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Cell Growth & Reproduction MITOSIS. Cell Growth. When a living thing grows it does so by producing more cells INSTEAD of making the cells it has larger Whether it be elephant, human, jellyfish or earthworm – all the cells are about the same size There are two reasons why this happens: - PowerPoint PPT Presentation
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Cell Growth & Reproduction
MITOSIS
Cell GrowthWhen a living thing grows it does so by producing more cells INSTEAD of making the cells it has larger
Whether it be elephant, human, jellyfish or earthworm – all the cells are about the same size
There are two reasons why this happens:
DNA OverloadExchange of Materials
Why are cells so small?
DNA Overload Exchange of Materials
All the information to run a cell is located in the nucleus as a code of DNA
If the cell were to get bigger and bigger there would not be enough “information” to run the whole cell
The cell must transport everything it needs through the membrane
If there isn’t enough membrane space, cells can’t get or get rid of what they need.
So there must be a balance between surface area (room to move stuff in & out) and volume (stuff)
Why must cells divide?What does the Cell Theory say?
3 Major Reasons Cells Divide:
◦Growth – you start as one cell◦Development – you get bigger, learn
& change◦Repair – your cells get worn out
What does a cell need to survive?
A FULL set of genetic material (DNA or RNA)
Biggest hurdle to cell division is making sure each cell transfers ALL the DNA when it makes new cells
This gets more difficult as there becomes more DNA to transfer
A Cell’s LifeA cell’s life can be divided into 2 stages:
Interphase (3 Parts) – Non-dividing stages
Gap 1 (G1)Growth phase #1 – cells get biggerMost cells are found in this phase – “Normal Cells”
Synthesis (S)New DNA is synthesized, or made
Gap 2 (G2)Growth phase #2Preparations for division are made
Mitosis (4 parts) – Dividing stagesProphaseMetaphaseAnaphaseTelophase
Cell Cycle: Interphase
Three phases of Interphase:• G1 – growing, increasing in
size, synthesis of new proteins and organelles
• S phase – Chromosomes are duplicated
• G2 – shortest phase, synthesis of organelles and molecules needed for cell division
Mitosis – Prophase
ProphaseChromatin condenses to Chromosomes• chromatids are joined by
centromere • Centrioles move to
opposite ends of cell• Nucleolus disappears• Nuclear membrane
dissolves
Mitosis – Metaphase
• Chromosomes line up at the equator
• Chromosomes attach to spindle fibers (from the centrioles) at centromeres
Mitosis – Anaphase
• Chromosomes get pulled apart
• Spindle fibers shorten and pull sister chromatids to the opposite ends of the cell
Mitosis – Telophase
• Chromosomes de-condense
• Spindle fibers disintegrate
• Nuclear membrane forms
• Nucleolus becomes visible
• Animal Cells – a contractile ring forms around the middle of the cell
• Plant cells – a band of cytoskeletal proteins called the cell plate forms
Cytokinesis – division of the cytoplasm
• Animal Cells – the contractile ring pinchesin the middle to fuse the membrane and separate the new nuclei
• Plant Cells – a new section of cell wall forms from the cell plate, between the nuclei to form two distinct cells
A B
C
D E
This is a complicated process… what happens when things go wrong?
There are several factors that try to control the cell cycle:
1. Before a cell divides the DNA is checked to make sure it was replicated correctly
2. Chemical signals tell a cell when to start and stop dividing
http://www.cancerquest.org/index.cfm?page=193
3. Cells also communicate to neighboring cells to tell them to stop growing
1. http://www.cancerquest.org/index.cfm?page=2463
Cancer
True or False?1.Cancer is contagious. True or False2.Cancer is one disease. True or False3.Cancer spreads with surgery. True or False4. cancer is inherited. True or False5.Cancer hurts. True or False6. cancer leads to death. True or False7.All tumors are cancerous. True or False8.The medical community is keeping the cure for cancer a secret, so the doctors can make more money. True or False