Mitosis
Part 1: Chromosomes Chromosome structure- DNA can exist in 2 different forms A. Chromatin- DNA protein complex that is not coiled (thin) B. Chromosome- rod-shaped; DNA is coiled tightly around proteins called histones. Formed before cell division. Each copy is called a chromatid.
FYI-The diagram will help you see the relationship in a cell. 1. Chromosomes are found in the nucleus 2. Chromosomes are made of DNA 3. Sections of chromosomes are called genes
Eukaryotic Chromosomes All eukaryotic cells store genetic information in chromosomes Most eukaryotes have between 10 and 50 chromosomes in their body cells Human body cells have 46 chromosomes or 23 identical pairs
Eukaryotic Chromosomes Each chromosome is composed of a single, tightly coiled DNA molecule Chromosomes can’t be seen when cells aren’t dividing and are called chromatin
Compacting DNA into Chromosomes DNA is tightly coiled around proteins called histones
Chromosomes in Dividing Cells Duplicated chromosomes are called chromatids & are held together by the centromere Called Sister Chromatids**
**Karyotype** A picture of the chromosomes from a human cell arranged in pairs by size First 22 pairs are called autosomes Last pair are the sex chromosomes XX female or XY male
The Y Chromosome Decides Boy or Girl? The Y Chromosome Decides Y - Chromosome X - Chromosome
II. Chromosome #’s-not related to complexity of species Each organism has a distinct number of chromosomes, in humans, every cell contains 46 chromosomes. Other organisms have different numbers, for instance, a dog has 78 chromosomes per cell. **There is no relationship between # of chromosomes and speed of mitosis. It all happens at the same rate.**
Chromosome #’s of various species Organism # of Chromosomes Ant 2 Mosquito 6 Bearded Dragon 32 Cat 38 Pig Axolotl 28 Dog 78 Hedgehog 90 Carp (highest animal) 104 Corn 20 Algae 148 Adder Fern (highest plant) 1260 Aulacantha (Protist) 1600
C. Sex Cells - also known as gametes C. Sex Cells - also known as gametes. These cells contain half the number of chromosomes as body cells and are called HAPLOID. (for us = 23) This is referred to as the N number. So, our N number is 23.
If you have XX sex chromosomes - you are female. If you have XY sex chromosomes - you are male. During fertilization, sperm cells will either contain an X or a Y chromosome (in addition to 22 other chromosomes - total of 23). If a sperm containing an X chromosome fertilizes an egg, the offspring will be female. If a sperm cell containing a Y chromosome fertilizes an egg, the offspring will be male.
This is our Diploid number (2N). D. Autosomes -all the other chromosomes; every cell of an organism has 2 copies of each autosome (2N). (N is 23, so 2N = 46) This is our Diploid number (2N). -We receive one copy from each parent, called homologous chromosomes- the same size and shape, and they carry genes for the same traits. Homologous chromosomes, 2 pair
Cell Division- Prokaryotes Cell Division in Prokaryotes. 1. Binary Fission- the division of a prokaryote into 2 identical cells. 2. Considered asexual (one parent) Remember- prokaryotes are bacteria!
B. 3 General Stages Chromosome makes a copy of itself, attached to the inside of the cell membrane. Cell doubles in size Cell wall forms between the 2 chromosomes and the cell divides, forming 2 equal cells.
Prokaryotes vs. Eukaryotes Bacteria All other organisms Binary Fission Mitosis In all bacteria All cells but sex cells Have circular DNA Have chromosomes Replicates at 500 bp/min. Replicates at 50 bp/min. Produces identical organisms Produces identical cells
What is Mitosis? The splitting or dividing of the nucleus **Produces two genetically identical cells from one cell. **Form of asexual reproduction, used for growth, repair, and reproduction. Occurs only in certain types of cells (body cells except the sex cells), and in single-celled protists.
B. The Cell Cycle- Stages B. The Cell Cycle- Stages (Use your WS for this part) -not considered part of mitosis- is time between divisions. 1. Interphase (longest part of the cell cycle) G1 (Growth 1) S (Synthesis) - DNA copies G2 (Growth 2) - cell prepares for division, organelles double
Interphase Cells spend most of its time in this phase Cells are growing DNA has to be replicated (all 2 meters of it) Proteins are being produced 90% of all cells are in this phase Three phases: G1, S, and G2
The Cell Cycle: G1 phase Growth phase 1: proteins are made, cell grows to normal size. If checkpoint here passed, cell will complete division Some cells, like nerve cells, stay in this phase forever.
The Cell Cycle: S phase All nuclear DNA is replicated Chromosome number doubles Checkpoint: does cell have all its chromosomes doubled properly?
The Cell Cycle: G2 phase Cell volume increases Centrioles with their microtubules form (centrosome) Organelles double. Checkpoint: is cell large enough to divide?
Photo of Interphase Whitefish blastula cells
C. Mitosis Phases This animation shows the process of mitosis.
1. Prophase DNA shortens and coils into chromosomes; nucleolus and nuclear membrane break down and disappear; centrioles appear and move towards opposite poles Spindle fibers appear and attach to centromere. Cells Alive Mitosis Animation (click here)
Early Prophase Photo
2. Metaphase Chromosome pairs line up in the center by the centromere. Move along spindle fibers.
Metaphase Photo
3. Anaphase Chromosomes split at centromere. Chromosomes move to opposite poles.
Anaphase Photo
4. Telophase DNA lengthens and disappears. nucleolus and nuclear membrane reappear. centrioles and spindle fibers disappear. Cell Splits (called cytokinesis), forming 2 equal cells.
Telophase Photo
Cytokinesis The process by which the cytoplasm divides and one cell becomes two individual cells. The process is different in plants and animals: Animal cells – cell membrane pinches in and separates the 2 cells = cleavage furrow Plant cells- vesicles from the Golgi apparatus fuse at the midline forming a cell plate, which will become the cell wall.
Cleavage Furrow
Animation of cell plate forming
Now, name the phases as they occur in the animation.