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Transcript
Overview of Cells Prokaryotic All bacteria Most have cell wall No membrane-bound organelles Biochemical reactions take place in cytoplasm or cell membrane Typically very small Eukaryotic Protist, fungi, plant and animal cells Some have cell walls Possess membrane-bound organelles Biochemical reactions take place in specialized compartments Much larger than bacteria Prokaryotic Cell Fimbriae Nucleoid Ribosomes Plasma membrane Bacterial chromosome Cell wall Capsule 0.5 µm (a) A typical rod-shaped bacterium Flagella (b) A thin section through the bacterium Bacillus coagulans (TEM) Animal Cells Surrounded by plasma membrane Allows certain molecules in or out of the cell Does not have a cell wall Nuclear envelope ENDOPLASMIC RETICULUM (ER) Flagellum Rough ER NUCLEUS Nucleolus Smooth ER Chromatin Centrosome Plasma membrane CYTOSKELETON: Microfilaments Intermediate filaments Microtubules Ribosomes Microvilli Golgi apparatus Peroxisome Mitochondrion Lysosome Plant Cells Have plasma membrane and cell wall Cell wall gives support Has chloroplasts (contain chlorophyll) and large vacuole Fig. 6-9b NUCLEUS Nuclear envelope Nucleolus Chromatin Rough endoplasmic reticulum Smooth endoplasmic reticulum Ribosomes Central vacuole Golgi apparatus Microfilaments Intermediate filaments Microtubules Mitochondrion Peroxisome Chloroplast Plasma membrane Cell wall Plasmodesmata Wall of adjacent cell CYTOSKELETON Why Small Cells? Cells obtain nutrients (gases, water other molecules) from the environment through the cell membrane High surface area:volume ratios maximizes the amount of cell/environment interaction Large cells would starve Cell Membrane Lipid bilayer Integral proteins “float” in fluid Hydrophobic region of proteins reside in fatty acid layer of membrane Hydrophilic regions are on cytoplasmic and extracellular surfaces Membrane fluidity may be altered by adjusting fatty acid chains Clip Fig. 7-3 Phospholipid bilayer Hydrophobic regions of protein Hydrophilic regions of protein Membranes are complex Membranes are embedded with: Integral proteins Peripheral proteins Glycoproteins Proteoglycans Carbohydrates Membranes are connected to cytoskeleton on the Cytoplasmic surface Fig. 7-7 Fibers of extracellular matrix (ECM) Glycoprotein Carbohydrate Glycolipid EXTRACELLULAR SIDE OF MEMBRANE Cholesterol Microfilaments of cytoskeleton Peripheral proteins Integral protein CYTOPLASMIC SIDE OF MEMBRANE Roles of Membranes Gatekeeper of cell Compartmentalization Actively move molecules into cell Signal transduction Every membrane-bound organelle is isolated Transport Determines what goes in or out of cell Environmental conditions trigger genetic and biochemical changes in cell via receptors Cell-cell communication and interaction Diffusion Starts with a gradient System will eventually reach equilibrium (even distribution) Happens passively without selective barriers Many small molecules diffuse through cell membrane Fig. 7-11 Molecules of dye Membrane (cross section) WATER Net diffusion Net diffusion Equilibrium (a) Diffusion of one solute Net diffusion Net diffusion (b) Diffusion of two solutes Net diffusion Net diffusion Equilibrium Equilibrium Osmosis Requires a gradient and a selectively permeable membrane Solute is unable to pass through membrane to reach equilibrium Water will move to area of greater solvent concentration until equilibrium is reached Fig. 7-12 Lower concentration of solute (sugar) Higher concentration of sugar H2O Selectively permeable membrane Osmosis Same concentration of sugar Facilitated diffusion An integral protein helps molecules across the membrane Often act as a revolving door (carrier) or tunnel (channel) Fig. 7-15 EXTRACELLULAR FLUID Channel protein Solute CYTOPLASM (a) A channel protein Carrier protein (b) A carrier protein Solute Active Transport Cell expends energy to move molecule or atom inside Often forms gradients to accomplish this Entry into Cell Summarized Diffusion and Facilitated diffusion are passive transport because no energy is required Facilitated diffusion and active transport can be very selective processes Membrane Pumps Can be used to remove unwanted molecule from cytoplasm (like sump pump) Can also be used to form a gradient across the membrane which can drive other transports (protomotor force) Fig. 7-17 Passive transport Active transport ATP Diffusion Facilitated diffusion