Cell growth and division
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Cell Growth and Division. Cell division is needed to…. Grow – most organisms grow by producing more cells Repair wounds and damaged cells Develop and change. Why do cells divide? (aka, why are cells small?). Two main reasons why cells can’t grow indefinitely:

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Cell Growth and Division

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Cell growth and division

Cell Growth and Division


Cell division is needed to

Cell division is needed to…

  • Grow – most organisms grow by producing more cells

  • Repair wounds and damaged cells

  • Develop and change


Why do cells divide aka why are cells small

Why do cells divide?(aka, why are cells small?)

  • Two main reasons why cells can’t grow indefinitely:

    • A larger cell places more demands on its DNA (more things to control and not enough DNA)

    • Surface-to-volume ratio decreases as size increases

  • Thus, before the cell becomes too large, it divides


When do cells divide or stop

When do cells divide (or stop)?

  • When cells crowd each other, they stop dividing

  • When internal factors signal the cell to start or stop dividing

    • e.g., p53 gene makes sure the cell doesn’t divide until chromosomes have doubled; cyclin enzymes start/stop the cell cycle

  • When external chemical or physical signals (growth regulators) stimulate or inhibit growth and division

    (Cancer is an example of uncontrolled cell growth….we will discuss cancer later in the unit)


Cells divide at different rates

Cells divide at different rates

  • The rate of cell division varies with the need for the type of cell…


What is the cell cycle

What is the cell cycle?

  • The series of phases that cells go through as they grow and divide.

  • A continuous process, but we divide it into 3 stages:

    • Interphase

    • Mitosis

    • Cytokinesis

http://images1.clinicaltools.com/images/gene/celldivision/cellcycle.jpg


Stage 1 interphase

Stage 1: Interphase

  • Cell life between divisions

  • The longest stage!

  • Nucleus is still present

  • Phases:

    • Gap 0 (G0) – grows and functions

    • Gap 1 (G1)– duplicates organelles and molecules needed for cell division

    • Synthesis (S) – duplicates DNA (in chromotin form)

    • Gap 2 (G2 ) – checks for errors


Stage 2 mitosis

Stage 2: Mitosis

  • Duplication and division of the cell nucleus

  • Phases:

    • Prophase

    • Metaphase

    • Anaphase

    • Telophase


Stage 3 cytokinesis

Stage 3: Cytokinesis

  • Pinching off of the cytoplasm

  • (Often grouped as part of mitosis)

    Mitosis + cytokinesis result in two identical daughter cells!

YouTube:

Mitosis


Now let s look at your mitosis flipbook and compare

Now!, Let’s look at your Mitosis Flipbook and compare…


Review interphase

(Review…) Interphase

  • Nucleus is still intact and the nucleolus is visible.

  • DNA is in chromatin form

  • Includes G1, S, and G2


Mitosis step 1 prophase

Mitosis step 1: Prophase

  • Centrioles separate and produce spindle fibers

  • Chromatin condenses to form chromosomes

  • Nuclear envelope and nucleolus break down

    prophase → pro (#1!)


Chromatin chromosomes

Chromatin? Chromosomes?

Chromatin= DNA unwound (looks like spaghetti)

Chromosome= DNA condensed and organized; looks like this: 2 chromosomes

Sister chromatids= a duplicated chromosome

Centromere = the place where chromotids are connected

Some useful DNA vocabulary!


Cell growth and division

To recap…

During prophase, chromatin condense into chromosomes… which have duplicated into sister chromatids, attached to each other at their centromeres.


Mitosis step 1 prophase1

Mitosis step 1: Prophase

  • Centrioles separate and produce spindle fibers

  • Chromatin condenses to form chromosomes

  • Nuclear envelope and nucleolus break down

    prophase → pro (#1!)


Mitosis step 2 metaphase

Mitosis step 2: Metaphase

  • Chromosomes line up at the middle of the cell

  • A spindle fiber attaches to each sister chromatid at the centromere

    metaphase → middle


Mitosis step 3 anaphase

Mitosis step 3: Anaphase

  • Spindle fibers contract and pull apart the chromosomes to opposite ends of the cell

    anaphase → apart


Mitosis step 4 telophase

Mitosis step 4: Telophase

  • Chromosomes return to chromatin form

  • Nuclear membranes and nucleolus reform

  • Spindle fibers disappear

  • Nuclear division is complete

    telophase → telephone


After mitosis stage 3 cytokinesis

After mitosis…Stage 3: Cytokinesis

  • Pinching of the cytoplasm, resulting in two identical daughter cells.

The cell cycle:

IPMATC

I

Passed

My

Algebra

Test with a

“C”

YouTube:

Mitosis Video

Mitosis Review


Mitosis in plants

Mitosis in plants

  • Plants don’t have centrioles

  • Cell plate forms during telophase

  • During cytokinesis, cell plate separates the daughter cells and becomes the new cell wall

Blood lily mitosis


Mitosis in real cells pmat

Mitosis in real cells…PMAT


Where doesn t mitosis happen

Where doesn’t mitosis happen?

  • Nerve and blood cells are different

  • Sex cells (gametes) undergo a different division process


Your summary

Your summary…


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