Fall 2005 – @ K. Malone Ch. 10, Cell Growth and Division Ch. 11, Meiosis (sec. 11-4) Ch. 10: –Cell Growth- why do cells divide instead of continue to grow?

Fall 2005 – @ K. Malone

Ch. 10, Cell Growth and Division

Ch. 11, Meiosis (sec. 11-4)

• Ch. 10:– Cell Growth- why do cells divide instead

of continue to grow?– Cell Division – Cell Cycle and when a cell

divides, Mitosis– Regulation of the Cell Cycle- how it’s

controlled, what happens when it’s out of control

• Ch. 11:– Phases of Meiosis– Comparing Mitosis and Meiosis


Section 10.1 – Cell GrowthCell Growth

• How do organisms grow? Do their cells get bigger? Or do they make more cells?

• Answer = Make more cells!!!• There is a limit to how big cells can grow!• Getting bigger does 2 things:1. Places more demands on DNA2. Makes it harder to move molecules across a

cell’s membrane

Just right

TooSmall

Too Big!

I’m out I’m out of of

controlcontrol!!

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Understanding the relationship between a cell’s Understanding the relationship between a cell’s Surface AreaSurface Area and and VolumeVolume is the key to understanding why cells is the key to understanding why cells mustmust divide divide

as they grow.as they grow.

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Surface Area to Volume Ratio

1 cm1 cm

1 1 cmcm

1 cm1 cm

6 sided cube6 sided cube

Volume (V):Volume (V): 1 x 1 x 1 = 1 x 1 x 1 = 1 1 cmcm33 (length x width x height)Ratio of SA to V:Ratio of SA to V: 6/1 = 6/1 = 6:16:1

Bigger 6 sided cubeBigger 6 sided cube

3 cm3 cm

3 cm3 cm

3 cm3 cm

SA:SA: 3 x 3 x 6 = 54 cm3 x 3 x 6 = 54 cm33

V:V: 3 x 3 x 3 = 27 cm3 x 3 x 3 = 27 cm33

Ratio of SA to V: 54/27 = 2:1Ratio of SA to V: 54/27 = 2:1

More More surface surface

area! Good!area! Good!

Less surface Less surface area! Bad!area! Bad!

Bigger is NOT better

!

Surface Area (SA): Surface Area (SA): 1 x 1 x 6 1 x 1 x 6 = = 6 cm6 cm33

(length x width x height x # sides)

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Volume increases more rapidly than Surface Area and this causes the ratio

of SA to V to decrease.

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Decreasing the SA to V ratio causes big problems for the cell.

More molecules trying to go through the membrane (SA)

and there’s less surface area for everything to move through!

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What’s the solution to this traffic problemWhat’s the solution to this traffic problem??

Instead of growing bigger, Instead of growing bigger, let’s make more cells! let’s make more cells!

And to do this, And to do this, 1 cell will divide into 2 cells.1 cell will divide into 2 cells.

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Cell Division• When a cell divides, the 2 cells that result are called “daughter”

cells• Cell Division = process by which a cell divides into 2 new

daughter cells• Before cell division, the cell replicates, or makes

copies of all of its DNA

• Solves the 2 problems with cell growth:• New daughter cells get one complete set of genetic

information- they get their own complete genetic library

• No more problems with SA to V ratio because daughter cells has an increased ratio of SA to V because their volume overall is reduced (one cell dividing into two makes both cells smaller)

I’m too fat

daughter daughter

Mommy?

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Cell Division• In Eukaryotes (you!), cell division occurs in 2 main

stages:1. Mitosis = division of the cell’s nucleus2. Cytokinesis = division of the cytoplasm

Section 10-2

(Sy-toh-kih-NEE-sis)

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Genetic information passed from 1 Genetic information passed from 1 generation to the next is carried by generation to the next is carried by ChromosomesChromosomes

ChromosomesChromosomes are made up of are made up of DNADNA- the - the part that carries the cell’s genetic part that carries the cell’s genetic informationinformation

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Mitosis is considered asexual because cells produced by it are genetically identical to the parent cell. Box

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chromatid

replication

Chromosomes

• When a cell isn’t in the process of dividing, chromosomes are not visible because they are spread out within the nucleus.

