Cell Size & Mitosis 2008 - BZ

7/28/2019 Cell Size & Mitosis 2008 - BZ

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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

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Cell Size & Mitosis 2008 - BZ