Introduction to Metabolism (Or Energy Management) Chapter 8

Transcription

1 Introduction to Metabolism (Or Energy Management) Chapter 8 Metabolism of the chemical reactions in the organism Building up molecules Breaking down molecules Managing energy and materials Route to end-product Sometimes simple Often complex Metabolic Pathways pathways Breakdown complicated molecules into component parts e.g. cellular respiration Glucose CO 2 + H 2 O Releases energy pathways Build complicated molecules from simple ones e.g. synthesizing protein from amino acids Requires energy input Energy Capacity to Do Work energy Energy of Physical movement Energy in the process of doing Electricity work Light Examples: Heat 8-1

2 Energy Capacity to Do Work energy energy, not in use at the moment Stored due to its location or structure Water behind a dam Chemical bonds energy Energy available to do work Laws of Thermodynamics 1. Energy can be transferred and transformed Cannot be created Cannot be destroyed 2. Every energy transfer or transformation increases disorder Entropy = disorder Changes in Free Energy Free energy Amount of energy available to perform e.g. Work of chemical reactions Amount of free energy can be measured From start point to end point Change in free energy: G ( ) G = G final state G starting state Energy of Chemical Reactions Reactions classed by their changes in free energy G = G final state G starting state reactions ( energy outward ) Spontaneous reactions that release free energy into environment Energy releasing G is negative 8-2

3 e.g. Letting water flow downhill reactions ( energy inward ) Reactions that require input of free energy from environment Energy storing G is positive e.g. Pumping water uphill Exergonic and Endergonic Reactions Systems Reactions in closed system eventually reach and work stops: G = 0 Water flows downhill till it gets to the bottom Unless you add more, no more work is done Systems Cells are not closed systems no equilibrium Living cells continue to have inputs from outside, so are in disequilibrium G 0 Metabolic in Cells Huge free energy difference Organisms in disequilibrium do work work (contracting muscles) work (pumping across membrane) work (synthesis of polymers) As long as work is done, cell is alive e.g. Respiration Glucose at uphill part of pathway Carbon dioxide at downhill part of pathway in cells means cell is No work is done 8-3

4 ATP and Using an exergonic process to an endergonic process Very common in metabolic pathways is the molecule that serves as the intermediate in these energy coupling pathways ATP (Adenosine Triphosphate) Nucleic acid (N-containing base) bonded to (a five carbon sugar) bonded to Chain of groups Phosphate tail unstable Can be broken down by hydrolysis (releases energy) ATP + H 2 O ADP + P i + energy Hydrolysis of ATP ATP Reactions Coupled Enzymes couple exergonic reactions to endergonic group to another molecule Molecule receiving the phosphate group is said to be More reactive (less stable) than unphosphorylated ATP is recycled: ADP + P i + energy ATP 8-4

5 Enzymes (catalytic proteins) Speed up the reaction Do not react as one of the substrates Enzymes lower the activation energy Activation Energy Energy required to start a reaction Activation Energy (energy required to break the bonds in the reactant molecules) Enzymes the Energy of Activation Reaction Terminology Starting material Results of a reaction What an enzyme acts on Enzymes are substrate-specific e.g. sucrase is specific to sucrose, and only acts on sucrose Can even differentiate between isomers of substrate Enzyme names often end in Enzyme and Reaction Notation Substrate(s) Enzyme Product(s) for example: Sucrose + H 2 O Sucrase Glucose + Fructose 8-5

6 More Reaction Terminology Where the substrate binds to the enzyme Just a few amino acids Pocket or groove where substrate fits like puzzle piece Once a substrate is bound, enzyme closes tightly around it induced fit Tightens the connection between enzyme and substrate Recycling Enzymes Speeds Reactions Factors Affecting Enzyme Activity Non-protein helpers Inorganic, e.g. zinc, iron, copper ions Organic coenzymes, e.g. vitamins & Competitive inhibitors Noncompetitive inhibitors inhibition Temperature ph Inhibitors Usually irreversible, but reversible if bonds are weak inhibitors Bind to another site on enzyme inhibitors Change shape of enzyme Compete for active site Shape of active site changes Block substrates from entering No longer available for substrate active site to fit 8-6

7 Competitive Inhibition Competitive inhibitor enters site and binds substrate May be overcome by adding more substrate Noncompetitive Inhibitors Binds elsewhere on enzyme of entire enzyme Alters conformation of active site Substrate no longer fits at active site Allosteric Regulation Allo = different (Greek) Steric = arrangement (Greek) Special case of non-competitve inhibition Applies to some with >1 subunit Allosteric sites located where subunits join Active form stabilized by activator Inactive form stabilized by inhibitor Feedback Inhibition Pathway switches off when end-product gets abundant - acts as Example is complex pathway of threonine to isoleucine Isoleucine inhibits enzyme 1 in this pathway 8-7