• However, when cell division is beginning, the chromosomes condense into compact, visible structures we can see in a microscope.

• Before cell division occurs, each chromosome is copied, or replicated, and the identical copies are called “sister” chromatids (KROH-muh-tids)

LYLAS!

Yo! Sis!

Sister chromatidSister chromatid

Centromere

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The Cell Cycle• The Cell Cycle is a series of events that cells

go through as they grow and divide 1. Cell grows2. Cell prepares for division3. Cell divides to form 2 daughter cells (each daughter cell will begin the cell cycle again)

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Cell Cycle consists of 4 Cell Cycle consists of 4 phases:phases:

1.1. Mitosis and CytokinesisMitosis and Cytokinesis = = MM phase phase

2.2. Growth phaseGrowth phase = G = G11 (“G” = (“G” = gap)gap)

3.3. Chromosome replicationChromosome replication = = S phaseS phase

4.4. Preparation for mitosis Preparation for mitosis = = GG22

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Interphase = “in between” period of growth for a cell

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Cell Cycle Phases

M phase

G2 phase

G1 phase

S ph

ase

IM I

I

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S phase = when chromosomes are replicated and synthesis of DNA molecules occurs

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G2 phase = when cells make many organelles and molecules needed for cell division

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M phase = when cell division occurs

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G1 phase = when cells do most of their growing- cells increase in size and make new proteins and organelles

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Mitosis

• Interphase then….• Mitosis has 4 phases:

• 1. Prophase• 2. Metaphase• 3. Anaphase• 4. Telophase

I then ..PMATI then ..PMAT

Interphase is NOT part of Mitosis!!!!! Remember that!

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Mitosis

InterphaseInterphase

Centrioles

ChromatinNuclear envelope

Interphase = cell grows and replicates its DNA and centrioles.

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Centrioles



Spindle forming

Chromosomes (paired chromatids)

Prophase = chromatin condenses into chromosomes, centrioles separate, spindle forms, nuclear envelope breaks down

ProphaseProphase

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Centromere



Centrioles



Spindle forming


Centromere

Prophase = chromatin condenses into chromosomes, centrioles separate, spindle forms, nuclear envelope breaks down.

ProphaseProphase

Centriole

Spindle

Centriole

MetaphaseMetaphase

Metaphase = chromosomes line up across the center of the cell, each chromosome is connected to a spindle fiber at its centromere

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Centrioles



Spindle forming


Centromere


ProphaseProphase

Centriole

Spindle

Centriole

MetaphaseMetaphaseIndividual chromosomes

AnaphaseAnaphase

Anaphase = sister chromatids separate into individual chromosomes and move apart

Metaphase = chromosomes line up across the center of the cell, each chromosome is connected to a spindle fiber at its centromere

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Centrioles



Spindle forming


Centromere


ProphaseProphase

Centriole

Spindle

Centriole


AnaphaseAnaphase Anaphase = sister chromatids separate into individual chromosomes and are moved apart

Nuclear envelope reforming

TelophaseTelophase

Telophase = chromosomes gather at opposite ends of the cell and lose their distinct shapes- 2 new nuclear envelopes form

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TelophaseTelophase


Centrioles



Spindle forming


Centromere


ProphaseProphase

Centriole

Spindle

Centriole


AnaphaseAnaphase

Anaphase = sister chromatids separate into individual chromosomes and are moved apart

Nuclear envelope reforming


Cytokinesis

Cytokinesis = cytoplasm pinches in ½ , each daughter cell has an identical set of chromosomes

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TelophaseTelophase




MetaphaseMetaphase

AnaphaseAnaphase

Anaphase = sister chromatids separate into individual chromosomes and are moved apart


