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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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Presentation Transcript
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

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!

slide14

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

where doesn t mitosis happen
Where doesn’t mitosis happen?
  • Nerve and blood cells are different
  • Sex cells (gametes) undergo a different division process