receptor proteinsReceptor proteins::– bind and respond to bind and respond to ligandsligands (ions, hormones) (ions, hormones)

5.5. Carrier proteinsCarrier proteins: : – transport specific solutes through membrane transport specific solutes through membrane

6.6. ChannelsChannels: : – regulate water flow and solutes through membrane regulate water flow and solutes through membrane

Membrane CarbohydratesMembrane CarbohydratesProteoglycans, glycoproteins, and glycolipids:Proteoglycans, glycoproteins, and glycolipids:– extend outside cell membraneextend outside cell membrane– form sticky “sugar coat” (form sticky “sugar coat” (glycocalyxglycocalyx))

Functions of Membrane CarbohydratesFunctions of Membrane Carbohydrates– Lubrication and protectionLubrication and protection– Anchoring and locomotionAnchoring and locomotion– Specificity in binding (receptors)Specificity in binding (receptors)– Recognition (immune response)Recognition (immune response)

CytoplasmCytoplasmAll materials inside the cell and outside the All materials inside the cell and outside the nucleus: nucleus: – cytosolcytosol (fluid): (fluid):

dissolved materials:dissolved materials:– nutrients, ions, proteins, and waste products nutrients, ions, proteins, and waste products

– organellesorganelles: : structures with specific functionsstructures with specific functions

What are cell organelles & their functions?What are cell organelles & their functions?Types of OrganellesTypes of Organelles

Nonmembranous organelles: Nonmembranous organelles: – no membraneno membrane– direct contact with cytosoldirect contact with cytosol

Membranous organelles: Membranous organelles: – covered with plasma membranecovered with plasma membrane– isolated from cytosolisolated from cytosol6 types of 6 types of nonmembranousnonmembranous organelles: organelles: – cytoskeletoncytoskeleton – microvillimicrovilli – centriolescentrioles

– ciliacilia – ribosomesribosomes – proteasomesproteasomes

The CytoskeletonThe CytoskeletonStructural proteinsStructural proteins for shape and for shape and strengthstrengthMicrofilamentsMicrofilaments– Thin filamentsThin filaments composed of the composed of the

protein protein actinactin:: provide additional mechanical strength provide additional mechanical strength interact with proteins for consistencyinteract with proteins for consistencyPairs with Pairs with thick filamentsthick filaments of of myosinmyosin for for muscle movementmuscle movement

IntermediateIntermediate– Mid-sized between microfilaments Mid-sized between microfilaments

and thick filaments:and thick filaments:durable (durable (collagencollagen))strengthen cell and maintain shapestrengthen cell and maintain shapestabilize organellesstabilize organellesstabilize cell positionstabilize cell position

Microtubules Microtubules – Large, hollow tubes of Large, hollow tubes of

tubulintubulin protein: protein:attach to attach to centrosomecentrosomestrengthen cell and anchor strengthen cell and anchor organellesorganelleschange cell shapechange cell shapemove vesicles within cell move vesicles within cell ((kinesinkinesin and and dyneindynein))form form spindle apparatusspindle apparatus

MicrovilliMicrovilliIncrease surface area for absorptionIncrease surface area for absorptionAttach to cytoskeletonAttach to cytoskeleton

Centrioles in the CentrosomeCentrioles in the CentrosomeCentriolesCentrioles form form spindle spindle apparatusapparatus during cell during cell divisiondivisionCentrosomeCentrosome: cytoplasm : cytoplasm surrounding centriolesurrounding centriole

Cilia PowerCilia PowerCilia move fluids across the Cilia move fluids across the cell surfacecell surface

RibosomesRibosomesBuild polypeptides in protein Build polypeptides in protein synthesissynthesisTwo types: Two types: – free ribosomesfree ribosomes in cytoplasm: in cytoplasm:

proteins for cellproteins for cell– fixed ribosomesfixed ribosomes attached to attached to

