Bài giảng Biology 25: Human Biology - Chapter 3

Chapter 3Biology 25: Human BiologyProf. GonsalvesLos Angeles City CollegeLoosely Based on Mader’s Human Biology,7th editionCell Theory: Developed in late 1800s.1. All living organisms are made up of one or more cells.2. The smallest living organisms are single cells, and cells are the functional units of multicellular organisms.3. All cells arise from preexisting cells. Microscope FeaturesMagnification:Increase in apparent size of an object. Ratio of image size to specimen size.Resolving power: Measures clarity of image.Ability to see fine detail.Ability to distinguish two objects as separate. Minimum distance between 2 points at which they can be distinguished as separate and distinct. Microscopes Light Microscopes: Earliest microscopes used. Lenses pass visible light through a specimen.Magnification: Highest possible from 1000 X to 2000 X.Resolving power: Up to 0.2 mm (1 mm = 1/1000 mm). Types of MicroscopeElectron Microscopes: Developed in 1950s. Electron beam passes through specimen.Magnification: Up to 200,000 X.Resolving power: Up to 0.2 nm (1nm = 1/1’000,000 mm). Two types of electron microscopes:1. Scanning Electron Microscope: Used to study cell or virus surfaces.2. Transmission Electron Microscope: Used to study internal cell structures.Components of All Cells:1. Plasma membrane: Separates cell contents from outside environment. Made up of phospholipid bilayers and proteins.2. Cytoplasm: Liquid, jelly-like material inside cell.3. Ribosomes: Necessary for protein synthesis.Prokaryotic versus Eukaryotic CellsFeature Prokaryotic EukaryoticOrganisms Bacteria All others (animals, plants, fungi, and protozoa)Nucleus Absent Present DNA One chromosome Multiple chromosomesSize Small (1-10 um) Large (10 or more um)Membrane Absent Present (mitochondria,Bound golgi, chloroplasts, etc.)OrganellesDivision Rapid process Complex process (Binary fission) (Mitosis)Eukaryotic CellsInclude protist, fungi, plant, and animal cells.Nucleus: Protects and houses DNAMembrane-bound Organelles: Internal structures with specific functions.Separate and store compoundsStore energyWork surfacesMaintain concentration gradientsFunctions of Cell Membranes 1. Separate cell from nonliving environment. Form most organelles and partition cell into discrete compartments.2. Regulate passage of materials in and out of the cell and organelles. Membrane is selectively permeable.3. Receive information that permits cell to sense and respond to environmental changes.HormonesGrowth factorsNeurotransmitters4. Communication with other cells and the organism as a whole. Surface proteins allow cells to recognize each other, adhere, and exchange materials. I. Fluid Mosaic Model of the Membrane1. Phospholipid bilayer: Major component is a phospholipid bilayer.Hydrophobic tails face inwardHydrophilic heads face water2. Mosaic of proteins: Proteins “float” in the phospholipid bilayer.3. Cholesterol: Maintains proper membrane fluidity.The outer and inner membrane surfaces are different.A. Fluid Quality of Plasma Membranes In a living cell, membrane has same fluidity as salad oil.Unsaturated hydrocarbon tails INCREASE membrane fluidityPhospholipids and proteins drift laterally.Phospholipids move very rapidly Proteins drift in membrane more slowlyCholesterol: Alters fluidity of the membraneDecreases fluidity at warmer temperatures (> 37oC)Increases fluidity at lower temperatures ( CO2 + H2O + ATP Change chemical energy of molecules into the useable energy of the ATP molecule. Oval or sausage shaped. Contain their own DNA, ribosomes, and make some proteins. Can divide to form daughter mitochondria. Structure:Inner and outer membranes.Intermembrane spaceCristae (inner membrane extensions)Matrix (inner liquid)Mitochondria Harvest Chemical Energy From FoodThe Cytoskeleton Complex network of thread-like and tube-like structures.Functions: Movement, structure, and structural support.Three Cytoskeleton Components:1. Microfilaments: Smallest cytoskeleton fibers. Important for:Muscle contraction: Actin & myosin fibers in muscle cells“Amoeboid motion” of white blood cellsComponents of the Cytoskeleton are Important for Structure and MovementThree Cytoskeleton Components:2. Intermediate filaments: Medium sized fibersAnchor organelles (nucleus) and hold cytoskeleton in place.Abundant in cells with high mechanical stress. 