Chapter 5 Ground Rules Of Metabolism

Chapter 5 Ground Rules Of Metabolism

Energy and the World of Life Energy Capacity to do work Two Forms Of energy Kinetic Energy is the energy an object has because it is moving Potential Energy is the energy of an object because of its position and shape

Two Laws Of thermodynamics 1 Energy cannot be created or destroyed It can be converted from one form to another and transferred between objects or system E.g. Chemical (potential )energy in food will be converted to the kinetic energy by movement 2 Entropy tends to increase Energy tends to disperse spontaneously Some energy disperses at each energy transfer, usually in the form of heat Entropy is the measure of energy dispersal

Energy In, Energy Out Reactant - Molecule that enter in a reaction Product A molecule remaining at the end of the reaction Exergonic & Endergonic Reactions in metabolism Exergonic reactions (energy-releasing) releasing) Aerobic respiration Endergonic reactions (energy-requiring) requiring) Photosynthesis

Exergonic and Endergonic Reactions

Energy Flows in One Direction Energy is not cycled In from the sun; into and out of ecosystems All living things harvest external energy Producers and consumers use energy to assemble, rearrange, and dispose of substances All organisms survive by tapping into the one way flow from sun

One-Way Energy Flow

ATP in Metabolism Adenosine triphosphate (ATP) Main energy carrier in cell ATP accepts energy released by exergonic reactions, and delivers to endergonic reactions Phosphorylation Phosphate-groups transfer to and from ATP When ATP gives up one of its phosphate, an ADP is formed ATP/ADP cycle drives most metabolic reactions

ATP: Energy Currency of Life

Enzymes in Metabolism Enzymes - Molecules that make chemical reactions occur much faster than they would on their own Activation energy Minimum energy needed to start a reaction Enzyme Structure & Function Enzymes are catalysts Catalyst- Chemical agent that speeds up a reaction Enzymes lowers the activation energy

Activation Energy

Enzyme Structure & Function Substrate A reactant molecule that is specifically acted upon by an enzyme Active site Small cleft in enzyme s s surface where reactions occur Microenvironment is more favorable for reaction than the surroundings

Enzyme- substrate

Enzyme Action Transition State The state in a chemical reaction when the reactants bond are at breaking point How enzymes lower activation energy By concentrating substrate molecules By orienting substrates to favor reaction By inducing fit between substrate and active site By excluding water from active site

Induced Fit model

Controls Over Enzymes Allosteric sites Allo Other, Steric - Structure Enzyme binding site other than active site Alters shape of enzyme to enhance or inhibit function Feedback Inhibition Mechanism by which a change that results from some activity stops that activity

Allosteric Control

Feedback Inhibition

Enzymes and the Environment Each enzyme functions best within a characteristic range of temperature, salt concentration and ph

Cofactors Many enzymes require non protein helpers for catalytic activity, these are called co-factors Some are inorganic metal ions Organic co-factors are called coenzymes All vitamins are coenzymes Co factors bind loosely or tightly with enzymes Example: Catalase (Antioxidant) Cofactor: Iron

Metabolism Organized, Enzyme-Mediated Reactions Cells concentrate, convert, and dispose of most substances in orderly, enzyme- mediated reaction sequences called metabolic pathways

Types of metabolic Pathways Biosynthetic (anabolic) pathway Pathways construct large molecules from smaller ones Require energy Degradative (catabolic) pathway Break down of large molecules into smaller products Release usable energy

Types of metabolic Pathways Photosynthesis Main biosynthetic pathway in the biosphere Autotrophs or Producers Aerobic respiration Main degradative pathway in the biosphere Heterotrophs

Main Metabolic Pathways

Chemical Equilibrium It is attained when the concentration of reactants and products no longer change

Redox reactions Oxidation Loss of electrons Reduction Gain of electrons Coenzymes and electron transfer chains Take part in organized sequences of reactions in photosynthesis and aerobic respiration

Controlled Energy Release

Diffusion, Membranes, and Metabolism Concentration of a substance Number of atoms or molecules in a given volume Concentration gradient of a substance A difference in concentration between two regions

Concentration gradient

Diffusion Diffusion Net movement of molecules to a region where they are less concentrated Diffusion rates are influenced by: Temperature Molecular size Gradients of pressure, charge, and concentration

Diffusion and Membrane Permeability Selective permeability Cell membrane allows some substance, but not others to cross it

Diffusion and Membrane Permeability Selective Permeability

How Substances Cross Membranes: Diffusion, Passive and Active Transport

Endocytosis and Exocytosis Endocytosis Process by which a cell takes in substances by engulfing it in a vesicle formed from a bit of plasma membrane Exocytosis A vesicle that formed in the cytoplasm fuses with the plasma membrane

How Substances Cross Membranes: Endocytosis and Exocytosis

Working With and Against Gradients Many solutes cross membranes through transport proteins (open or gated channels) Passive transport (Facilitated diffusion) Does not require energy input Solute diffuses down its concentration gradient through a transporter Example: Glucose transporters

Extracellular Fluid passive transport protein Lipid Bilayer Cytoplasm glucose, more concentrated outside cell than inside glucose transporter

Fig. 5.19, p. 85

Active Transport Active transporters require ATP energy to move a solute against its concentration gradient Specific solutes can bind to the active transporter Example: Calcium pumps Cotransporters move two substances at the same time Example: Sodium-potassium pump

Movement of water Osmosis Diffusion that involves the movement of water molecules across a semi permeable membrane Water molecules follow their concentration gradient, influenced by solute concentration

Osmosis

Tonicity Relative concentrations of two solutes separated by a semipermeable membrane Hypertonic fluid (higher solute concentration) Hypotonic fluid (lower solute concentration) Isotonic solutions (two solutions with the same tonicity)

Effects of Fluid Pressure Hydrostatic pressure (turgor( turgor) Exerts pressure on cell walls of plants supports plants Osmotic pressure The amount of hydrostatic pressure that can stop water from diffusing into a hypertonic solution

Membrane Traffic To and From the cell surface By the process of exocytosis and endocytosis,, vesicles move substances to and from the plasma membrane

Three Types of Endocytosis Receptor-mediated endocytosis Substance binds to surface receptors Pit forms endocytotic vesicle Phagocytosis ( cell( eating ) Amoebas use pseudopods to engulf prey Bulk-phase endocytosis Vesicle forms around extracellular fluid

Endocytosis Molecules get concentrated inside coated pits at the plasma membrane. Exocytosis coated pit The pits sink inward and become endocytic vesicles. Many of the sorted molecules cycle to the plasma membrane. Vesicle contents are sorted. Some vesicles and their contents are delivered to lysosomes. Some vesicles are routed to the nuclear envelope or ER membrane. Others fuse with Golgi bodies.

Night Lights Bioluminescence - Fluorescent light released by enzyme-mediated mediated reactions in organisms