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An Introduction to Metabolism and Enzymes. Metabolism. is the sum total of an organism ’ s chemical reactions. Metabolism- e.g. oxidation of sugar. Catalase. Facts to be explained. Enzymes are proteins Enzymes are required in minute quantities
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Metabolism • is the sum total of an organism’s chemical reactions
Facts to be explained • Enzymes are proteins • Enzymes are required in minute quantities • Enzymes show striking specificity. They catalyze specific reactions involving specific substrates • Enzymes increase the speed of a chemical reaction - Both forward and backward reaction • The action of enzyme is greatly affected by temperatures. • Enzymatic activity is affected by H+ ions concentration (pH) • The rate of reaction is affected by substrate and enzymeconcentration • Enzyme itself is not used up in the reaction it catalyzes so it can be used over again and again
Mechanism of enzyme reaction • The substrate • is the reactant an enzyme acts on • The enzyme • binds to its substrate, forming an enzyme-substrate complex
1Substrates enter active site; enzyme changes shape so its active site embraces the substrates (induced fit). 2Substrates held in active site by weak interactions, such as hydrogen bonds and ionic bonds. Substrates Enzyme-substrate complex 3Active site (and R groups of its amino acids) can lower EA and speed up a reaction by • provide correct substrate orientation, • stress the substrate bonds • stabilize the transition state, • provide a favorable microenvironment, 6Active site Is available for two new substrate Mole. Enzyme 5Products are Released. 4Substrates are Converted into Products. Products The catalytic cycle of an enzyme
Interaction between Active site and substrate fitting of a substrate brings chemical groups of the active site into positions that enhance their ability to catalyze the chemical reaction
The active site can lower an EA • The active site can lower an EA barrier by • Orienting substrates correctly • Straining substrate bonds • Stabilizing transition state • Providing a favorable microenvironment
Chemical reaction takes place only if the particles collide at the right orientation and with sufficient energy (activation energy) Effect of temperature on rate of chemical reaction: http://www.absorblearning.com/media/attachment.action?quick=w2&att=2298
Are all enzymes equally susceptible to denaturation by high temperature ? Some bacteria survive in hot spring at the yellow stone national park US) at ~ 70°C
Some bacteria survive in deep sea hydrothermal vent at > 110°C
Optimal temperature for typical human enzyme Optimal temperature for enzyme of thermophilic (heat-tolerant) bacteria Rate of reaction 80 0 20 100 40 Temperature (Cº) (a) Optimal temperature for two enzymes Effects of Temperature • Each enzyme • Has an optimal temperature in which it can function best
Optimal pH for different enzymes Optimal pH for pepsin (stomach enzyme) Optimal pH for trypsin (intestinal enzyme) Rate of reaction 5 6 7 8 9 3 4 0 2 1 (b) Optimal pH for two enzymes
Coenzymes-- Non-protein molecules that are enzyme helpers • Some enzymes work only in the presence of other molecules E.g. NAD+ in dehydrogenation • Some vitamins are important because they are co-enzymes e.g. Vitamin B groups
Co-enzyme e.g. NAD+ NAD+ helps the enzyme dehydrogenase accepting H removed from substrates
It is the loss of the specific tertiary structure of a protein molecule. Lose its normal biological function. The change may be temporary or permanent, but the amino acid sequence (primary structure) of the protein could remain un________ --- renaturation, though rare, might occurs and restore the enzyme function. Denaturation of enzyme
Mitochondria, sites of cellular respiraion 1 µm Specific Localization of Enzymes • Within the cell, enzymes may be • Grouped into complexes • Incorporated into membranes • Contained inside organelles
Is 37 degree Celcius the optimum temperature for human enzyme? • Why then our body temperature is 37 degree Celcius?
