Chapter 4 Cells and Organelles - Part 1 PDF

Chapter 3 4 Cells and Organelles  Chapter 4 Cell Size Wide range of sizes Some bacteria 0.2 – 0.3 µm Some nerve cells > 1 meter Average bacterial cell = 1 – 5 µm Average animal cell = 10 - 100 µm ...

Chapter 3 4 Cells and Organelles  Chapter 4 Cell Size Wide range of sizes Some bacteria 0.2 – 0.3 µm Some nerve cells > 1 meter Average bacterial cell = 1 – 5 µm Average animal cell = 10 - 100 µm  Chapter 4 Why are cells so small? Size limiting factors: Adequate surface area/volume ratio necessary Rates at which molecules diffuse Maintenance of local concentrations of substances  Chapter 4 Diffusion Rate of Molecules Diffusion – free unassisted movement of a substance from areas of high concentration to low concentration  Chapter 4 A Typical Animal Cell Figure 4-5  Chapter 4 Function of Membrane 1. Some protection and support 2. Communication (cells recognize each other and work together). 3. Regulation of transport of materials IN and OUT of the cell.  Chapter 4 Organization of the Plasma Membrane Defines cell boundary lipid bilayer Fluid-Mosaic Model Phospholipid bilayer fluid fluid (50:1 / Lipid to protein) Figure 4-9  Chapter 4 P Phospholipi Cholestero Glycolipid ds (75%) l (20%) s (5%) Form lipid bilayer – Strengthens the framework of Identity markers and stabilizes the membrane. on cell’s surface cell membrane Due to the basic lipid structure, only small and nonpolar substances are able to cross the lipid bilayer without assistance  Chapter 4 Organization of the Plasma Membrane Defines cell boundary Fluid-Mosaic Model Phospholipid bilayer Proteins embedded Enzyme Figure 4-9 Anchor Transport Receptor lipid bilayer fluid fluid Chapter 4  Chapter 4 To stay alive, our cells require: water, a constant supply of O2 , food (energy and matter). ______________________ a constant removal extra of water, CO2 , wastes. _________________________ As the result, there is a need for constant transport of substances across the  Chapter 4 Transport within Eukaryotic Cells Selectively Permeable Allows controlled passage Crucial to proper cell or organelle function Selective Transport: Ability to move ions and small molecules across membranes selectively Substances Ions Organic molecules (non-polar) Some macromolecules  Chapter 4 Transport within Eukaryotic Cells Passive Transport Diffusion Simple Facilitated Osmosis Active Transport Direct Indirect  Chapter 4 Diffusion and Osmosis Neither requires energy. Molecules always move down the gradient Diffusion Movement of solutes Osmosis Movement of water Figure 8-4  Chapter 4 Simple Diffusion Simple Diffusion is direct, unaided movement of solutes Dictated by the concentration gradients Small, non-polar molecules e.g., CO and O 2 2 Figure 8-2  Chapter 4 Facilitated Diffusion Facilitated Diffusion involves moving down a gradient but is mediated by proteins Types: Carrier protein – binds solute molecules on one side of the membrane and changes the conformation which allows solute to diffuse Channel protein – form hydrophilic channels in membrane that allow diffusion to occur  Chapter 4 Facilitated Diffusion  Chapter 4 Comparison of Carrier Uniport Transport Proteins Moves a single solute Symport Moves two solutes in the same direction Antiport Figure 8-7 Moves two solutes in the opposite direction  Chapter6 3 Chapter 4 Carrier-Mediated Transport Molecules too large (i.e., glucose), non lipid soluble, and/or polar need assistance getting across the plasma membrane. 1. Facilitated diffusion (i.e., glucose) a process of diffusion, a form of passive transport facilitated by transport proteins (transmembrane proteins creating channels through the plasma membrane).  Chapter6 3 Chapter 4 Active transport – the utilization energy, (i.e., ATP), and transport proteins to move molecules against a concentration gradient. Steps of Active transport: (primary active transport) a) The transport molecule binds to the carrier protein b) ATP is converted into ADP + Pi (energy released) c) Conformational change in the carrier moves the molecule across the membrane d) The molecule is released into the opposite compartment and the carrier returns to its starting conformation. Chapter6 3 Chapter 4  Chapter6 3 Chapter 4 Ex. Sodium-potassium pump - primary active transport mechanism to move 3 Na+ ions out of the cell (12% of the ATP used in the body is used by this pump). - secondary active