ER:ER:proteins for secretionproteins for secretion

ProteasomesProteasomesContain enzymes (proteases)Contain enzymes (proteases)Disassemble damaged proteins for recyclingDisassemble damaged proteins for recycling

Membranous OrganellesMembranous Organelles5 types of 5 types of membranousmembranous organelles: organelles:– endoplasmic reticulum (ER)endoplasmic reticulum (ER)– Golgi apparatusGolgi apparatus– lysosomeslysosomes– peroxisomesperoxisomes– mitochondriamitochondria

Endoplasmic Reticulum (ER)Endoplasmic Reticulum (ER)endoendo = within, = within, plasmplasm = cytoplasm, = cytoplasm, reticulumreticulum = = networknetworkCisternaeCisternae are storage chambers within are storage chambers within membranesmembranes

Functions of ERFunctions of ERSSynthesisynthesis of proteins, carbohydrates, and lipids of proteins, carbohydrates, and lipidsSStoragetorage of synthesized molecules and of synthesized molecules and materialsmaterialsTransportTransport of materials within the ER of materials within the ERDetoxificationDetoxification of drugs or toxins of drugs or toxins

Smooth Smooth Endoplasmic Reticulum (SER)Endoplasmic Reticulum (SER)No ribosomes attachedNo ribosomes attachedSynthesizes lipids and carbohydrates:Synthesizes lipids and carbohydrates:– phospholipids and cholesterol (membranes)phospholipids and cholesterol (membranes)– steroid hormones (reproductive system)steroid hormones (reproductive system)– glycerides (storage in liver and fat cells)glycerides (storage in liver and fat cells)– glycogen (storage in muscles)glycogen (storage in muscles)

Rough Endoplasmic Reticulum (RER)Rough Endoplasmic Reticulum (RER)Surface covered with ribosomes:Surface covered with ribosomes:– active in protein and glycoprotein synthesisactive in protein and glycoprotein synthesis– folds polypeptides protein structuresfolds polypeptides protein structures– encloses products in encloses products in transport vesiclestransport vesicles

Golgi ApparatusGolgi ApparatusVesicles enter forming face and exit maturing faceVesicles enter forming face and exit maturing face– Secretory vesiclesSecretory vesicles::

modify and package products modify and package products for exocytosisfor exocytosis

– Membrane renewal Membrane renewal vesiclesvesicles::

add or remove membrane add or remove membrane components components

– Transport vesicles:Transport vesicles:Carry materials to and Carry materials to and from Golgi apparatusfrom Golgi apparatus

LysosomesLysosomesPowerful enzyme-Powerful enzyme-containing vesicles:containing vesicles:– lysolyso = dissolve, = dissolve,

somasoma = body = body

Primary lysosomePrimary lysosome: : – formed by Golgi and formed by Golgi and

inactive enzymesinactive enzymesSecondary lysosomeSecondary lysosome: : – lysosome fused with lysosome fused with

damaged organelledamaged organelle– digestive enzymes digestive enzymes

activatedactivated– toxic chemicals toxic chemicals

isolatedisolated

Exocytosis Exocytosis – Ejects secretory products and wastesEjects secretory products and wastes

Lysosome FunctionsLysosome Functions

Clean up inside cells:Clean up inside cells:– break down large moleculesbreak down large molecules– attack bacteriaattack bacteria– recycle damaged organellesrecycle damaged organelles– ejects wastes by exocytosisejects wastes by exocytosis

AutolysisAutolysisSelf-destruction of damaged cells:Self-destruction of damaged cells:– autoauto = self, = self, lysislysis = break = break– lysosome membranes break downlysosome membranes break down– digestive enzymes releaseddigestive enzymes released– cell decomposescell decomposes– cellular materials recyclecellular materials recycle

PeroxisomesPeroxisomesAre enzyme-containing vesicles:Are enzyme-containing vesicles:– break down fatty acids, organic compoundsbreak down fatty acids, organic compounds– produce hydrogen peroxide (Hproduce hydrogen peroxide (H22OO22))– replicate by divisionreplicate by division

KEY CONCEPTKEY CONCEPT

CellsCells: basic structural and functional : basic structural and functional units of lifeunits of life– respond to their environmentrespond to their environment– maintain homeostasis at the cellular levelmaintain homeostasis at the cellular level– modify structure and function over timemodify structure and function over time

Mitochondrion StructureMitochondrion Structure

Figure 3–9a

Mitochondrion StructureMitochondrion StructureHave smooth outer membrane and folded inner Have smooth outer membrane and folded inner membrane (cristae)membrane (cristae)Matrix: Matrix: – fluid around cristaefluid around cristae

Mitochondrial FunctionMitochondrial FunctionMitochondrionMitochondrion takes chemical energy from food takes chemical energy from food ((glucoseglucose):):– produces energy molecule produces energy molecule ATPATP

Figure 3–9b

How does the nucleus control the cell?How does the nucleus control the cell?Is the cell’s control centerIs the cell’s control centerNucleusNucleus::– largest organellelargest organelleNuclear envelopeNuclear envelope::– double membrane double membrane

around the nucleus around the nucleus Perinuclear spacePerinuclear space::– between 2 layers of between 2 layers of

nuclear envelope nuclear envelope Nuclear poresNuclear pores::– communication passagescommunication passages

Within the NucleusWithin the NucleusDNADNA::– all information to build and run organismsall information to build and run organisms

NucleoplasmNucleoplasm::– fluid containing ions, enzymes, nucleotides, fluid containing ions, enzymes, nucleotides,

and some RNAand some RNA

Nuclear matrixNuclear matrix::– support filamentssupport filaments

NucleoliNucleoli in Nucleus in NucleusAre related to protein productionAre related to protein productionAre made of RNA, enzymes, and Are made of RNA, enzymes, and histoneshistonesSynthesize rRNA and ribosomal subunitsSynthesize rRNA and ribosomal subunits

Organization of DNAOrganization of DNA

Figure 3–11

Nucleosomes:Nucleosomes:– DNA coiled around DNA coiled around

histones histones

Chromatin:Chromatin:– loosely coiled DNA loosely coiled DNA

(cells not dividing)(cells not dividing)

Chromosomes:Chromosomes:– tightly coiled DNA tightly coiled DNA

(cells dividing)(cells dividing)

DNA and GenesDNA and GenesDNADNA::– instructions for every protein in the bodyinstructions for every protein in the body

GeneGene::– DNA instructions for 1 proteinDNA instructions for 1 protein

What is genetic code?What is genetic code?

Genetic CodeGenetic CodeThe chemical language of DNA instructions:The chemical language of DNA instructions:– sequence of sequence of basesbases (A, T, C, G) (A, T, C, G)– triplet codetriplet code::

3 bases = 1 amino acid 3 bases = 1 amino acid

KEY CONCEPTKEY CONCEPTThe nucleus contains chromosomesThe nucleus contains chromosomesChromosomes contain DNAChromosomes contain DNADNA stores genetic instructions for DNA stores genetic instructions for proteinsproteinsProteins determine cell structure and Proteins determine cell structure and functionfunction

How do DNA instructions become proteins?How do DNA instructions become proteins?

Protein SynthesisProtein SynthesisTranscription:Transcription:– copies instructions from DNA to mRNA (in nucleus)copies instructions from DNA to mRNA (in nucleus)

Translation:Translation:– ribosome reads code from mRNA (in cytoplasm)ribosome reads code from mRNA (in cytoplasm)– assembles amino acids into polypeptide chainassembles amino acids into polypeptide chain ProcessingProcessing::– by RER and Golgi apparatus produces proteinby RER and Golgi apparatus produces protein

1.1. Important FeaturesImportant Featuresa. DNA contains genetic template" for a. DNA contains genetic template" for

proteins.proteins.b. DNA is found in the nucleusb. DNA is found in the nucleusc. Protein synthesis occurs in the c. Protein synthesis occurs in the

cytoplasm - cytoplasm - ribosomeribosome..d. "Genetic information" must be d. "Genetic information" must be

transferred transferred to the cytoplasm to the cytoplasm where where proteins are synthesized.proteins are synthesized.

2. Processes of Protein 2. Processes of Protein SynthesisSynthesis

a. a. TranscriptionTranscription - genetic template - genetic template for a protein is copied and carried for a protein is copied and carried out to the cytoplasmout to the cytoplasm

b. b. TranslationTranslation - template serves as - template serves as a series of codes for the amino a series of codes for the amino acid sequence of the proteinacid sequence of the protein

3. Steps of Transcription3. Steps of Transcriptiona. DNA unwindsa. DNA unwindsb. One side of DNA "codes for a b. One side of DNA "codes for a

protein"protein"c. Genetic code of DNA is a triplet c. Genetic code of DNA is a triplet

code of 3 nucleotides or basescode of 3 nucleotides or basesd. Each triplet is specific for the d. Each triplet is specific for the

coding of a single amino acidcoding of a single amino acid

A view of transcriptionA view of transcription

Fig. 14.12 Brum

Transcription (cont.)Transcription (cont.)e.e.Sequence of triplet codes on DNA will specify Sequence of triplet codes on DNA will specify

the amino acid sequence on the proteinthe amino acid sequence on the proteinf.f. Major step is the synthesis of the coded Major step is the synthesis of the coded

""messenger" molecule messenger" molecule - - mRNAmRNAg. mRNA is "transcribed" from DNA by g. mRNA is "transcribed" from DNA by

complementary base pairing (mRNA has no complementary base pairing (mRNA has no thymine, which is replaced by uracil)thymine, which is replaced by uracil)

h. mRNA passes out to cytoplasm to the ribosomeh. mRNA passes out to cytoplasm to the ribosome

fig. 15.5 from Ravenfig. 15.5 from Raven

4.4. TranslationTranslationa. a. mRNAmRNA attaches to the ribosome attaches to the ribosomeb. b. tRNA'stRNA's attach to free amino acids attach to free amino acids

in the cytoplasmic "pool" of amino in the cytoplasmic "pool" of amino acidsacids

c. c. tRNAtRNA carries its specific amino carries its specific amino acid to the ribosomeacid to the ribosome

fig. 15.5 from Ravenfig. 15.5 from Raven

Translation (cont.)Translation (cont.)d. d. tRNAtRNA "delivers" its amino acid based on "delivers" its amino acid based on

complementary pairing of a triplet code complementary pairing of a triplet code (anticodon) with the triplet code (codon) of the (anticodon) with the triplet code (codon) of the mRNAmRNA..

e.e.Enzyme "hooks" the amino acid to the last one in Enzyme "hooks" the amino acid to the last one in the chain forming a peptide bond.the chain forming a peptide bond.

f.f. Protein chain continues to grow as each tRNA Protein chain continues to grow as each tRNA brings in its amino acid and adds it to the chain. - brings in its amino acid and adds it to the chain. - This is translationThis is translation!!!!

