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-Interphase is the normal growth and living stage of a cell
There are 3 steps to interphase.
-G1 is the first growth stage where a cell grows
-S phase is the synthesis stage. This is the time that a cell starts copying all of its DNA so when it comes time to divide it will have a copy for both cells
-G2 is the 2nd growth stage where the cell grows for the purpose of division.
-Prophase is the first phase is division. During prophase the nucleus breaks apart and the chromatin condenses into chromosomes. The chromosomes then begin to get pulled to the center of the cell
-Metaphase is when the chromosomes are all aligned in the middle of the cell
-Anaphase is when the sister chromatids are being pulled apart to opposite ends of the cell
-Telephase is when 2 nuclei start to form around the separated chromatids, the chromatids unwind, and cytokinesis begins to split the cell
Mitosis
The difference between Mitosis and Meiosis
Meiosis is the making of haploid cells
-These haploid cells are used for sexual reproduction
-The point of meiosis and therefore the point of sexual reproduction is diversity
-Joining of two gametes from two different parents allows for millions of different genetic combinations
-Even the joining of two gametes from the same parent allows for diversity since the genes expressed will be different
-Meiosis is NOT SEX! Meiosis is the process to make the cells used during sexual fertilization
-Once again Mitosis is the process of dividing and copying regular body cells (somatic cells)
-And Meiosis is the process of dividing and copying sex cells (gametic cells)
-The reason Meiosis is different than Mitosis is because the genetic material has to be split in half
-The other important
Meiosis I
Meiosis II
Meiosis produces variation...but how much variation?
A Mosquito has 3 pairs of chromosomes so mathematically we can figure out how many different possible gametes a mosquito can make by taking 2 to the power of 3. 2 to the power of 3 equals 8 so a mosquito can make 8 different gametes.
How many different gametes can a human produce?
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Not all organisms have the same life cycle as a human
-There are 3 different common life cycles
Cancer
How cells know when to divide. The body releases growth factors which are a lipid based hormone. The growth factor diffuses through your blood stream and spreads throughout your body. The growth factor binds to any cells that have a growth factor receptor protein in their cell membrane. The receptor protein releases cyclin. The cyclin binds to cyclin dependent kinases (CDK). The CDK phosphorylates the proteins involved in mitosis. Phosphorylation means adding a phosphate group to a protein which is the way you activate proteins.
There are three major checkpoints for mitosis or cell division. These checkpoints are in place to make sure everything goes right. If something were to go wrong with cell division it could lead to cancer or other problems. There is a checkpoint between G1 and the S phase. If the cell is not ready to replicate its DNA it will not be allowed to enter the S phase. There is another checkpoint after G2 to make sure the cell is ready for mitosis. At this checkpoint the cell makes sure that the DNA was replicated properly. The last major checkpoint is after metaphase to make sure all the chromosomes lined up properly before they enter anaphase and are separated. Each one of these checkpoints requires phosphorylation by CDK's to move on.
Cancer
Cancer is caused by unregulated cell division. It is basically mitosis gone wrong.
There are many tumor suppressors inside our cells that help us fight against cancer. There are many ways that cancer can happen. Many of the ways that cancer is formed happens when one of our tumor suppressors breaks or mutates. This happens from damaged DNA.
Here are the normal working tumor suppressors
And here is what happens when these suppressors break or mutate
What is the Rb Gene?
The retinoblastoma protein (abbreviated pRb, RB or RB1) is a tumor suppressor protein that is dysfunctional in several major cancers.[1] One function of pRb is to prevent excessive cell growth by inhibiting cell cycle progression until a cell is ready to divide.
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