CytokinesisCytokinesis

Cytokinesis = cytoplasm pinches in half, each daughter cell has an identical set of duplicate chromosomes

ProphaseProphase

Metaphase = chromosomes line up across the center of the cell, and each is connected to a spindle fiber at its centromere

I…then PMATI…then PMAT


Interphase Metaphase

Prophase

Anaphase

Telophase

Cytokinesis

Product of Mitosis?2 identical daughter cells

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Cell Cycle Tree Map

InterphaseInterphaseis divided into…is divided into…

MitosisMitosisis divided into…is divided into…

GG11 phase phase S phaseS phase GG22 phase phase ProphaseProphase MetaphaseMetaphase AnaphaseAnaphase TelophaseTelophase

Cell CycleCell Cycleincludes…..includes…..

And then………Cytokinesis


Title: The Cell Cycle and MitosisYour Name: ex. by Fred Cooks

1st : The Cell Cycle & Interphase

2nd : Mitosis - Prophase

3rd : Mitosis - Metaphase

4th : Mitosis - Anaphase

5th : Mitosis - Telophase

P

M

A

T

6th : Cytokinesis

Draw the cell cycle diagram on pg. Label the parts. List the stages of the cell cycle, describe what happens in each stage (G1, G2, S and M)Prophase. Draw a cell in prophase using pg. 246 as a reference. List 3 facts describing events in Prophase.Metaphase. Draw a cell in metaphase, and list 3 facts describing events in this phase.

Cytokinesis. Draw a cell in cytokinesis and define what happens to the cell.

Anaphase and Telophase. Draw a cell in anaphase and telophase, and list 3 facts describing events in each phase.

Chromosome CentromereCentriole SpindleSister chromatids

Include these definitions:


Regulation of the Cell Cycle

• For very obvious reasons, the cell cycle is a tightly, highly controlled process.

• Do you know why?

• Uncontrolled cell growth is cancer!!! Cancer can be deadly!

• Not all cells need to divide all the time, or at all.

• There is a time and place for cell division, and controlling the cell cycle is important because it is part of homeostasis- keeping an organism alive and healthy.

Section 10-3

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Controls on Cell Division

In the lab, scientists can grow cells by placing them in a petri dish, along with nutrients.

Cells will grow until they form a single layer covering the bottom of the dish, then they stop growing when they come into contact with one another.

These experiments show that controls on cell growth and division can be turned onon and offoff.

If you remove cells from the center of the dish, cells bordering the open space begin dividing and filling the empty space.

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What happens in your body?

• Similar processes happen in your own body.

• What if you get a cut on your finger? A broken bone?

• When you’re injured, cells at the edge of the cut or break are stimulated to divide rapidly and produce new cells, starting the process of healing.

• When the gap is repaired, the controls for cell division turn off again, and everything returns to normal.

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Cell Cycle Regulators

• Tim Hunt and Mark Kirschner found a protein that, when injected into non-dividing cells, would cause mitotic spindle fibers to form.

• Levels of this protein rose and fell, depending on the phases of the cell cycle – produced when needed for division, not produced when no cell division is occurring.

• They called the protein Cyclin (for cycle)• Cyclins = regulate the timing of the Cell Cycle

in Eukaryote cells (your cells!)

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Hunt and Kirschner’s Experiment

The reason for this effect is the protein Cyclin, which triggers cell division in non-dividing cells.

A sample of cytoplasm is removed from a cell in mitosis.

The sample is injected into a second cell in G2 of interphase.

As a result, the second cell enters mitosis.

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Internal and External Regulators

• Internal regulators = regulating proteins that respond to events inside the cell, and control the cell cycle; allow cell cycle to proceed only when certain process have happened inside the cell.

• Similar to: You can’t eat your dessert until you clean your plate!

