Cellular Reproduction

Transcription

1 Cellular Reproduction How do we know that cells divide to form other cells? Growth Chapter 9 Cuts or wounds heal New blood is produced Hair and fingernails grow back Do cells grow? 1

2 Hollywood Limits to cell growth 1. The larger a cell becomes, the more demands the cell places on its DNA. (DNA overload) 2. The more trouble the cell has moving enough nutrients and wastes across the cell membrane. DNA overload DNA controls the cell s function When a cell is small, the information stored in that DNA is able to meet all of the cell s needs. As the cell increases in size, it does not make extra DNA and is no longer able to serve the needs of the growing cell. Exchanging materials Cells must obtain all of their food, oxygen and water through their membrane The rate at which food and oxygen are used up and waste produced depends on the cell s volume As cells grow large their ability to obtain materials through their membrane goes down Surface area to volume ratio Ratio of Surface Area to Volume in Section 10-1 Cells Cell Cycle Period of time from the beginning of one cell division to the beginning of the next. Cell Size Surface Area (length x width x 6) Volume (length x width x height) Ratio of Surface Area to Volume G1 phase cell growth and activity S phase replication (DNA) G2 time gap, preparation for mitosis M phase mitosis (cell division) G1, S, G2-2

3 Figure 10 4 The Cell Cycle Section 10-2 How long does a cell cycle take? G 1 phase Bean cell 19 hours Mouse cell 22 hours Sea urchin 2 hours M phase S phase Average time = 8 10 hours G 2 phase 1. DNA strand carries the cell s genetic code. 2. Protein - centromere * are not visible in most cells except during cell division. 3

4 The cells of every organism have a specific number of chromosomes. Cat 38 Dog 78 Goldfish 94 Onion 16 Sunflower 34 Human 46 Chimpanzee - 48 House fly 12 Carrot 18 Fruit fly 8 Elephant 56 Pigeon 80 Aulacantha (protozoa) Normal cellular function (G1) DNA get replicated (S) Cell prepares for cell division (G2) are not visible Mitosis The process by which the chromosome s in a cell duplicate themselves and then separates into two identical cells. Mitosis is the division of body cells (somatic cells) 4 stages of mitosis DNA begins to coil up become visible (scrambled) Nuclear membrane dissolves s move to opposite ends Spindle fibers form Prophase 4

5 10/29/2013 Metaphase meet in the middle 5

6 pull apart Cell membrane pinches in (animal cell) Cell wall begins to form in (plant cells) Cytokinesis uncoil- become thread like Spindle fibers break apart Nuclear forms around each set of chromosomes 6

7 Formation of two Daughter cells that are identical to each other. The daughter cells then enter G1 or Section 10-2 Figure 10 5 Mitosis and Cytokinesis Section 10-2 Figure 10 5 Mitosis and Cytokinesis s Spindle forming s Spindle forming Nuclear Chromatin Centromere (paired chromatids) Prophase Spindle Cytokinesis Individual Metaphase chromosomes Nuclear reforming Nuclear Chromatin Centromere (paired chromatids) Prophase Spindle Cytokinesis Individual Metaphase chromosomes Nuclear reforming 7

8 Section 10-2 Figure 10 5 Mitosis and Cytokinesis Section 10-2 Figure 10 5 Mitosis and Cytokinesis s Spindle forming s Spindle forming Nuclear Chromatin Centromere (paired chromatids) Prophase Spindle Cytokinesis Individual Metaphase chromosomes Nuclear reforming Nuclear Chromatin Centromere (paired chromatids) Prophase Spindle Cytokinesis Individual Metaphase chromosomes Nuclear reforming Section 10-2 Figure 10 5 Mitosis and Cytokinesis Section 10-2 Figure 10 5 Mitosis and Cytokinesis s Spindle forming s Spindle forming Nuclear Chromatin Centromere (paired chromatids) Prophase Spindle Cytokinesis Individual Metaphase chromosomes Nuclear reforming Nuclear Chromatin Centromere (paired chromatids) Prophase Spindle Cytokinesis Individual Metaphase chromosomes Nuclear reforming 8

