AP Biology 2007-2008

Chapter 12

The Cell Cycle:

Cell Growth, Cell Division

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Where it all began…

You started as a cell smaller than

a period at the end of a sentence…

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And now look at you…

How did you get from there

to here?

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Going from egg to baby….

the original fertilized egg has to divide…

and divide…

and divide…

and divide…

Getting from there to here…

AP Biology Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 7.5

Metabolic requirements also set an upper limit

to the size of a single cell.

As a cell increases in size its volume

increases faster (X3)than its surface area (X2).

Smaller objects have a greater ratio of

surface area to volume.

Cell membrane cannot keep up with the

nutrient supply needed by an enlarging

cytoplasm…. The solution to the problem is

to split into two cells.

Why do cells divide?

AP Biology Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 7.5

Why do cells divide?

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For reproduction

asexual reproduction

one-celled organisms

For growth

from fertilized egg to

multi-celled organism

For repair & renewal

replace cells that die

from normal wear &

tear or from injury

What are the benefits

of Cell Division?

amoeba

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Making new cells

Nucleus

chromosomes

DNA

Cytoskeleton

centrioles

in animals

microtubule

spindle fibers

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nuclear pores

nuclear pore

nuclear envelope

nucleolus

histone protein

chromosome

DNA

Function

protects DNA

Structure

nuclear envelope

double membrane

membrane fused in spots to create pores

allows large macromolecules to pass through

Nucleus

What kind of molecules need to

pass through?

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Cytoskeleton

Function

structural support maintains shape of cell

provides anchorage for organelles

protein fibers

microfilaments, intermediate filaments, microtubules

motility cell locomotion

cilia, flagella, etc.

regulation

organizes structures

& activities of cell

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actin

microtubule

nuclei

Cytoskeleton

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Centrioles

Cell division

in animal cells, pair of centrioles organize microtubules spindle fibers

guide chromosomes in mitosis

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Getting the right stuff

What is passed on to daughter cells?

exact copy of genetic material = DNA

mitosis

organelles, cytoplasm, cell membrane,

enzymes

cytokinesis

chromosomes (stained orange)

in kangaroo rat epithelial cell

notice cytoskeleton fibers

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Overview of mitosis

interphase prophase (pro-metaphase)

metaphase anaphase telophase

cytokinesis

I.P.M.A.T.

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Interphase

90% of cell life cycle

cell doing its “everyday job”

produce RNA, synthesize proteins/enzymes

prepares for duplication if triggered

I’m working here!

Time to divide & multiply!

Checkpoints

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The distinct events of the cell cycle are

directed by a distinct cell cycle control

system.

These molecules trigger and coordinate key

events in the cell cycle.

The control cycle has

a built-in clock, but it

is also regulated by

external adjustments

and internal controls.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 12.13

Password

please!

MPF

please!

Chromatids Attached?

Than activate the APC!

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A checkpoint in the cell cycle is a critical

control point where stop and go signals

regulate the cycle.

Three major checkpoints are found in the:

G1 , G2, and M phases.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

AP Biology

For many cells, the G1 checkpoint, the

restriction point in mammalian cells, is the

most important.

If the cells receives a go-ahead signal, it

usually completes the cell cycle and divides.

If it does not receive a go-ahead signal, the cell

exits the cycle and switches to a nondividing

state, the G0 phase.

Most human cells are in this phase.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Read the ppt “Regulation of the Cell Cycle”

for details!

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Cell cycle

M

Mitosis

G1

Gap 1

G0

Resting

G2

Gap 2

S

Synthesis

Cell has a “life cycle”

cell is formed from

a mitotic division

cell grows & matures

to divide again

cell grows & matures

to never divide again

G1, S, G2, M G1G0

epithelial cells,

blood cells,

stem cells

liver cells

brain / nerve cells

muscle cells

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Interphase

Divided into 3 phases:

G1 = 1st Gap (Growth)

cell doing its “everyday job”

cell grows

S = DNA Synthesis

copies chromosomes

G2 = 2nd Gap (Growth)

prepares for division

cell grows (more)

produces organelles, proteins, membranes

G0

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Interphase

Nucleus well-defined

DNA loosely packed in long chromatin fibers

Prepares for mitosis

replicates chromosome

DNA & proteins

produces proteins & organelles

green = key features

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Synthesis phase of Interphase

dividing cell replicates DNA

must separate DNA copies

correctly to 2 daughter cells

human cell duplicates ~3 meters DNA

each daughter cell gets complete

identical copy

error rate = ~1 per 100 million bases

3 billion base pairs in mammalian

genome

~30 errors per cell cycle

mutations (to somatic (body) cells)

