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 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 23 23 1 2 4 11.5 11.5 11.5 11.5 8 16 Cell division
46 chromosomes
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 46 46 1 2 4 46 46 46 46 8 16 Cell division 46 46 32
46 chromosomes
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. Cells divide as part of growth or reproduction
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. Period of growth and normal cell activity
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.
Centrioles found 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. Animals Plants Differences in plant and animal cells: centrioles
summary
Animals
Plants
centrioles
no centrioles
cleavage furrow
cell plate
cell wall