9 Prophase Metaphase 9

10 Prophase Metaphase 10

11 Cell cycle regulation The cell cycle is driven by a combination of two substances that signal the cellular reproduction process. Protein called CYCLINS Enzyme called CYCLIN-dependent KINASES (CDKs) **** Cyclin binds to the enzyme (CDKs) which kick off the cell cycle and drives it through MITOSIS. Quality Control checkpoints Checkpoints monitor the cell cycle for errors and can stop the cycle if an error has occurred. Example a check point near the end of the G1 stage monitors for DNA damage and can stop the cycle before entering the S phase. Apoptosis Programmed cell death, is a naturally occurring process in the body. It involves a controlled sequence of steps in which cells signal self termination. Apoptosis works to keep the body's natural process of cell division or mitosis in check. There are several instances in which cells may need to be destroyed. Cells may need to be removed to ensure proper development. Cells may also become damaged or undergo some type of infection. One way to remove these cells without causing harm to other cells is through apoptosis. During apoptosis, a cell triggers a process that will allow it to "commit suicide." In this process, the cell undergoes a reduction in size as its cellular components break down and condense. 11

12 Uncontrolled Cell growth CANCER A disease of the cell cycle Occurs when cells do not respond to the signals that normally stop them from dividing. Cells divide uncontrolled (malignant cells) Forms masses of cells called TUMORS Tumors disrupt normal cellular activities, cause serious medical problems and even death Cancer cells may break loose from the tumors and spread throughout the body Cells are the building blocks of living things. Cancer grows out of normal cells in the body. Normal cells multiply when the body needs them, and die when the body doesn't need them. Cancer appears to occur when the growth of cells in the body is out of control and cells divide too quickly. There are many different kinds of cancers. Cancer can develop in almost any organ or tissue, such as the lung, colon, breast, skin, bones, or nerve tissue Skin Cancer (malanoma) Treatment for Cancer 1- Chemotherapy (cancer drugs) 2- Radiation - the use of ionizing radiation to kill cancer cells and shrink tumors 3- Surgery Stem cells Revolutionized Medicine Or Frankenstein Technology 12

13 Stem cells They are cells whose job in the body is not yet determined. (blank cell or undifferentiated) Have the potential to develop into any type of cell in the body Every single cell in the body stems from this type of cell. - Hence the name stem cells Stem Cells Stem cells have the remarkable potential to develop into many different cell types in the body. Serving as a sort of repair system for the body, they can theoretically divide without limit to replenish other cells. When a stem cell divides, each new cell has the potential to either remain a stem cell or become another type of cell with a more specialized function, such as a muscle cell, a red blood cell, or a brain cell. Sources of stem cells: Embryonic stem cells - are harvested from the inner cell mass of the blastocyst seven to ten days after fertilization. Fetal stem cells - are taken from the germline tissues that will make up the gonads of aborted fetuses. Umbilical cord stem cells - Umbilical cord blood contains stem cells similar to those found in bone marrow. Placenta derived stem cells - up to ten times as many stem cells can be harvested from a placenta as from cord blood. Adult stem cells - Many adult tissues contain stem cells that can be isolated. Stem cell type Description Examples Toti-potent Pluri-potent Multi-potent Each cell can develop into a new individual Cells can form any (over 200) cell types differentiated, but can form a number of other tissues Cells from early (1-3 days) embryos cells of blastocyst (7 to 10 days) fetal tissue, cord blood, and adult stem cells 13

14 Perhaps the most important potential application of human stem cells is the generation of cells and tissues that could be used for cell-based therapies. Today, donated organs and tissues are often used to replace ailing or destroyed tissue, but the need for transplantable tissues and organs far outweighs the available supply. Stem cells, directed to differentiate into specific cell types, offer the possibility of a renewable source of replacement cells and tissues to treat diseases including Parkinson's and Alzheimer's diseases, spinal cord injury, stroke, burns, heart disease, diabetes, osteoarthritis, and rheumatoid arthritis. A South Korean woman paralyzed for 20 years is walking again after scientists repaired her damaged spine using stem cells derived from umbilical cord blood. The woman had been bedridden since damaging her back in an accident two decades ago, but is walking again with the help of a walking frame. Research stem cell controversy Because harvesting stem cells destroys the embryo, this medical research has become entangled in the abortion debate. Research opponents say it is wrong because it destroys human life. Supporters say the embryos were going to be destroyed anyway, and that research from their cells holds the potential to cure debilitating diseases. Creating embryos intended only for research raises new questions about the ethics of stem cell science. Stem Cells Stem Cell Gold Rush - KQED QUEST Television Segment Nova Stem Cell Video 14