Cellular Basis of Reproduction and Inheritance: Cell Division and DNA Replication

1. Chapter 8 Cellular Basis of Reproduction and Inheritance

2. LM 340 8.1 Like begets like, more or less • Some organisms reproduce asexually • And their offspring are genetic copies of the parent and of each other Figure 8.1A

3. Other organisms reproduce sexually • Creating variety in the offspring Figure 8.1B

4. 8.3 Prokaryotes reproduce by binary fission • As the cell replicates its single chromosome, the copies move apart • And the growing membrane then divides the cells

5. Colorized TEM 32,500 One-celled protists also do fission, but must do mitosis first to divide chromosomes evenly Prokaryotic chromosomes

6. 8.4 Chromosomes of eukaryotes duplicate in cell division Eukaryotic cells have many chromosomes – each contains thousands of genes - are visible only when the cell is dividing Before cell division - DNA replicates a. helicase “unzips” molecule b. templates – original strands c. Polymerase – base-pairing rules  two identical molecules

7. DNA condenses Before a cell divides, it packs its DNA into CHROMOSOMES - ALREADY COPIED (replicated) - tightly packed and condensed - keeps copies organized and intact until cell splits

8. DNA chromatin DNA wraps around histones Groups of histones form nucleosomes These group to form chromatin This coils and wraps until it all fits into the nucleus. One chromosome (copied and packed for cell division)

9. SEM of human chromosomes Sister chromatids identical copies Centromere holds chromatids together Prokaryotes have a single, circular chromosome - no histones; no nucleus Double-stranded (replicated) chromosome

10. INTERPHASE G1 S(DNA synthesis) G2 Cytokinesis Mitosis MITOTICPHASE (M) • 8.5 The cell cycle multiplies cells • The cell cycle consists of two major phases Figure 8.5

11. Cell Cycle INTERPHASE - non-dividing cells - normal function - most of cell life MITOTIC PHASE - cell divides  2 new cells G1 growth, normal life functions S “synthesis” – DNA replicates G2 final growth; prepares to divide INTERPHASE MITOTIC PHASE Mitosis – chromosomes condense, organize and divide - each new cell gets one copy of every chromosome Cytokinesis – cytoplasm divides

12. LM 250 INTERPHASE PROPHASE PROMETAPHASE Centrosomes(with centriole pairs) Fragmentsof nuclearenvelope Centrosome Early mitoticspindle Kinetochore Chromatin Nucleolus Centromere Chromosome, consistingot two sister chromatids Spindlemicrotubules Nuclearenvelope Plasmamembrane • The stages of cell division Figure 8.6 (Part 1)

13. PHASES OF MITOSIS • PROPHASE – cell organizes and prepares • chromatin • nuclear membrane, nucleolus • spindle and asters • centrioles • PROMETAPHASE – chromosomes condensed • move toward middle • centrioles to opposite poles • spindle • METAPHASE – chromosomes in middle • Centromeres and spindle fibers

14. TELOPHASE AND CYTOKINESIS ANAPHASE METAPHASE Nucleolusforming Cleavagefurrow Metaphaseplate Daughterchromosomes Nuclearenvelopeforming Spindle Figure 8.6 (Part 2)

15. ANAPHASE -chromosomes separate • spindle fibers pull • single copies to opposite poles of cell • TELOPHASE – return to normal • chromosomes relax/uncoil into chromatin • nuclear membranes form; nucleoli appear • spindle fibers disappear • CYTOKINESIS- division of cytoplasm • identical daughter cells Cleavage furrow

16. Cleavagefurrow SEM 140 Cleavage furrow Contracting ring ofmicrofilaments Daughter cells Cell division differs for plant and animal cells • 8.7 Animal cytokinesis • Microfilaments • Cleavage furrow • Pinch cytoplasm in two Figure 8.7A

17. Daughternucleus Cell plateforming Wall ofparent cell TEM 7,500 Cell wall New cell wall Vesicles containingcell wall material Cell plate Daughter cells In plants - no centrioles, asters (but spindle) - cell plate - new cell wall grows along sides of cell plate Figure 8.7B

