Cell Division in Organisms: Mitosis and Binary Fission

1. MITOSIS CHAPTER 12

2. Cell division in two types of organisms: Unicellular: reproduces entire organism (clone) Multicellular: allows growth, development, repair, replacement

3. Genome Distribution: a cell’s entire set of DNA Genome = Genome consists of 1 or more long DNA molecules. Each DNA molecule = 100’s or 1000’s of genes In eukaryotic cells: DNA (& proteins) are folded into compact (visible in mitosis) chromosomes Cell division maintains the genome from generation to generation: replicate, then divide

4. EUKARYOTIC CELLS: Each species = characteristic # of chromosomes Humans: Somatic cells = 46, gametes = 23 Chromatin = chromosome material during interphase. Individual chromosomes are indistinct. BEFORE cell division, each chromosome is copied: Sister chromatids join at centromere

5. CELL CYCLE: Life cycle of a cell. Two main parts = Interphase and Mitosis

6. Interphase: 90% of cell’s life, doing normal functions, 3 parts: G1 phase: (Gap) growth S phase: (Synthesis) chromosome replication G2 phase: growth and preparation for mitosis. Mitosis MUST occur – Why? Cell cannot function normally with double the DNA

7. Mitosis: division of nucleus, usually followed by cytokinesis (cell division). 5 parts: Prophase: Nuclear membrane and nucleolus begin to dissolve. Chromatids condense and become visible Spindle fibers start to form (microtubules) Centrosomes (w/ centrioles in animals) migrate toward poles

8. Prometaphase: Chromatids attach to spindle via the kinetochores (1 per chromatid) Nuclear membrane is completely fragmented. Why do pieces remain? To reconstruct new nuclear membranes for daughter cells

9. Metaphase: Meta = “middle” Chromatid pairs line up at equatorial plate

10. Anaphase: Centromeres divide in half Each chromatid is now considered a full chromosome Spindle fibers pull chromosomes toward poles by shortening the kinetochore microtubules(their centromeres lead the way) Nonkinetochore microtubules lengthen to move poles away from each other. Cytokinesis may begin

11. Telophase: Nuclear membrane and nucleoli reform Chromosomes uncoil, return to chromatin state Spindle fibers dissolve Cell enters interphase to restart cycle

12. Structure & Function of the Mitotic Spindle Spindle formation is initiated in the centrosome: Called the “microtubule-organizing center” Animal cells have centrioles at the core of their centrosome, but they are not essential for functioning. A single centrosome exists during interphase: It replicates during G2 Centrosome pair begins to segregate toward poles during prophase.

13. Spindle microtubules radiate from the centrosomes to form: mitotic spindle. Mitotic spindle = microtubules & proteins (esp. tubulin) Microtubules attach to centromeres at a kinetochore (1 kinetochore per chromatid). The protein dynein helps chromosomes move toward poles along the spindle apparatus: using ATP! Microtubules which are not attached to the chromosomes = –(Responsible for elongating the cell along its polar axis) nonkinetochore microtubules

14. Cytokinesis: Division of the cell’s cytoplasm. Occurs differently in plant and animal cells. Animal Cells: Cleavage occurs beginning at a using microfilaments associated with myosin (protein). cleavage furrow Actin Plant Cells: Vesicles form a Cell plate, which becomes a cell wall

15. Place these cells in order and name the phase or process.

17. Bacterial Reproduction: (Binary fission) Most bacterial genes are carried on a single chromosome (circular DNA) Chromosome is still LONG: 500X length of cell (must be folded) Steps: Chromosome replication begins. Origin of replication regions move rapidly apart. As replication finishes, plasma membrane grows inward and – new cell wall is deposited.

18. Control of Cell Cycle: Normal growth, development, and maintenance depend upon proper timing and rate of mitosis. Different cells exhibit different patterns: skin: divide continuously stop dividing but retain ability (for wounds, etc) liver: highly specialized (nerve & muscle): do NOT divide in adults

19. Cell culture research: Identifies conditions that affect cell division. Research suggests the cell cycle is driven by specific chemical signals in the cytoplasm. Cell cycle control system: cyclic set of molecules triggers and coordinates cell cycle events. Checkpoint: critical control point (stop / go) G1 checkpoint (called the Restriction Point in mammals) seems to be the most important: Late G1, cell must decide to divide _____ _ or not (enters S phase) (enters G0 phase)

20. 2 Main Types of Regulatory Molecules (both proteins): Protein Kinases: enzymes which activate or inactivate other proteins via phosphorylation. Give the “go ahead” signal at the G1 & G2 checkpoints Concentration in cell is constant, but they are normally in: inactive form

21. 2 Main Types of Regulatory Molecules (both proteins): Cyclins: proteins with a concentration that fluctuates during the cell cycle. Cyclins attach to kinases to make them active, therefore called: cyclin-dependent kinases (Cdks) Maturation promoting factor (MPF): First Cdk to be discovered Concentration of cyclin rises during G2 until a certain threshold level triggers: start of prophase. MPF transfers phosphates to target proteins to cause a cascade of events: “Master switch” Cyclin is destroyed during mitosis to: restart cycle

22. Internal & External Clues help Regulate the Cell Cycle Internal: Kinetochores not yet attached to spindle send a signaling pathway – keeps anaphase-promoting complex (APC) inactive External (In animal cells): Essential nutrients needed. required by some mammal cells Growth factors: Density-dependent inhibition: crowding stops cell division Anchorage-dependence: Cells will only divide if they are attached to a substratum, such as the extracellular matrix of tissue (or a culture dish)

23. Abnormal Cell Division = Cancer Cells: Do not respond normally to the body’s control mechanisms. Divide excessively, invade other tissues. No density-dependent inhibition or Anchorage-dependence May stop at any point in the cell cycle. “Immortal” in culture: HeLa cells from 1951 (vs. normal mammal cells which can only divide 20-50X) Normal cells become cancer cells when they are “transformed” by changes in the genes controlling the cell cycle.

