Enzymes Biological Catalysts Review

Transcription

1 Enzymes Biological Catalysts Review Catalyst a substance that speeds up a reaction but is not actually a part of the reaction nor changes because of the reaction Catalysis the process of speeding a chemical reaction with a catalyst Enzymes biological catalysts: globular proteins Oxidative (oxidoreductases) Enzymes Hydrolytic catalyse redox rxns catalyse hydrolysis rxns

2 Catabolic Reactions Decomposition reactions that break down molecules (nucleotides, proteins, lipids...) e.g. found in lysosomes Enzyme Roles Anabolic Reactions Synthesis reactions build up molecules (proteins, glycogen, nucleic acids, phospholipids...) e.g. DNA polymerase is needed for DNA replication

3 Enzymes are specific for substrates (reactants) in different ways: Tb. 2.1 absolute group linkage stereochemical Tb.2.2 Enzymes belong to one of 6 groups based on what kind of reaction they assist: hydrolases and hydrases hydrolysis isomerases change molecule structure ligases C to C, S, O or N (condens or hydro using ATP) lysases C C oxidoreductases redox transferases Most enzymes work to complete one step or reaction in a series of reactions called a metabolic pathway. C C

4 Enzymes work by lowering the Activation Energy (E A ) for a reaction. p 37-41

5 How does the enzyme lower the E A to speed the reaction? Physical Stress (bend and stretch bonds in substrate molecule) [H] + Transfer e- Transfer Temperature Increases rxn rate only up to the point that the enzyme is denatured What affects Enzyme activity? Inhibition Cofactors ph Most work optimally between 6 to 8 pepsin is an exception

6 Enzymes have two important sites: Active Site (where substrate fits) Induced Fit (site changes shape in presence of substrate) Lock and Key model (requires correct orientation of substrate) In either case, multiple weak bonds, such as H-bonds, hold substrate in place. Allosteric Site (on other side) Inhibiting reactions Activating reactions = allosteric regulation

7 Enzymatic Inhibition Inhibitors chemicals that bond to enzymes and change the enzyme's shape, therefore reducing or eliminating its ability to catalyse a reaction. This process is usually reversible in cells. Non Competitive Inhibition Molecule binds to allosteric site, preventing catalysis. (May be used for feedback inhibition when inhibitor is a product in a metabolic pathway) 2 kinds of inhibition Competitive Inhibition Molecule binds to active site, blocking true substrate (Competitive inhibitor molecule is similar in structure to substrate)

8 One more type of enzyme regulation: Co-factors and Coenzymes Cofactors are inorganic ions and non proteins that help enzymes function. Coenzymes are organic (small proteins). Many vitamins are actually coenzymes. Deficiencies in these can disrupt cellular metabolism and lead to diseases. (e.g. rickets Vit D, Scurvy Vit C, Spina Bifida folic acid Vit B 9 ) The coenzyme, NAD+ (Nicotinamide Adenine Dinucleotide), a molecule we will meet in more detail when we discuss photosynthesis, is from the niacin vitamin. The NAD+ coenzyme is involved with many types of oxidation reactions where alcohols are converted to ketones or aldehydes.

9 Now... Read pages 41 54, Answer #1, 3, 4, 8 and 11 on page 54.

10 1. Catalysis is the process of increasing a reaction rate with a substance that is not used up in the reaction. 3. Hydrolytic enzymes assist in hydrolysis to break down molecules. Oxidative enzymes assist in oxidation reduction (re dox) reactions by pulling one or more electrons from a substrate. The Enzymesubstrate complex puts stress on the bond, making it easier for the electron to leave.

11 4. A metabolic pathway is a series of linked reactions: Substrate Enzyme 1 Enzyme 2 Enzyme 3 Final Product

12 8. Factor Temperature ph Inhibitors Cofactors Impact of Factor If the temperature is below the optimum value, the enzyme can be stiff and the active site might not bind the substrate effectively. If the temperature is too high, the bonds within the enzyme can break and the enzyme (which is a protein) is denatured. Outside of the optimal ph, bonds within the enzyme can be disturbed by the presence of to many H + ions or OH ions. These ions can interfere with H bonds formed by the polypeptide backbone, or the bonds formed by among the R groups. Inhibitors can change the shape of an enzyme when they bind to it, causing the enzyme to stop functioning. If the inhibitor is not permanently bound to the enzyme, the inhibition is reversible. (and vs versa) Cofactors such as inorganic ions can interact with the bonds within the enzyme and break the protein. They can also cause the protein to change shape by removing electrons or bonding with an R group.

13 11. Non competitive inhibitors change the shape of the protein, preventing a substrate from fitting into the active site. catalysis go! catalysis no! Competitive inhibitors bind to the active site, blocking the substrate from binding to the I WIN! enzyme. Boo Hoo