1. Cellular Reproduction

2. Why Cells Reproduce/Divide
Growth
Cell Repair
Cell Replacement

3. Why do cells multiply and not just grow bigger?
DNA overload:
-the DNA can handle only so many requests for ‘information’
ex: library in growing town
2. Exchange of materials:
-the cell must have enough surface area (cell membrane) to transport waste and nutrients into/out of cell
-cells need HIGH surface area to volume ratio

4. Ratio of Surface Area to Volume in Cells
3:1
2:1

5. -if a cell gets too large, it is difficult to get sufficient amounts of oxygen and nutrients in and out of cell -this is why cells do not grow much even if the organism they are a part of does

6. -before it gets too large, a growing cell divides forming two daughter cells -called cell division -before the cell divides, it replicates(copies) all of its DNA -helps with information b/c each daughter cell gets its own genetic info

7. Chromosomes -carry genetic info -condensed form of DNA and protein -only visible during cell division b/c they come together -are copied before cell division to get two sister chromatids -chromatids are attached by centromeres -most human cells have 46 chromosomes (each with 2 sister chromatids)

9. -a duplicated chromosome has two sister chromatids which become divided during mitosis and are distributed to each daughter cell

10. Cell Cycle -the series of events that cells go through as they grow and divide into two daughter cells -occurs in all cells (except sex cells) -every 20 hours in humans

11. Phases of the Cell Cycle INTERPHASE -longest phase of the cell cycle
Phases of the Cell Cycle INTERPHASE -longest phase of the cell cycle *G1: cell growth/making of organelles *S: chromosomes are copied to prep for mitosis (DNA replication) *G2: making of more organelles in prep for M phase, shortest phase of interphase

12. CELL DIVISION *M: division of the nucleus (mitosis) and the cytoplasm (cytokinesis) occurs -made up of five total steps

14. Interphase -longest part of the cell cycle -3 distinct parts  G1, S, G2 -cell increases in mass -number of organelles doubles -DNA is duplicated

15. Interphase looks like:
Nucleus and nucleolus visible.
chromatin
nuclear membrane
cell membrane
nucleolus

16. Maintaining Chromosome Number
chromosomes (unduplicated) in
parent cell at interphase
same chromosomes (duplicated) in interphase prior to mitosis
mitosis, cytoplasmic division
chromosome (unduplicated)
in daughter cell
at interphase

17. Mitosis – Division of the nucleus
Made up of 4 smaller phases:
Prophase
Metaphase
Anaphase
Telophase
*can last from a few minutes to a few days

18. Prophase longest of the 4 stages (50% of the time)
nucleus and nucleolus disappear
chromosomes become visible
centrioles appear and separate
spindle fibers gap the space in between the two centrioles

19. The Spindle Fibers -a web type structure made up of microtubule fibers
-is essential for mitosis because it arranges the chromosomes into their correct positions to prep for cell division.
Mitotic centre
Click the return button to return to the prophase slide. Or the house button to return to the main menu.
The purpose of the spindle is to organise the chromosomes during mitosis. It is a cradle of microtubule fibres which cause constriction around the centre of the cell, causing the cytoplasm to split.
A cell at metaphase
a spindle
Microtubule

22. Metaphase shortest phase (only a few minutes)
chromosomes line up along the center of the cell
centromeres attach to spindle fibers

23. Anaphase centromeres split
chromatids move towards the separate poles (centrioles)

24. Telophase
chromosomes become invisible again
2 distinct nuclei form

25. CYTOKINESIS: the separation of the cytoplasm between the two daughter cells
begins during anaphase and usually extends past
animal cells:
-membrane pinches in on both sides until they meet in the center
plant cells:
-a cell plate forms (becomes new cell wall)

26. Animal Cell Division

27. Plant Cell Division cell wall former spindle equator
vesicles converging
cell wall
former spindle equator
cell plate

28. REVIEW:

29. Mitosis

30. Mitosis Part One

31. Mitosis Continued

32. Mitosis Song

33. Cell Turnover - The speed of mitosis
-skin and epithelial cells have a rapid turnover in the human body in order to replace the ones constantly being worn away
-cells which make up organs such as the eye and the brain, need not multiply as often once they reach adult size
Extra information and pictures of tumours can be seen by clicking on the tumours button. The forward button will carry on discussing rapidly dividing cells, with pictures. The return button will take you back to the contents page.
The rate at which cells die and are being made is known as cell turnover.
Cells from different parts of the body replicate at different speeds. This is due to the need for new cells. Skin cells are permanently being damaged, so need new cells to replace the old ones which have died. Protected organs, such as the brain don’t need replicating cells for repair, as it rarely gets damaged and no longer needs to grow in size when it reaches adult size. The brain will have a very low cell turnover, especially compared to skin cells.

34. -organs which need to produce new cells continuously have the highest turnover
ex: bone marrow
produces replacement
blood cells
Photographs of red blood cells and sperm cells. The forward button will take you to a slide about tumours.
An animated sperm will appear without warning, simply click to finish the animation.
Red blood cells have no nucleus so they themselves cannot divide mitotically. They are reproduced by the marrow in bones. Red blood cells are always needed for repairing the surface of skin etc, so will have a high turnover.
Sperm cells do have a nucleus, but is a gamete or sex cell. This means it only has one set of chromosomes. The average healthy human male can produce up to 1000 new sperm every second.

35. Cell Division Regulation:
internal regulators: determine when phases occur
ex: cyclin protein
external regulators: respond to events outside cell
ex: hormones
uncontrolled growth is known as cancer

36. Meiosis -a process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell homologous pairs- each chromosome set has one from male and one from female parent

38. diploid- has both sets of homologous chromosomes haploid- has one set of chromosomes diploid (2N)  haploid (N) diploid = full set of chromosomes haploid = half set of chromosomes

39. -meiosis produces 4 haploid gamete cells from one diploid cell gametes cells- sex cells (egg and sperm)

40. -two rounds of cell division in meiosis
-this is how the amount of chromosomes gets cut in half
-homologous chromosomes are separated

41. Meiosis I -first round of division -homologous chromosomes separated Meiosis II -second round of division -chromosome number cut in half

42. MEIOSIS I and II

43. MEIOSIS I -similar to mitosis:. cell prepares for division
MEIOSIS I -similar to mitosis: *cell prepares for division *DNA is replicated BUT: *homologous chromosomes pair up *form a tetrad- made up of 4 chromatids **called synapsis *exchange portions of their genes *called crossing over (this adds to diversity)

46. MEIOSIS II -no interphase II (no more DNA replication) -very similar to mitosis -chromosomes line up as individuals, have already been separated from partner -sister chromatids split

47. PROPHASE II

48. METAPHASE II

50. TELOPHASE II and CYTOKINESIS

51. During meiosis: -chromosomes independently assort (separation of genes during gamete formation) -haploid gametes in men = sperm cell -haploid gametes in women = egg cell *other three cells (in females) are called polar bodies

52. MITOSIS MEIOSIS -2 identical diploid cells -4 different haploid cells
-only in asexual reproduction
-occurs during sexual reproduction
-allows for replacement and growth of cells
-produces gamete cells

53. Meiosis