• External regulators = regulating proteins that respond to events outside the cell, and control the cell cycle

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Uncontrolled Cell Growth

• Cancer.• Such a scary word, isn’t it?• Most common cancers:• Men: Prostate cancer (33%)

Lung (13%)• Women: Breast (32%)

Lung (13%)

Affects 1 in 6 men

Affects 1 in 13 men

Affects 1 in 7 women

Affects 1 in 17 women

Pretty frightening,

yes?

American Cancer Society 2004 Statistics

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44.77% chance of a man getting cancer44.77% chance of a man getting cancer33.08% chance of a woman getting cancer33.08% chance of a woman getting cancer

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Cancer• Cancer cells do not respond to the signals that

regulate growth of most cells.• They divide uncontrollably and form masses of cells

called Tumors that can damage the surrounding tissues.

Untreated Breast CancerUntreated Breast Cancer Tumor on the eyeTumor on the eye

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Tumors = masses of uncontrollably dividing cells that damage surrounding tissues

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•Cancer cells may Metastasize, or break loose and spread throughout the body.

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Cancer• Cancer is a disease of the Cell Cycle.

• To find a cure for this horrible disease, we must first deeply and completely understand the Cell Cycle, what regulates it, and how it can go wrong, resulting in cancer.

• This is a major scientific challenge, but at least we know now where to start searching for a cure- the Cell Cycle.

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Stem Cells• When you were first conceived, you started out as a

SINGLE cell. One cell. • That one cell then divided over and over, (Mitosis)

producing cells that could and would become all the specialized parts of your body.

• Fetal Stem Cells= the cells in the earliest stages of fetal (baby) development, they can potentially become any cell type in the body.

• Adult Stem Cells = usually found in the bone marrow, can be induced (pushed) to become other cell types like muscle, nerve and liver cells

Controversial – Unethical?

Has the promise to repair many injuries and replace damaged organs (ex. liver)

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Meiosis

• Humans have 46 chromosomes in every cell of our bodies except the sex cells or gametes (eggs and sperm)- they have 23 chromosomes

• When a baby is conceived, an egg from mom and a sperm from dad, combine into the first cell of the new baby. 23+23 = 46

Section 11-4

What would happen if the What would happen if the egg and sperm both had 46 egg and sperm both had 46 chromosomes?chromosomes?Baby would have Baby would have 9292 chromosomes!! Disaster!chromosomes!! Disaster!

46 46

92chromosomes

= death, disease

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Remembering Meiosis

• Mitosis is a process that occurs in almost every cell of your body (body cells), except the sex cells, or gametes.

• Mitosis = My toe sis, it happens in your toes!

• Meiosis is a process of cell division that doesn’t happen in your toes, it only happens in your sex cells, gametes

• Meiosis = My OH! Sis (as in uh-oh!)

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Meiosis• To solve this problem, the cells in the gametes (eggs

and sperm), undergo Meiosis instead of Mitosis, when they divide.

• Why Meiosis?

• Most cells in our body are Diploid (“di” = 2)• Diploid = have 2 sets of chromosomes, 2n

(one from mom, one from dad)• Sex cells, or gametes, are Haploid • Haploid = have 1 set of chromosomes, 1n

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Meiosis results in cells with ½ the # of chromosomes, so they can combine in sexual

reproduction, which results in an embryo with the normal amount of chromosomes.

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Chromosome Number

• An example.

• Fruit Flies (Drosophila), have 8 chromosomes total – 4 from dad fruit fly, 4 from mom fruit fly.

Diploid number?2n = 8

Haploid number?

1n = 4

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Homologous chromosomes= 2 sets of similar chromosomes, one from mom, one from dad

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Phases of Meiosis

• How are haploid (1n) gamete cells produced from diploid (2n) cells?

