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CELL GROWTH & DIVISION

Mitosis & Meiosis

Preview (Honors)

� Read: Chapter 10-1

� Page 256: Define ALL vocabulary

� Page 257: #1-10 & 14

� Page 282: Define Section 11-4 vocabulary

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Preview (Academic)

� Read: Chapter 10-1

� Page 256: Define ALL vocabulary

� Page 257: #12

� Page 282: Define Section 11-4 vocabulary

CELL GROWTH & DIVISION

Mitosis & Meiosis

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Discussion

� Why do we need cell growth?

� Why do we need cell division?

Limitation to Cell Growth

1.) DNA “Overload”

� Amount of DNA in a cell controls all of the cellular processes.

� If you make the cell bigger, but do not increase the amount of DNA, the cell may not survive.

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Limitation to Cell Growth

2.) Exchange of materials

� Cell membrane allows what comes in and out of the cell (i.e. water, oxygen, waste)

� Total Area of Cell Membrane

� How much the cell needs exchange depends on the volume of the cell

Cell Size & Scale

� http://learn.genetics.utah.edu/content/cells/scale/

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Why Are Cells So Small?

� One of the most important factors affecting the size of the cell is the SIZE of the CELL MEMBRANE.

� Cells have to remain small to survive because:

� They have to take in enough nutrients and eliminate wastes (using the cell membrane).

� As a cell gets bigger, the volume increases faster than the surface area of the cell membrane.

� For a cell to survive it needs a LARGE SURFACE AREA to VOLUME RATIO.

Why Are Cells So Small?

� Small cells have a larger surface area to volume ratio than larger cells.

� When a cell reaches its max size, the nucleus starts cell division, called MITOSIS or MEIOSIS.

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Mitosis vs. Meiosis

Key Note:

Only occurs in Eukaryotic Cells

Mitosis & Meiosis

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MITOSIS

Mitosis

� Mitosis: cell division that results in 2 daughter cells each having the same number and kind of chromosomes as the parent cell.

Parent: 2 chromosomes Daughter:

2 chromosomes

Daughter: 2 chromosomes

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Mitosis

� General Information:

� Nickname: “Normal” Cell Division

� Occurs in somatic (body/germ) cells ONLY

� Produces somatic cells ONLY

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Mitosis

� Background Information:

� Starts with somatic cell in DIPLOID (2n) state

�Each cell contains homologous chromosomes

�Chromosomes that control the same traits but not necessarily in the same way

�1 set from MOM & 1 set from DAD

� Ends in DIPLOID (2n) state as somatic cells.

� Goes through ONE SET of divisions

� Start with 1 cell and end with 2 cells

Why Mitosis?

� Accounts for 3 Essential Life Processes:

� 1.) Growth:

� Result of cells producing new cells

� Cells develop specialized shapes/functions in a process called differentiation.

� Rate of cell division controlled by GH (Growth Hormone), which is produced in the pituitary gland.

� Ex. Fertilized egg � Baby/Infant

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Why Mitosis?

� 2.) Repair

� Cell regenerates at the site of injury

� Ex. Skin (replaced every 28 days), Bone (after a fracture)

Why Mitosis?

� 3.) Reproduction

� Asexual

� Offspring produced by only ONE parent

� Offspring produced are genetically identical

� MITOSIS

� Ex. Bacteria, fungi, certain plants & animals

� Sexual

� Offspring produced by TWO parents

� Offspring produced are a genetic combination of the two parents

� MEIOSIS

� Ex. Most animals (humans), plants

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Why Mitosis?

� Some organisms can combine any of the three processes.

� Ex. Sea star can re-grow a lost arm (repair) and a lost arm can form a new sea star (reproduction).

MEIOSIS

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Meiosis

� Meiosis: two cell divisions that result in daughter cells having ½ the chromosomes (23) as the parent cell (46)

� Note: Meiosis I & Meiosis II

Parent Cell

2 DaughterCells

4 DaughterCells

Meiosis

� General Information:

� Only happens in GAMETES (sex cells)

�Males: sperm cells

� Females: egg cells

� Nickname: “Reduction” Division

�Produce GAMETES

�Number (#) of chromosomes is reduced in the process

� This is important so the # of chromosomes doesn’t double with each generation.

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Meiosis

� Background Information:

� Start: 1 germ cell in diploid (2n) state

� End: 4 gametes in haploid (n) state

�Are there sets of homologous chromosomes? NO

� Goes through 2 sets of divisions:

�Meiosis I

�Meiosis II

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Important Terms/Concepts

How Do Cells Divide?

Chromosomes

� Made of DNA

� Carry genetic information

� Chromatin:

� Thin, fibrous form of DNA (looks like plate of spaghetti)

� Form of DNA when cells is resting (NOT dividing)

� Shortens, thickens to form chromosomes before cell division

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Chromosomes

� To prepare for cell division, chromosomes duplicate (replicate)

� Each replicated chromosome has two sister chromatidsthat are identical and are joined by a centromere.

