8.1 – 8.11 Cell Reproduction and Growth Chapter 8 Notes 8.1 – 8.11 Cell Reproduction and Growth

Where are we in our tour of the cell?

WHY DO CELLS DIVIDE?? to make more cells for replacing old, worn out or damaged cells for growth and development of an organism create a new organism; reproduction (single-celled) BINARY FISSION – division of a single celled organism that creates a whole new organism (Bacteria)

The Cell Cycle The cell cycle is the a series of events cells go through to divide and create more cells. Some cells divide constantly: cells in the embryo, skin cells, gut lining cells, etc. Other cells divide rarely or never: only to replace themselves (liver, muscle cells, nerve cells)

Interphase Most of the cycle was called interphase. During interphase, the cell increases in size, but the chromosomes are invisible. The 3 stages of interphase are called G1, S, and G2. CdK and Cyclin are 2 protein enzymes involved in regulating the cell cycle.

G1 and G2 Both stages are part of interphase, and include the cell increases in size (G=GROWTH!) G1 comes before S phase, and G2 comes after S phase

S phase S phase = “Synthesis” S phase involves DNA synthesis; creating a copy of the DNA from one cell to send a copy into the new cell. The process of copying of DNA (DNA Replication) will be covered in more detail in Ch. 10!

Duplicated chromosomes AFTER S BEFORE S

S phase – DNA and Chromosomes DNA contains all the genetic information for creating and running the organism. Chromosome- a single long strand of DNA wrapped around protein, clumped into an X shaped Sister chromatids – Half of the ALREADY DUPLICATE X SHAPE of a chromosome (IDENTICAL!) Each chromosome has a central constricted region called a centromere that serves as an attachment point for each sister chromatid.

M phase M phase = “Mitosis” Mitosis – division of the chromosomes and organelles that were duplicated in S phase M phase sends a copy of all the genetic information and necessary organelles into the new cell. Occurs in most somatic cells (All cells of the body EXCEPT the reproductive cells!)

Machinery of Mitosis Spindle fibers - The chromosomes are pulled apart by these extending strands of microtubules. The spindle fibers are attached to each centromere. Centrioles (in animal cells) and anchored on the other end of the spindle When the spindle fibers contract, the chromosomes are pulled to the opposing poles.

4 stages of mitosis Prophase Metaphase Anaphase Telophase (PMAT)

Prophase First stage of mitosis. 1) The chromosomes condense. 2) The nuclear envelope disappears. 3) The centrioles move to opposite poles. *During interphase, the pair of centrioles were together just outside the nucleus. 4) The spindle starts to form, growing out of the centrioles towards the chromosomes.

Metaphase 1) Short resting period where the chromosomes are lined up on the equator of the cell (MIDDLE) with the centrioles at opposite ends. 2) The spindle fibers attached to the centromeres.

Anaphase The centromeres separate. 2) The spindle fibers contract, and the chromosomes are pulled to opposite poles, towards the centrioles.

Telophase 1) The cell cytoplasm begins to divide. (cleavage furrow) 2) The chromosomes are at the poles of the spindle. 3) The spindle disintegrates The nuclear envelope forms around the two separated sets of chromosomes.

Cytokinesis Cell plate: In plant cells, a new cell wall made of cellulose forms between the 2 new nuclei Cytokinesis- separation of the cytoplasm into 2 separate cells. Last stage of cell division (NOT considered part of mitosis) The organelles get divided up into the 2 daughter cells, whichever cell they find themselves in. Cleavage furrow: In animals, a indentation begins from the outside, pinching inwards.

Summary of Mitosis Prophase: Metaphase Anaphase Telophase Chromosomes condense Nuclear envelope disappears centrosomes move to opposite sides of the cell Spindle forms Metaphase Chromosomes lined up on equator of spindle centrosomes at opposite ends of cell Spindles attach to centromeres on the chromosomes Anaphase Centromeres divide: each 2-chromatid chromosome becomes two 1-chromatid chromosomes Chromosomes pulled to opposite poles by the spindle Telophase Chromosomes de-condense Nuclear envelope reappears Cytokinesis: the cytoplasm is divided into 2 cells

Animations Mitosis and Cytokinesis Binary Fission Cancer

Cancer Cancer is a disease of uncontrolled cell division. It starts with a single cell that loses its control mechanisms due to a genetic mutation. (loss of CdK/cyclin functioning). Cancer cells enter the S phase without waiting for a signal. Normal cells are mortal. This means that they can divide about 50 times and then they lose the ability to divide, and eventually die. Cancer cells will continue to divide Tumor - a small mass of cells. Benign – stops growing and stays at original site. Malignant – continues to grow in a new site from origninal.

Cancer Progression Metastasis- cancer cells will break loose and move through the blood supply to other parts of the body, where they start to multiply. There are many different forms of cancer, affecting different cell types and working in different ways. All cancers start mutations in specific genes. The mutations are caused by radiation (i.e. UV), certain chemicals (carcinogens- nicotine, pesticides, plastics), and various random events during DNA replication.

Cancer Treatment Two basic treatments: Surgery to remove the tumor Radiation and/or chemicals to kill actively dividing cells. Radiation and chemotherapy are aimed at killing actively dividing cells, but killing all dividing cells is lethal. If any tumor cells are resistant to the chemical treatment, they will survive and multiply. The cancer seems to have disappeared, but it comes back a few years later in a form that is resistant to chemotherapy. Using multiple drugs can decrease the risk of relapse: it’s hard for a cell to develop resistance to several drugs at the same time.

Mitosis Skit Now you will show mitosis! NEED (per group) 4 spindles (white strings) 2 nuclear envelopes (long strings) 4 chromatids (2 chromosomes) = 4 people 2 centrioles (2 people) 1 narrator (no reading from book!)