Cell Growth and Cell Growth and ReproductionReproductionSection 10.1 and 10.2Section 10.1 and 10.2

BiologyBiology

Limits to cell growthLimits to cell growth 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 cell if it’s materials in/out of the cell if it’s too low like 2/1too low like 2/1

The larger the cell, the lower the The larger the cell, the lower the ratio (surface area to volume), the ratio (surface area to volume), the harder to transport materials.harder to transport materials.

Solves these problems with cell Solves these problems with cell division (making 2 new cells)division (making 2 new cells)

Cell Division – when a cell gets Cell Division – when a cell gets too large to control or function too large to control or function efficiently, cell division takes placeefficiently, cell division takes place

Cell divisionCell division

10.210.2

ChromosomesChromosomes Chromosomes are carriers of Chromosomes are carriers of

our genetic material & must be our genetic material & must be copied & transmitted accuratelycopied & 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 chromosomes exists as chromatin (long strands of DNA chromatin (long strands of DNA wrapped around proteins called wrapped around proteins called histones)histones)

Cell Cycle (3 stages)Cell Cycle (3 stages)

Sequence of growth Sequence of growth (interphase), nuclear (interphase), nuclear division (mitosis), and division (mitosis), and cytoplasmic division cytoplasmic division (cytokinesis) of a cell(cytokinesis) of a cell

Interphase (1Interphase (1stst stage) stage) 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 – preparation G2 – growth phase – preparation

for mitosis; produce more for mitosis; produce more organelles, enzymes, centrioles organelles, enzymes, centrioles are replicated, etc.are replicated, etc.

Mitosis – PMAT (2Mitosis – PMAT (2ndnd stage)stage)nuclear 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

4 stages to mitosis4 stages to mitosis

Prophase - prepareProphase - prepareMetaphase - middleMetaphase - middleAnaphase - awayAnaphase - awayTelophase – two cellsTelophase – two cells

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

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 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 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 (3Cytokinesis (3rdrd stage) stage)

Cytoplasmic DivisionCytoplasmic Division Begins during anaphaseBegins during anaphase In animal cells a furrow / ring In animal cells a furrow / ring

starts to develop in the starts to develop in the middle of the cell membrane middle of the cell membrane (pinching of the middle)(pinching of the middle)

Cytokinesis Cytokinesis

In plants, you start to In plants, you start to develop a cell plate (starts in develop a cell plate (starts in middle of the 2 cells)middle of the 2 cells)

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

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

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

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 (50 - 70 billion cells die each 50 - 70 billion cells die each day in the average human adult.) day in the average human adult.)

Once cells stop dividing or Once cells stop dividing or specializing; special enzymes specializing; special enzymes will break it down & scavenger will break it down & scavenger WBCs come & clean up WBCs come & clean up