1. Cell Division Life Cycle of the Cell Life Cycle of the Cell Mitosis Mitosis Meiosis Meiosis

2. Cell Cycle Overview Video

3. Cellular Division Cell division is a process by which a cell, called the parent cell, divides into two or more cells, called daughter cells. Cell division is usually a small segment of a larger cell cycle. cell cycle cell cycle 3 major types of cell division Prokaryotic CellsEukaryotic Cells

4. Cellular Division The size of the cell signals time for division. Cell Grows until it reaches a size large enough to start division.

5. Prokaryotic Division  Ex. Bacteria  Prokaryotic Division is called Binary fission, it is the division of a prokaryotic cell into 2 daughter cells  Consists of 3 stages: 1.The 1 chromosome in the cell makes a copy of itself (in a process that is similar to unzipping and then reforming each side) 2.Cell grows until it reaches twice its original size 3.A cell wall forms between the 2 chromosomes and the cell splits into 2 new cells Identical to Original cell

6. Example: Example: Escherichia coli  Under optimal environment conditions, a population of E. coli cells doubles in size every 20 minutes. Theoretically, in about one week a single E. coli cell could produce a ball of bacteria the size of Earth! Thankfully for other organisms the E. coli would run out of nutrients long before that happened.

7. Eukaryotic Division  More complex than prokaryotic cells because of organelles (ex. Mitochondria, endoplasmic reticulum, golgi bodies, chloroplasts, etc.)  The life of the eukaryotic cell is diagrammed as the cell cycle – the repeating sequence of growth and division of eukaryotic cells (4 major phases)

8. Cell Life Cycle Organelles are copied here G 1,S, & G 2 all make up Interphase Therefore, the cell is usually in interphase Cytokinesis happens here

9. Cell Cycle Cell Cycle Animated Animated

10. Cell Cycle   The cell cycle is driven by a chemical control system that both triggers and coordinates key events in the cell cycle. The cell cycle control system is regulated at certain checkpoints.   Signals from inside the cell (internal signals) and from outside the cell (external signals) are involved in turning the process of cell division off and on. An internal signal involves the cell sensing the presence of chemicals, called enzymes, which are produced inside the cell An external signal involves the cell sensing the presence of a chemical (such as a growth factor) which was produced in other specialized cells.

11. Cell Cycle   Cells can also respond to physical signals from their environment. Cells sense when they are too closely packed and cell division is turned off. Cells sense when they are not in contact with a surface and cell division is turned on.   A checkpoint in the cell cycle is a critical control point where stop and go signals can regulate the cycle. The cell division mechanism in most animal cells is in the “off” position when there is no stimulus present. Specific stimuli are required to start the processes

12. Mitosis – is the process that results in two nuclei with the exact same information Interphase – pre-mitotic phase Prophase – 1 st phase Metaphase – 2 nd phase Anaphase – 3 rd phase Telophase – 4 th phase Cytokinesis – cell divides PMAT:

13. Chromosomes are copied (# doubles) Chromosomes are copied (# doubles) Chromosomes appear as threadlike coils (chromatin) at the start, but each chromosome and its copy(sister chromosome) change to sister chromatids at end of this phase Chromosomes appear as threadlike coils (chromatin) at the start, but each chromosome and its copy(sister chromosome) change to sister chromatids at end of this phase Longest phase of the cell cycle – G 1, S, & G 2 Longest phase of the cell cycle – G 1, S, & G 2 CELL MEMBRANE Nucleus Cytoplasm chromatin

14. Chromosomes A chromosome is an organized structure of DNA and protein that is found in cells. It is a single piece of coiled DNA containing many genes DNAprotein cells genesDNAprotein cells genes

15. Chromosomes

16. Animal Cell Plant Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

17. Mitosis begins (cell begins to divide) – nucleus breaks down and nucleolus disappears Mitosis begins (cell begins to divide) – nucleus breaks down and nucleolus disappears Centrioles (or poles) appear and begin to move to opposite end of the cell. Centrioles (or poles) appear and begin to move to opposite end of the cell. Spindle fibers form between the poles. Spindle fibers form between the poles. Chromosomes condense & become visible Chromosomes condense & become visible Centrioles Sister chromatids Spindle fibers

18. Animal Cell Plant Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm There are no centrioles in plant cells they can divide without them

19. Chromatids (or pairs of chromosomes) attach to the spindle fibers. Chromatids line up at the equator (center of the cell) Chromatids (or pairs of chromosomes) attach to the spindle fibers. Chromatids line up at the equator (center of the cell) Centrioles Spindle fibers

20. Animal Cell Plant Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

21. Chromatids (or pairs of chromosomes) separate at the centromere and begin to move to opposite ends of the cell. Chromatids (or pairs of chromosomes) separate at the centromere and begin to move to opposite ends of the cell. Centrioles Spindle fibers

