Chapter 10: Cell Reproduction Mitosis and Meiosis

1. Chapter 10:Cell Reproduction Mitosis and Meiosis

2. What would happen to a cell if it continued to grow? Calculate the Surface area (Length2 x 6) and Volume (Length3) then the Surface area to Volume ratio As the length of the cell >, its volume > faster than its surface area. Surface area to volume ratio would decrease. Makes it difficult to move needed materials in and wastes out of the cell efficiently.

3. Where is all the genetic information found in a cell? • On the genes on the Chromosomes • Chromosomes are actually DNA and proteins • If cells were the size of a basketball, your DNA would stretch 64km (40 miles)

4. A Tale of Tall DNA If you unraveled all your chromosomes from all of your cells and laid out the DNA end to end, the strands would stretch from the Earth to the Moon about 6,000 times.

5. Every species has a set number of chromosomes • Chromosome number: • Number of Chromosomes in a body cell • Diploid (2N) number • Specific for each species of organisms • Human – 46 • Chimpanzee – 48 • Gorilla – 48 • Potato – 48 • Bat – 44 • Fruit fly – 8 • Mosquito – 6 • King Crab – 208 • Dog - 78 • Horse – 64 • Donkey - 62 • Adder’s tongue fern 1,262

6. Chromosome structure • Before coiling starts, DNA and proteins w/in nucleus are called Chromatin • DNA starts coiling around a protein histone (spool) • Coiling continues and supercoils • Structure shortens up Chromosome • When DNA makes a copy of itself, the two “twins” are called chromatids & are held together by a centromere

7. A Paired Chromosome

8. Uncoiled DNA

9. Animation 1 Animation 2

10. What would happen if a cell were to just split into two without any advance preparation? Instead, it is more efficient to shorten up and then organized the replicated DNA prior to dividing the DNA up evenly into two cells. This is what happens in The Cell Cycle • Imagine trying to divide up pieces of yarn by color if they were all just thrown into a pile together. • It would take a long time to do this efficiently and accurately.

11. The Cell Cycle • Entire process that a cell undergoes in cell division from start to finish. • Cells grow, prepare for division, divide to form two daughter cells and begin the cell cycle over gain. • Cells such as skin, lining of digestive tract and blood cells go through this process frequently

12. The Cell Cycle The Cell Cycle

13. Divided into 2 parts • Interphase • G1 - “Gap” - Cell grows from last cell cycle • S – Synthesis of DNA (DNA makes a copy of itself) • G2 – Cell growth and gets ready for cell division • G0 – No cell division – typical of cells like nerve cells that stop dividing at maturity • Mitosis – Mphase • Prophase • Metaphase • Anaphase • Telophase • Cytokinesis

14. Interphase • Longest phase in the Cell Cycle – over half the time is spent in this phase

15. Mitosis • Prophase – longest phase in Mitosis • Copied chromosomes pair up. Held together by Centromere (each is called a chromatid) • Shortening up of chromosomes, makes them visible • Replicated Centrioles (of animal cells) migrate to opposite poles • Nuclear envelope & nucleolus start to break down • Spindle fibers (microtubules) extend from centrioles to centromeres

16. Metaphase – shortest part of Mitosis • Chromosomes line up on the equator (middle)

17. Anaphase – “An away they go!” • Chromatids separate and go to opposite poles. Now called chromosomes!! • Spindle fibers shorten up

18. Telophase • “the end” – Final phase • Chromosomes reach opposite ends • Cell membrane pinches in (cleavage furrow) or Cell plate forms (if plants) • Chromosomes uncoil • Nuclear membrane & nucleolus reappear • Spindle fibers disassembles

19. Cytokinesis – dividing up of cellular contents. Occurs simultaneously with Telophase

20. Mitosis animationsTry them all! • http://www.sumanasinc.com/webcontent/animations/content/mitosis.html • cellsalive. • John Kryk • You tube (really good) • Hybrid (love the music) • http://www.csuchico.edu/~jbell/Biol207/animations/mitosis.html • Arizona • Movie Clip • McGraw

21. Difference between Plant and Animal mitosis • No centrioles or asters in plant cells • A cell plate forms in plant cells

22. How do cells “know” when to undergo cell division? • Experiment with thin layer of cells on agar plates. • Wouldn’t grow anymore once the plate was filled. • When cells were removed, the area opened up would fill with cells and the cells that were removed would grow and spread out on another plate.

23. Cyclin is a protein that regulates the timing of the cell cycle. • Amount of cyclin in a cell rises and falls with the steps in the cell cycle. • There are other internal and external proteins that are also involved the cell cycle. • Cancer – uncontrolled cell growth. Cells do not respond to normal signals and grow out of control. Cause masses called tumors.

24. Mitosis

25. What would happen to our normal chromosome number if the gametes (sex cells) each had 46 chromosomes & reproduced by mitosis? • The chromosome number would constantly be changing – not human 23 + 23 = 46 46 + 46 = 92 92 + 92 = 184

26. So how do we solve this problem? Meiosis • Process that reduces the chromosome number in half (1N) during the production of gametes (sex cells). • By doing this, the normal chromosome number (2N) can be returned at fertilization. 1N sperm + 1N egg = 2N zygote 23 + 23 = 46 (zygote)

27. Meiosis occurs in two divisions Meiosis I: Interphase I: • Replication of chromosomes. Like chroms are called homologous chromosomes Prophase I: • The homologous chroms come together (Synapsis) and form a group of 4 called a tetrad. • Twisting & exchange parts of adjacent chromatids will occur – Crossing over • This results in genetic recombination & unlinks genes that are located on the same chromosome.

28. Anaphase I& Telophase I Chromosomes separate independently of each other. This is known as Independent assortment. Results in random separation of chroms genetic recombination.

29. At the end of Meiosis I, there are 2 - 1N cells No interphase Meiosis I Results in 2 - 1N cells Meiosis II Results in 4-1N cells

30. Meiosis II • Occurs immediately following Telophase I. • NO INTERPHASE!! • 1N cells immediately go into Prophase II, then Metaphase II, Anaphase II, and Telophase II • Split into four 1N cells, each with unpaired chromosomes At the end of Meiosis II, there are four 1N cells.

31. Meiosis Animation

32. Meiosis Animations • **http://www.sumanasinc.com/webcontent/animations/content/meiosis.html • *John Kryk • Cells Alive • Biology.about • You Tube • http://www.csuchico.edu/~jbell/Biol207/animations/meiosis.html • McGraw • ****How Mitosis and Meiosis Differ

33. GametogenesisCreation of gametes (sex cells) Spermatogenesis (testes) Makes 4 haploid sperm cells from 1 - 2N primary sperm cell. Looks like normal Meiosis Oogenesis (ovaries) Produces ovum (eggs) from 1 diploid primary egg cell. Difference occurs during cytokinesis during meiosis I and meiosis II. Unequal distribution of the cytoplasm resulting in 1 large ovum and 3 small polar bodies. Polar bodies serve no function in animals but are needed in to plant embryos.

34. 1st Meiotic Division 2nd Meiotic Division