transport (ATP not directly required) mechanism to move 2 K+ ions into the cell. - An antiport mechanism (Na+ out / K+ in). Most sensitive to intracellular Na+ levels; High Na+ levels turns pump on. Chapter6 3 Chapter 4  Chapter 4 Exchange of Materials Endocytosis Portions of the membrane invaginate and are pinched off to form vesicles inside the cell Exocytosis Vesicles inside the cell fuse with the plasma membrane and release their content outside the cell  Chapter 4 Organelles Defined: membrane-bound compartments Internal membranes used to segregate function Examples: Nucleus Endoplasmic reticulum Golgi complex Vacuole Lysosomes Peroxisomes Mitochondria Chloroplasts Figure 4-5  Chapter 4 Endomembrane System (one each per eukaryotic cell) Nucleus – genome, nucleic acid synthesis, ribosomal subunit assembly Endoplasmic Reticulum – protein and lipid synthesis, protein modifications Golgi complex – modification, sorting and packaging of proteins. Vacuole – acid compartment in plants that resemble lysosomes Figure 4-5  Chapter 4 Endomembrane System (many per eukaryotic cell) Lysosomes – intracellular degradation (scores to hundreds per cell) Peroxisomes – degradation (oxidation) of toxins (scores to hundreds per cell)  Chapter 4 The Nucleus of a Eukaryotic Cell Nucleus Genetic material localized inside nuclear envelope Nuclear envelope Double-membrane nucleoplasm Contains pores Nucleolus nucleolus Site of ribosome synthesis Message formed from DNA, RNA, must be transported out of the nucleus Figure 4-4  Chapter 4 Nuclear Envelope Inner membrane lined with nuclear lamina and binds to chromosomes Outer membrane continuous with ER and encloses lumen Perforated with nuclear (gated) pores.  Chapter 4 Nuclear Pore Structure Elaborate structure of about 100 proteins Small water soluble molecules pass unimpeded Larger molecules pass only with “approval”: Outward – completed mRNA, assembled ribosomal subunits.  Chapter 4 The Endoplasmic Reticulum Network of membranes Continuous with the outer membrane of the nucleus Rough endoplasmic reticulum Secretory and membrane proteins produced Glycosylation begins  Chapter 4 The Endoplasmic Reticulum Figure 4-15 Network of membranes Continuous with the outer membrane of the nucleus Rough endoplasmic reticulum Secretory and membrane proteins produced Glycosylation begins Smooth endoplasmic reticulum Synthesis of lipids and steroids; detoxification of compounds  Chapter 4 Ribosomes Strictly speaking not an organelle Protein synthesis Found in pro- and eukaryotes Two subunits Large (60S) Small (40S)  Chapter 4 The Golgi Complex Synthesis of complex polysaccharides Processing and packaging of secretory proteins Vesicles from the ER  Chapter 4 Secretion in Eukaryotic Cells Outbound biosynthetic–secretory pathway: e.g., pancreas (digestive enzymes & insulin) ER to Golgi Golgi to plasma membrane (unconcentrated) Golgi to secretory vesicle to secretion (concentrated)  Chapter 4 Lysosomes Surrounded by a single membrane Stores enzymes Hydrolases Breaks down specific molecules Proteins, carbohydrates, or fats Cellular recycling Packaged in a way to protect the cell until needed Pathway for formation Synthesized on the rough ER Transported to the Golgi complex Tagged as containing lysosomal enzymes Mannose-6-phosphate tag  Chapter 4 Peroxisomes Look similar to lysosomes Single membrane Found in animals, plants, and fungi Note location in cell Generate and degrade hydrogen peroxide (H2O2) catalase Animals Prominent in liver and kidney cells Detoxification of ethanol, breakdown fatty acids Plants Involved in photorespiration O taken up & CO released using 2 2 photosynthetic pathway  Chapter 4 Organelles Endomembrane System Nucleus Endoplasmic Reticulum (ER) Golgi complex Vacuole Lysosomes Peroxisomes Mitochondria Chloroplasts  Chapter 4 Mitochondria Functions at the site of respiration Double membrane system Outer membrane Porous to molecules in the cytoplasm Inner membrane = cristae Site of ATP synthesis Contains DNA (circular) Free to move about Chapter 4 Figure 4-12  Chapter 4 Cytoskeleton Found throughout the cytoplasm Network of protein filaments Microtubules Microfilaments Intermediate filaments Function Internal framework Distinctive shape Involved in cell division & growth Serves as scaffolding for movement of organelles Human epithelial cells  Chapter 4 Microtubules, Microfilaments, and Intermediate Filaments Figure 4-24