Unit 5 - F24 - Mitosis and Cancer (3).pptx

Week 3 - Agenda 2hr: Review Cell Structure and Function Unit 4 – Cellular Respiration (Metabolism) 2hr Finish Unit 4 – Cellular Respiration (Metabolism) Unit 5 – Cellular Reproduction (mitosis)  Chromosomes and Cell Division Chapter 3.5 Chromosomes Chromosomes are located within the...

Week 3 - Agenda 2hr: Review Cell Structure and Function Unit 4 – Cellular Respiration (Metabolism) 2hr Finish Unit 4 – Cellular Respiration (Metabolism) Unit 5 – Cellular Reproduction (mitosis)  Chromosomes and Cell Division Chapter 3.5 Chromosomes Chromosomes are located within the nucleus Each chromosome is a tightly coiled combination of DNA and specialized proteins called histones DNA contains genetic information, which directs body development and maintenance Histones help with support and control of gene activity Genes are specific segments of the DNA Genes direct protein synthesis, which plays a structural or functional role in the cell Chromatin, Chromosomes and DNA DNA and histones become much more tightly coiled during cell division Chromatin  DNA and histones are coiled to form thin, thread-like structures Exists in the nucleus in between cell divisions Chromosomes  the same DNA and histones become super-condensed to form thicker, visible structures Occurs during cell division Chromosomes All somatic cells (body cells except germ cells - eggs and sperm) have 46 chromosomes Two sets (pairs) of 23 chromosomes: one set of 23 from each parent Chromosomes occur in pairs called homologous pairs One chromosome of the pair is from the mother One chromosome of the pair is from the father Chromosomes Diploid (2n): a cell with two sets of chromosomes - one from each parent All cells in the human body are diploid except sperm and egg cells (haploid) Genes also occur in pairs in diploid cells Members of each gene pair are located at the same position on homologous chromosomes Chromosomes 23 pairs total 22 of the pairs are called autosomes and determine the expression of most of a person’s inherited characteristics The last pair are sex chromosomes that determine the biological sex of an individual XX  genetic female XY  genetic male Karyotype A karyotype is a complete set of chromosomes from a cell Shows the exact number and visual appearance of the chromosomes (also can show anomalies) The Cell Cycle The Cell Cycle Cell cycle: Predictable set of events that a cell goes through from its origin to its own division into two daughter cells Two major phases 1) Interphase: A period of growth and preparation for cell division 2) Mitosis: The process of cell division for somatic (body) cells When one nucleus divides into two daughter nuclei with the same number and kinds of chromosomes Cytokinesis – division of the cytoplasm into two distinct cells The Cell Cycle The Cell Cycle - Interphase Interphase is a period of growth and preparation for cell division and has three phases  G1, S, & G2 G1 phase “Gap 1” Time of major growth before DNA synthesis begins Chromosomes consist of a strand of DNA and proteins Lasts from a couple of hours to days The Cell Cycle - Interphase S phase “Synthesis” During the “S” stage, DNA is replicated, and the two copies of the chromosome, called chromatids, remain attached at the centromere Two attached chromatids are genetically identical and called sister chromatids Growth continues Lasts 8-10 hours The Cell Cycle - Interphase G2 phase “Gap 2” Period after DNA is synthesized and before mitosis begins Growth continues Lasts around 5 hours G0 Resting phase of the cell cycle Cells that have temporarily stopped dividing or have permanently stopped dividing (nerve cells) are in G0. The Cell Cycle – Interphase The Cell Cycle - Cell Division Consists of two processes Mitosis occurs in four 1. Mitosis phases Division of the nucleus I. Prophase 2. Cytokinesis II. Metaphase Division of the III. Anaphase cytoplasm IV. Telophase Stages of Mitosis I) Prophase First part of cell division Centrioles migrate to the poles to direct assembly of mitotic spindle fibers DNA condenses and becomes visible as short, thick, double-stranded chromosomes Nuclear envelope breaks down and disappears Stages of Mitosis II) Metaphase The mitotic spindle attaches to the centromere of each chromosome Chromosomes moved by the spindle fibers so that they are aligned in the center of the cell along the equatorial plane Stages of Mitosis III) Anaphase The mitotic spindle pulls the chromosomes apart and the sister chromatids move toward the opposite ends of the cell Cell begins to elongate Stages of Mitosis IV) Telophase Chromosomes uncoil and take on the thread-like structure of chromatin Nuclear envelope reforms around chromatin Spindles break down and disappear Stages of Mitosis Cytokinesis Beginning during telophase, cytokinesis is the physical dividing of cytoplasm, organelles and cell membrane into two separate cells A ring of microfilaments contracts at the midline of the cell, eventually pinching the cell in two Mitosis Learning Check Complete the worksheet “Mitosis Worksheet” found on Moodle Cell Cycle Control Regulation of the Cell Cycle As a cell moves through the various stages of the cell cycle, a number of checkpoints exist where the genetic material is checked for errors and mutations Internal and external controls provide “stop” and “advance” signals to the cells If errors and/or mutations are discovered in the genetic material: Cell DNA is