19. Control of Cell Division Chemical signals tell a cell when to divide Normal rate: growth, repair - asexual reproduction in some organisms Slow rate: some cell types divide rarely (liver) - aging  slow healing, lose some cells Fast rate: some cell types (skin, digestive lining) Uncontrolled cancer

20. G1 checkpoint G0 Controlsystem S G1 G2 M Mcheckpoint G2 checkpoint Cell cycle checkpoints Check cell conditions - Cycle won’t proceed unless okay • G1 checkpoint: Cell has enough materials? - Yes? Go to S; No? Go to G0 (nondividing) • G2 checkpoint: DNA copied correctly? Yes? Go to M • M checkpoint ( in metaphase): - chromosomes lined up correctly? - centromeres attached to spindle?

21. After forming asingle layer,cells havestopped dividing. Providing anadditional supply ofgrowth factorsstimulatesfurther cell division. Growth factors & cyclins • Chemicals secreted by cells • Can start or stop cell division Figure 8.8B

22. Cells anchor todish surfaceand divide. When cells haveformed a completesingle layer, theystop dividing (density-dependent inhibition). If some cells arescraped away, theremaining cells divideto fill the dish with asingle layer and thenstop (density-dependentinhibition). Anchorage and Contact Inhibition Anchored to a solid substance - ex. Extracellular matrix Contact: stop dividing when they touch other cells - density-dependent Figure 8.8A

23. Programmed Cell Deathapoptosis • Cells damaged too much to repair • – self-destruct • 2. Embryonic development – lose unneeded cells

24. 8.10 Cancer – uncontrolled cell division • Cancer cells ignore cycle controls • Repeated and rapid cell divisions • tumor – mass of non-functioning cells • Benign – not cancer; do not spread to nearby tissue • May get so large it stops tissue function • Malignant tumor – cancer • Will invade and destroy neighboring tissue • Metastatic tumor – spreads to other body parts • Starts new cancers

25. Cells begin to divide abnormally Continue dividing, invade healthy tissue Spread through blood or lymph stream, can start new tumors

26. Lymphvessels Tumor Bloodvessel Glandulartissue Cancer cells invadeneighboring tissue. Cancer cells spread throughlymph and blood vessels toother parts of the body. A tumor grows from asingle cancer cell. • If not treated early, cancer will spread • - kills by destroying organ function Figure 8.10

27. The most common cancer - skin Most dangerous - MELANOMA

28. Cancer treatment Radiation – high-energy, carefully aimed at tumor Chemotherapy – drugs specific for tumor types • interfere with cell division • some normal cells destroyed, too • Skin (lose hair); digestive lining (nausea) Surgery – remove tumor and nearby cells Boost immune system – healthydiet, reduce stress

29. LM 700 LM 500 8.11 Review mitosis: Growth, cell replacement, and asexual reproduction • Mitosis functions in growth – adds new cells In repair: replace old or damaged cells

30. LM 10 In Asexual Reproduction One-celled organisms, some simple multicelled Hydra with bud vegetative propagation in plants

31. Regeneration – replace lost body part • starfish can replace an arm flatworms can regrow a body Lizards can replace a tail

32. Stem cells and differentiation Differentiate – cells specialize as embryo develops Stem cell – unspecialized cell - can differentiate to form many kinds of cells - depends on chemical signals from nearby cells

33. Stem cells for cloning tissues

34. Meiosis & Sexual Reproduction Sexual Reproduction - two parents a. Offspring are genetic mix of both parents b. Have a NEW combination of genes Advantage – genetic variation in offspring a. Some may have traits that favor survival b. Can pass these traits on to offspring c. Darwin’s theory - “ survival of the fittest” d. Variation in individuals allows species to evolve

35. Crossing over a. Only in meiosis b. Chromatids trade pieces c. Further increases genetic variation

36. Simple organisms – exchange some DNA a. Bacteria and protists - conjugation Sexual Reproduction Complex organisms – special cells a. gametes – sperm and egg b. Gametes combine in fertilization  zygote  new organism

37. Chromosome Number: Diploid and Haploid Somatic (body) cells a. have matched chromosome pairs - homologous - one member of pair from each parent - carry genes for the same traits b. 22 pairs autosomes; one pair sex chromosomes X, Y

