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Cell Division Part One: Mitosis In this lesson… • Explain the difference between double and single stranded chromosome, chromatin and chromatid • List the steps of mitosis and describe what happens in each • Identify what stage of mitosis a cell is in by looking at the chromosomes • List three reasons cells divide by mitosis • Describe cytokinesis In the nucleus • In non-dividing cells, the genetic material is stored as thin DNA super coils called CHROMATIN • When a cell divides, the chromatin will shorten and thicken into CHROMOSOMES • One strand of a double stranded chromosome is called a CHROMATID Mitosis • MITOSIS: a process by which the nucleus of a cell divides while maintaining the chromosome number One cell two cells New cells have identical genetic material (DNA) of the parent cell • Four stages of division (Prophase, Metaphase, Anaphase and Telophase - PMAT) plus a period of growth and metabolism called Interphase The Cell Cycle Interphase • • • • • Period between divisions Longest part of the cell cycle Cell is growing and metabolizing Nuclear membrane present Genetic information in the form of chromatin and cannot be seen with a microscope • Before division each strand of DNA will replicate (copy) itself to become double stranded • Near the end of interphase the DNA begins to condense (shorten) Interphase Draw a double stranded chromosome. Label chromosome, chromatid and centromere Chromosome Chromatid Chromatid Centromere Phase One: Prophase • Chromatin contracts and becomes visible (spaghetti). It is now called CHROMOSOMES • Each is a double chromosome with a pair of SISTER chromatids which are joined to each other by a centromere • Chromosomes begin to move towards the equator (center) of the cell • Nuclear membrane disintegrates (breaks down) • CENTRIOLES will form SPINDLE FIBERS that will attach to each centromere and move around the chromosomes Prophase Phase Two: Metaphase • The centromeres of each chromosome line up along equator ( looks like praying hands) • Centromeres divide so the doubled chromosomes become two identical single stranded sister chromatids • Centrioles are now at the poles of the cell and are attached to each centromere by spindle fibers Metaphase Phase Three: Anaphase • The spindle fibers begin to shorten and the chromosomes begin moving to opposite ends or poles of the cell (fingers) • Each side gets one chromatid from each double stranded chromosome Anaphase chromosomes Phase Four: Telophase • Begins when single stranded chromosomes reach the poles • Chromosomes uncoil and turn into chromatin • Nuclear membrane reappears • Reverse of prophase • Division of the cytoplasm or CYTOKINESIS is completed by pinching off in animals or by building a cell wall in plants Telophase What’s the point of Mitosis? • Mitosis creates identical copies of cells for: 1. growth 2. Repair/regeneration of damaged tissue 3. Asexual reproduction (animals) or vegetative reproduction (plants) Asexual Reproduction • Reproduction that involves only one parent; parent and offspring have identical genetics • No special reproductive cells or organs used to create offspring • Occurs through mitosis and cytokinesis • Both single and multi-celled organisms, plants and simple animals can reproduce asexually • In multi-cellular organisms, the offspring develop from undifferentiated, unspecialized cells from the parent • Usually a rapid form of reproduction Binary Fission • Simplest form of asexual reproduction • Parent divides into two approximately equal sized daughter cells • Bacteria: circular chromosome attaches to plasma membrane then replicates, cell wall separates each copy • Protozoa: eg. Amoeba become circular and use mitosis Budding • New individuals develop from small outgrowths of the parent (buds) • May develop colonies (sponges) or break off to be individuals (hydra, yeast) • Some organisms can both bud and reproduce sexually Spores • Specialized single cells that are released from the parent organism, germinate and grow by mitosis • New cells differentiate to form a new organism • Can reproduce quickly and in large quantities • Often have thick protective coats • Eg. Fungi, algae, protozoa Regeneration • The ability to regrow lost body parts • Some animals can regrow entire new organisms from parts • Ability to regenerate decreases as organisms increase complexity • Even simple organisms that can regenerate entire organisms generally prefer to utilize a different method to reproduce Vegetative reproduction • MERISTEM: area on plant with unspecialized cells (cells that can become any kind of cell) that frequently divide using mitosis • Meristematic cells can be found in the vegetative structures of a plant (roots, stems, leaves) • Given proper treatment, meristem cells can reproduce mitoticlly then differentiate into new independent plants • Structures include bulbs, corms, tubers, runners, rhizomes • Can also be artificially propagated using cuttings, layerings or grafting Bulb • short underground stem with thickened storage leaves • small new bulbs sprout from the old ones • Eg. onions, tulips Corm • short underground stems with no fleshy leaves • Eg. gladiolas, crocuses Tuber • enlarged part of an underground stem that contains stored food • potatoes (eyes are tiny buds) Runner • AKA stolon • is a stem that runs sideways and contains buds • Eg. strawberry Rhizome • a stem that grows sideways under the ground • ferns, irises Cutting • a stem, root or leaf cutting used to make a new plant Layering • part of a stem is bent and covered in soil • once it roots the original can be cut off • Eg. raspberries, roses Grafting • stem or bud removed from one plant and permanently joined to another plant • Eg. grapes and many seedless fruits
