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Download L4 Prokaryotes eukaryotes and onion cheek preps
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Transcript
Lesson 4 – Prokaryotic cells and cell preparations • Today we will carry out slide preps of onion and cheek cells • Complete some calculation of magnification • Learn about some differences between prokaryotes and eukaryotes Learning aims: • To understand the similarities and differences between Eukaryotes and Prokaryotes. • To be able to prepare, describe and draw a cheek cell slide preparation, onion cell slide preparation and plant material slides Cell types. Eukaryotic cells: These include plant and animal cells. They contain a nucleus that contains the cell’s DNA and they a collection of complex organelles that have specific functions. ( Animal, plant, fungi and protoctista are all eukaryotes) Prokaryotic cells: Bacteria are prokaryotes. (Evolved long before eukaryotes). The major difference is, they contain nucleic acids, but they are not confined inside a definite nucleus with a nuclear membrane. Instead there are strands of DNA in the centre of the cell that are collectively known as the nucleoid. • Prokaryotes are all bacteria: • Escherichia coli: Human gut, harmless feeds on food and breakdown products of digestion. • 65 billion in your body! • Makes up 0.1% of bacteria that live in your body! EXCEPTIONS! • Epulopiscium fishelsoni : discovered 1980’s, lives in intestine of Red Sea sturgeon, visible by the naked eye. • Thiomargarita namibiensis: lives in marine sediments off the coast of Afica, 180 micometres in diameter( just visible without a microscope)But can reach 750 micometres, size of a pinhead. Prokaryotic cells. Much smaller than eukaryotic cells,0.5-3.0 micrometres. Parts and their function: Much simpler in structure, lack membrane bound organelles (mitochondria, chloroplasts). Lack complex structures such as Golgi bodies, cytoskeleton and lysosomes. • Nucleotide (or Nuclear Zone). The region of the cytoplasm that contains DNA. It is not surrounded by a nuclear membrane. • DNA. Always circular, and not associated with any proteins to form chromatin.( bacterial chromosome) • Plasmid. Small circles of DNA, used to exchange DNA between bacterial cells, and very useful for genetic engineering. • Cell Wall. Made of murein (not cellulose), which is a glycoprotein (i.e. a protein/carbohydrate complex, also called peptidoglycan). Protects the shape of cell,prevents it from bursting. • Some have a slime capsule, helps cells to stick together and for protection ( phagocytes) • Flagellum. A rigid rotating helical-shaped tail used for propulsion. Each consist of a single rod of proteins,rather than 9+2 hollow structure in Eukaryotes. • Cytoplasm. Contains all the enzymes needed for all metabolic reactions, since there are no organelles. Contains glycogen (CHO storage) and lipid droplets. • Ribosomes. The smaller (70 S) type, scattered in the cytoplasm. • There are no membrane bound organelles, but bacteria often have infolds of the plasma membrane: • Mesosome. A tightly-folded region of the cell membrane containing all the membrane-bound proteins required for respiration and photosynthesis. • Thylakoids. Present in photosynthetic bacteria, where bcterial chlorophyll and enzymes of photosynthesis are located. Differences between Prokaryotes and Eukaryotes: