1. Mitosis and Meiosis
8.2, 8.3, & 10.2

2. Levels of Biological organization
Cells  Tissues
Tissues  Organs
Organs  Organ Systems
Organ Systems  Organisms

3. From zygote to Trillions of Cells
Zygote=Cell that forms when sperm and egg join
Sperm gives you DNA from dad, egg gives you DNA from mom
Shortly after sperm fertilizes egg, the zygote splits into a 2nd cell
These 2 cells split into 4, then 8, then 16, etc.
Each of these cells contains IDENTICAL DNA (Recall DNA replication)

4. Why must cells divide Diffusion limits cell size
Cells get materials from surroundings through their membrane. This is also how they expel wastes
If the cell gets too large, it would take a long time for these processes to occur
DNA also limits cell size
DNA  RNA  Proteins
There is a limit on how fast this can happen.
If the cell is too large, it takes too long to make all of the structures from the proteins.

5. Surface area-to-volume

6. Cell Cycle

7. I-PMAT The cell cycle can be divided into 2 (or 3) stages
Interphase, Mitosis, and Cytokinesis
Interphase and Mitosis are further divided by certain events that happen
Interphase=G1, S, G2
Mitosis=Prophase, Metaphase, Anaphase, Telophase
NEITHER INTERPHASE NOR CYTOKINESIS ARE PARTS OF MITOSIS

8. Interphase (G1, S, G2) Think “Intermission”
Most of the cell’s life is spent in Interphase
Period of growth and development
G1 (Growth Phase 1)
Cell grows in size and synthesizes mRNA and proteins
S Phase (Synthesis phase)
DNA replicates
G2 (Growth Phase 2)
Cell grows again, organelles are duplicated, and proteins are synthesized to prepare for cell division

9. Mitosis Period of division 4 parts (PMAT)
Prophase (“Prologue”)
Metaphase (“Middle”)
Anaphase (“Apart”)
Telophase (“Two”)
Happens only in somatic (body) cells

10. Prophase (“Prologue”)
First and longest stage of mitosis
Prophase begins as strands of chromatin coil around proteins called histones and become a chromosome (tightly wound strand of DNA and proteins)
Each copy of DNA (from Interphase) coils and forms 2 identical strands
Called sister chromatids
These sister chromatids join together at the center (called a centromere)
Each chromosome has a “partner” (remember, you get one from your mom and one from your dad)
These are called homologous chromosomes
The nucleus disappears
Centrioles move to opposite ends of the cell
A structure called a spindle forms
Made up of rod-like structures called microtubules

11. DNA to Chromosomes

12. Chromosome Structure

15. Metaphase (“Middle”)
Spindle fibers attach to centromeres of chromosomes
Spindles extend from centriole on one side and attach to sister chromatid on that same side
Fibers help chromosomes line up in the middle
Very important because it ensures that ½ of the chromosomes end up in each cell

18. Anaphase (“Apart”)
Spindle fibers shorten and pull sister chromatids apart at the centromere
Each identical sister chromatid moves to one of the sides of the cell

21. Telophase (“Two”) Chromatids reach opposite ends
Chromatids begin to unwind into chromatin
Nuclei form around chromatin
Spindle breaks down
Cells begin to split
This ends Mitosis

24. Cytokinesis Division of cytoplasm
Cell divides and 2 new daughter cells are formed
Process differs in plants and animals
In plant cells, a structure called a cell plate forms and separates the 2 daughter cells
In animals cells, the cells “pinch in” until the cells are separated

26. Control of the Cell cycle
Cancer=uncontrolled cell division
Proteins (called cyclins) created during protein synthesis help to regulate the cell cycle
When these proteins are damaged by mutations of DNA, the cell’s normal cycle is disrupted and cells divide out of control
Forms a tumor
Cancer cells take nutrients from healthy cells, and can occasionally move around in the body.
When cancer cells move around, it is called metastasis.
This forms new tumors throughout the body

27. Meiosis Occurs only in sex cells (males-sperm and female-egg cells)
The goal is to cut the original number of chromosomes in half
Offspring need to inherit from both parents
If the number was not cut in half, the offspring would have 2x the chromosomes as the parents
Terms
A diploid cell is a cell that contains 2 of each chromosome (di=2)
These are typical body cells
A haploid cell is a cell that contains 1 of each chromosome (hap~half)
These have ½ the number of chromosomes as typical cells

28. Phases of Meiosis Very similar to mitosis IPMATPMAT
Starts with Interphase
Only occurs once before meiosis begins
Basically does mitosis twice
Meiosis I
Prophase I, Metaphase I, Anaphase I, Telophase I
Meiosis II
Prophase II, Metaphase II, Anaphase II, Telophase II
Each ends with cytokinesis

29. Meiosis-Interphase Exactly the same as in Mitosis
Occurs only before Meiosis I, NOT Meiosis II

30. Meiosis-Prophase I Very similar to Prophase in Mitosis
One huge difference
Homologous chromosomes line up and form a structure called a tetrad
They tangle up and can actually break portions off and exchange DNA
Process is called crossing over
Increases genetic diversity by potentially allowing you to pass on traits from both grandparents to offspring

31. Meiosis-Metaphase I
Again, similar to Metaphase in Meiosis, but with a key difference
Spindle fibers attach to tetrads, and line them up in the middle
This means that there are 2 chromosomes next to one another in the center, instead of one as was the case in Mitosis
Mitosis Meiosis

32. Meiosis-Anaphase I Probably the most different from Mitosis
Whereas in Mitosis, sister chromatids separate at the centromere and move towards opposite ends of the cell, in Meiosis, tetrads are pulled apart and chromosomes (the pair of sister chromatids) move to each side of the cell
This ensures that there will be a full chromosome in the daughter cells

33. Meiosis-Telophase I
Occurs exactly as it did in Mitosis, except this time there is an entire chromosome (pair of sister chromatids) in each of the 2 new cells
Another division is necessary to split the genetic material in half
Cytokinesis occurs, same as Mitosis
2 diploid cells are formed

34. Meiosis II NO INTERPHASE
This process occurs EXACTLY THE SAME AS MITOSIS
Only it is occurring in 2 cells at once

35. Results of Mitosis and Meiosis
In Mitosis, 1 cell splits into 2 daughter cells
The daughter cells are identical
In Meiosis I, a single cell splits into 2 daughter cells
Each of these cells contains the same amount of chromosomes as the parent cell
Still diploid, and not identical
In Meiosis II, the 2 daughter cells from Meiosis I undergo another cell division, and split into 2 more daughter cells
Each of these cells contains ½ of the original genetic material
Now haploid, and each unique