1 / 62

Cell Growth and Division:

Cell Growth and Division:. Mitosis vs. Meiosis and What’s going on the rest of the time. Why does a cell need to divide?. A little geometry: As an object grows, the volume increases at a faster rate than the surface area. The same happens with a cell. What is the surface area?

doli
Télécharger la présentation

Cell Growth and Division:

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Cell Growth and Division: Mitosis vs. Meiosis and What’s going on the rest of the time

  2. Why does a cell need to divide? • A little geometry: As an object grows, the volume increases at a faster rate than the surface area

  3. The same happens with a cell • What is the surface area? • What is the volume? • The more cytoplasm there is the more materials are needed. • How do the materials enter?

  4. Oh no… diffusion is back! • By limiting the ratio of membrane to cytoplasm you limit the “doorways” into the cell. • Cell can’t get enough materials to support its large size • Cell dies, unless it divides in half!

  5. What do our cells need to do before they can divide? • Get bigger • Make another copy of DNA • Make more organelles

  6. Cell Cycle

  7. Cell Cycle G1 – growth and protein synthesis S – DNA replication (copying the DNA) G2 – Make organelles M – Mitosis (Nuclear division) and Cytokinesis – division of cytoplasm and membrane

  8. What is DNA again? • A Chain of nucleotides • Twisted into a double helix (spiral) • VERY LONG • Contains ALL the recipes for every protein our body needs • Recipes are called genes

  9. Understanding DNA structure • Most of the time out DNA is in the form of chromatin: strings of DNA wrapped around proteins called histones

  10. Understanding DNA structure • DNA is in chromatin form through G1. • In S phase, each strand of chromatin is duplicated and the duplicated copies remain attached together at the centromere.

  11. Understanding DNA structure • During M phase the chromatin is folded into chromosomes • DNA remains in chromosome form until cell division is over

  12. Understanding DNA structure

  13. Remember DNA contains the information needed to build an organism • Each chromosome contains some of the information. • Each organism has a specific number of chromosomes.

  14. Humans have 23 types of chromosomes and 2 of each type = total of 46 chromosomes • One of each type came from your mom the other from your dad. • Every cell in your body has all 46 chromosomes with the exception of egg/sperm cells

  15. Cells that contain two of each chromosome are called Diploid cells • Cells that contain one of each chromosome are called Haploid cells

  16. Chromosome Analogy • Think of the Information in a cell as an Encyclopedia - Each chromosome is one book • Haploid = one set of info / one encyclopedia A B C D E

  17. Chromosome Analogy Diploid = two different sets of info/ two different encyclopedias! A B C D E A B C D E

  18. A B C D E A B C D E Chromosome Analogy • Genome = total information in cell • If a cell is haploid, the genome consists of all the information in one encyclopedia • If Diploid, all the info in both encyclopedias

  19. Chromosome Analogy • Chromosome = One volume • Genes: segments of DNA; each contains a specific message • Genes are like Articles in encyclopedia A F jkasdkfjh Jadlfl he; Kjadh fchw Laksjdfh Kasjdf;aj Skdjfa;ie F jkasdkfjh Jadlfl he; Kjadh fchw Laksjdfh Kasjdf;aj Skdjfa;ie

  20. Chromosome Analogy • Genes can have different variations. The variations are called Alleles. • Think of the alleles as two different articles on the aardvark! A F jkasdkfjh Jadlfl he; Kjadh fchw Laksjdfh Kasjdf;aj Skdjfa;ie F jkasdkfjh Jadlfl he; Kjadh fchw Laksjdfh Kasjdf;aj Skdjfa;ie

  21. Chromosome Analogy • Homologous Chromosomes : • Contain same genes, but may contain different alleles • Example: both might contain Hair color gene but one might have brown hair info the other blonde • One from Mom, one from Dad

  22. Chromosome Analogy • Homologous Chromosomes = Volume “A” from each encycl. A A HomologousChromosomes

  23. Chromosome Analogy When DNA duplicates itself before cell division it makes two identical copies of each of chromosome Identical Copies are Sister Chromatids SisterChromatids SisterChromatids A A A A

  24. Single, unduplicated Chromosome 1 duplicated chromosome, 2 sister chromatids 2 separated chromatids become individual chromosomes

  25. Centromere Telomeres

  26. Mitosis • One Fluid Event; no stopping and starting. • BUT: for ease of study, we break it into 4 stages • REMEMBER: all phases are continuous and may, in part, overlap

  27. 1. Prophase • Longest phase of Mitosis • Chromatin folds up into Chromosomes which can now be seen

  28. 1. Prophase • Centrosomes separate and move toward opposite poles • These are parts of the cell that make microtubules

  29. 1. Prophase • Centrosomes start to form the Mitotic spindle • Made of microtubules

  30. 1. Prophase • Nuclear membrane breaks down • Nucleolus disappears

  31. 2. Metaphase • Chromosomes line up along equator • Spindle fibers attach to the centromeres of chromosomes

  32. 3. Anaphase • Centromeres connecting sister chromatids separate and one chromatid of each chromosome moves toward each poles

  33. 4. Telophase • Chromosomes begin to unwind back into chromatin • Nuclear Envelope reforms around chromosomes • Spindle breaks down • Nucleolus reappears

  34. Cell Division is not yet Done!! • What have we made? • One Cell with Two complete Nuclei What is left to do? - Cytokinesis: Divide the cytoplasm and separate the cells

  35. Cytokinesis • Animal cells: Membrane pinches inward forming a Cleavage Furrow until it divides the cytoplasm into two equal parts

  36. Cytokinesis • Plant cell: Cell plate forms in the middle of the cytoplasm and extends toward the edges. Cell wall forms from this cell plate

  37. Cell division is done! • Now you have Two Identical daughter cells

  38. Controlling Cell Division • Cells know when they need to divide • When? • During growth • Repair – injury • Replacement (cells are not immortal!)

  39. Controlling Cell Division • Cells know when they don’t need to divide • Cells stop when they reach other cells

  40. How do cells “know”? • Cells communicate by releasing molecules • To control cell division cells release proteins called “cyclins” • Some cyclins are “Go” signals • Trigger the cell division process • Some cyclins are “Stop” signals • shut down the cell division process

  41. Loss of control • What happens if the control signals don’t work?!? • cells divide uncontrollably • Pile up on top of each other • Form big balls of cells called????? • TUMORS!!!

  42. Tumors • Tumor cells do not respond to (or do not have) the body’s control signals • missing a “stop” signal so cell division doesn’t stop • Hyperactive “go” signal so cell is constantly dividing

  43. Tumors Vs. Cancer • Tumor = uncontrolled but isolated growth of cells • Tumor cells become cancer when they start to invade healthy tissue • What if 1 cancer cell breaks off and enters the blood stream? • Where ever it “lands” = new tumor = metastasis

  44. That’s how Somatic (or body) cells divide! • What would happen if we made Egg and Sperm cells this way? • Way too much DNA • What do we have to do when forming these cells? • Reduce the amount of DNA

  45. Meiosis • Happens ONLY in sex cells • Reduces information by ½ • Requires two different divisions • How many cells at the end??

  46. Meiosis begins the same as Mitosis • Cell in G1 enters S phase. • ALL DNA is copied • Chromatin folds up to form 46 duplicated chromosomes

  47. Meiosis I Prophase I - homologous chromosomes pair up forming tetrad; 4 chromatids together;

  48. Meiosis I Prophase I - Centrosomes separate to poles - Nuclear envelope breaks down

  49. Meiosis I Prophase I - Crossing occurs between homologous chromosomes

More Related