* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Enzyme - kyoussef-mci
Nicotinamide adenine dinucleotide wikipedia , lookup
Proteolysis wikipedia , lookup
Deoxyribozyme wikipedia , lookup
Mitogen-activated protein kinase wikipedia , lookup
Photosynthetic reaction centre wikipedia , lookup
Ultrasensitivity wikipedia , lookup
Restriction enzyme wikipedia , lookup
NADH:ubiquinone oxidoreductase (H+-translocating) wikipedia , lookup
Metabolic network modelling wikipedia , lookup
Oxidative phosphorylation wikipedia , lookup
Biochemistry wikipedia , lookup
Metalloprotein wikipedia , lookup
Evolution of metal ions in biological systems wikipedia , lookup
Amino acid synthesis wikipedia , lookup
Biosynthesis wikipedia , lookup
Catalytic triad wikipedia , lookup
ENZYMES • A catalyst – Is a chemical agent that speeds up a reaction without being consumed by the reaction – An enzyme is an organic catalyst • Enzymes are proteins 1. An Enzyme Active Site Substrate (Reactants) Enzyme Inhibitor Allosteric Site 2. Enzyme Specificity • Enzymes can only work with certain substrates • The shape of the enzyme must match the shape of its substrate - The root of the enzyme’s name typically indicates the substrate which it acts upon e.g. ATPase, Amylase, Sucrase 3. Induced Fit Model Substate Active site Enzyme- substrate complex Enzyme Figure 8.16 (a) Figure 8.16 (b) • When the substrate binds to the active site, the enzyme changes conformation (shape) to make a better fit. • Interactions between chemical groups on substrate and those of the amino acids as well as the shape of the active site cause the induced fit Sucrose Sucrase Glucose + Fructose Sucrose + Sucrase Glucose + Fructose + Sucrase Activation Energy • The initial amount of energy needed to start a chemical reaction (i.e. break the bonds) A B C D Free energy Transition state A B C D EA activation energy EA Reactants A B C D Products Progress of the reaction Figure 8.14 8.15 What do enzymes do? Free energy Course of reaction without enzyme EA without enzyme EA with enzyme is lower Reactants Course of reaction with enzyme Products Progress of the reaction • Enzymes lower the activation energy • How? – Orienting substrates correctly – Putting stress on substrate bonds – Providing a favorable environment • This increases the rate of the reaction. 5. Increasing the Rate of Reaction (1)Increase the number of substrate molecules in solution (increase conc’n) (2)Increase the number of enzymes in solution (increase conc’n) (3)Increase the temperature of the solution (up to a certain point) 6. Saturation • A reaction is said to be “saturated” when 100% of enzymes have their active sites filled with substrate. • Vmax is maximum velocity (speed) of rxn Question 7. • If there are left-over reactants (substrates), then you could add more enzymes. • If there are no more leftover reactants (substrates), then adding more enzymes will not increase the rate. 8. Stopping a Reaction • Change the pH so it is above or below its optimal value. • This changes the enzyme’s conformation (shape) making it lose it dysfunctional • e.g. add H2SO4(aq) – Sulfuric Acid 9. Effect of Increasing Temperature • Above a certain temperature, enzymes’ activity starts to decline because the enzyme begins to denature (unravel) Metabolic Pathways • Reactions occur in a sequence and specific enzymes catalyze each step 10. Cyclic Metabolic Pathways Z U Y V X W (a) Z + Y U UVW WX+Y (b) Initial Reactant: Z End product: X (desired product) 11. Competitive vs. Non-competitive Inhibition A substrate can bind normally to the active site of an enzyme. Substrate Active site Enzyme (a) Normal binding A competitive inhibitor mimics the substrate, competing for the active site. Competitive inhibitor • If the inhibitor attaches by weak bonds, it is usually reversible. A noncompetitive inhibitor binds to the enzyme away from the active site, altering the conformation of the enzyme so that its active site no longer functions. Noncompetitive inhibitor Figure 8.19 (b) Competitive inhibition Figure 8.19 (c) Noncompetitive inhibition • If the inhibitor attaches by covalent bonds, it is usually irreversible (usually (c) is) 0 12. Allosteric Regulation: Activation and Inhibition Allosteric enyzme with four subunits Regulatory site (one of four) Active site (one of four) Allosteric activater stabilizes active from Activator Active form Stabilized active form Oscillation Allosteric activater stabilizes active form NonInactive form Inhibitor functional active site Stabilized inactive form – When one activator or inhibitor bind to an allosteric site, and have an effect on all four subunits of an enzyme – Bonds are noncovalent, so they are reversible (a) Allosteric activators and inhibitors. In the cell, activators and inhibitors dissociate when at low concentrations. The enzyme can then oscillate again. Feedback Inhibition • The end product of a metabolic pathway shuts down the pathway • Prevents the cell from wasting chemical resources Active site available Initial substrate (threonine) Threonine in active site Enzyme 1 (threonine deaminase) Isoleucine used up by cell Intermediate A Feedback inhibition Active site of enzyme 1 no longer binds threonine; pathway is switched off Enzyme 2 Intermediate B Enzyme 3 Intermediate C Isoleucine binds to allosteric site Enzyme 4 Intermediate D Enzyme 5 Figure 8.21 End product (isoleucine)