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Transcript
Cell Division and Mitosis Work to begin class with • Why do humans always have to cut our hair, fingernails, and even the lawn? (and your answer cannot be because it gets long). There is a scientific answer Cellular differentiation • Cell tissues organs organ systems • As cells grow and divide, many of them may form tissues inside the body – Muscle Tissue • If many tissues group together, they form organs – Ex: Liver • Organ systems are the same as body systems it is when multiple organs work together to achieve a common goal – Ex: digestive system Cell Growth • Living organisms obviously grow in size as they age, but how? • When a cell grows, do the individual cells get larger therefore increasing the size of the organism? • Do the number of cells increase therefore increasing the size of the organism? • On average, the size of a cell in a baby, and the size of a cell in an adult are about the same • Instead the number of cells dictate size of the organism Why do cells divide instead of just get larger? • The larger a cell gets, the more demand it puts on DNA to control the cell (DNA is the same regardless of size) • Large cells are not very efficient • Transport is very difficult • Cell division makes it easier to dispose of bad cells • If you had fewer larger cells, you would lose large portions of information when a cell dies Exchanging materials • The larger a cell gets, it is harder to remove unwanted objects from the cell, and it is harder to obtain the things the cell needs from its outside environment • The surface area of the cell dictates the rate at which objects can be transported into and out of the cell • This is better known as the surface area to volume ratio • It is optimal to have a high surface area to volume ratio • Analogy a small town with limited supplies is good as long as there are not a lot of people – As the town gets larger, the amount of supplies per person decreases, causing problems – It is in the best interest to keep the town small, everyone will be happier Cell division and Mitosis If you want to make two batches of cookies instead of just one, what do you have to do to the recipe? Double it For a cell to be able to split in two, what does it need to do? Double the “ingredients” Organelles, DNA, etc. The cell cycle Two main stages 1. Interphase G1 (Gap 1) cell goes through normal functions (growth) Checkpoint-cell must be big enough, mature enough, and have undamaged DNA Preparation stage for cell division Synthesis (S) cell makes a copy of DNA; nucleus now contains two sets of DNA G2 (Gap 2) additional growth-normal functions Checkpoint 2. Mitosis and cytokinesis Cell splits into two cells Vocabulary Chromosome one long continuous thread of DNA that contains many genes Looks like an “X” Chromatin loose combination of DNA, like a shoe string with knots in it Chromatid one half of a duplicated chromosome Half of the X Centromere junction between two halves Telomere tip of DNA or chromosome What’s the relationship between a chromosome and DNA A chromosome is made up of DNA DNA twists and folds itself to make a condensed chromosome Mitosis and cytokinesis In the end, there will be two genetically identical “daughter” cells Interphase G1, S, G2 Mitosis Prophase Metaphase Anaphase Telophase Interphase • Preparing the cell to divide • Growth phase • DNA duplication • Cell has two identical sets of DNA, or chromatids and is large enough to divide Prophase Chromatin condenses into tightly coiled chromosomes Nuclear membrane breaks down The nucleolus disappears Centrioles begin to migrate to opposite poles Spindle fibers-made up of microtubules begin to grow from centrioles and form whats called the mitotic spindle Metaphase • Spindle fibers attach to centromere of each chromosome • Chromosomes line up on the “middle” Anaphase Chromosomes split, resulting in two sister chromatids X splits in half Spindle fibers begin to shorten which pulls the chromatids away from each other Telophase • A complete set of identical chromatids is positioned at each pole • Nuclear membrane begins to reform in each cell • Chromosomes begin to uncoil back into chromatin • Spindle fibers fall apart Cytokinesis • Divides the rest of the cell into two pieces • Actual splitting process The cell cycle control system • Checkpoints critical control point where stop and go-ahead signals can regulate the cycle – G1 checkpoint – G2 checkpoint – M checkpoint • External factors – Cell to cell contact – Growth factors protein signals from neighboring cells that stimulate cell division • Internal factors – Apoptosis programmed cell death Cellular differentiation • Cell tissues organs organ systems • As cells grow and divide, many of them may form tissues inside the body – Muscle Tissue • If many tissues group together, they form organs – Ex: Liver • Organ systems are the same as body systems it is when multiple organs work together to achieve a common goal – Ex: digestive system Differentiation • When sperm and egg come together, one cell is created • That fertilized egg gives rise to an increased number of cells through cell division, which must divide creating identical cells • As cell division proceeds, cells also undergo differentiation, becoming specialized in structure and function • This happens, because all cells contain the same DNA, all cells initially have the potential to become any type of cell • Once a cell differentiates-becomes specific cell- it cannot be reversed Stem cells • Stem cells unspecialized cells that continually reproduce themselves and have, under appropriate conditions, the ability to differentiate into one or more types of specialized cells • Two types: – Embryonic-embryos at a very early stage – Adult- various places in body can be stem cells • Under appropriate laboratory conditions, stem cells can differentiate into specialized cells Application-Uncontrolled cell division • Cancers use the process of cell division to make bad cells multiply without any control • Cancers form disorganized groups of cells called tumors – Two types: • Benign cancer cells typically remain clustered together. This usually means that the tumor is harmless and can be removed • Malignant some of the cancer cells can break away, or metastasize from the tumor. These cells can be carried in the bloodstream or in lymph nodes and can form new cancerous tumors in other places Carcinogens • Carcinogen substances known to promote or produce the development of cancer cells • Smoking, drinking, drugs, too much of a lot of things can lead to cancer and apoptosis • Sometimes your body can detect when there is a problem • Ex: skin cells Treatment for cancer • Radiation therapy the use of radiation to kill cancer cells and shrink tumors. – It works by damaging the DNA of cells so they cannot divide – Radiation is localized-its use is targeted to a specific region-because it can hurt regular cells • Chemotherapy the use of drugs/poisons to kill actively dividing cells On your final sheet to turn in • Write a good test question on something we covered today. • Write down something that you are still struggling with and need some more explanation on. • What was the main idea of the lesson today? (your answer must be a sentence, not just mitosis)