S phase: Copying / Replicating DNA

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Organizing DNA

DNA is organized in chromosomes double helix DNA molecule

wrapped around histone proteins like thread on spools

DNA-protein complex = chromatin organized into long thin fiber

condensed further during mitosis

DNA

histones

chromatin

duplicated mitotic chromosome

ACTGGTCAGGCAATGTC

double stranded chromosome http://www.dnalc.org/

resources/3d/DNAWr

apAdvanced06.html

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Copying DNA & packaging it…

After DNA duplication, chromatin condenses

coiling & folding to make a smaller package

DNA

chromatin

mitotic chromosome

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double-stranded mitotic human chromosomes

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Mitotic Chromosome Duplicated chromosome

2 sister chromatids

narrow at centromeres

contain identical

copies of original DNA homologous

chromosomes homologous

chromosomes

sister chromatids homologous = “same information”

single-stranded double-stranded

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Mitosis

Dividing cell’s DNA between

2 daughter nuclei

“dance of the chromosomes”

4 phases

prophase

metaphase

anaphase

telophase

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Prophase Chromatin condenses

visible chromosomes chromatids

Centrioles move to opposite poles of cell

animal cell

Protein fibers cross cell to form mitotic spindle

microtubules

actin, myosin

coordinates movement of chromosomes

Nucleolus disappears

Nuclear membrane breaks down

green = key features

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Transition to Metaphase Prometaphase

spindle fibers attach to

centromeres

creating kinetochores

microtubules attach at

kinetochores

connect centromeres to centrioles

chromosomes begin moving

Nuclear envelope dissolves

green = key features

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Metaphase

Chromosomes align

along middle of cell

metaphase plate

meta = middle

spindle fibers coordinate

movement

helps to ensure

chromosomes separate

properly

so each new nucleus

receives only 1 copy of

each chromosome

green = key features

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Anaphase

Sister chromatids separate at

kinetochores

move to opposite poles

pulled at centromeres

pulled by motor proteins

“walking”along microtubules

actin, myosin

increased production of

ATP by mitochondria

Poles move farther apart

polar microtubules lengthen

green = key features

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Separation of chromatids

In anaphase, proteins holding together sister

chromatids are inactivated

separate to become individual chromosomes

2 chromosomes 1 chromosome

2 chromatids single-stranded

double-stranded

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Kinetochores use

motor proteins that

“walk” chromosome

along attached

microtubule

microtubule

shortens by

dismantling at

kinetochore

(chromosome) end

Chromosome movement

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Telophase

Chromosomes arrive at opposite poles

daughter nuclei form

nucleoli form

chromosomes disperse

no longer visible under light microscope

Spindle fibers disperse

Cytokinesis begins

cell division

green = key features

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Cytokinesis

Animals

constriction belt of

actin microfilaments

around equator of cell

cleavage furrow forms

splits cell in two

like tightening a draw

string

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Cytokinesis in Animals

The Stages of Mitosis

http://www.youtube.com/watch?v=VGV3fv-uZYI

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Mitosis in whitefish blastula

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Mitosis in animal cells

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Cytokinesis in Plants

Plants

cell plate forms

vesicles line up at

equator

derived from Golgi

vesicles fuse to form

2 cell membranes

new cell wall laid

down between

membranes

new cell wall fuses

with existing cell wall

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Cytokinesis in plant cell

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Mitosis in plant cell

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onion root tip

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Origin of replication

chromosome: double-stranded

DNA replication

of DNA

elongation of cell

cell pinches in two

ring of proteins

Evolution of mitosis

Mitosis in

eukaryotes

likely evolved from

binary fission in

bacteria

single circular

chromosome

no membrane-

bound organelles

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Evolution of

mitosis

A possible

progression of

mechanisms

intermediate

between binary

fission & mitosis

seen in modern

organisms

protists

dinoflagellates

protists

diatoms

eukaryotes

yeast

eukaryotes

animals

prokaryotes

(bacteria)

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Dinoflagellates

algae

“red tide”

bioluminescence

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Diatoms

microscopic algae

marine

freshwater

AP Biology 2007-2008

Any Questions??

AP Biology 2007-2008

Ghosts of Lectures Past

(storage)

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Control of Cell Cycle

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Kinetochore

Each chromatid

has own kinetochore

proteins

microtubules

attach to

kinetochore

proteins

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nucleosome DNA

histone

DNA double helix chromosome

rosettes of chromatin loops

scaffold protein

chromatin loop

Chromosome structure

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G2

S G1

M

metaphase

prophase

anaphase

telophase

interphase (G1, S, G2 phases)

mitosis (M)

cytokinesis (C)

C

Phases of a dividing cell’s life

interphase cell grows

replicates chromosomes

produces new organelles, enzymes, membranes…

G1, S, G2

mitotic phase cell separates & divides chromosomes mitosis

cell divides cytoplasm & organelles cytokinesis

Cell Division cycle

AP Biology 2007-2008

Substitute Slides

for Student Print version

(for student note-taking)

AP Biology

How did you

get from there

to here?

And now look at you…