• By Meiosis (my-OH-sis)

• Meiosis = process of reduction cell division where the # of chromosomes per cell is cut in ½ by the separation of homologous chromosomes

Homologous = same chromosome, it just comes from different parents (mom or dad)

Meiosis involves 2 distinct divisions, 1. Meiosis I 2. Meiosis II Results of Meiosis? = cells with a haploid (1n)

number of chromosomes

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Meiosis I

Chromosome duplicationChromosome duplication

2 sister chromatids2 sister chromatids

4 sister chromatids 4 sister chromatids form a Tetradform a Tetrad

Interphase I Prophase I

Interphase I = Cells undergo a round of DNA replication, forming duplicate chromosomes

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Prophase I = Each chromosome pairs up with its matching homologous chromosome forming a tetrad

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Tetrads= in prophase I, chromosomes duplicate and form a structure with 4 chromosomes (tetrad)

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During prophase I of Meiosis, when the tetrads form, a phenomenon called “Crossing Over” can occur.

Owww! My

arm!

Sorry!

Who me?

Hey hot stuff, wanna dance?

I think he likes

me!

You got chocolate in my peanut

butter!

You got peanut butter

in my chocolate!

Help!Crossing Over = results in the exchange of genetic information between homologous chromosomes

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Meiosis I

Interphase I Prophase I Metaphase I


Prophase I = Each chromosome pairs up with its corresponding homologous chromosome to form a tetrad

Anaphase I = Fibers pull the homologous chromosomes towards opposite ends of the cell (“A” for apart)

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Metaphase I = Spindle fibers attach to the chromosomes, then they line up in the middle (“M” for middle)

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Anaphase I


Meiosis I

Interphase I Prophase I Metaphase I Anaphase I Telophase and Cytokinesis

Prophase I = Each chromosome pairs up with its corresponding homologous chromosome to form a tetrad


Anaphase I = Fibers pull the homologous chromosomes towards opposite ends of the cell (“A” for apart)

Metaphase I = Spindle fibers attach to the chromosomes, then they line up in the middle (“M” for middle)

Telophase I and Cytokinesis = Nuclear membranes form, the cell separates into 2 new cells

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Meiosis IIThe 2 new cells now enter a 2nd round of meiotic division

No more chromosome duplication

prophase II

Prophase II = of meiosis I results in 2 haploid daughter cells, each with ½ the # of chromosomes as the original cell Box

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Meiosis II

prophase II metaphase II

Prophase II = of meiosis I results in 2 haploid daughter cells, each with ½ the # of chromosomes as the original cell

Metaphase II = chromosomes line up in the middle Box

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Meiosis II

anaphase II

1

2

3

4

telophase IIprophase II metaphase II

Metaphase II = chromosomes line up in the middle

Prophase II = of meiosis I results in 2 haploid daughter cells, each with ½ the # of chromosomes as the original cell

Anaphase II = sister chromatids separate and move to opposite ends of the cell

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Telophase II and Cytokinesis = of meiosis II results in 4 haploid (1n) daughter cells

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Prophase I

Anaphase I

Telophase I&

Cytokinesis

Prophase II

IP

MA

T

P

MAT

I then …PMAT…..PMATI then …PMAT…..PMAT

Telophase II&

CytokinesisAnaphase II Metaphase II

4 daughter cells4 daughter cellswith haploid # (1n)with haploid # (1n)

Humans = 2n = 46

9292

92 92

46

46

464623

Flow Chart for MeiosisFlow Chart for Meiosis

Interphase I

Metaphase I


Gamete Formation

• Why do we even have Meiosis?• To make gametes (eggs and sperm).• Male gametes = sperm• Female gametes = eggs

Why do we need eggs and sperm?Why do we need eggs and sperm?

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End of Chapter 10 and Chapter 11 Section 11-4

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For For Sexual ReproductionSexual Reproduction, where egg , where egg and sperm unite to make an embryoand sperm unite to make an embryo

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Documents

Fall 2005 – @ K. Malone Ch. 10, Cell Growth and Division Ch. 11, Meiosis (sec. 11-4) Ch. 10: –Cell Growth- why do cells divide instead of continue to grow?