CELL DIVISION.

Presentation on theme: "CELL DIVISION."— Presentation transcript:

1 CELL DIVISION

2 According to the cell theory: all cells come from preexisting cells
According to the cell theory: all cells come from preexisting cells. Why, when and how cells divide is the subject of this unit.   Simply put, cells divide to make more cells.

3 Cells reproduce in order to make new cells.
Reproduction Cells reproduce in order to make new cells. A bacterium divides to become two bacteria.

4 Growth An organism gets larger because its cells reach a certain size and then divide Each one of us started out as a single cell no bigger than the period at the end of this sentence.

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10 Cells divide in order to repair or replace worn out or damaged cells.
Repair and Replacement Cells divide in order to repair or replace worn out or damaged cells. Young cells (human) Old cells (human)

11 Here’s Kim Kardashian after an unfortunate sun tanning incident
Here’s Kim Kardashian after an unfortunate sun tanning incident. poor Kim fell asleep with her sunglasses on after tanning and woke up looking like this. how many skin cells did Kim damage….? Lucky for Kim, cells divide when damaged or need to be replaced.

12 The damaged cells of a skinned knee will divide quickly
Patrick Robinson’s Injured hamstring will heal as a result of the muscle and tendon cells diving.

13 What causes a Cell to Divide?
Cells grow to a certain size and then divide. Bozeman Science Video The efficiency of moving materials into the cell decreases as the cell becomes larger. The volume of the cell increases faster then its surface area. Cells that grow too large no longer have enough surface area to take in nutrients and remove waste

14 Chromosomes - Video A chromosome is DNA in a coiled, rod-shape form that occurs during cell division. The term chromosome originates from the Greek word “chroma” which means color and “soma” meaning body. It is organized into a rodlike body of a tightly coiled chromatin and visible only during cell division. It is a single twisted DNA structure containing thousands of genes that makes up the blueprint of living organisms. The term chromosome originates from the Greek word “chroma” which means color and “soma” meaning body. It is organized into a rodlike body of a tightly coiled chromatin and visible only during cell division. It is a single twisted DNA structure containing thousands of genes that makes up the blueprint of living organisms. Read more:

15 Every species has a characteristic number of chromosomes in each cell
Every species has a characteristic number of chromosomes in each cell. Humans have 46 chromosomes or 23 pairs. The number of chromosomes varies among species but is not an indication of the complexity of the species. Fruit Flies: 8 Carrots: 20 Humans: 46 Fern: 480 Goldfish: 94 Turkey: 82 Potato: 48 PLUM: 48 Chimpanzee: 48

16 Mitosis Mitosis is the division of the cell nucleus in which the chromosomes in the parent cell divide into sets. two identical In mitosis, the number of cells increases without changing the genetic material. Thus, mitosis is like making a photocopy. When injury occurs such as a scrape or burn, new cells grow to replace the damaged ones-this happens as a result of mitosis. Mitosis occurs for the purpose of growth and replacement of worn out or damaged cells.

17 The Stages of mitosis in a plant cell
Mitosis is the part of cell division that divides the nuclear material of the cell.  Each resulting cell will have the same complete set of chromosomes. Mitosis takes place in non-sex cells also known as body cells or somatic cells. Khan Academy Video The Stages of mitosis in a plant cell

18 Controls on Cell Division
Effects of controlled cell growth can be seen by placing some cells in a petri dish containing nutrient broth Cells grow until they form a thin layer covering the bottom of the dish Cells stop growing when they come into contact with other cells If cells are removed, the remaining cells will begin dividing again Something can turn cell division on or off

19 Regulating Cell Growth
Cyclins- proteins that regulate the timing of the cell cycle in eukaryotic cells Internal regulators: proteins that respond to events inside the cell i.e. make sure all chromosomes have been replicated; make sure all chromosomes are attached to the spindle before entering anaphase External regulators: proteins that respond to events outside the cell i.e. embryonic development; wound healing

20 Uncontrolled Cell Growth
Cancer- disorder in which some of the body’s own cells lose the ability to control growth Cancer cells do not respond to the signals that regulate the growth of most cells P53 gene halts the cell cycle until all chromosomes have been properly replicated A damaged or defective p53 gene causes the cells to lose the information needed to respond to signals that would normally control their growth

21 Why this is important About 1 in 4 of us get cancer, 1 in 5 die of it- at least. It’s very much a disease that can be understood at the molecular level. Our understanding has not resulted in the cures we’d like

22 No particular relevance- painted by Van Gogh in the 1880’s!

23 Cancers vary in terms of getting a type of cancer and dying from that type
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24 Basic Properties of cancer cells Video
Uncontrolled- grow at the usual rate, but then keep growing when other cells would normally stop- ignore stopping signals, or grow w/o added signals. Invasive Immortal- normal cells undergo senescence- telomerase is 1 factor. Chromosomal abnormalities- aneuploid

25 Well-behaved- stop growing when they cover the dish.

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27 Not well-behaved- keep growing after they cover the dish.

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29 INTERPHASE Interphase looks like the resting stage, but inside the nucleus a lot is happening!  The nucleus makes a copy of its genetic material (DNA) and the cell gets bigger so it can divide.

30 PROPHASE The DNA strands coil up to form thick rope-like chromosomes that you can see with a light microscope.  The nuclear membrane begins to disintegrate (break down). In animal cells, spindle fibers form and are stretched across the cell by centrioles. Centrioles are the parts of the cell that produce spindle fibers that the chromosomes attach to when they move to opposite ends of the cell. Plant cells do not have centrioles.

31 METAPHASE Chromosomes line up in the middle of the cell.
Can you see the spindle fibers? What do they do? Spindle fibers are what chromosomes attach to in order to move to opposite ends of the cell.

32 ANAPHASE The spindle fibers shorten and pull the centromeres apart.  This causes the chromosomes to move to opposite sides of the cell. Anaphase ends when the chromosomes reach opposite end of the cell. Centromeres are what hold the chromosomes together.

33 TELOPHASE The spindle fibers disappear and the nuclear membrane reforms around each new set of chromosomes.  Chromosomes start to uncoil and form strands of DNA.  Cytoplasmic division takes place to form two identical cells. This is called cytokinesis.

34 Cell Division can be summarized in the following:
Each chromosome makes a copy of itself. Interphase The membrane around the nucleus begins to fade away, the chromosomes begin to shorten and thicken. Prophase Chromosomes line up along the center of the cell. Metaphase The doubled chromosomes begin to separate and move to opposite ends of t cell. Anaphase A nuclear membrane begins to form around both sets of chromosomes. Telophase The cytoplasm separates as a new cell membrane forms. Cytokinesis