2. TERM
• Chromosome
– A structure made of DNA and histones
• DNA (deoxyribonucleic acid)
– A polynucleotide that contains the pentose sugar
deoxyribose.
• Chromatid
– One of two identical parts of a chromosome held
together by a centromere
• Centromere
– The centralize region joining two sister chromatids
3. • Genome
– The complete complement of an organism’s genes
– An organism’s genetic material
• Chromatin
– Content of the nucleus
– Consisting of protein, DNA and RNA, which form threads
• Euchromatin
– Loosely packed chromatin
• Heterochromatin
– Densely packed chromatin
• Cytokinesis
– Division of the cytoplasm during cell division
4. • Karyokinesis
– Division of the nucleus during cell division
• Gene
– Functional unit of heredity
– Composed of DNA which carries information from
one generation to the next
• Gamete
– A haploid cell, formed by meiotic cell division of a
germ cell
– Required for sexual reproduction
5. The concept of cell division
• Basic characteristics of cell division
• Characteristics of cell survival, DNA and
chromosome
6. THE CONCEPT OF CELL DIVISION.
• Modern cell theory states that ‘All new cells
are derived from other cell’.
– All cells which comprise a human are derived,
through the cell division, from single zygote formed
by the fusion of two gametes.
– These gametes in turn were derived from the
division of certain parental cell.
7. There are two basic types:
1.Mitosis which results in all daughter cells
having the same number of chromosomes
as the parent.
2. Meiosis which results in the daughter cells
having only half the number of
chromosomes found in the parent cell.
8. • Cell division
– involves the distribution of identical genetic material
(DNA) to two daughter cells.
• A dividing cell
– duplicates its DNA, allocates the two copies to
opposite ends of the cell
– then split into daughter cells.
9. The cell cycle
• Description of the four stages in the cell cycle
• General explanation events during the G1, S
and G2 followed by events in the mitotic
phase.
10. THE CELL CYCLE.
1. The complete sequence of
events in the life of an
individual diploid cell.
2. The four stages of the cell
cycle;
i. G1
• The first growth Phase
ii. S Phase
iii. G2
• The second growth phase
iv. Mitotic Phase
11. i. G1 - The first growth
phase
• The longest phase
• Volume of cytoplasm
increase
• Protein synthesis
• Increase number of
organelles
12. ii. S phase
• DNA synthesis phase
• The cell’s DNA replicates
and non consist of two
identical chromatids.
iii. G2 - The second growth
phase
• Energy stores are increased.
13. iv. Mitosis
• This process of
nuclear division and
followed by division
of cytoplasm called
cytokinesis.
14. Mitosis
• Explain the mitotic cell division using diagrams and
photographs
• Show the position of the chromosomes at each stage
• State the changes in the chromosomes
• Describe briefly the cytokinesis process and list the
differences between cell division in animal and plant
cells
• Significances of mitosis
15. MITOSIS
2 phases :
i. nucleus division ( karyokinesis )
ii. cytoplasm division ( cytokinesis )
4 stages:
i. prophase
ii. metaphase
iii. anaphase
iv. telophase.
17. Prophase
• Chromosomes
– visible as long, thin tangled threads.
– shorten and thicken
– comprise two chromatids joined at the
centromere.
• Centrioles
– migrate to opposite ends of poles of the cell
(except for plant).
– microtubules develop and form a star-shaped
structure called an aster.
– Some of these microtubule, called spindle fibers,
span the cell from pole to pole.
• The nucleolus disappears
• Nuclear envelope disintegrates
19. Metaphase
• The chromosomes
arranged themselves at
the centre of equator of
the spindle, and become
attached to certain
spindle fibers at the
centromere.
• Contraction of these
fibers draws the
individual chromatids
slightly apart.
21. Anaphase
• The centromeres split and further shortening of the spindle fibers causes the
two chromatids of each chromosome to separate and migrate to opposite
poles.
• The shorting of the spindle fibers is due to the progressive removal of the
tubulin molecules of which they are made.
• The energy for this process is provided by mitochondria which are observed
to collect around the spindle fibers.
23. Telophase
• The chromatids reach their respective poles and a new nuclear envelope
forms around each group.
• The chromatids uncoil and lengthen, thus becoming invisible again.
• The spindle fibers disintegrate and nucleolus reforms in each new nucleus.
25. Cytokinesis – division of cytoplasm
In Animal Cells
• Occur by a process known
as cleavage.
• The first sign of cleavage is
the appearance of cleavage
furrow. (Begins as a
shallow growth in the cell
surface)
26. Cytokinesis – division of cytoplasm
In Plant Cells
• Have walls but no cleavage furrow.
• During telophase, vesicles derived
from Golgi apparatus move along
microtubules to the middle of the cell
producing a cell plate.
• The cell plate enlarges until its
surrounding membrane fuses with the
plasma membrane along the perimeter
of the cell.
• Two daughter cells result, each with its
own plasma membrane. A new cell
wall arising from the contents of the
cell plate has formed between the
daughter cells.
28. Differences between mitosis in plant and animal cells
Animal Cells Plant Cells
1. Involve aster or 1. Do not form
spindle formation. centrioles and lack
centrioles.
2. Cytokinesis occurs 2. Occurs by the
by the constriction growth of a cell
of microtubules – plate through the
cleavage furrow. fusion of vesicles.
29. Significance of mitosis
Genetic stability
• Mitosis produce two nuclei which have the same
number of chromosomes as the parent cell.
• Daughter cells are genetically identical to the
parent cell and no variation in genetic information
can be introduced during mitosis.
• This result in genetic stability within populations of
cells derived from the same parental cells.
30. Significance of mitosis
Growth
• The number of cell within organism increases by mitosis and this is the
basis of growth in multicellular organisms.
Cell replacement
• Replacement of cells and tissues involves mitosis.
Regeneration
• Some animal are able to regenerate whole parts of the body, such as
legs in crustacea and arms in star fish. Production of the new cells
involve mitosis.
Asexual reproduction
• Mitosis is the basis of asexual reproduction, the production of new
individuals of a species by one parent organism.
