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The Cell Cycle
Chapter 8Sections 8.2 & 8.3
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Cell Growth andReproduction
Section 8.2
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Cell Size
Cells can come inmany different sizes
Red Blood Cells ~ 8micrometers
Nerve cells ~ 1 m long
Yolk of Ostrich egg ~8 cm
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Cell Size
Most living cells are between 2 and200 micrometers in diameter
Why may this be? Whatadvantage does a cell have
with staying small?
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Cell Size
As a cell gets bigger, itssurface area and
volume change.
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Cell Size
Surface area- areaof each surface
Length x Width
Volume - L x W x H
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Cell Size
Cells rely on diffusion to moveparticles throughout the cell.
How would the diffusion rate of substances into andout of the cell change as the cell gets larger?
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Calculate the SA & V
1 mm1 mm
1 mm
2 mm 2 mm
2 mm
4 mm 4 mm
4 mm
Surface Area = (l * w) * 6
Volume = l * w * h
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Cell Size
Compare the surface area to the volume of each cellby dividing the surface area by the volume.
SA cube 1 = 6 cm
Volume cube 1 = 1cm
Ratio: 6 / 1 = 6
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Cell SizeIf a cell got too large, it would either starve to death or bepoisoned from the buildup of waste products due to the slowrate of diffusion!
If a cell is too large, diffusion cannot work efficiently enough
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Cell Size
2 major factors thatlimit cell size
Rate of DiffusionDNA
What is the function of
DNA?
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Cell Size
The cell cantsurvive if it
doesnt haveenough DNA tosupport its
protein needs
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Cell Size
How can a largecell compensatefor being so big?
Have more thanone nucleus!
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Cell Reproduction
When a cell gets too big, it must replicateitself and divide
Why?Prevent itself from getting too big for itsbritches"
Replication usually ensures survival
Worn out cells need to be replaced
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Cell Reproduction
Remember the celltheory ?
All cells comefrom preexistingcells
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Cell Reproduction
Cell reproduction(cell division) isthe process bywhich cells producenew cellsResults in two cellsthat are identical to the originalparent cell
Identical sets
of geneticinformation!
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Cell Reproduction
Cell reproduction isa well orchestratedevent
Division is differentin prokaryotes
(bacteria) andeukaryotes
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Prokaryotic Cell Division
Prokaryotes reproduce by binary fissionDNA is copied and cell splits in half
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The Eukaryotic Cell Cycle
Eukaryotic celldivision is a highlyorchestrated event
The cell cycle isthe sequence of growth and divisionof a eukaryotic cell
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What process is shownhere?
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Yesterdays Highlights
The larger a cellbecomes, the moredemands the cellplaces on its DNA andthe more trouble thecell has movingenough nutrients andwastes across the cellmembrane.
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The Eukaryotic Cell Cycle
There are threemajor parts to thecell cycle
InterphaseMitosisCytokinesis
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Chromosomes
When a cell is notdividing, geneticinformation exists
as chromatinwrapped aroundhistones (structuralproteins)
Like beads on a
stringChromatin
Histone
*Cell division results in two cells thatare identical to the original parentcell*
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Chromosomes
Finally, chromosomesare duplicated so thateach cell has a copy
Each copy is called asister chromatid andis held together by acentromere
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Chromosomes
What is the difference betweenchromosomes and chromatin?
Nothing! Just how its arranged.
Chromatin ChromosomesCondensingand doubling
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The Cell Cycle
INTERPHASE - busiest time ina cells life
Cell performs its normalfunctions and produces proteinsso it can perform its particular
job
Most of a cells life is spent inthis phase
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Interphase
Divided into three partsPart 1 (G 1) -
Cell grows and protein production ishigh
Part 1
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Interphase
Part 2 (S phase)-Chromatin is copied
Part 2
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Interphase
Part 3 (G 2)-Cell prepares for division
Centrioles and other organelles are copiedto aid in cell division
Part 3
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Cell Reproduction
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The Phases of Mitosis
There are four important phases thatoccur during mitosis
Prophase Metaphase Anaphase Telophase
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Prophase
Chromatids condenseNuclear envelopedisappears
Centrioles align near nucleusSpindle fibers form
Sister Chromatids
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Metaphase
Chromosomesattach to spindlefibers Line up along themiddle of the cell
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Anaphase
Sister chromatids are separated andpulled to oppositesides of the cell
Caused by theshortening of themicrotublues inthe spindle fibers
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Telophase
Prophase reverses
Chromosomes unwind for usein the new cell
Spindle fibers break down;nucleolus and nuclear envelope reappears
New membrane formsbetween the cells
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Cytokinesis
Cytoplasm splitting
In animal cells, plasma
membrane pinches atthe equator formingcleavage furrow
In plant cells, cell
plate is laid down andnew cell walls andmembranes formaround it
f