3. Microtubules: Largest cytoskeleton fibers. Found in:Centrioles: A pair of structures that help move chromosomes during cell division (mitosis and meiosis). Found in animal cells, but not plant cells.Movement of flagella and cilia.Cilia and Flagella Projections used for locomotion or to move substances along cell surface. Enclosed by plasma membrane and contain cytoplasm. Consist of 9 pairs of microtubules surrounding two single microtubules (9 + 2 arrangement). Flagella: Large whip-like projections. Move in wavelike manner, used for locomotion.Example: Sperm cell Cilia: Short hair-like projections.Example: Human respiratory system uses cilia to remove harmful objects from bronchial tubes and trachea.Structure of eukaryotic FlagellumSummary of Eukaryotic Organelles Function: ManufactureNucleusRibosomesRough ERSmooth ERGolgi ApparatusFunction: BreakdownLysosomesVacuolesSummary of Eukaryotic Organelles Function: Energy ProcessingChloroplasts (Plants and algae)MitochondriaFunction: Support, Movement, CommunicationCytoskeleton (Cilia, flagella, and centrioles)Cell walls (Plants, fungi, bacteria, and some protists)Extracellular matrix (Animals)Cell junctionsMetabolism: All chemical processes that occur within a living organism. Either catabolic or anabolic reactions.I. Catabolic Reactions: Release energy (exergonic). Break down large molecules (proteins, polysaccharides) into their building blocks (amino acids, simple sugars). Often coupled to the endergonic synthesis of ATP. Examples: 1. Cellular respiration is a catabolic process: C6H12O6 + 6 O2 -------> 6 CO2 + 6 H2O + Energy Sugar Oxygen Carbon dioxide Water 2. The digestion of sucrose is a catabolic process: Sucrose + Water -------> Glucose + Fructose + Energy Disaccharide MonosaccharidesMetabolism: Catabolism + Anabolism II. Anabolic Reactions: Require energy (endergonic). Build large molecules (proteins, polysaccharides) from their building blocks (amino acids, simple sugars). Often coupled to the exergonic breakdown or hydrolysis of ATP. Examples: 1. Photosynthesis is an anabolic process: 6 CO2 + 6 H2O + Sunlight ----> C6H12O6 + 6 O2 Carbon Water Sugar Oxygen Dioxide 2. Synthesis of sucrose is an anabolic process: Glucose + Fructose + Energy -------> Sucrose + H2O Monosaccharides DisaccharideV. ATP: Shuttles Chemical Energy in the CellCoupled Reactions: Endergonic and exergonic reactions are often coupled to each other in living organisms.The energy released by exergonic reactions is used to fuel endergonic reactions.ATP “shuttles” energy around the cell from exergonic reactions to endergonic reactions. One cell makes and hydrolyzes about 10 million ATPs/second.Cells contain a small supply of ATP molecules (1-5 seconds).ATP powers nearly all forms of cellular work:1. Mechanical work: Muscle contraction, beating of flagella and cilia, cell movement, movement of organelles, cell division.2. Transport work: Moving things in & out of cells.3. Chemical work: All endergonic reactions.A. Structure of ATP (Adenosine triphosphate)Adenine: Nitrogenous base.Ribose: Pentose sugar, same ribose of RNA.Three Phosphate groups: High energy bonds.B. ATP Releases Energy When Phosphates Are Removed:Phosphate bonds are rich in chemical energy and easily broken by hydrolysis: ATP + H2O ----> ADP + Energy + Pi ADP + H2O ----> AMP + Energy + PiVI. Enzymes: Protein molecules that catalyze the reactions of living organisms.Enzymes increase the rate of a chemical reaction without being consumed in the process.Name: Substrate (or activity) + ase suffix Examples:SucraseLipaseProteinaseDehydrogenase (Removes H atoms)Enzymes are specific: Catalyze one or a few related reactions.Enzymes are efficient. Can increase the rate of a reaction 10 to billions of times!!!!VI. Enzymes: Enzymes increase the rate of a chemical reaction by lowering the activation energy required to initiate the reaction.Activation energy of a reaction: Energetic barrier that reactant molecules must overcome for reaction to proceed. Creation of new bonds requires breaking of old bonds.Both exergonic and endergonic reactionsTransition state :“Intermediate” state of reactantsEnzyme Mechanism of Action: 1. Binding: Enzyme binds to the reactant(s), forming an enzyme-substrate complex.Substrate: The reactant the enzyme acts upon to lower the activation energy of the reaction.Active