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Notes Cell Division _ the Cell Cycle _Ch. 12_

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					Notes: Cell Division & the
   Cell Cycle (Ch. 12)
• One of the major characteristics of a
 living thing is the ability to GROW.

• What does growth mean in terms of
 the cell? Bigger cells or more cells?
Why more cells?

• cell size is limited by its surface
  area to volume ratio (SA:V)
  – if a cell gets too large, it wouldn’t be
    possible for it to get oxygen/nutrients
    in and wastes out by diffusion
            Cell Division
• In simple terms: 1 cell divides into 2
  new cells
3 main stages of the Cell Cycle
  1. Interphase
    •   longest stage (90%); preparation for
        cell division
  2. Mitosis (10%)
    •   nucleus divides into 2 nuclei, each with
        the same # and kind of chromosomes
        (DNA) as the parent cell
  3. Cytokinesis
    •   cytoplasm divides forming 2 distinct
        cells
Cell Cycle
        G1 = growth (producing
        proteins & organelles)


        S = DNA Synthesis
        (duplicated) & more
        growth


        G2 = growth &
        completes preparation
        for division
• MITOSIS = the division of the
  nucleus




• Why is it important that the
  nucleus divides?
  – it stores the DNA (information of life)
  – all new cells need this information
 • Chromosomes = tightly
   coiled chromatin
   (DNA); consist of 2
   identical chromatids
   (sister chromatids);
   which are connected in
   the center by a
   CENTROMERE


**a human cell entering mitosis contains
 46 chromosomes (=DIPLOID number)
           chromosome




                    centromere
      chromatin




DNA
How Does Chromatin Coil so Tightly?
• Chromatin wraps around 8 histone proteins
• A second type of histone (H1) holds the
  nucleosome “beads” together to increase
  compaction further
Mitosis is one, continuous event, but it can
 be described as happening in 5 phases:


1.   Prophase
2.   Prometaphase
3.   Metaphase
4.   Anaphase
5.   Telophase
**Remember, the cell
  is coming out of
    Interphase…
PROPHASE
    • chromatin condenses
      & chromosomes
      become visible

    • Centrosomes/
      centrioles separate
      and start to move to
      the opposite sides of
      the nucleus;
PROMETAPHASE
      • nuclear envelope
        breaks down and the
        nucleolus disappears

      • spindle fibers (from
        centrioles) connect to
        chromosomes at their
        centromeres
        (kinetochore);
                METAPHASE
• **chromosomes line up in
  the center of the cell
  (metaphase plate);

 **fibers connect from
 the poles (end) of the
 spindle to the
 centromere/kinetochore
 of each chromosome
ANAPHASE
   • centromeres split,
     causing the sister
     chromatids to
     separate, becoming
     individual chromosomes

   • chromosomes are
     pulled apart to opposite
     ends of the cell
                 TELOPHASE
•   chromosomes uncoil into
    chromatin;

•   new nuclear envelope
    forms around the
    chromatin

•   spindle breaks apart

•   nucleolus reappears in
    each new nucleus
   Finally…
 CYTOKINESIS
• in animal cells: cell
  membrane pinches
  in & divides
  (cleavage furrow)
• in plant cells: a cell
  plate (new cell wall)
  forms
Then the cell returns to
 Interphase… and the
   process continues
     Which of the following processes take SL
           place during interphase?
A.   Cell division
B.   Cell division & Active Transport
C.   Active Transport & Protein Synthesis
D.   Active Transport, Protein Synthesis, Replication of DNA
              How are all cells formed?
A.   By cell division
B.   By mitosis
C.   By fragmentation
D.   By cytokinesis
                   Chromatids are
A.   Made of microtubules
B.   Bacterial chromosomes
C.   Strands of duplicate genetic material
D.   Supercoils of protein
       What is the correct order for Mitosis?
A. Interphase, Prophase, Prometaphase, Metaphase, Anaphase,
   Telophase
B. Prophase, Prometaphase, Metaphase, Anaphase, Telophase
C. Telophase, Anaphase, Metaphase, Prometaphase, Prophase
D. Interphase, Prophase, Prometaphase, Metaphase, Anaphase,
   Telophase, Cytokinesis
     This cell is in which phase of Mitosis?
A.   Prophase
B.   Prometaphase
C.   Anaphase
D.   telophase

				
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