Cell Cycle

Mitosis video from book http://static-movie-usa.glencoesoftware.com/source/10.1083/499/52dd14fb7a59d64efea2e298248d5eef7bcd2c8c/JCB_201202112_V4.mov

Cell Division Interphase The cytoplasmic contents double Two centrosomes form Chromosomes duplicate in the nucleus during the S phase

Cell Division Prophase In the nucleus, chromosomes become more tightly coiled and folded. In the cytoplasm, the mitotic spindle begins to form as microtubules rapidly grow out from the centrosomes.

Cell Division Prometaphase The nuclear envelope breaks into fragments and disappears. Microtubules extend from the centrosomes into the nuclear region. Some spindle microtubules attach to the chromosomes. Other microtubules meet those from the opposite poles and connect.

Cell Division Metaphase The mitotic spindle is fully formed. Chromosomes align in the middle. Centromeres of sister chromatids are facing the opposite poles of the spindle.

Recall - Chromatid After DNA replication there are two identical copies called sister chromatids Sister chromatids are connected together at the centromere

Cell Division Anaphase Sister chromatids separate at the centromeres. Daughter chromosomes are moved to opposite poles of the cell (motor proteins) Spindle microtubules not attached to chromosomes lengthen, moving the poles farther apart. The two sides of the cell end with equal numbers of chromosomes.

Cell Division Telophase The cell continues to elongate. The nuclear envelope forms around chromosomes at each pole, establishing daughter nuclei. Chromosomes uncoil (chromatin). The mitotic spindle disappears.

Cell Division During cytokinesis, the cytoplasm is divided into separate cells. Cytokinesis usually occurs simultaneously with telophase.

Cell Division Cytokinesis - Animals Cytokinesis - Plants Cleavage furrow forms and divides cell in two Cell plate forms and divides cell in two

Cell Cycle How does the cell “know” when to move on to the next step?

Cell Cycle Control How does the cell “know” when to move on to the next step? Growth Factors (type of protein) are being produced during the G1 and G2 phases. When they reach a high enough level, the cell knows to move on to the next phase. This is an important area of research in biology

G1 checkpoint G0 G1 S Control system M G2 M checkpoint G2 checkpoint Figure 8.8a A schematic model for the cell cycle control system G2 M checkpoint G2 checkpoint

Cancer and the Cell Cycle Cancer cells do not follow the normal signals that regulate the cell cycle They keep dividing and can possibly spread to new areas of the organism often through the lymphatic system

Cancer and the Cell Cycle Radiation is a treatment to destroy cells (kills both cancerous cells and healthy cells) Chemotherapy is a treatment that slows/stops the growth of cells (stops good cells and bad) Can lead to hair loss, intestinal issues, other symptoms

Cancer and the Cell Cycle Fully understanding the human genome could lead to improved treatment Certain mutations cause the cell cycle to go out of control, if we can fix those mutations perhaps we can also treat cancer more successfully

Recall: Chromosomes vs Chromatin Individual chromosomes not visible, described as chromatin Chromosomes visible Draw these Onion cells under light microscope

G0 Phase Some cells enter a phase where they will no longer divide. These cells are still functioning (just stop the division process) Brain neurons, heart muscle cells are a couple examples. They are still functioning and working, but they no longer enter mitosis.

Quiz Put name on top of page and number 1-8

1 In which phase is the chromatin beginning to condense and become visible?

2 In which phase do the chromosomes meet in the middle?

3 When the chromosomes are replicated and attached together they are called ‘sister ______________’.

4 What is the organelle that forms the mitotic spindle (microtubules)?

5 During which phase do the chromosomes duplicate, they are in the form of uncondensed chromatin, and more organelles are made?

6 What are the proteins called that the DNA wraps around?

7 Which phase is shown in the picture? (All three are in the same phase)

8 Which phase is shown in the picture?

A Fern Life Cycle Gametophyte plant (n) Key Haploid (n) Diploid (2n) Male gametangium Spores Sperm Female gametangium Egg Mature sporophyte Meiosis Fertilization Zygote New sporophyte growing from the gametophyte Figure 17.3-6-5 Fern life cycle (step 5)

Diploid vs Haploid Most cells have a two sets of chromosomes, one from the mother and one from the father These cells are diploid cells (2n) 2n - Two sets

Diploid vs Haploid A haploid cell only has one set of chromosomes 1n – one set The gametes are ‘sex cells’ and are haploid. A male produces the sperm A female produces the egg

Why? 2n 1n 2n x 2

A Fern Life Cycle Gametophyte plant (n) Key Haploid (n) Diploid (2n) Male gametangium Spores Sperm Female gametangium Egg Mature sporophyte Meiosis Fertilization Zygote New sporophyte growing from the gametophyte Figure 17.3-6-5 Fern life cycle (step 5)

n n Haploid gametes (n = 23) Key n Haploid stage (n) Egg cell Figure 8.12a Haploid gametes (n = 23) Key n n Haploid stage (n) Egg cell Diploid stage (2n) n n Sperm cell Meiosis Fertilization Ovary Testis Figure 8.12a The human life cycle 2n Diploid zygote (2n = 46) Mitosis and development Multicellular diploid adults (2n = 46)

Chromosome 2n = 46 (2n because one from mom, one dad) (new info) Because most cells have one set from mom and one set from dad they are diploid 2n = 46 (2n because one from mom, one dad) (46 total chromosomes when counting) 23 pairs of homologous chromosomes 46 individual chromosomes

The locus (loci) are the different positions on the chromosome where genes are located

Haploid vs diploid https://www.youtube.com/watch?v=1yu1Zuy_uEQ

Mitosis – In which cells? Almost all cells Somatic Cells are all the cells except the gametes (sperm/egg) or the cells that divide into the gametes (germ cells)

Meiosis – which cells The germ cells undergo meiosis to form the gametes (1n - haploid)

Look at 138-139 – take 3 minutes to read it over and look at the images How is this similar to Mitosis? How is is different than Mitosis?

https://www.youtube.com/watch?v=toWK0fIyFlY

Meiosis

Meiosis Interphase – similar to mitosis Chromosomes duplicate (in the uncondensed chromatin state), more organelles are formed.

Meiosis I Prophase I Homologous chromosomes, each composed of two sister chromatids, come together in pairs forming tetrads. Chromatids of homologous chromosomes exchange segments in a process called crossing over. (also chromatin condenses and nuclear envelope breaks down like mitosis)

Meiosis

Meiosis Metaphase I Anaphase I Tetrads align in the middle Homologous pairs separate and move toward opposite poles of the cell. Unlike mitosis, the sister chromatids making up each doubled chromosome remain attached.

Meiosis I: Metaphase I Anaphase I Spindle microtubules attached to a centromere Sister chromatids remain attached Figure 8.13-3 The stages of meiosis (part 3) Metaphase plate Centromere (with a kinetochore) Homologous chromosomes separate

Meiosis Telophase I Duplicated chromosomes have reached the poles. Usually, cytokinesis occurs along with telophase.

Meiosis 1n (x 2) 2n 2n x 2 1n (x 2)

Meiosis II The two haploid cells formed from Meiosis I enter Meiosis II

Meiosis Prophase II Metaphase II Anaphase II A spindle made of microtubules forms and moves chromosomes toward the middle of the cell. Metaphase II Duplicated chromosomes align in the middle like they are in mitosis. Anaphase II Sister chromatids separate. Individual chromosomes move toward opposite poles.

Meiosis II: Sister chromatids separate Telophase II and Cytokinesis Figure 8.13-6 Meiosis II: Sister chromatids separate Telophase II and Cytokinesis Prophase II Metaphase II Anaphase II Haploid daughter cells forming Sister chromatids separate Figure 8.13-6 The stages of meiosis (part 6)

Meiosis Telophase II Chromosomes have reached the poles of the cell. A nuclear envelope forms around each set of chromosomes. With cytokinesis, four haploid cells are produced. Two plant cells undergoing telophase II