2. AP Biology 2007-2008 Biology is the only subject in which multiplication is the same thing as division…

3. AP Biology Cell Cycle  Interphase  Mitosis  Cytokinesis

4. AP Biology Interphase  90% of cell life cycle  Nucleus well-defined  DNA loosely packed in long chromatin fibers  cell doing its “everyday job”  produce RNA, synthesize proteins/enzymes  prepares for duplication if triggered

5. AP Biology Interphase  Divided into 3 phases:  G 1 = 1 st Gap  cell doing its “everyday job”  cell grows  S = DNA Synthesis  replicates DNA  each daughter cell gets exact DNA copy  G 2 = 2 nd Gap  prepares for division  cell grows (more)  produces organelles, proteins, membranes G 0 resting phase signal to divide

6. AP Biology Organizing DNA  DNA is organized in chromosomes  double helix DNA molecule  wrapped around histone proteins  like thread on spools  DNA-protein complex = chromatin  organized into long thin fiber DNA histones chromatin ACTGGTCAGGCAATGTC double stranded chromosome

7. AP Biology Copying DNA & packaging it…  After DNA duplication, chromatin condenses  coiling & folding to make a smaller package DNA chromatin mitotic chromosome

8. AP Biology double-stranded mitotic human chromosomes

9. AP Biology Mitotic Chromosome  Duplicated chromosome  2 sister chromatids  narrow at centromeres  contain identical copies of original DNA homologous chromosomes homologous chromosomes sister chromatids homologous = “same information” single-stranded double-stranded

10. AP Biology Cdk / G 1 cyclin Cdk / G 2 cyclin (MPF) G2G2 S G1G1 C M G 2 / M checkpoint G 1 / S checkpoint APC Active Inactive Active Inactive Active mitosis cytokinesis Replication completed? DNA integrity ? Chromosomes attached at metaphase plate? Spindle checkpoint Growth factors? Nutritional state of cell? Size of cell?

11. AP Biology Mitosis  Dividing cell’s DNA between 2 daughter nuclei  “dance of the chromosomes”  4 phases  prophase  metaphase  anaphase  telophase

12. AP Biology Prophase  Chromatin condenses  visible chromosomes  chromatids  Centrioles move to opposite poles of cell  Protein fibers cross cell to form mitotic spindle  Nucleolus disappears  Nuclear membrane breaks down

13. AP Biology Transition to Metaphase  Prometaphase  spindle fibers attach to centromeres  creating kinetochores  kinetochores connect centromeres to centrioles  chromosomes begin moving

14. AP Biology Metaphase  Chromosomes align along metaphase plate  meta = middle  spindle fibers coordinate movement  so each new nucleus receives only 1 copy of each chromosome

15. AP Biology Anaphase  Sister chromatids separate at kinetochores and  move to opposite poles  pulled at centromeres by motor proteins along microtubules

16. AP Biology Telophase  Chromosomes are at opposite poles  daughter nuclei form  chromosomes disperse  Spindle fibers disperse

17. AP Biology Cytokinesis  Animals  cleavage furrow forms  splits cell in two

18. AP Biology Cytokinesis in Animals

19. AP Biology Overview of mitosis interphaseprophase(pro-metaphase) metaphaseanaphasetelophase cytokinesis I.P.M.A.T.

20. AP Biology Mitosis in whitefish blastula

21. AP Biology Cancer & Cell Growth  Cancer is essentially a failure of cell division control  unrestrained, uncontrolled cell growth  What control is lost?  lose checkpoint stops  gene p53 plays a key role in G 1 /S restriction point  p53 protein halts cell division if it detects damaged DNA  options: stimulates repair enzymes to fix DNA forces cell into G 0 resting stage keeps cell in G 1 arrest causes apoptosis of damaged cell  ALL cancers have to shut down p53 activity p53 discovered at Stony Brook by Dr. Arnold Levine p53 is the Cell Cycle Enforcer

