1. The Cell Cycle and How Cells Divide

2. Phases of the Cell Cycle
Interphase – normal cell activity
The mitotic phase – cell division
Cytokinesis - division of cytoplasm
INTERPHASE
Growth
G 1
(DNA synthesis)
Growth G2
Cell Divsion

3. Functions of Cell Division
20 µm
100 µm
200 µm
(a) Reproduction. An amoeba, a single-celled eukaryote, is dividing into two cells. Each new cell will be an individual organism (LM).
(b) Growth and development This micrograph shows a sand dollar embryo shortly after the fertilized egg divided, forming two cells (LM).
(c) Tissue renewal. These dividing bone marrow cells (arrow) will give rise to new blood cells (LM).

4. Cell Division Results in genetically identical daughter cells
Cells duplicate their genetic material before they divide, ensuring that each daughter cell receives an exact copy of the genetic material, DNA

5. DNA
Genetic information - genome
Packaged into chromosomes

6. DNA
Chromatin: DNA in its “unwound” state.
Sister Chromatids: Two identical sides of a chromosome attached by a centromere
Chromosome: Condensed DNA

7. Chromosomes
Most eukaryotes have between 10 and 50 chromosomes in their body cells.
Human cells have 46 chromosomes/23 pairs
Karyotype: a picture of chromosomes

8. Chromosomes
In a diploid cell, the chromosomes occur in pairs. The 2 members of each pair are called homologous chromosomes or homologues.
Same length
Control same traits
One from mom; one from dad
Sex chromosomes
Are distinct in their characteristics
Are represented as X and Y
XX: female, XY: male

9. Chromosomes A diploid cell has two sets of each of its chromosomes
A human has 46 chromosomes (2n = 46)
In a cell in which DNA synthesis has occurred all the chromosomes are duplicated and thus each consists of two identical sister chromatids
**the number of chromosomes has not changed, only the appearance has changed from a single rod to a double rod shape
Maternal set of
chromosomes (n = 3)
Paternal set of
2n = 6
Two sister chromatids
of one replicated
chromosome
Two nonsister
chromatids in
a homologous pair
Pair of homologous
chromosomes
(one from each set)
Centromere

10. More about Homologues Homologous chromosomes: Look the same
Control the same traits
May code for different forms of each trait
***homologous chromosomes are not the same as sister chromatids

11. Non-sister chromatids Two duplicated chromosomes
Chromosome Duplication
Because of duplication, each condensed chromosome consists of 2 identical chromatids joined by a centromere.
Each duplicated chromosome contains 2 identical DNA molecules (unless a mutation occurred), one in each chromatid:
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Two unduplicated
chromosomes
Centromere
Sister
chromatids
Duplication
Non-sister chromatids
Two duplicated chromosomes

12. Structure of Chromosomes
The centromere is a constricted region of the chromosome containing a specific DNA sequence, to which is bound 2 discs of protein called kinetochores.
Kinetochores serve as points of attachment for microtubules that move the chromosomes during cell division:
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Metaphase chromosome
Kinetochore
microtubules
Centromere
region of
chromosome
Sister Chromatids

13. Structure of Chromosomes
Diploid - A cell possessing two copies of each chromosome (human body cells).
Homologous chromosomes are made up of sister chromatids joined at the centromere.
Haploid - A cell possessing a single copy of each chromosome (human sperm and egg).

14. Phases of the Cell Cycle
Interphase
G1 - primary growth
S - genome replicated
G2 - secondary growth
M - mitosis
C - cytokinesis

15. Mitosis: nuclear division.
Produces 2 new cells that are both genetically identical to the original cell.
DNA duplication during interphase
Mitosis
Diploid Cell

16. Interphase Phase that a cell spends a majority of its life-span
Growth phase
Chromosomes are duplicated here
Precedes mitosis
Divided into three parts
G1: protein synthesis is high as cell grows
S : chromosomes are replicated and divide to form sister chromatids
G2: chromosomes coil, proteins are being synthesized as cell prepares for mitosis

17. Prophase First and longest mitotic stage
Chromatin coils into chromosomes
Sister chromatids are form
Nuclear envelope begins to disappear
Centrioles begin to migrate to opposite ends of the cell (ANIMAL cells only)
Spindle fibers form between the centrioles

18. Metaphase Short, second phase of mitosis
Chromosomes attach to spindle fibers
Chromosomes line up on the midline of the spindle

19. Anaphase Centromeres split Chromatids separate
Chromatids are pulled apart by spindle fibers

20. Telophase Final phase Chromatids reach opposite sides of the cell
Chromosomes unwind
Spindle disappears
Nuclear envelope reappears

21. Cytokinesis Cleavage of cell into two halves Animal cells
Forms a cleavage furrow
Plant cells
Forms a cell plate

22. Cytokinesis In Animal And Plant Cells
Cleavage furrow
Contractile ring of microfilaments
Daughter cells
100 µm
1 µm
Vesicles forming cell plate
Wall of patent cell
Cell plate
New cell wall
(a) Cleavage of an animal cell (SEM)
(b) Cell plate formation in a plant cell (SEM)
Daughter cells

23. Mitosis in Plant Cells