repaired if possible Cell cycle is arrested permanently if not repairable Apoptosis occurs if errors and/or mutations are severe Cell Cycle Checkpoi nts Checkpoints – G1 G1 checkpoint This checkpoint determines whether the cell should divide and enter S phase. Some cells never pass this point and are said to be in G0 Checkpoints – G2 and M G2 checkpoint This checkpoint leads to mitosis. M checkpoint This checkpoint occurs during metaphase and triggers the exit process of the M phase and entry to the G1 phase. Regulation of the Cell Cycle Two types of genes regulate normal cell division A. Proto-oncogenes Stimulate cell division B. Tumor-suppressor genes Inhibit cell division These genes regulate cell division, so that it normally occurs only for growth/repair. In normal cells, programmed cell death (apoptosis) is initiated when genes regulating cell division have been damaged Cancer Cancer Cancer is a growth disorder of cells. It begins when abnormal cells grow uncontrollably If the continue to grow, they can damage surrounding tissues, and spread to other parts of the body. The result is a growing cluster of cells called a tumour or a neoplasm Benign Malignant Benign or Malignant Tumors Benign tumor Abnormal mass of tissue that is surrounded (encapsulated) by a healthy layer of cells Usually remains at the site where it forms – does not spread Often can be removed completely by surgery Malignant tumor Are not encapsulated and are invasive (invades surrounding tissue) Spreads to multiple locations (this is called metastasis) – cells are called metastases Cancerous Mutations that Lead to Cancer Cancer results from damaged genes failing to control cell division. Mutations in proto-oncogenes Proto-oncogenes can undergo mutations that cause them to significantly speed up the rate of cell division (stuck accelerator of a car) Mutations in tumor-suppressor genes Mutations in tumor-suppressor genes prevent the cell cycle from stopping at checkpoints when the DNA is damaged – this leads to uncontrolled cell division (no brakes in a car) Cancer Cells – Malignant Tumors Cancer cells usually have 2 or more of the following characteristics i. Up-regulated oncogenes (mutated proto-oncogenes) or down-regulated tumour-suppressor genes both cause increased cell division and tumour development. ii. Cancer cells do not undergo cell death, they become immortalized. iii. Cancer cells spread to other regions of the body iv. Cancer cells cause growth of new blood vessels so that more nutrients can be accessed by cancer cells; this is called angiogenesis. Progression of Malignant Tumor Known Causes of Cancer DNA mutations can be random, inherited (~5%) or caused by carcinogens (anything that fosters the development of cancer) Chemical carcinogens: May cause mutations in genes that regulate cell division (ie. chemicals in tobacco smoke, alcohol in excess, formaldehyde, benzene, certain pesticides) May stimulate cell division (ie. Estrogen stimulates cell division in breast and endometrial tissues, can cause cancer to progress) Known Causes of Cancer Viruses Cause about 5% of cancers in the U.S. Radiation Causes mutations in DNA that can lead to cancer Includes cosmic rays, radon, uranium, and UV light from sun Cancer Treatments Surgery Performed when tumor is accessible and can be removed without damaging vital tissue Complete cure possible with early tumors (carcinoma in situ) If cancer has spread, then other forms of treatment necessary Radiation & Chemotherapy: Goal: damage DNA in rapidly dividing cells, which should prompt the cells to self-destruct Problem: although treatment may damage DNA in cancer cells, many cancer cells do not self-destruct (due to mutations to genes that cause apoptosis), so treatment fails, also affects healthy cells Cancer Treatments RADIATION CHEMOTHERAPY Used when cancer has spread Used when cancer has spread from initial site but is still at diagnosis localized & typically follows Drugs are administered into the surgery blood stream Damages DNA Greatest Used to kill rapidly dividing cells damage done to rapidly throughout the body (side dividing cells, which include effects similar to radiation) both cancer cells and normal cells of renewal tissues Actions of drugs: Destruction of renewal tissues Block DNA synthesis causes side effects of Damage DNA radiation, such as temporary sterility, nausea, anemia, and Prevent cell division hair loss Cancer Treatments – Immunotherapy Immunotherapy: Cytotoxic T cells of the immune system continually search for abnormal cells, including cancer cells, and destroy them tumour-infiltrating lymphocytes (TILs) are cells sometimes found around tumours, indicating the immune system is responding to the tumour Goal: boost the natural immune responses against cancer cells Immune checkpoint inhibitors – allows the immune system to respond more vigorously than usual T-cell transfer – t-cells currently attacking the tumour are removed, altered in a lab to be more effective, and then placed back into the tumour Cancer Treatment – Gene Therapy Gene Therapy: Insert normal tumor-suppressor genes into cancerous cells Insert a piece of DNA that prevents the accelerated cell division rate into a cancer cell Insert a gene into tumor cells that will make them more sensitive to a drug that will kill them  Read: Chapter 3.5 – Cell Growth and Division Homewo Extra Practice: rk Activities on Moodle Looking forward: Unit 6 - DNA Structure and Function