1. Chromosomes and Cell Reproduction Chapter 6

2. Chromosomes DNA must be present in any new cell that is formed so it must be copied and distributed so each cell has a complete set

3. Prokaryotic Cell Reproduction Single circular DNA attached to inner cell membrane Binary Fission – asexual reproduction producing identical offspring

4. 2 Stages of Binary Fission Stage 1: DNA is copied Stage 2: Cell divides by adding a new cell membrane between 2 DNA copies Squeezes in middle New cell wall forms until pinched in 2

5. Eukaryotic Cell Reproduction DNA is organized into genes These are segments that code for a protein of RNA molecule Thousands of genes in DNA When genes are being used the DNA is stretched out

6. Chromosomes Chromosomes are the DNA and the proteins associated with it

7. As a eukaryote prepares to divide, chromosomes become visible (DNA is copied before this) Chromatids – 2 exact copies of each Chromosome attached at point called centromere During cell division chromatids separate and are placed into new cells

8. Each Human somatic cell (anything besides sperm and egg) has 2 copies of 23 different chromosomes = 46 chromosomes These 23 pairs are different in size, shape, and the genes they carry

9. Sets of Chromosomes 23 pairs made of 2 homologous chromosomes (a.k.a. homologues) which are similar in size and shape, and genetic content Each Homologue comes from 1 parent Again, you have 46 chromosomes, 23 from each parent

10. Diploid or Haploid? Diploid – somatic cells contain 2 sets Haploid – gametes contain 1 set n = 1 set of chromosomes n = 23 = human haploid #; gametes 2n = 46 = human diploid #; somatic cell Fertilization is when 2 haploid gametes fuse Forms a diploid zygote (fertilized egg), the first cell of an individual

11. Each organism has a characteristic number of chromosomes Some may have 1 pair, some plants have over 500

12. Sex Chromosomes 23 chromosome pairs in human somatic (body) cells 22 of these are autosomes, not directly involved in determining gender The other pair are sex chromosomes that contain genes that determine gender Humans have X and Y chromosome

13. Y chromosomes have genes that cause fertilized egg to develop into a male (XY) Females can only donate X so sex is determined by man

14. Sex chromosomes are different in other organisms Male grasshopper = X0 (0 = missing) Female grasshopper = XX

15. Change in Chromosome Number All 46 chromosomes are needed for normal development and function If you have more than 2 copies of a chromosome – trisomy – don’t develop properly

16. Karyotype Photo of chromosomes in a dividing cell that shows them in order by size

17. Change in Chromosome Structure These are called mutations Breaking of chromosome in 4 different ways Deletion Duplication Inversion Translocation

18. Deletion Piece breaks off completely Certain genes are missing in new cell Usually fatal to zygote

19. Duplication Chromosome fragment attaches to homologous chromosome giving it 2 copies of certain genes

20. Inversion Chromosome reattaches to original but in reverse order

21. Translocation Reattaches to nonhomologous chromosome

22. 6.2 The Cell Cycle A repeating sequence of growth and division 90% of the time cells are in 1 st three phases called Interphase Last 2 phases only when it’s about to divide

23. 5 Phases of Cell Cycle: Phases 1 through 3 = Interphase G1 = 1 st Growth Phase Cell grows rapidly Carries out normal functions Major portion of life Stay here if not dividing S = Synthesis Phase DNA is copied At end each chromosome is 2 chromatids attached by/at centromere G2 = 2 nd Growth Phase Prepares for nucleus to divide Microtubules are rearranged preparing for next stage = Mitosis

24. Mitosis Nucleus divides into 2 nuclei with same number and kind of chromosomes Cytokinesis Cytoplasm divides These 2 stages produce new cells identical to original and allow growth, repairs and in some cases asexual reproduction

25. Control of Cell Cycle Feedback information tells cell what to do Checkpoints/Inspection Points Feedback can trigger next phase or delay the next phase The cycle is controlled by many proteins and has 3 principal checkpoints

26. G1 Checkpoint - Growth Decides whether cell will divide Proteins will stimulate cell to begin S phase if conditions are right

27. G2 Checkpoint – DNA Synthesis DNA replication is checked by DNA repair enzymes Once passed, proteins trigger mitosis

28. Mitosis Checkpoint Triggers an exit from mitosis

29. Cancer Uncontrolled growth of cells May promote growth-promoting molecules May inactivate off/slow switch

30. 6.3 Mitosis and Cytokinesis When cells divide the chromatids on each chromosome are moved to opposite sides with the help of a spindle A spindle is a cell structure made up of both centrioles and individual microtuble fibers

31. Forming The Spindle Centrosomes found at cells poles organize assembly of spindle In animal cells there are a pair of centrioles found inside each centrosome (plants don’t have centrioles) Centrioles and spindle fibers are both made of microtubules (hollow tubes of protein) Each spindle fiber is made of 1 microtubule Each centriole is made of 9 triplets of microtubules arranged in a circle

32. Separation of Chromatids by Attaching Spindle Fibers Some microtubules interact, others attach to centromere 2 sets of microtubules extend out from poles When poles and centomeres are attached the 2 chromatids can be separated Once separated called chromosomes

33. One chromosome goes to one pole while the other is pulled towards the other They move along microtubule paths and move closer to poles as microtubules are broken down

34. Mitosis – 4 Stages Prophase Chromosomes coil and become visible Nuclear envelope dissolves Metaphase Chromosomes line up along equator Chromatids linked to poles by spindle fibers Anaphase Centromeres divide Chromosomes move toward poles Telophase Nuclear envelope reforms Chromosomes uncoil Spindle dissolves

36. Cytokinesis Cytoplasm divided in half Cell membrane grows to enclose each cell Animal Cells – pinched in half by belt of protein threads Plant Cells – Golgi apparatus forms vesicles that fuse at midline forming cell plate (cell wall in middle of cell) Each offspring is equal in size, amount of cytoplasm, number of organelles and has an identical copy of chromosomes