� After cell division, each cell receives a full set of chromosomes (one chromatid from each pair)

� Chromosomes come in pairs (like shoes)

� Humans have 46 chromosomes OR 23 pairs (one each from mom and dad)

Chromosomes

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Chromosomes

� Homologous Chromosomes:

� Paired chromosomes that control the same traits, but not necessarily the same way

� Ex. Both have eye color, but one codes for blue eyes and the other for brown eyes.

Homologous Chromosomes

� Each locus may code for the same or different traits.

Hair Color Hair Color

Eye Color Eye Color

Ear Lobes Ear LobesLobed Not Lobed

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Sister Chromatid

� Exact copies of a chromosome from 1 parent

� Identical in every way

� Formed during early stages of Mitosis and Meiosis

� Separate during new cell formation

� Held together with a centromere

Hair Color

Eye Color

Ear Lobes Not Lobed

Hair Color

Eye Color

Ear LobesNot Lobed

Helpful Prefixes

� “Haplo-” = half or single

� “Homo-” = same

� “Hetero-” = different

� “Locus” = location

� “Pro-” = first

� “Meta-” = middle

� “Ana-” = back

� “Telo-” = last or away from

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Karyotype

Phases of Mitosis

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Phases of Mitosis (IPMAT)

IPM

AT

1. Interphase

2. Early Prophase

3. Late Prophase

4. Metaphase

5. Anaphase

6. Telophase

Interphase

IPM

AT

� “Resting” stage

� All other cellular processes are happening

� Cell is growing

� DNA (chromatin) and centriolesreplicate

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Early Prophase

IPM

AT

� Nuclear membrane begins to disappear

� Nucleolus disappears

� Chromatin shortens and thickens into chromosomes

� Centrioles migrate

Late Prophase

� Aster rays appear

� Surround the centrioles

� Spindle fibers appear

IPM

AT

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Metaphase

� Chromosomes line up in the Middle, on cell equator (metaphase plate)

� Homologous chromosomes are present, but do not pair (match up)

� Spindle fibers are attached to each half of a chromosome pair

IPM

AT

Anaphase

� Sister chromatids begin to migrate to the poles (centrioles), being pulled by the spindle fibers

IPM

AT

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Telophase

� Chromosomes lengthen/thin to chromatin

� Aster rays & spindle fibers disappear

� Nuclear membrane reforms

� Nucleolus reforms

� Centrioles reformIPM

AT

Cytokinesis

� Cell cytoplasm divides and partition forms to make 2 daughter cells

� Each has 2 complete sets of chromosomes, or diploid (2n)

� Plant cell: cell plate/cell wall created

� Animal cell: cell membrane pinches off

IPM

AT

C

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Interphase (again)

� Cell is at rest with 2 identical cellsIP

MA

T C

The Steps of Mitosis

IPMAT C

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Phases of Meiosis

Phases of Meiosis

IPM

AT

I&II Meiosis I:

1. Interphase

2. Prophase I

3. Metaphase I

4. Anaphase I

5. Telophase I

Meiosis II:

1. Interphase II (very short)

2. Prophase II

3. Metaphase II

4. Anaphase II

5. Telophase II

**Same stages as mitosis, EXCEPT they happen TWICE.**

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Meiosis

Prophase I

� Same as Mitosis Prophase

� Differences:

� Homologous pairs attach to each other to form a Tetrad

� Crossing over occurs – recombination of DNA from one sister chromatid to the otherIP

MA

T

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Prophase I – Crossing Over

Metaphase I

� Same as Mitosis Metaphase

� Difference:

� Tetrads line up at the cell equator.

IPM

AT

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Anaphase I

� Same as Mitosis Anaphase

� Difference:

� Homologous chromosome pair separate and go BACK toward the poles, instead of the sister chromatids.

� This creates HAPLOID CELLS.

� Maternal and paternal chromosomes mix.IPM

AT

Telophase & Cytokinesis I

� Same as Mitosis Telophase & Cytokinesis, nucleus is back to normal and cells divide into two.

� Difference:

� Two HAPLOID cells

� Each chromosome still has two sister chromatids, but NO homologous chromosomes are present. IP

MA

T C

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Prophase II

� Chromosomes condense

� NO DUPLICATION!!!IP

MA

T

Metaphase II

� Chromosomes line up at the equator

� Spindle fibers attach to each sister chromatid

IPM

AT

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Anaphase II

� Sister chromatids pull apart and move BACK to the poles

IPM

AT

Telophase & Cytokinesis II

� Nuclear membrane and nucleolus reappear

� Aster rays and spindle fibers disappear

� Cytokinesis produces 4 haploid cells

IPM

AT

C

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Telophase & Cytokinesis II

IPM

AT

C

Meiosis I

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Meiosis II

Mitosis vs. Meiosis

Mitosis Meiosis

Nickname“Normal” cell

division“Reduction” cell

division

Starting Cell � Ending Cell2n (diploid) � 2n

(diploid)2n (diploid) � n

(haploid)

Starting Cell Type �Ending Cell Type

Somatic � SomaticGerm �Gametes

# of Cell Divisions 1 2

# Start Cell � # Cells Produced

1 cell � 2 cells 1 cell � 4 cells