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Structure and Function
Cells: Structure and Function
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Introduction to Cells – Brief Summary
Cell Theory – Several scientists such as van Leeuwenhoek (microscopes), Hooke (light microscopes), Schleiden, Schwann, and Verchow together “sculpted” the Cell Theory: All living things composed of cells Cells are the basic units of structure and function in living things New cells are produced from existing cells
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Prokaryotes vs. Eukaryotes
Prokaryotes – no nucleus, usually one-celled, no membrane-bound organelles Eukaryotes – have a nucleus, single-celled or multicellular, have organelles, typically larger in size Cell membrane Cytoplasm Prokaryotic Cell Nucleus Eukaryotic Cell Organelles
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Plant Cells vs. Animal Cells
Plant cells – cell wall, chloroplasts, no lysosomes Animal cells – no cell wall, little to no vacuoles, no chloroplasts, have lysosomes Animal Cells Plant Cells Cell membrane Ribosomes Nucleus Endoplasmic reticulum Golgi apparatus Vacuoles Mitochondria Cytoskeleton Cell Wall Chloroplasts Lysosomes
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Plant Cell Plant Cell Smooth endoplasmic Vacuole reticulum (free)
Nuclear envelope Ribosome (attached) (free) Smooth endoplasmic reticulum Nucleus Rough endoplasmic reticulum Nucleolus Golgi apparatus Mitochondrian Cell wall Cell Membrane Chloroplast Vacuole Plant Cell
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Animal Cell Animal Cell (attached) Ribosome Nucleolus (free) Nucleus
Centrioles Nucleolus Nucleus Nuclear envelope Rough endoplasmic reticulum Golgi apparatus Smooth Mitochondrian Cell Membrane Ribosome (free) (attached) Animal Cell
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Cell Membranes and Movement: Cell membrane
AKA Plasma Membrane Regulates what enters and leaves the cell and also provides protection and support. Food and water enter, while wastes are eliminated Made of a double-layered sheet called the phospholipid bilayer Lipid bilayer – tough, flexible structure forming a strong barrier Also contains proteins (channels and pumps) and carbohydrates (ID cards) Most biological membranes are selectively permeable – some substances can pass and others cannot
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Cell Membrane: Fluid Mosaic
Lipids and proteins free to drift around the membrane = “fluid” Many different molecules attached to the membrane = “mosaic” of different molecules Outside of cell Cell membrane Proteins Protein channel Lipid bilayer Carbohydrate chains Inside of cell (cytoplasm)
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Types of Movement through Membrane
Four major types of movement: Diffusion Facilitated Diffusion Osmosis Active Transport
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Diffusion Living cells contain liquid interiors and are surrounded by liquid. Cytoplasm is a solution of many different substances in water Molecules tend to move from high concentration to low concentration = diffusion Diffusion causes many substances to move across a cell membrane but does NOT require energy to do so Equilibrium – when there is equal concentration of substances on both sides of the membrane – everything is moving back and forth across the membrane at the same rate Example: freshly baked cookies smell strongest near cookies, but smell eventually diffuses across room.
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Diffusion
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Facilitated Diffusion
Proteins in membrane acts as channels to help (facilitate) substances cross the membrane. There are different protein channels for different substances – ions, salts, sugars Only occur if there is a higher concentration on one side of the membrane than the other and requires NO energy to do so Moves substances from high to low concentration
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Facilitated Diffusion (continued)
Glucose molecules High Concentration Cell Membrane Protein channel Low Concentration
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Osmosis Osmosis allows water molecules to pass easily through the membrane – requires NO energy to do so Moves water from high to low concentration
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Osmosis (continued) Membrane is permeable to water but not to sugar. Sugar is concentrated on one side of the membrane and dilute on the other side. More water enters the concentrated sugar side because there is less water there – high to low concentration Water molecules Higher Concentration of Water Cell membrane Lower Concentration of Water Sugar molecules Water moves across until equilibrium is reached – at this point, concentrations of water and sugar will be the same = isotonic. At first, concentrated sugar solution was hypertonic and diluted sugar concentration was hypotonic.
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Osmosis: The Fishy Saga…
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The Saga Continues…
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Osmotic Pressure Osmosis exerts pressure (osmotic pressure) on the hypertonic side of the membrane = possible problems. If a cell is placed in fresh water, water rushes in and bursts the cell Fortunately, most cells live in isotonic environments
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Active Transport Molecule to be carried Move substances AGAINST a concentration difference. Substances move from low to high concentration by active transport, which requires energy to do so Membranes have protein “pumps” to transport substances against the concentration Low Concentration Cell Membrane High Concentration Molecule being carried Low Concentration Cell Membrane High Concentration Energy Energy
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Other Ways to Move Substances
Movement of membrane can also transport materials Endocytosis – take material into cells by means of infoldings, or pockets, of the membrane Exocytosis – removal of large amounts of materials Phagocytosis – large particles engulfed by extensions of cytoplasm
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Endocytosis and Exocytosis
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Diversity of Cellular Life
Levels of organization – cells → tissues → organs → organ system Muscle cell Smooth muscle tissue Stomach Digestive system
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Unicellular and multicellular organisms
Unicellular – both prokaryotes and eukaryotes Bacteria (prokaryotes) Algae (eukaryotes) Yeast (eukaryotes) Multicellular – eukaryotes Cell specialization – separate roles for each type of cell in the body
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