fig. 15.5 from Ravenfig. 15.5 from Raven

U C G UU C A A AmRNA

A

GC TTCA AAT

GC AA TTG TCoding Stran

U C G UU C A A AmRNA

A

GC TTCA AAT

GC AA TTG TCoding Stran

Nucleus

Cytoplasm

Ribosome

A

GC TTCA AAT

GC AA TTG TCoding Stran

Nucleus

Cytoplasm

U C G UU C A A A

U C G UU C A A AmRNA

U C G UU C A A A

A

GC TTCA AAT

GC AA TTG TCoding Stran

Nucleus

CytoplasmAA1

AGC

tRNA’s

U C G UU C A A A

A

GC TTCA AAT

GC AA TTG TCoding Stran

Nucleus

CytoplasmAA1

AGCtRNA’s

U C G UU C A A A

A

GC TTCA AAT

GC AA TTG TCoding Stran

•AA2

AAG

AA1

AGCtRNA’s

Nucleus

Cytoplasm

ATP

U C G UU C A A A

A

GC TTCA AAT

GC AA TTG TCoding Stran

AA3

U U U

•AA2

AAG

AA1

Nucleus

CytoplasmAGC

AA1

ATP

U C G UU C A A A

A

GC TTCA AAT

GC AA TTG TCoding Stran

AA3

U U U

•AA2

AAG

AA1

Nucleus

Cytoplasm

AGC

AA1

U C G UU C A A A

A

GC TTCA AAT

GC AA TTG TCoding Stran

AA3

U U U

•AA2

AAG

AA1

Nucleus

Cytoplasm

AGC

AA1

U C G UU C A A A

A

GC TTCA AAT

GC AA TTG TCoding Stran

AA3

U U U

•AA2

AAG

AA1

Nucleus

Cytoplasm

AGC

AA1

The Genetic CodeThe Genetic Code1.1.A triplet code comprised of three nucleotide bases A triplet code comprised of three nucleotide bases

in a sequence.in a sequence.2.2.How many triplet codes?How many triplet codes?

20 common amino acids in a protein20 common amino acids in a protein4 diff. bases on DNA4 diff. bases on DNA A,T,C, & GA,T,C, & G

| | || | | | |4 diff. bases on RNA4 diff. bases on RNA U,A,G, & CU,A,G, & C

4 things put together in combinations of 3 = 44 things put together in combinations of 3 = 433= 64= 64Therefore - 64 different DNA triplet codes or RNA codonsTherefore - 64 different DNA triplet codes or RNA codons

The 64 triplet codesThe 64 triplet codes60 code for amino acids 60 code for amino acids 4 act as "stop" and "start " codes4 act as "stop" and "start " codesDegenerate Code- more than one Degenerate Code- more than one triplet code for some amino acids triplet code for some amino acids e.g.,e.g.,

The 64 triplet codesThe 64 triplet codes60 code for amino acids 60 code for amino acids 4 act as "stop" and "start codes4 act as "stop" and "start codesDegenerate Code- more than one Degenerate Code- more than one triplet code for some amino acids triplet code for some amino acids e.g.,e.g.,

All code for the amino acid glycine

GGGGGUGGCGGA

CodonsCodons

Table 3–2

Nucleus Controls Cell Nucleus Controls Cell Structure and FunctionStructure and Function

Direct controlDirect control through synthesis of: through synthesis of: – structural proteinsstructural proteins– secretions (environmental response) secretions (environmental response)

Indirect controlIndirect control over metabolism through over metabolism through enzymesenzymes

KEY CONCEPTKEY CONCEPTGenes: Genes: – are functional units of DNA are functional units of DNA – contain instructions for 1 or more proteins contain instructions for 1 or more proteins

Protein synthesis requires:Protein synthesis requires:– several enzymesseveral enzymes– ribosomesribosomes– 3 types of RNA3 types of RNA

Mutation is a change in the nucleotide sequence of a gene:Mutation is a change in the nucleotide sequence of a gene:– can change gene functioncan change gene function

Causes:Causes:– exposure to chemicalsexposure to chemicals– exposure to radiationexposure to radiation– mistakes during DNA replicationmistakes during DNA replication

Table 3–3

The 7 methods of transportThe 7 methods of transport

Cell Life CycleCell Life Cycle

Figure 3–3

How do cells reproduce?How do cells reproduce?