24. mass of cancer cells. Can be benign Tumor = (non-moving) or malignant (spreads) Malignant cells: abnormal metabolism, may have dif. chromosome #, stop functioning completely. Metastasis = spread of cancer due to loss of adhesions (can enter blood and lymph vessels)

26. MEIOSIS CHAPTER 13

27. The fact that organisms reproduce their own kind is a result of heredity. Heredity: transmission of traits from one generation to the next. Variation: individuality (differences among individuals in a species) scientific study of heredity and variation Genetics:

28. Genome Inheritance: Chromosomes consist of hereditary units called: genes Locus = a gene’s location on a chromosome. The specific of in a gene sequence nucleotides determine its function. Gene function may also be affected by: environment

29. Asexual and Sexual Reproduction: 2 parent cells required Each parent passes ½ its genes to its offspring Offspring are a unique combo of genes more genetic variation in the species Process is faster, easier, often more prolific

30. MITOSIS: Works for asexual reproduction but not for sexual. WHY? Parent cells fuse -- must only contain ½ the chromosomes. (Mitosis maintains chromosome number) Sexual reproduction: can only occur after meiosis has cut the chromosome # in half!

31. Sample chromosome numbers (somatic):Can you match them up? Human 200-300 Turkey 24 Potato 46 Oak tree 82 Crayfish 96 crayfish oak human turkey potato Chromosome number is NOT related to: size, complexity, evolutionary development... always even (occur in pairs) Chromosome number IS:

32. CHROMOSOMES: Occur in homologous pairs in the somatic cells. a pair of chromosomes Homologous chromosomes = that have genes for the same traits located at the same positions (2 homologues)

33. Karyotype: Display of an individual’s somatic cell metaphase chromosomes arranged in pairs (by size, centromere position, and banding pattern) Sex chromosomes: Autosomes: Human chromosome pairs #1-22. Not pair #23. related to gender. Males = XY, Females = XX

34. CHROMOSOME NUMBER: Diploid: both members of each homologous pair present. (2n) Haploid: only ONE member of each homologous pair present. (n) meiosis Mitosis produces ______ cells while diploid gametes produces ______ cells called haploid

35. SEXUAL LIFE CYCLES: Organisms which reproduce sexually halve the chromosome number through meiosis and return it to diploid through: fertilization Lifecycles vary in regards to timing. 3 main cycles: ANIMALS (including humans): The ONLY haploid cells = Gametes produced by meiosis No further cell division before fertilization. gametes

36. FUNGI and some protists (incl. ALGAE): The ONLY diploid cells = zygote Meiosis occurs immediately AFTER fertilization, then mitosis creates a multicellular adult that is haploid! Gametes produced by mitosis (organism is already haploid) Either diploid or haploid cells can undergo mitosis, but ONLY ______ cells can undergo meiosis. diploid

37. PLANTS and some ALGAE: Alternate between multicellular haploid and diploid generations Called: Alternation of generations Multicellular diploid produces haploid by sporophyte spores meiosis Haploid spores: divide mitotically to make multicellular gametophyte gametophyte Multicellular haploid produces haploid by gametes mitosis

38. Identify as plant, animal, or fungus: A. B. fertilization C.

39. MEIOSIS Preceded by Interphase: chromosome replication during S phase creates 4 haploid daughter cells Cell divides twice:

40. Steps of Meiosis I: First division Prophase I: Longer and more complex than mitotic prophase. (90% of meiotic time) Chromosomes condense and (each w/ 2 sister chromatids) homologues pair up Synapsis occurs when homologous chromosomes come together as tetrads: The nonsister chromatids intertwine at spots called chiasmata

41. Prophase I: Like mitosis: Nuclear membrane and nucleolus disperse. Spindle apparatus forms Centrosomes (w/ centrioles in animals) migrate toward poles Chromosome kinetochores attach to spindle

42. Metaphase I: TETRADS line up at equatorial plate (Double file line)

43. Anaphase I: Centromeres DO NOT divide in half! Entire duplicated chromosomes move toward poles (homologues separate)

44. Telophase I and Cytokinesis: Cytokinesis occurs simultaneously with Telophase I Forms: 2 haploid daughter cells (but chromosomes are still duplicated)

45. Steps of Meiosis II: Similar to mitosis, second division Prophase II: If the cells entered interkinesis, nuclear membrane and nucleolus dissolve. Spindle apparatus forms & chromatids attach Centrosomes (w/ centrioles in animals) migrate toward poles

46. Metaphase II: Chromosomes line up at equatorial plate (SINGLE file line)

47. Anaphase II: Centromeres divide in half Each chromatid is now considered a full chromosome Spindle fibers pull chromosomes (by their kinetochore) toward poles

48. Telophase II and Cytokinesis: Nuclear membrane and nucleoli reform Chromosomes uncoil, return to chromatin state Spindle fibers dissolve Cytokinesis results in a total of 4 haploid cells

49. MEIOSIS = gametogenesis Females: oogenesis (egg formation) Males: spermatogenesis

50. Sexual Sources of Genetic Variation Evolution (by Natural Selection) depends upon inheritable variations in a species that favor the reproductive success of some individuals. Variation is ensured by these mechanisms: Independent Assortment of Chromosomes Crossing Over Random Fertilization Drosophila bifurca (fruit flies)