This document discusses chromosomes, the cell cycle, and mitosis. It notes that chromosomes form during cell division and contain DNA and genes. The cell cycle consists of interphase, mitosis, and cytokinesis, resulting in two identical cells. Mitosis allows organisms to grow, repair tissues, and reproduce. It occurs in somatic cells and includes prophase, metaphase, anaphase, and telophase where chromosomes separate and two daughter cells form. Cancer occurs when cells lose cell cycle controls and continue dividing uncontrollably.

1. Life sciences
(
Miss Cybil N. Khumalo
University of Johannesburg
201212375@student.uj.ac.za

2. CHROMOSOMES
 Chromosomes form when the chromatin network in the nucleus of
the cell, coil up, shortens and thickens.
 Each organism has a specific amount of chromosomes.
 All humans have 46 chromosomes.
 These chromosomes are arranged in identical pairs called
homologous chromosome pairs –
 Therefore humans have 23 homologous pairs of chromosomes.
 These chromosomes is only visible during cell division processes.
 One chromosome consist of 2 chromatids and one centromere
that attach the chromatids together.
 Each chromatid consist of genes which in turn consist of DNA.

3. CHROMOSOME
STRUCTURE
X and Y chromosomes:
gonosomes/sexchromosomes
Colored bands
represents
different genes

4. THE PHASES OF THE CELL CYCLE
The cell cycle includes the following phases:
 Interphase (include G1- , S- [DNA synthesis] and G2
phase)
 Mitosis
 Cytokinesis
 Growth
The result is 2 identical cells.

5. Why is Mitosis
important?
Allow an organism to
grow.
Repairs damaged
cells/tissue.
Replace dead cells/tissue.
Reproduction in some
simple organisms.

6. Where does Mitosis take place?
 In all somatic cells (include all body cells and
excludes the sex cells – sperm/egg cells)

7. The process of Mitosis.
 CONSIST OF A FEW PHASES:
 INTERPHASE
 PROPHASE
 METAPHASE
 ANAPHASE
 TELOPHASE

8. INTERPHASE
 Cell builds up enough energy for division
process.
 DNA replication occurs
 Cell look normal, like before division

9. PROPHASE
 Nuclear envelope and nucleolus
disappear.
 Chromatin become more tightly
coiled, and condenses into
individual chromosomes.
Chromosomes arrange randomly
in the cell.
 Centrioli move to opposite
poles, with spindle fibers
stretching between them.

10. METAPHASE
 The centrioli reached the opposite poles
with the spindle fibers in between.
 The chromosomes arrange randomly on
the equator, each single chromosome
attaching to a separate spindle fiber by
means of the centromere.

11. ANAPHASE
 The spindle fibers pull tight.
 The centromers attaching the
chromatids of the chromosomes split in
half.
 Daughter chromosomes move to
opposite poles.

12. EARLY TELOPHASE – KARYOKINESIS
(DIVISION OF NUCLEUS
 Daughter chromosomes reach poles.
 Nuclear envelope surrounds
chromosomes.
 Nucleolus reappear at each pole.
 Chromosomes become less condense
forming chromatin.
 Two identical nuclei has been formed

13. LATE TELOPHASE – CYTOKINESIS
(DIVISION OF THE CYTOPLASM)
 Invagination of the cytoplasm and plasma
membrane occurs. (Cleavage furrow forms in
animal cells and a cytoplasmic plate forms in
plant cells)
 Continues until the cell in divided into 2 separate
cells. (Identical to one another and to the original
cell)

14. MITOSIS PROCESS

15. CANCER
 Cancer is caused by the loss of cell cycle controls in
cancer cells.
 Cancer cells usually continue to divide well beyond a
single layer, forming a clump of overlapping cells called
a tumor.
 Malignant tumors invade surrounding tissues and can
metastasize exporting cancer cells to other parts of the
body, where they may form secondary tumors.
 They do not exhibit anchorage dependence or
density dependent inhibition.
(information from Campbell & Reece, Biology: 2010)

16. Ovarian cancer cells
Breast tumor
Ovarian cancer
cells dividing