Cell Growth and Cell Growth and ReproductionReproductionSection 8.2Section 8.2

BiologyBiology

What Limits Cell Size?What Limits Cell Size? DiffusionDiffusion – diffusion slows – diffusion slows

w/larger distancesw/larger distances DNADNA – DNA can only control – DNA can only control

the needs of a small cellthe needs of a small cell Cell SizeCell Size - Surface area-to- - Surface area-to-

volume ratio must be high; 6/1; volume ratio must be high; 6/1; cell has trouble transporting cell has trouble transporting materials in/out of the cellmaterials in/out of the cell

Purpose of Cell DivisionPurpose of Cell Division When a cell gets too large to When a cell gets too large to

control or function efficiently, control or function efficiently, cell division takes placecell division takes place

Results in Results in 22 cells identical to cells identical to the parent cellthe parent cell

Old cells are replaced; new Old cells are replaced; new cells produced as an organism cells produced as an organism growsgrows

ChromosomesChromosomes Chromosomes are carriers of our Chromosomes are carriers of our

genetic material & must be copied genetic material & must be copied & transmitted accurately& transmitted accurately

Chromosomes are tightly coiled Chromosomes are tightly coiled chromatin.chromatin.

Most of the time our Most of the time our chromosomes exists as chromatin chromosomes exists as chromatin (long strands of DNA wrapped (long strands of DNA wrapped around proteins called histones)around proteins called histones)

Cell CycleCell Cycle

Sequence of growth, Sequence of growth, nuclear division, and nuclear division, and cytoplasmic division of a cytoplasmic division of a cellcell

InterphaseInterphase – cell spends most – cell spends most of it’s time in this phaseof it’s time in this phase

Interphase Interphase G1 – growth phase – cell gets G1 – growth phase – cell gets

bigger and developsbigger and develops S – synthesis phase – DNA in S – synthesis phase – DNA in

nucleus is copiednucleus is copied G2 – growth phase – more G2 – growth phase – more

growing and developing; produce growing and developing; produce more organelles, enzymes, more organelles, enzymes, centrioles are replicatedcentrioles are replicated, etc., etc.

Mitosis - PMATMitosis - PMATnuclear division nuclear division yields two daughter nuclei yields two daughter nuclei that are genetically that are genetically identical identical

used for growth and used for growth and healing healing

Prophase – 1Prophase – 1stst stage of stage of mitosismitosis

ProphaseProphase Chromatin condenses into Chromatin condenses into

chromosomes, 2 identical strands chromosomes, 2 identical strands of DNA attached by a centromereof DNA attached by a centromere

Centrioles move to opposite ends Centrioles move to opposite ends of the cellof the cell

Nuclear envelope and nucleolus Nuclear envelope and nucleolus disappeardisappear

Spindle starts to appearSpindle starts to appear

METAPHASEMETAPHASE

MetaphaseMetaphase

Chromosomes line up about Chromosomes line up about midway between the midway between the centriolescentrioles

Spindle fibers attach to Spindle fibers attach to chromosomes at chromosomes at centromerescentromeres

AnaphaseAnaphase

AnaphaseAnaphase Centromeres are pulled apart Centromeres are pulled apart

as spindle fibers contractsas spindle fibers contracts Chromatids (half of a Chromatids (half of a

chromosome) are pulled in chromosome) are pulled in opposite directionsopposite directions

Chromatids are pulled to Chromatids are pulled to opposite ends of the cellopposite ends of the cell

TelophaseTelophase

TelophaseTelophase Chromatids complete journey to Chromatids complete journey to

the ends of the cellthe ends of the cell Chromatin is formed as DNA Chromatin is formed as DNA

elongateselongates Nuclear envelope forms around Nuclear envelope forms around

each set of DNAeach set of DNA Spindle disappearsSpindle disappears Nucleoli appear in each nucleusNucleoli appear in each nucleus

Cytokinesis Cytokinesis

Cytoplasmic DivisionCytoplasmic Division Begins during anaphaseBegins during anaphase Furrow / ring starts to Furrow / ring starts to

develop in the middle of the develop in the middle of the cell membranecell membrane

Cytokinesis Cytokinesis

In plants, you start to In plants, you start to develop a cell platedevelop a cell plate

Ring contracts until it Ring contracts until it completely separates the two completely separates the two new nuclei and about ½ new nuclei and about ½ organelles into each new cellorganelles into each new cell

Results of MitosisResults of Mitosis Unicellular organisms remain as Unicellular organisms remain as

single cellssingle cells Multicellular organisms - cell Multicellular organisms - cell

growth results in cell growth results in cell specialization & organization for a specialization & organization for a complex organismcomplex organism

Cells Cells > Tissues > Organs > Organ > Tissues > Organs > Organ systemssystems

Results of MitosisResults of Mitosis Cells – still the basic level of Cells – still the basic level of

organizationorganization Tissues are groups of cells Tissues are groups of cells

working together to perform a working together to perform a specific functionspecific function

Organs – tissues organized in Organs – tissues organized in various combinationsvarious combinations

Organ systems – multiple organsOrgan systems – multiple organs

Control of the cell cycleControl of the cell cycle

8.38.3

Control of the Cell CycleControl of the Cell Cycle

cyclins (proteins) regulate cyclins (proteins) regulate cell growth cell growth

Internal regulators – only Internal regulators – only move to the next phase of move to the next phase of the cell cycle when the the cell cycle when the previous phase is previous phase is completecomplete

Control of the Cell CycleControl of the Cell Cycle

External regulators – if External regulators – if there is room, a cell there is room, a cell divides; if neighboring divides; if neighboring cells are touching, cell cells are touching, cell growth is inhibited growth is inhibited because space is scarcebecause space is scarce

Apoptosis – programmed Apoptosis – programmed cell deathcell death

Normal part of development for Normal part of development for most cells in a multi-celled most cells in a multi-celled organism organism

Once cells stop dividing or Once cells stop dividing or specializing; special enzymes specializing; special enzymes will break it down and will break it down and scavenger WBCs come and scavenger WBCs come and clean up the messclean up the mess

CancerCancer Uncontrolled cell growth Uncontrolled cell growth Tumors are cells that do not Tumors are cells that do not

respond to cell regulatorsrespond to cell regulators Cells could also become Cells could also become

“immortal”; they don’t finish cell “immortal”; they don’t finish cell development and die, so new development and die, so new cells just build upcells just build up

Cancer CausesCancer Causes 22ndnd leading cause of death in leading cause of death in

the USthe US Caused by genetic & Caused by genetic &

environmental influencesenvironmental influences Env. Factors include: smoking, Env. Factors include: smoking,

air/water pollution, viral air/water pollution, viral infections, & UV exposureinfections, & UV exposure

Cancer preventionCancer prevention Diets low in fat, high in fiberDiets low in fat, high in fiber Lots of fruits, veggies, and Lots of fruits, veggies, and

grain productsgrain products Foods high in Vit. A, C & E, & Foods high in Vit. A, C & E, &

the mineral calciumthe mineral calcium Exercise & no smokingExercise & no smoking