cell growth and reproduction section 8.2 biology
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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
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