This document summarizes key aspects of cell division and chromosomes. It explains that chromosomes form through coiling of chromatin and contain genes made of DNA. Humans have 23 pairs of homologous chromosomes. The cell cycle is described, including the phases of interphase, mitosis, and cytokinesis. Mitosis allows organisms to grow and repair tissues. The specific stages of mitosis - interphase, prophase, metaphase, anaphase and telophase - are then outlined in detail. The roles of centrioles, spindle fibers and chromosomes are explained. Cancer is summarized as uncontrolled cell growth beyond a single layer due to loss of cell cycle controls.

1. Life sciences

2. CHROMOSOMES
 Chromosomes form when the chromatin network in the
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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
CHAPTER 11 P. 164
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
BioFlix: Mitosis

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
Chapter 11 p.170-171
 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.

16. Ovarian cancer cells
Ovarian cancer cells
dividing
Breast tumor

17. Credit to
 J.Williamson
 E.Pretorius
 P. Stewart
 R Drevale
 K.Segui