cell division part one: mitosis in this lesson… explain the difference between double and single...
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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
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)
Draw a double stranded chromosome. Label chromosome, chromatid and centromere
ChromosomeChromatid
Centromere
Chromatid
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
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
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
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
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
Tuber
• enlarged part of an underground stem that contains stored food
• potatoes (eyes are tiny buds)
Layering
• part of a stem is bent and covered in soil
• once it roots the original can be cut off
• Eg. raspberries, roses
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