1. Cell Growth and Division

2. Cell Division — process by which a cell divides into 2 new cells
Why do cells need to divide?
Living things GROW by producing more cells, NOT because each cell increases in size; If cell gets too big, it cannot get enough nutrients into the cell and wastes out of the cell
REPAIR of damaged tissue
REPRODUCTION

3. Types of Cell Reproduction
Asexual reproduction - single cell dividing to make 2 new, identical daughter cells
Ex: Mitosis & binary fission
Sexual reproduction - egg & sperm joining to make a zygote, NOT identical to the original cells
Ex: Meiosis

4. Cell Division in Prokaryotes (Binary Fission)
Parent cell
Chromosome (plasmid) doubles
Cell splits
2 identical daughter cells

5. Animation of Binary Fission

6. Cell Division
in Eukaryotes

7. Parent Cell 2 Daughter Cells Cell Division
The original cell is called the parent cell; 2 new cells are called daughter cells
Before cell division occurs , the cell replicates (copies) all of its DNA, so each daughter cell gets complete set of genetic information from parent cell
Each daughter cell is exactly like the parent cell – same kind and number of chromosomes as the original cell
2 Daughter Cells
Parent Cell

8. DNA
DNA is located in the nucleus and controls all cell activities including cell division
Long and thread-like DNA in a non-dividing cell is called chromatin
Doubled, coiled, short DNA in a dividing cell is called chromosome
Consists of 2 parts: chromatid and centromere

9. 2 identical “sister” chromatids attach at an area in the middle called a centromere
When cells divide, “sister” chromatids separate and 1 goes to each new cell

10. Coils up into chromosomes
Chromatin to chromosomes illustration:
Chromatin
Coils up into chromosomes
Duplicates itself
Why does DNA need to change from chromatin to chromosome?
More efficient division

11. Eukaryotic Chromosomes
Eukaryotic cells store genetic information in chromosomes
Eukaryotes can have 10 to 50 chromosomes in their body cells (somatic).
Human body cells have 46 chromosomes or 23 identical pairs.

12. Chromosomes Every organism has its own specific number of chromosomes
Human = 46 chromosomes or 23 pairs
Dog = 78 chromosomes or 39 pairs
Goldfish = 94 chromosomes or 47 pairs
Lettuce = 18 chromosomes or 9 pairs

13. All somatic (body) cells in an organism have the same kind and number of chromosomes.
Ex: Human = 46 chromosomes
Human skin cell = 46 chromosomes
Human heart cell = 46 chromosomes
Human muscle cell = 46 chromosomes
Fruit fly = 8 chromosomes
Fruit fly skin cell = 8 chromosomes
Fruit fly heart cell = 8 chromosomes
Fruit fly muscle cell = 8 chromosomes

14. Cells prepare for Division Cell Divides into Identical cells
The Cell Cycle
DNA Copied
Cells Mature
Cells prepare for Division
Daughter Cells
Cell Divides into Identical cells

15. Interphase - G1 Stage 1st growth stage
Cells mature by making more cytoplasm & organelles
Cell carries on its normal metabolic activities

16. Two identical copies of DNA
Interphase – S Stage
Synthesis stage
DNA is copied or replicated
Two identical copies of DNA
Original DNA

17. Interphase – G2 Stage 2nd Growth Stage
Occurs after DNA has been copied
Both organelles & proteins are synthesized

18. Mitosis Division of the nucleus Only occurs in eukaryotes
Has four stages
Doesn’t occur in some cells such as brain cells

19. 1st Phase (Prophase) Longest Phase
DNA and proteins condense (PACK) into chromosomes
Nuclear membrane breaks apart (or pops)

20. 1st Phase: DNA PACKS into Chromosomes

21. 2nd Phase (Metaphase)
Chromosomes line up across the center (middle) of the cell
Spindle fibers attach at centromere

22. 2nd Phase: Chromosomes line up in the MIDDLE of the cell

23. 3rd Phase (Anaphase) Centromeres divide Spindle fibers shorten
Sister chromatids separate (move apart) into individual chromatids
Spindle fibers pull the chromatids to opposite sides of the cell
Chromatids are now called
Each ½ of the pair is now called a chromosome

24. 3rd Phase: Chromosomes are pulled APART to opposite ends of the cell

25. 4th Phase: (Telophase)
Chromosomes gather at opposite ends of the cell and lose their shape
Two new nuclear membranes form

26. 4th Phase: TWO new cells are formed (still attached)

27. Cytokinesis
Division of cell into two, identical halves called daughter cells
In plant cells, cell plate forms at the equator to divide cell
In animal cells, cleavage furrow forms to split cell

28. Mitosis Dance Review Discuss the following with your table:
 1. What color shirts were the kids wearing who were part of the cell membrane?
2. The students in the white shirts represent what organelle?
3. What color shirts were the kids wearing who were the chromosomes?
4. What did the kids do during metaphase?
5. How many cells were there at the end of mitosis?

29. Uncontrolled Mitosis
DNA controls all cell activities including cell division
Some cells lose their ability to control their rate of cell division – the DNA of these cells has become damaged or changed (mutated)
These super-dividing cells form masses called tumors

30. Benign tumors are not cancerous – these cells do not spread to other parts of the body
Malignant tumors are cancerous – these cells break loose and can invade and destroy healthy tissue in other parts of the body (called metastasis)

31. Cancer is not just one disease, but many diseases – over 100 different types of cancers

32. Meiosis Formation of Gametes (Egg,Sperm,Pollen,Ovule)

33. Why Do we Need Meiosis?
It is the fundamental basis of sexual reproduction
Two haploid (1n) gametes are brought together through fertilization to form a diploid (2n) zygote

34. Fertilization

35. Meiosis
Daughter cells contain half the number of chromosomes as the original cell
Produces gametes
Occurs in the testes in males (Spermatogenesis)
Occurs in the ovaries in females (Oogenesis)
rossing-over occurs and causes greater genetic variety

36. Meiosis

37. Four sperm cells are made from meiosis.
They are carrying one of each chromosome.
Four eggs cells are made.
Three are very small and called polar bodies. They die.

38. Meiosis Forms Haploid Gametes
Meiosis must reduce the chromosome number by half
Fertilization then restores the 2n number
from mom
from dad
child
meiosis reduces
genetic content

39. This is a Karyotype. It shows the Homologous chromosomes.

40. Crossing-Over Homologous chromosomes in a tetrad cross over each other
Pieces of chromosomes or genes are exchanged
Produces Genetic recombination in the offspring

41. Why would genes on separate chromosomes be inherited differently than genes on the same chromosome?
Independent assortment of chromosomes leads to greater genetic variety!

42. Genetic variation in sexually reproducing organisms
1. Crossing over- during meiosis, homologous chromosomes exchange DNA

43. Genetic variation in sexually reproducing organisms
2. Gene mutation- when the DNA changes
3. Fertilization- gametes join in sexual reproduction.

44. Genetic variation in sexually reproducing organisms
4. Nondisjunction - Occurs when the homologous chromosomes do not separate properly during meiosis. Results in a wrong # of chromosomes and conditions such as Down syndrome.

45. Comparison of Divisions
Mitosis
Meiosis
Number of divisions 1 2
Number of daughter cells 4
Genetically identical?
Yes No
Chromosome #
Same as parent
Half of parent
Where
Somatic cells
Germ cells
When
Throughout life
At sexual maturity
Role
Growth and repair
Sexual reproduction