Most of a cell’s life is spent in a nondividing Most of a cell’s life is spent in a nondividing state (interphase)state (interphase)

Body (somatic) cells divide in 3 stages:Body (somatic) cells divide in 3 stages:– DNA replicationDNA replication duplicates genetic material exactly duplicates genetic material exactly– MitosisMitosis divides genetic material equally divides genetic material equally – CytokinesisCytokinesis divides cytoplasm and organelles into 2 divides cytoplasm and organelles into 2

daughter cellsdaughter cells

InterphaseInterphaseThe nondividing period: The nondividing period: – G-zero phaseG-zero phase——

specialized cell functions specialized cell functions only only

– GG11 phase phase—cell growth, —cell growth, organelle duplication, organelle duplication, protein synthesis protein synthesis

– S phaseS phase——DNA DNA replicationreplication and histone and histone synthesissynthesis

– GG22 phase phase—finishes —finishes protein synthesis and protein synthesis and centriole replicationcentriole replication

DNA ReplicationDNA Replication

Figure 3–24

DNA strands unwind DNA strands unwind DNA polymeraseDNA polymerase attaches complementary attaches complementary nucleotidesnucleotides

Somatic Cell Nuclear Division Somatic Cell Nuclear Division Two important processes to Two important processes to

maintain constant number of maintain constant number of chromosomes.chromosomes.Duplication of chromosomesDuplication of chromosomesDistribution of duplicated chromosomes Distribution of duplicated chromosomes into two daughter cellsinto two daughter cells

1

2 3

4

5

6 7 8

9

1 0

1 1

1 2

1 3

1 4

1 5 1 6

1 7

1 8

1 9 2 0 2 1 2 2

Y

X

X Y

The HumanKaryotype

4646

462N or Diploid Numberin Humans

Mother Cell

Daughter Cells

Importance of Mitosis Importance of Mitosis

Importance of Mitosis (cont.)Importance of Mitosis (cont.)

a. Cellular replacementa. Cellular replacementb. Tissue Repairb. Tissue Repairc. Developmentc. Developmentd. Tumor growthd. Tumor growth

Cell cycle prior to mitosis:Cell cycle prior to mitosis:Interphase: nondividing state but cell is Interphase: nondividing state but cell is metabolically active.metabolically active. nucleus clearly visiblenucleus clearly visible one or more nucleoli-nucleolar organizer one or more nucleoli-nucleolar organizer regions of chromosomes.regions of chromosomes. chromosomes long and thinchromosomes long and thin centriole (animal cells only) located along centriole (animal cells only) located along margin of nucleusmargin of nucleus

Replication of DNA and duplication Replication of DNA and duplication of chromosomes occurs in the cell of chromosomes occurs in the cell

cycle.cycle.

Centromere

Chromatids

Prophase:Prophase: prepares the cell for divisionprepares the cell for divisionchromosomes shorten and thickenchromosomes shorten and thickencentriole divides into two entities which centriole divides into two entities which migrate down sides of nuclear envelope, migrate down sides of nuclear envelope, spindle fibers stretch between spindle fibers stretch between centriolescentrioles

Prophase: The cell is prepared for Prophase: The cell is prepared for nuclear divisionnuclear division

Nuclear envelope has disappeared

Spindle has formed

Chromosomes short and thick

Metaphase: final preparation for Metaphase: final preparation for nuclear divisionnuclear division

chromosomes line up on equatorial chromosomes line up on equatorial plate of divisionplate of division centromeres of chromosomes attached centromeres of chromosomes attached by kinetocores (protein) to spindle fibers, by kinetocores (protein) to spindle fibers, microtubules made up of tubulinmicrotubules made up of tubulin

A single chromosome A single chromosome attached to spindle fibersattached to spindle fibers

Anaphase: chromosome Anaphase: chromosome halves migrate to poleshalves migrate to poles

centromeres dividecentromeres divide chromosome halves migrate to opposite chromosome halves migrate to opposite poles of cellpoles of cell chromosomes migrate by sliding of chromosomes migrate by sliding of microtubulesmicrotubules

Telophase:Telophase: reverse of activities of prophasereverse of activities of prophase chromosomes reach poles of cellchromosomes reach poles of cell spindle fibers degradedspindle fibers degraded nuclear membrane reassemblednuclear membrane reassembled chromosomes elongatechromosomes elongate nucleoli reassemblednucleoli reassembled

Cytokinesis - division of the cellCytokinesis - division of the cellCytokinesis occurs by constriction of actin Cytokinesis occurs by constriction of actin fibers forming a belt around cell in animal cells fibers forming a belt around cell in animal cells Plant cells form a cell plate from nuclear Plant cells form a cell plate from nuclear membrane and then cellulose is added to the membrane and then cellulose is added to the plate.plate.

