1. Cell Division
Part 1

2. A Generalized Cell (b) Animal cell Golgi body Nuclear envelope
Chromosomal
DNA
Nucleus
Nucleolus
Polyribosomes
Ribosome
Rough ER
Cytoplasm
Membrane protein
Plasma membrane
Smooth ER
Mitochondrion
Centrioles
Microtubules
Microfilaments
Lysosome
(b) Animal cell

3. The Cell Cycle Synthesis Gap 1 Gap 2 DNA Synthesis Growth
Interphase S
Synthesis G1 G2
Gap 1 M
Gap 2
Mitosis
Cytokinesis
Prophase
Telophase
Anaphase
Growth
Gene expression
Differentiation
Metaphase
Prometaphase
Two
daughter
cells
Gene expression
Quality control
Actual division process

4. Three Little Words Geneticist Need to Hear… Homolog, Loci, Allele
Gene loci (location)
Unreplicated chromosome pair A b c
Homologous
pair of
chromo-
somes A B c
Genotype: AA Bb cc
Homozygous
for the
dominant
allele
Heterozygous
Homozygous
for the
recessive
allele

5. Replicated Chromosome
Pair of sister chromatids
Centromere
(DNA that is
hidden beneath
the kinetochore
proteins)
Kinetochore
proteins
One
chromatid
(dark blue)
One
chromatid
(light blue)
(a)
(b)

6. Chromatids, Chromosomes… What the…
At the end of S phase, a cell has twice as many chromatids as there were chromosomes in G1 phase
i.e. - human cell
46 chromosomes in G1 phase
46 pairs of sister chromatids in G2 phase
chromosome is therefore a relative term
In G1, anaphase, & telophase it refers to the equivalent of one chromatid
In G2, prophase, & metaphase, it refers to a pair of sister chromatids

7. Interphase Chromosomes are decondensed chromosomes replicate
Two centrosomes,
each with centriole pairs
Nuclear membrane
Chromosomes are decondensed
chromosomes replicate
The centrosome divides
Chromosomes

8. Prophase Nuclear envelope dissociates
Microtubules
forming mitotic spindle
Sister chromatids
Nuclear envelope dissociates
Centrosomes move to opposite poles
mitotic spindle apparatus forms
Centromere

9. (d) METAPHASE Astral microtubule Metaphase plate Polar microtubule
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Astral microtubule
Metaphase
plate
Polar microtubule
Kinetochore
proteins attached
to centromere
Kinetochore microtubule
(d) METAPHASE

10. Spindle Apparatus Composed of microtubules originated from centrioles
Microtubules are formed polymerization of tubulin proteins
3 types of spindle microtubules
Aster microtubules
Important for positioning of the spindle apparatus
Polar microtubules
Help to “push” the poles away from each other
Kinetochore microtubules
Attach to kinetochore , at the centromere

11. Kinetochore Spindle Fibers
Figure 3.8

12. Spindle fibers bind kinetochores
Prometaphase
Nuclear membrane
fragmenting
Spindle fibers bind kinetochores
The two kinetochores on a pair of sister chromatids are attached to kinetochore MTs from opposite poles
Mitotic
spindle
Spindle pole

13. Metaphase
Astral microtubule
Pairs of sister chromatids align themselves at the metaphase plate
Metaphase
plate
Polar microtubule
Kinetochore
proteins attached
to centromere
Kinetochore microtubule

14. Anaphase Centromeres separate
Chromosomes
Centromeres separate
Each chromatid, is linked to only one pole
As anaphase proceeds
Kinetochore MTs shorten
Chromosomes move to opposite poles
Polar MTs lengthen
Poles themselves move further away from each other

15. Telophase & Cytokinesis
Chromosomes reach poles & decondense
Nuclear membrane reforms
Quickly followed by cytokinesis
In animals
Formation of a cleavage furrow
In plants
Formation of a cell plate

16. Some Key Points
Mitosis ultimately produces two daughter cells genetically identical to the mother cell
Barring rare mutations
Processes requireing mitotic cell division
Development of multicellularity
Organismal growth
Wound repair
Tissue regeneration