38. Cells with paired chromosomes are diploid a. 2n (n = number) b. Human: 2n = 46 (23 pairs) Fruit fly 2n = 8 2 sets of chromosomes - 2 sets of genes

39. Homologous pairs separate in MEIOSIS Diploid cell Has pairs (2n=2) TWO cell divisions - Daughter cells have ½ parent chromosome number Meiosis I Pairs separate (n = 1) Meiosis II copies separate (n = 1) Haploid cells - NO pairs (n = 1)

40. Sex cells are haploid gametes – sperm and egg Haploid (n) - one set of chromosomes - one member from each homologous pair human: n = 23

41. Meiosis Reduces the Chromosome Number 2n parent cell DNA replicates in interphase First division – pairs separate Second division – sister chromatids separate  4 haploid daughter cells

42. Special organs produce gametes 2n  n Sperm + egg = fertilization zygote n + n  2n Plants have alternating generations too Sexual Life Cycle Alternates between diploid and haploid generations

43. MEIOSIS I: Homologous chromosomes separate INTERPHASE PROPHASE I METAPHASE I ANAPHASE I Sister chromatids remain attached Microtubulesattached to kinetochore Centrosomes (with centriole pairs) Metaphaseplate Sites of crossing over Spindle Centromere(with kinetochore) Homologouschromosomes separate Sisterchromatids Nuclearenvelope Tetrad Chromatin Meiosis I: homologous pairs separate- makes two daughter cells, but sister chromatids are still attached 2n parent cell synapsis pairs line up pairs separate

44. MEIOSIS II: Sister chromatids separate TELOPHASE IAND CYTOKINESIS TELOPHASE IIAND CYTOKINESIS PROPHASE II METAPHASE II ANAPHASE II Cleavagefurrow Sister chromatidsseparate Haploid daughter cellsforming Meiosis II: sister chromatids separate  4 haploid cells 2n  n two daughter cells chromatids 4 daughters one chromosome set each separate one set two copies (sisters) single copies

45. Mitosis Meiosis 2n copies 2n copies 2n single Parent cell(before chromosome replication) Meiosis i 2n copies 2n copies n copies n single Prophase I Prophase Tetrad formedby synapsis ofhomologouschromosomes Chromosome replication Chromosome replication Duplicated chromosome(two sister chromatids) 2n = 4 Chromosomes align at themetaphase plate Tetradsalign at themetaphase plate Metaphase I Metaphase Homologous chromosomesseparate duringanaphase I;sister chromatidsremain together Anaphase ITelophase I Sister chromatidsseparate during anaphase AnaphaseTelophase Haploidn = 2 Daughtercells of meiosis I No furtherchromosomalreplication; sisterchromatids separateduringanaphase II Meiosis ii 2n 2n Daughter cellsof mitosis n n n n Daughter cells of meiosis II 8.15 Review: Comparing mitosis and meiosis

46. Making sperm and egg Sperm: 2n parent cell  4 haploid sperm Ovum: 2n parent cell  1 haploid egg + haploid polar bodies

47. Ovum needs all the cytoplasm Sperm needs only DNA - and flagellum - and mitochondria for power - and acrosome to penetrate ovum Ovum and polar body (0.1mm)

48. Causes of genetic variation 1. Homologous pairs have different genes • same traits, but may be different forms 2. Crossing over – homologs trade pieces before separating 3. Pairs position in Metaphase I • n pairs  2n possible combinations 4. Random fertilization of eggs by sperm • Any egg or sperm is equally likely to be used 5. Gene or chromosome mutation - Error in replication or cell division

49. Possibility 1 Possibility 2 Two equally probablearrangements of chromosomes at metaphase I Metaphase II Gametes Combination 2 Combination 4 Combination 1 Combination 3 8.16 Chromosomes line up randomly in meiosis • Many different gene combinations in haploid gametes Figure 8.16

50. When meiosis goes wrong Nondisjunction - do not separate correctly - pairs or chromatids In mitosis  defective nucleus, cell usually dies In meiosis  defective gamete  wrong number in zygote