22. AP Biology DNA damage is caused by heat, radiation, or chemicals. p53 allows cells with repaired DNA to divide. Step 1 DNA damage is caused by heat, radiation, or chemicals. Step 1 Step 2 Damaged cells continue to divide. If other damage accumulates, the cell can turn cancerous. Step 3 p53 triggers the destruction of cells damaged beyond repair. ABNORMAL p53 NORMAL p53 abnormal p53 protein cancer cell Step 3 The p53 protein fails to stop cell division and repair DNA. Cell divides without repair to damaged DNA. Cell division stops, and p53 triggers enzymes to repair damaged region. Step 2 DNA repair enzyme p53 protein p53 protein p53 — master regulator gene

23. AP Biology Tumors  Mass of abnormal cells  Benign tumor  abnormal cells remain at original site as a lump  p53 has halted cell divisions  most do not cause serious problems & can be removed by surgery  Malignant tumors  cells leave original site  carried by blood & lymph system to other tissues  start more tumors = metastasis  impair functions of organs throughout body

24. AP Biology Traditional treatments for cancers  Treatments target rapidly dividing cells  high-energy radiation  kills rapidly dividing cells  chemotherapy  stop DNA replication  stop mitosis & cytokinesis  stop blood vessel growth

25. AP Biology 2007- 2008 Meiosis & Sexual Reproduction

26. AP Biology Cell division / Asexual reproduction  Mitosis Mitosis  produce cells with same information  identical daughter cells  exact copies  clones  same amount of DNA  same number of chromosomes  same genetic information Aaaargh! I ’ m seeing double!

27. AP Biology Asexual reproduction  Single-celled eukaryotes  yeast (fungi)  Protists  Paramecium  Amoeba  Simple multicellular eukaryotes  Hydra What are the disadvantages of asexual reproduction? What are the advantages? budding

28. AP Biology How about the rest of us?  What if a complex multicellular organism (like us) wants to reproduce?  joining of egg + sperm  Do we make egg & sperm by mitosis? 46 + 92 eggspermzygote What if we did, then…. Doesn’t work!

29. AP Biology Human female karyotype 46 chromosomes 23 pairs

30. AP Biology Human male karyotype 46 chromosomes 23 pairs

31. AP Biology Homologous chromosomes  Paired chromosomes  both chromosomes of a pair carry “matching” genes  control same inherited characters  homologous = same information diploid 2n 2n = 4 single stranded homologous chromosomes double stranded homologous chromosomes

32. AP Biology How do we make sperm & eggs?  Must reduce 46 chromosomes  23  must half the number of chromosomes 23 46 egg sperm 46 meiosis 46 fertilization 23 gametes zygote

33. AP Biology Meiosis: production of gametes  Alternating processes, alternating stages  chromosome number must be reduced  diploid  haploid  2n  n  humans: 46  23  meiosis reduces chromosome number  makes gametes  fertilization restores chromosome number  haploid  diploid  n  2n

34. AP Biology 2nd division of meiosis separates sister chromatids 1st division of meiosis separates homologous pairs Double division of meiosis DNA replication Meiosis 1 Meiosis 2

35. AP Biology DNA replication Meiosis 1 Homologous pairs separate (2n  1n) “Reduction Division” prophase 1  1st division of meiosis _________________________ tetrad synapsis telophase 1 metaphase 1

36. AP Biology Meiosis 2 metaphase 2 telophase 2 prophase 2  2nd division of meiosis _________________________ 4 Sister chromatids Separate (1n  1n) “just like mitosis” 2 cells from meiosis I

37. AP Biology

39. Mitosis vs. Meiosis

40. AP Biology The value of sexual reproduction  Sexual reproduction introduces genetic variation  genetic recombination during meiosis  independent assortment (of chromosomes)  random alignment of homologous chromosomes in Meiosis 1  crossing over – chromosomal segments are exchanged between a pair of homologous chromosomes (8 million different gametes possible)  random fertilization  which sperm fertilizes which egg ?  Driving evolution  variation for natural selection  random assortment in humans produces 2 23 (8,388,608) different combinations in gametes

41. AP Biology Variation from random fertilization  Sperm + Egg = ?  any 2 parents will produce a zygote with over 70 trillion (2 23 x 2 23 ) possible diploid combinations