Chromosomes & Cell Division Notes

1. Chromosomes & Cell Division Notes About two trillion cells are produced by an adult human body every day!

2. DNA (deoxyribonucleic acid): Stores info and tells the cells when to make proteins, and what kind to make. GENE: unit of heredity, enough DNA to instruct for the construction of one protein. Each DNA molecule is made up of thousands of genes.

3. Forms of DNA • Chromatin- genetic material in non-dividing cell’s nucleus; DNA in thin, non-coiled strands. • DNA is in this form 99% of the time because cells are generally not dividing. • DNA must be in this form in order to be copied (replicated). (2) Chromosomes - genetic material in dividing cell’s nucleus; DNA in coiled, rod-shaped form. • DNA must be in chromosome form in order for the cell to divide or reproduce.

4. Steps in Chromosome Formation • Chromatin  DNA in thin, uncoiled strands. • DNA replicates. • DNA coils. • Chromosomes  DNA in 2 joined identical chromatids.

5. Chromosomes • Chromatids - one of two duplicated, joined, identical parts of a chromosome; found after DNA replication but before cell division. • Centromere – Point at which sister chromatids are attached

6. Chromatid Gene Centromere Chromosome DNA supercoil Gene

7. Chromosome Number • Every species has a characteristic number of chromosomes which is different from other species. Example: nematode worm 2 pairs protozoan 300 pairs human 23 pairs • Chromosomes occur in pairs in sexually reproducing organisms. One of the pair comes from the MOM, the other comes from the DAD.

8. Chromosome Number • HOMOLOGOUS CHROMOSOMES: two members of a pair of chromosomes that carry genes for the same traits, have the same size and shape. (ONE FROM MOM AND ONE FROM DAD)

9. Human Chromosomes - Karyotype

10. Diploid vs. Haploid • DIPLOID (2N): total chromosome number in a body or somatic cell, having both chromosomes of a homologous pair. Diploid or 2N number in humans is 46 chromosomes or 23 homologous pairs. • HAPLOID (1N): chromosomes number in sex cell (egg or sperm), only one chromosome from each homologous pair. Haploid or 1N number in human egg or sperm is 23, there are no homologous chromosomes.

11. MITOSIS the key to growth

12. Mitosis - the division of the nucleus into two equal halves or sets of genetic information Basically, simple cell division

13. Purpose: Each cell must have the complete “blueprint” of their DNA. Every time the cell divides, it must pass on a copy of each chromosome.

14. Without Mitosis 1 46chromosomes Cell division 2 23 23 4 11.5 11.5 11.5 11.5 8 5.75 5.75 16 2.875 2.875 32 1.4 1.4 64 .7 .7 128 .35 256 .175 512 .0875

15. With Mitosis 1 46chromosomes Cell division 2 46 46 4 46 46 46 46 8 46 46 16 46 46 32 46 46 64 46 46 128 46 256 46 512 46

16. Every cell in the body (except 1 kind that we will talk about later) has the same DNA. Each cell will just use their part of it. (Ex. Heart cells will use heart DNA). Therefore; all cells divide using mitosis. Cells divide as part of growth or reproduction “Growth” includes: *getting larger *repair *replacement (for normal “wear and tear”)

17. Mitosis is part of the Cell Cycle The cell cycle is divided into 5 phases. 1. Interphase 2. Prophase 3. Metaphase Mitosis 4. Anaphase 5. Telophase **This is a moving, continuous process. Stages are for study.

18. Interphase Period of growth and normal cell activity Events of Interphase: • The cell spends most of its life in interphase. • DNA is in chromatin form, spread throughout the nucleus. • DNA replicates, cell then contains two exact copies of each chromosome. • Centriolesfound just outside the nuclear membrane of the cell. • Stages: • G1 (Gap 1) – normal cell activities • S (Synthesis) – DNA synthesis (replication) • G2 (Gap 2) – prepares for cell division

19. Interphase Look for a distinct nucleus

20. Mitosis: Prophase The first stage of cell division Three things happen: Chromosomes coil and become visible The nuclear membrane breaks down and disappears The spindle forms *Animal cells have centrioles

21. Mitosis: Prophase Look for chromosomes in the center

22. Mitosis: Metaphase Chromatids attach to the spindle fibers at the centromere Chromosomes line up on the “equator” (in the middle of the cell)

23. Mitosis: Metaphase Look for chromosomes lined up on the “equator”

24. Mitosis: Anaphase • Centromeres split apart • Chromatids move away from each other toward opposite poles

25. Mitosis: Anaphase Look for chromosomes in two groups pulling apart

26. Mitosis: Telophase The fourth and final phase of mitosis The opposite of Prophase (the cell is ending its division and going back to normal) Chromosomes unwind to form chromatin Two new nuclei form with new membranes The spindle disappears

27. Mitosis: Telophase Look for two groups of chromosomes with a cell plate or cleavage furrow

28. Stages of Mitosis • Prophase • Metaphase • Anaphase • Telophase • P – M – A - T

29. Cytokinesis The division of the cytoplasm Animal cells pinch inward forming a cleavage furrow. Plant cells divide from the inside towards the outside by forming a cell plate which becomes the cell wall.

30. Cytokinesis Animals: Cleavage furrow Cell plate cell wall

31. Differences in plant and animal cells: summary Animals Plants centrioles no centrioles cleavage furrow cellplate cell wall