22. Animal Cell Plant Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

23. Spindle fibers disappear Spindle fibers disappear Two new nuclei form. Nucleolus returns to the inside of each nucleus Two new nuclei form. Nucleolus returns to the inside of each nucleus Chromosomes uncoil and appear as chromatin (threads rather than rods). Chromosomes uncoil and appear as chromatin (threads rather than rods). Mitosis ends. Mitosis ends. Nuclei Chromatin

24. Animal Cell Plant Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

25. Cell membrane or cell plate moves inward to create two daughter cells – each with its own nucleus with identical chromosomes. Cell membrane or cell plate moves inward to create two daughter cells – each with its own nucleus with identical chromosomes. - animal cells → cleavage (pinching) furrow forms in the cell membrane to separate the cell. - plant cells → cell wall forms to separate cell.

26. Animal Mitosis -- Review Interphase Interphase Prophase Prophase Metaphase Metaphase Anaphase Anaphase Telophase Telophase Cytokinesis Cytokinesis

27. Plant Mitosis -- Review Interphase Interphase Prophase Prophase Metaphase Metaphase Anaphase Anaphase Telophase Telophase Cytokinesis Cytokinesis Cell wall plate

28. http://www.cellsalive.com/mitosis.htm Mitosis Song

29. Meiosis

30. Meiosis  Meiosis – the process that divides the # of chromosomes in cells in half (formation of gametes); vital to sexual reproduction  2 successive nuclear divisions (goes through PMAT twice)  Before 1 st division, DNA is copied just like in mitosis  However, DNA is not copied before 2 nd division

31. Meiosis  Broken down into 2 parts – Meiosis I and Meiosis II  Meiosis I – homologous chromosomes separate into 2 diploid cells  Meiosis II – Each Cell Sister chromatids separate into 2 haploid cells Diploid Haploid Copied Meiosis I Meiosis II Haploid Diploid Copied  1 Diploid Cell = 4 Haploid Cells

32. Difference between Animals & Plants  In Animals – meiosis makes gametes (reproductive cells / sex cells – sperm & eggs)  In Plants – meiosis makes spores

33. 2 Unique Events of Meiosis: 1. Crossing Over: Homologous chromosomes pair up next to each other Homologous chromosomes pair up next to each other Arms of chromosomes exchange segments (same sized) of DNA Arms of chromosomes exchange segments (same sized) of DNA 2. Skipping Replication: Only 1 replication of DNA, but 2 divisions → meiosis halves the number of chromosomes Only 1 replication of DNA, but 2 divisions → meiosis halves the number of chromosomes

34. Meiosis I 1. Prophase I: a. Chromosomes condense (become thick) and become visible as a cluster of 4 chromatids called a tetrad b. Nuclear envelope breaks down c. Centrioles move to poles and begin to produce spindle fibers d. Homologous chromosomes pair up e. Crossing over occurs 2. Metaphase I: a. Pairs of homologous chromosomes attach to spindle fibers at centromere and move to the equator (center) of the cell

35. Meiosis I 1. Anaphase I: a. Homologous pairs separate b. Chromosomes of each pair pull apart and move to the poles (opposite ends) of cell a.Note: Sister chromatids of chromosome remain attached

36. Meiosis I 4. Telophase I: a. Chromosomes gather at each of the 2 poles and nuclear membrane forms around them. b. Cytokinesis occurs at the end of Telophase I: Cytoplasm divide, forming 2 new cells. c. Each of the two daughter cells contains only one chromosome (consisting of two sister chromatids) from each parental pair. d. Meiosis I often called reduction division Skipping Replication – DNA does not copy between meiosis I and meiosis II

37. Prophase II Spindle fibers form in each of the daughter cells from meiosis I and attaches to the centromeres of the sister chromatids The chromosomes progress towards the midline of each cell. The nuclear membrane breaks down. Metaphase II Chromosomes, made up of two sister chromatids, line up across the center of the cell. Spindle fibers from opposite poles of the cell attach to one of each pair of chromatids. Anaphase II The chromosomes separate so that one chromatid from each chromosome goes to each pole. Telophase II & Cytokinesis Nuclear member forms around each set of chromosomes. The resulting daughter cells are haploid, containing one single chromosome from each pair of chromatids, either from the maternal or paternal contributor. Meiosis II

38. Genetic Recombination  The formation of new combinations of genes  2 chromatids of chromosomes no longer contain identical genetic material  Provides a source for genetic variation, which impacts the rate of evolution in organisms

39. Mitosis vs Meiosis Mitosis 1. PMAT Once 2. Ends with 2 diploid cells that are identical to parent cell 3. Somatic Cells (Body cells) undergo this cellular reproduction Meiosis 1. PMAT Twice 2. Ends with 4 haploid cells that are different from the parent 3. Gametes (Sex cells) undergo this cellular reproduction

40. Mitosis vs Meiosis