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Transcript
CELLS The Fundamental Units of Life Cell Theory 1. All organisms are composed of 1 or more cells. 2. The cell is the basic living unit, providing organization for all organisms. 3. All cells arise from preexisting cells. Cells Are Small • Most are too small to be seen with the unaided eye…so Microscopes are used. • A Light Microscope uses visible light shone through glass lenses. • A “thin section” of specimen is required. • van Leeuwenhoek Principles of Microscopy • • • • LIGHT REFRACTION MAGNIFICATION RESOLUTION MAGNIFICATION • Image size exceeds real size. • Achieved with convex lenses. • There are limits… …involving the nature of light. • First, you need enough light to penetrate the thin specimen. RESOLUTION • Next, you need light of appropriate wavelength…or RESOLUTION is compromised. • A measure of clarity – of focus. • Minimum distance between two points that allow the points to be distinguishable. • Light microscopy not very useful below 0.2um. RESOLUTION Electron Microscopy • Uses e- rather than light. • Electrons have a much shorter wavelength. • SEM = Scanning Electron Microscopy • TEM = Transmission Electron Microscopy Electron Microscopy Cells! ALL CELLS • Plasma Membrane (Cell Membrane) – Separate the contents of the cell from the environment. • Cytoplasm (Cytosol) – Semi-fluid contents of the cell – Lots of “floaties” • Nucleus “area” – Location of DNA CELLS • Eukaryotic Cells (animals, plants, fungi, protists) – Complex & relatively large. – Membrane-bound nucleus & organelles. – 80-S Ribosomes. • Prokaryotic Cells (archaea, bacteria) – Simple & relatively small. – NO Membrane-bound nucleus & organelles. – 70-S Ribosomes. CELLS PROKARYOTIC EUKARYOTIC EUKARYOTIC CELLS Organelles = “little organs” (not really) Membrane-bound ORGANELLES • Nucleus – Isolates the DNA & provides access to its hereditary information. – The “control center” of the cell (Transcription). Nucleus 1. Nuclear Envelope (a double membrane) with Pores. 2. Nucleolus • • • rRNA Proteins Ribosomes 3. Nucleoplasm with Chromatin/Chromosomes. Ribosomes • • • • Not true organelles, more “structures”. Protein factories. 2 sub-units. Free (in cytosol/cytoplasm), more for intracellular activities. • Bound (on E.R.), often for extracellular activities (secretion) & packaging within certain organelles. Endomembrane System • Synthesis of Proteins & their transport into membranes and/or organelles. • Packaging of Proteins for transport out of the cell (secretion) or to other areas of the cell. • Modification of Proteins. • Transport of lipids, lipoproteins, glycoproteins, etc. Endomembrane System 1. Endoplasmic Reticulum (E.R.) – Rough E.R. – Smooth E.R. 2. Golgi Apparatus 3. Vesicles – Lysosomes (also, nuclear envelope, vacuoles, and plasma membrane) Endoplasmic Reticulum • Network of interconnected membranes (continuous with the nuclear envelope). • Flattened or tubular Cisternae. Rough E.R. • The site of protein synthesis, particularly secretory proteins. • Initial modification of proteins. – Especially, formation of Glycoproteins. • Formation (budding) of Transport Vesicles. • Formation of NEW Membrane = Phospholipid Synthesis Smooth E.R. • Modification of Proteins. • Formation of Lipids, detoxification. – Lipid-derived hormones (steroids) are synthesized, including sex hormones (testosterone, etc.) in certain glands. – Solubilization of toxins (drugs, alcohol, caffeine, etc. ) in liver cells. – Calcium ion storage & release in muscle cells. Golgi Apparatus • Modification, storage, sorting, & shipping of ERproduced molecules (esp. for secretion). • Addition of non-protein portions to protein molecules. Golgi Apparatus • Stacks of cisternae, with cis & trans faces. – Cis – receiving (takes in vesicles). – Trans – sending (gives rise to vesicles). Lysosomes • Specific vesicles carrying digestive enzymes – hydrolytic (proteolytic) enzymes. • Animal Cells. • Digestion of food brought in by phagocytosis. Lysosomes • Digestion and recycling of old & damaged organelles within the cell: Autophagy. Endomembrane System Vacuoles • Large vesicles with particular functions. – Food Vacuoles. – Contractile Vacuoles. – Central Vacuole w/ tonoplast in Plant Cells. •Storage. •Dissolved Solutes. •Dumping Ground. •Protection. •Shape. Mitochondrion • Surrounded by a double membrane – an envelope. Outer Membrane Inner membrane (Cristae) Matrix Mitochondrion • Site of cellular respiration = energy production. Carbohydrates ATP • Not part of endomembrane system. • Have their own DNA, RNA, Proteins, and Ribosomes (70-S). • Grow and reproduce independently. • Animals, Plants, Fungi, Protists. Chloroplast • Surrounded by a double membrane – an envelope. Outer Membrane Inner Membrane (Grana composed of stacked Thylakoids) Stroma Chloroplast • Site of Photosynthesis = acquisition of chemical energy from sunlight. Sunlight + CO2 Carbohydrates • A plastid (not part of endomembrane system). • Have their own DNA, RNA, Proteins, and Ribosomes (70-S). • Grow and reproduce independently. • Plants, Protists. Peroxisomes • Odd vesicles that carry Hydrogen to Oxygen, forming Hydrogen Peroxide (H2O2). • Used to break down larger molecules. • Detoxify alcohol in Liver Cells. Cytoskeleton • Fiber-like structures that lend organization. • Support (providing a scaffolding onto which organelles & vesicles can be organized). • Shape (maintain particular shape depending on the cell’s location and/or function). • Transport of materials around or out of the cell. • Motility of the whole cell from one location to another. Cytoskeleton Microtubules Microfilaments Intermediate Filaments Keratin Subunits Tubulin Actin Keratin Cytoskeleton • Permanent – Flagella – Cilia – Muscle Contraction – Scaffolding & Shape Maintenance Cytoskeleton • Transient – Spindle Fibers – Transport filaments Cell Wall • OUTSIDE the Cell Membrane (technically, outside the cell!) • Various proteins & glycoproteins in Prokaryotes. • Cellulose in Plants. • Chitin in Fungi. Eukaryotic Cell Endosymbiont Theory Onion Cells