GENBIO-1-Lesson-3.pdf

THE CELL CYCLE GENBIO 1 Lesson 3 Part 1 Introduction All organisms reproduce for one reason – to ensure the survival of their species. Reproduction makes use of the process of cell division. Cell division is important for two reasons: To be able to produce offspring To gen...

THE CELL CYCLE GENBIO 1 Lesson 3 Part 1 Introduction All organisms reproduce for one reason – to ensure the survival of their species. Reproduction makes use of the process of cell division. Cell division is important for two reasons: To be able to produce offspring To generate new cells that will replace worn out or damaged cells There are two types of cell division, namely mitosis which happens in body cells or somatic cells and meiosis which involves the gametes or sex cells. Overview In order to better understand cell division, you need to learn first the cell cycle. This cycle involves distinct and regular phases of growth, DNA duplication, and cell division that are needed to allow growth and repair. The cell cycle is divided into two main stages: 1. Interphase – non-dividing stage (G1, S, and G2 phases, G0) 2. Cell division – dividing stage (mitosis for somatic cells and meiosis for sex cells Stage 1: INTERPHASE Interphase is the growth period in the cell cycle characterized by cell preparation by replication of its genetic information and all of its organelles. Stage 2: Cellular Division Some cells undergo the cell cycle only once or they stop dividing and enter the stage known as the gap zero or G0. In this stage, cells are unlikely to divide but still continue to perform normal functions. Such cells, like neuron cells and heart muscle cells that are highly differentiated or specialized and that the body cannot easily replace, are said to be permanently in G0. Immune cells that are needed at a later time, such as lymphocytes, remain in G0 for many years until such time that the body needs to recognize an invader. Only when an invader binds to the lymphocyte’s receptor that the lymphocyte starts to divide rapidly to help get rid of the infection. Cell Cycle Checkpoints In order to prevent mutations/chromosomal aberrations and ensure major events occur at correct times, several cell cycle checkpoints are present at various times in the cycle preventing cells from proceeding to the next stage unless all criteria had been met.  “Checkpoints” or control points are moments when the cell can “check” its internal conditions and “decide” whether to progress to the next phase or remain. It is similar to what happens during a police operation checkpoint. When you have met the requirements asked by the police officer in-charge, you can go pass the checkpoint. Malfunction during Cell Cycle  The key to understanding the different disorders and diseases as a result of the malfunction of cells lies on our knowledge of the cell cycle. If you can still recall in the previous discussion , we have tackled that cell cycle has different phases and each part has its own checkpoint in order to monitor the activities of the cell. Failure to regulate cell activities may result to various disease and disorder.  CANCER One of the most common disorder we know today but without cure yet is cancer. Cancer refers to a group of diseases characterized by uncontrolled and abnormal cell division. It occurs when there is a disruption in the cell cycle. Instead of stopping and starting at appropriate points, cancerous cells divide continuously until a disorganized solid mass of cells called tumor is formed. Tumors can be categorized as benign or malignant. Benign tumors are cancer cells that remain clustered together, which may be harmless or not and can probably be cured when removed out of the body. Malignant tumors are cancer cells that has break away or metastasized. This cancer cells are transported to the bloodstream of the lymphatic system to the other parts and form more tumors. What causes Cancerous cells ? Cancer is caused mainly by changes or mutations to the DNA within cells.  What are some of the risk factor contributing to cancer? > Lifestyle factors (e.g.: smoking, high-fat diet, working with toxic chemicals) Family history, inheritance, and genetics (e.g., inheritance of breast cancer) Some genetic disorder Exposure to certain viruses (e.g., cervical cancer which is caused by human papilloma virus) Environmental exposures (e.g., exposure to pesticides and fertilizers, radiations, and carcinogens)  Why are tumors dangerous inside the body? Generally, cancer cells do not perform the specialized functions of the normal cells in the body Example, if the cancer cells are in the brain, they do not perform their supposed function which is to transmit electrical signals for response. Moreover, if they continue to grow and form tumors, it can cramp the brain in the limited skull. This might affect the other parts of the brain and their functions because cancer cells also compete for nutrients and blood supply with other healthy cells. If left unchecked, it may hinder the proper functioning of the body.  How is cancer treated? Chemotherapy – uses certain drugs to kill actively dividing cells. This procedure is systemic, which means that drugs are introduced throughout the body orally (taken by mouth) or intravenously (injection). Surgery – involves removal of the cancerous body part Radiation therapy – involves the exposure of X-rays to kill cancer cells and shrink the tumor size  Genetic Disorders A change in the number or structure of chromosomes can dramatically change the traits of an organism and can cause serious problems. Abnormal chromosomes most often happen as a result of an error during cell division. Chromosome abnormalities often happen due to one or more of these: Errors during dividing of sex cells (meiosis) Errors during dividing of other cells (mitosis) Exposure to substances that can cause birth defects (teratogens)  Karyotyping is the process by which photographs of chromosomes are taken in order to determine the chromosome complement of an individual, including the number of chromosomes and any abnormalities. Numerical abnormality also called aneuploidy, a condition which occurs when an individual has a missing chromosome from a pair (monosomy) or has more than two chromosomes of a pair (trisomy, tetrasomy, etc.).  Down Syndrome (Trisomy 21) ✓ The most common disorder of trisomy is Down syndrome, wherein the 21st chromosome has three instead of two chromosomes. ✓ Most cases of Down syndrome are not due to inheritance but on random mistakes during formation of reproductive cells of the parents. ✓ Physical manifestations: Short neck, with excess skin at back of the neck. Flattened facial profile and nose. Small head, ears, and mouth. Upward slanting eyes.  Turner Syndrome (45, XO) ✓ A condition that affects only female as a result of one of the X chromosomes (sex chromosome) is missing or partially missing. ✓ Physical manifestations: Webbed neck, short stature, swollen hands and feet. Some have skeletal abnormalities, kidney problems, and/or congenital heart defect. Klinefelter Syndrome (47, XXY) ✓ A condition resulting from two or more X chromosomes in males ✓ Manifestations are typically more severe if three or more X chromosomes are present as in (48, XXXY) or (49, XXXXY). ✓ Physical manifestations: Primary features are infertility and small poorly functioning testicles. Sometimes includes weaker muscle, greater height, poor coordination, less body hair, breast growth and less interest in sex.  Trisomy X Syndrome (47, XXX) ✓ Characterized by the presence of extra X chromosome in each cell of a female ✓ Physical manifestations: Often taller than normal, affected individuals have usually mild symptoms to none at all. Occasionally there are learning difficulties, delayed speech, decreased muscle tone, seizures, or kidney problems. Patau Syndrome (Trisomy 13) ✓ Caused by having an additional copy of chromosome 13 in some or all of the body’s cells. ✓ Physical manifestations: Clenched hands, cleft lip or palate, extra fingers or toes (polydactyly), hernias, kidney, wrist or scalp problems, low-set ears, small head, undescended testis. Edward Syndrome (Trisomy 18) ✓ Caused by having additional copy of chromosome 18 ✓ Physical manifestations: Cleft palate, Clenched fists, defects of lungs, kidneys and stomach, deformed feet, heart defects, low-set ears, severe developmental delays, chest deformity, slowed growth, small head, small jaw.  Structural Abnormalities Occur when the chromosome’s structure is altered, which can take several forms such as: Deletion – a portion of a chromosome is missing or deleted; Duplication – segment of a chromosome is repeated twice; Translocation – transfer of a section of one chromosome to non-homologous chromosome; Inversion – a section of the chromosome becomes changed by rotation at 180 degrees  Cri-du-chat Syndrome (5p minus syndrome) ✓ A genetic condition caused by the deletion of genetic material on the small arm (p arm) of chromosome 5 ✓ Physical manifestations: mentally retarded, has abnormal development of glottis and larynx resulting from a crying sounds that sound like the meowing of a cat. Minimum of 400 Words and Maximum of 800 Words Criteria: Neatness - 6 Points Relevance of the Answer to the Question - 7 Points ______________________________________________ 20 Points Next Lesson: Mitosis and Meiosis