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Cell Division and Mitosis

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Title: Cell Division and Mitosis


1
Cell Division and Mitosis
2
Understanding Cell Division
  • What instructions are necessary for inheritance?
  • How are those instructions duplicated for
    distribution into daughter cells?
  • By what mechanisms are instructions parceled out
    to daughter cells?

3
Reproduction
  • Parents produce a new generation of cells or
    multicelled individuals like themselves
  • Parents must provide daughter cells with
    hereditary instructions, encoded in DNA, and
    enough metabolic machinery to start up their own
    operation

4
Division Mechanisms
  • Eukaryotic organisms
  • Mitosis
  • Meiosis
  • Prokaryotic organisms
  • Prokaryotic fission

5
Roles of Mitosis
  • Multicelled organisms
  • Growth
  • Cell replacement
  • Some protistans, fungi, plants, animals
  • Asexual reproduction

6
Chromosome
  • A DNA molecule attached proteins
  • Duplicated in preparation for mitosis

one chromosome (unduplicated)
one chromosome (duplicated)
7
Chromosome Number
  • Sum total of chromosomes in a cell
  • Somatic cells
  • Chromosome number is diploid (2n)
  • Two of each type of chromosome
  • Gametes
  • Chromosome number is haploid (n)
  • One of each chromosome type

8
Human Chromosome Number
  • Diploid chromosome number (n) 46
  • Two sets of 23 chromosomes each
  • One set from father
  • One set from mother
  • Mitosis produces cells with 46 chromosomes--two
    of each type

9
Lots of DNA
  • Stretched out, the DNA from one human somatic
    cell would be more than two meters long
  • A single line of DNA from a salamander cell would
    extend for ten meters

10
Organization of Chromosomes
DNA
one nucleosome
DNA and proteins arranged as cylindrical fiber
histone
11
Cell Cycle
  • Cycle starts when a new cell forms
  • During cycle, cell increases in mass and
    duplicates its chromosomes
  • Cycle ends when the new cell divides

12
Interphase
  • Usually longest part of the cycle
  • Cell increases in mass
  • Number of cytoplasmic components doubles
  • DNA is duplicated

13
Stages of Interphase
  • G1
  • Interval or gap after cell division
  • S
  • Time of DNA synthesis (replication)
  • G2
  • Interval or gap after DNA replication

14
Mitosis
  • Period of nuclear division
  • Usually followed by cytoplasmic division
  • Four stages
  • Prophase
  • Metaphase
  • Anaphase
  • Telophase

15
Control of the Cycle
  • Once S begins, the cycle automatically runs
    through G2 and mitosis
  • The cycle has a built-in molecular brake in G1
  • Cancer involves a loss of control over the cycle,
    malfunction of the brakes

16
Stopping the Cycle
  • Some cells normally stop in interphase
  • Neurons in human brain
  • Arrested cells do not divide
  • Adverse conditions can stop cycle
  • Nutrient-deprived amoebas get stuck in interphase

17
The Spindle Apparatus
  • Consists of two distinct sets of microtubules
  • Each set extends from one of the cell poles
  • Two sets overlap at spindle equator
  • Moves chromosomes during mitosis

18
Spindle Apparatus
one spindle pole
one of the condensed chromosomes
spindle equator
microtubules organized as a spindle apparatus
one spindle pole
19
Stages of Mitosis
  • Prophase
  • Metaphase
  • Anaphase
  • Telophase

20
Early Prophase - Mitosis Begins
  • Duplicated chromosomes begin to condense

21
Late Prophase
  • New microtubules are assembled
  • One centriole pair is moved toward opposite pole
    of spindle
  • Nuclear envelope starts to break up

22
Transition to Metaphase
  • Spindle forms
  • Spindle microtubules become attached to the two
    sister chromatids of each chromosome

23
Metaphase
  • All chromosomes are lined up at the spindle
    equator
  • Chromosomes are maximally condensed

24
Anaphase
  • Sister chromatids of each chromosome are pulled
    apart
  • Once separated, each chromatid is a chromosome

25
Telophase
  • Chromosomes decondense
  • Two nuclear membranes form, one around each set
    of unduplicated chromosomes

26
Results of Mitosis
  • Two daughter nuclei
  • Each with same chromosome number as parent cell
  • Chromosomes in unduplicated form

27
Cytoplasmic Division
  • Usually occurs between late anaphase and end of
    telophase
  • Two mechanisms
  • Cell plate formation (plants)
  • Cleavage (animals)

28
Cell Plate Formation
29
Animal Cell Division
30
Animation of Mitosis
  • Mitosis An Interactive Animation
  • www.biology.arizona.edu/cell_bio/tutorials/cell_cy
    lcle/cells3.html

31
HeLa Cells
  • Line of human cancer cells that can be grown in
    culture
  • Descendents of tumor cells from a woman named
    Henrietta Lacks
  • Lacks died at 31, but her cells continue to live
    and divide in labs around the world
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