Animal cell - cytokinesis occurs byconstriction of actin fibers

Plant cell - cytokinesisoccurs by synthesis of cell plate.

Typical Timing of MitosisTypical Timing of Mitosis

What regulates cell division?What regulates cell division?Mitotic RateMitotic Rate and Energy and Energy

Rate of cell division:Rate of cell division:– slower mitotic rate means longer cell lifeslower mitotic rate means longer cell life– cell division requires energy (ATP)cell division requires energy (ATP)

Long Life, Short LifeLong Life, Short LifeMuscle cells, neurons rarely divideMuscle cells, neurons rarely divideExposed cells (skin and digestive tract) Exposed cells (skin and digestive tract) live only days or hourslive only days or hours

Chemicals Controlling Cell DivisionChemicals Controlling Cell Division

Table 3–4

Regulating Cell LifeRegulating Cell Life Normally, cell division balances cell lossNormally, cell division balances cell loss

Factors Increase Cell DivisionFactors Increase Cell DivisionIncreases cell division:Increases cell division:– internal factors (internal factors (Maturation Promoting FactorMaturation Promoting Factor) ) – extracellular chemical factors (extracellular chemical factors (growth factorsgrowth factors))

Factors Decrease Cell DivisionFactors Decrease Cell DivisionDecreases cell division:Decreases cell division:– repressor genesrepressor genes (faulty repressors cause cancers) (faulty repressors cause cancers)– worn out worn out telomerestelomeres (terminal DNA segments) (terminal DNA segments)

CancerCancer

Figure 3–26

Cancer illness that disrupts cellular controls andCancer illness that disrupts cellular controls andOncogenesOncogenes: mutated genes that cause cancer: mutated genes that cause cancer

produces malignant cellsproduces malignant cellsCancer Stages - develops in steps:Cancer Stages - develops in steps:– abnormal cellabnormal cell– primary tumorprimary tumor– metastasismetastasis– secondary tumorsecondary tumor

Cell Division and TumorsCell Division and TumorsTumorTumor ( (neoplasmneoplasm):):– enlarged mass of cellsenlarged mass of cells– abnormal cell growth and divisionabnormal cell growth and division

Benign TumorsBenign TumorsBenign tumorBenign tumor: : – containedcontained– not life threateningnot life threatening

Malignant TumorsMalignant TumorsMalignant tumorMalignant tumor: : – spread into surrounding tissues (spread into surrounding tissues (invasioninvasion))– start new tumors (start new tumors (metastasismetastasis))

KEY CONCEPTKEY CONCEPTMutations disrupt normal controls over cell Mutations disrupt normal controls over cell growth and divisiongrowth and divisionCancers often begin where stem cells are Cancers often begin where stem cells are dividing rapidly dividing rapidly More chromosome copies mean greater More chromosome copies mean greater chance of errorchance of error

Cell DiversityCell Diversity All cells carry complete DNA instructions for all All cells carry complete DNA instructions for all body functionsbody functions

What makes cells different?What makes cells different?

Cells specialize or Cells specialize or differentiatedifferentiate::– to form tissues (liver cells, fat cells, and neurons) to form tissues (liver cells, fat cells, and neurons) – by turning by turning offoff all genes not needed by that cell all genes not needed by that cellAll body cells, except sex cells, contain the All body cells, except sex cells, contain the same 46 chromosomes same 46 chromosomes Differentiation depends on which genes are Differentiation depends on which genes are active and which are inactiveactive and which are inactive