site: Region on enzyme where binding to substrate occurs.Active site dependent upon proper 3-D conformation.Enzyme Mechanism of Action: 2. Induced fit model: After enzyme binds to substrate, it changes shape and lowers activation energy of the reaction by one of several mechanisms:Straining chemical bonds of the substrateBringing two or more reactants close togetherProviding “micro-environment” conducive to reaction3. Release: Once product is made, it is released from active site of enzyme. Enzyme is ready to bind to another substrate molecule. CELLULAR RESPIRATION BANKS ATP REACTION: C6H12O6 + 6O2 ----> 6CO2 + 6H2O + ENERGY(Glucose) (Oxygen) (Carbon dioxide) (Water) What happens to the energy in glucose or other food molecules?Only about 40% of energy is turned into ATPThe rest is lost as metabolic heat.One ATP molecule has about 1% of the chemical energy found in glucose.MAJOR CATABOLIC PATHWAYSA. Aerobic (Cellular) respiration: Requires oxygen.Most commonly used catabolic pathway.Over 30 reactions. Used to extract energy from glucose molecules.Final electron acceptor: Oxygen.Most efficient: 40% of glucose energy is converted into ATP.REACTION: C6H12O6 + 6O2 ---> 6CO2 + 6H2O + ENERGY Glucose Oxygen Carbon dioxide Water V. Three Stages of Cellular Respiration A. Glycolysis B. Kreb’s Cycle C. Electron Transport Chain & Chemiosmosis A. Glycolysis: “Splitting sugar” Occurs in the cytoplasm of the cellDoes not require oxygen9 chemical reactionsNet result: Glucose molecule (6 carbons each) is split into two pyruvic acid molecules of 3 carbons each.Yield per glucose molecule: 2 ATP ( Substrate-level phosphorylation) 2 NADH + 2 H+ (2 ATP are “invested” to get 4 ATP back)Pyruvic acid diffuses into mitochondrial matrix where all subsequent reactions take place. Conversion of Pyruvate to Acetyl CoABefore entering the next stage, pyruvic acid (3C) must be converted to Acetyl CoA (2 C). A carbon atom is lost as CO2. Yield per glucose molecule: 2 NADH + 2 H+ B. Kreb’s CycleOccurs in the matrix of the mitochondrionA cycle of 8 reactionsReaction 1: Acetyl CoA (2C) joins with 4C molecule (oxaloacetic acid) to produce citric acid (6C).Reactions 2 & 3: Citric acid loses 2C atoms as CO2.Reactions 4 & 5: REDOX reactions produce NADH and FADH2.Reactions 6-8: Oxaloacetic acid is regenerated. B. Kreb’s CycleCarbons are released as CO2Yield per glucose molecule: 2 ATP (substrate-level phosphorylation) 6 NADH + 6 H+ 2 FADH2 C. Electron Transport Chain & Chemiosmosis Most ATP is produced at this stageOccurs on inner mitochondrial membraneElectrons from NADH and FADH2 are transferred to electron acceptors, which produces a proton gradientProton gradient used to drive synthesis of ATP.Chemiosmosis: ATP synthase allows H+ to flow across inner mitochondrial membrane down concentration gradient, which produces ATP.Ultimate acceptor of H+ and electrons is OXYGEN, producing water. C. Electron Transport Chain & Chemiosmosis Yield of ATP through Chemiosmosis:Each NADH produces 3 ATPEach FAHD2 produces 2 ATP 2 NADH (Glycolysis) x 3 ATP = 6 ATP2 NADH (Acetyl CoA) x 3 ATP = 6 ATP6 NADH (Kreb’s cycle) x 3 ATP = 18 ATP2 FADH2 (Kreb’s cycle) x 2 ATP = 4 ATP ________________ 32 - 34 ATP These ATPs are made by oxidative phosphorylation or chemiosmosis.VIII. Total Energy from cellular respiration Substrate OxidativeProcess Phosphoryl e-Carrier Phosphoryl TOTALGlycolysis 2 ATP 2 NADH ---> 4 - 6 ATP 6-8 ATPAcetyl CoA 2 NADH ---> 6 ATP 6 ATPFormationKreb’s 2 ATP 6 NADH ---> 18 ATP 2 FADH2 ---> 6 ATP 24 ATP __________ Total yield per glucose : 36-38 ATPTHREE MAJOR CATABOLIC PATHWAYSB. Anaerobic respiration: Does not require oxygen.Used by bacteria that live in environments without oxygen.Final electron acceptor: Inorganic molecule.Very inefficient: Only 2% of glucose energy is converted into ATP.Final products: Carbon dioxide, water, and other inorganic compounds.THREE MAJOR CATABOLIC PATHWAYSC. Fermentation: Does not require oxygen.Used by yeast, bacteria, and other cells when oxygen is not available.Final electron acceptor: Organic molecule.Very inefficient: Only 2% of glucose energy is converted into ATP.Products depend on type of fermentation:Lactic acid fermentation: Used to make cheese and yogurt. Carried out by muscle cells if oxygen is low.Alcoholic fermentation: Used to make alcoholic beverages. Produces alcohol and carbon dioxide.