Denaturation of Proteins; Enzymes and Enzyme Inhibition
Denaturation of Proteins; Enzymes and Enzyme Inhibition MCB 150
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This 2 page Class Notes was uploaded by Julianne Yang on Monday September 5, 2016. The Class Notes belongs to MCB 150 at University of Illinois at Urbana-Champaign taught by Bradley G Mehrtens in Fall 2016. Since its upload, it has received 10 views. For similar materials see Molecular and Cellular Biology in Biology at University of Illinois at Urbana-Champaign.
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Date Created: 09/05/16
I. Explain the process of protein denaturation and renaturation, including the use of chaperones when necessary. II. Compare and contrast anabolic and catabolic reactions. III. Categorize reactions in terms of energy transfer and change in free energy. IV. Explain the energy of activation of a reaction and how it is decreased in the presence of enzyme. V. Describe the conditions that affect enzyme activity. VI. Compare and contrast irreversible, competitive, and noncompetitive enzyme inhibition. Protein denaturation Denaturation, or the unfolding of proteins down to primary structure, occurs due to a variety of different factors, which include: ● High temperature can disrupt hydrogen bonds and hydrophobic interactions ● A large change in pH some interactions depend on the acidity or alkalinity of amino acids ● Salinity the ions can interfere with the ionic bonds that are holding the protein together Molecular chaperones ● Proteins that facilitate folding of polypeptide chains ● Bind to hydrophobic stretches of protein in denatured proteins that would not normally be exposed → blocks interactions that aren’t supposed to occur, allowing refolding Energy Catabolic and anabolic reactions: ● Catabolic breaks down molecules for energy ● Anabolic uses energy for macromolecule biosynthesis ● BAD MNEMONIC DEVICE: Catabolism sounds like cannibalism, and cannibalism involves breaking down people for digestion……….. What does it mean for a reaction to be spontaneous? ● They run in the direction that lowers the free energy ● Gibbs free energy ΔG quantity that takes into account heat and disorder ○ If ΔG>0, reaction is nonspontaneous, or endergonic ○ If ΔG<0, reaction is spontaneous, or exergonic ○ If ΔG=0, reaction is at equilibrium For reactions to occur, reactants must (1) collide in a precise orientation Enzymes help do this because they make this orientation much more likely to occur. Substrates bind to an enzyme’s active site with Hbonding, shortlived covalent bonds, and other weak interactions between amino acids. (2) have enough kinetic energy to reach the transition state, where the bonds in the original substrates are all destabilized because new bonds need to be formed. Amount of kinetic energy required is also known as the activation energy. Enzymes help do this because interactions between enzyme and substrate at the active site stabilize the transition state, which lowers the activation energy. Enzymes Since most enzymes are proteins, conditions that cause proteins to denature are likely to affect enzymes as well. ● Temperature affects the movements of the substrates and enzymes because higher temperatures increase the kinetic energy of molecules ● pH affects the enzyme’s shape and reactivity by affecting the charge on carboxyl and amino groups in residue side chains Inhibition ● Reversible modifications: when molecules bind noncovalently to the enzyme to either activate or inactivate it ○ Competitive inhibition: regulatory molecule is similar in size and shape to the natural substrate and inhibits catalysis by binding to the enzyme’s active site. ○ Noncompetitive inhibition: regulatory molecule binds at an allosteric site (place that is not the active site) which causes the enzyme to change shape so that its active site can no longer bind with the natural substrate
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