Biochemical Reactions Chapter 1.3 McGraw-Hill Ryerson Biology 12 (2011)

Neutralization Acid: substance that produces hydrogen ions when dissolved in water – Increases [H + ] in aqueous solution Base: substance that produces hydroxide ions when dissolved in water – Increases [OH - ] in aqueous solution

Neutralization pH scale: measures relative concentration of [H + ] ions in aqueous solution

Neutralization Neutralization reaction: When acid and base react – Produces a salt and water

Neutralization Buffers: substances that resist changes in pH by donating or accepting hydrogen ions as needed – Buffers require their reactions to occur in both directions (i.e. must be able to reverse) – Human blood pH ranges from ; carbonic acid is a buffer present in blood to maintain this pH

Oxidation-Reduction Reactions Oxidation: When molecules loses electrons – but electrons are highly reactive and do not exist on their own/freely – Thus another molecule must complement the reaction by receiving electrons … Reduction: When molecules gains electrons Reactions are labelled redox reactions because they occur simultaneously Examples of redox reactions: cellular respiration, iron rusting, combustion “LEO goes GER” – LEO – Losing Electrons: Oxidation – GER – Gaining Electrons: Reduction

Condensation and Hydrolysis Condensation: reaction forms a covalent bond between two molecules with production of a water molecule Hydrolysis: reaction that cleaves a covalent bond by adding a water molecule *Present in polymerization of sugars, lipids, amino acids, and nucleic acids*

Enzymes Enzymes are protein molecules that act as catalysts – Speeds up chemical reactions in the body All chemical reactions require energy to start – Referred to as Activation Energy (E a ).

Enzymes Enzymes work by lowering the activation energy (E a ) of a reaction – As a result, the reaction goes FASTER because less energy is required for it to begin

Enzymes Heat usually provides the source for activation energy in many chemical reactions – Increase in temperature can increase rate of most reactions But proteins denature at high temperature… – Thus cells use enzymes to promote reactions

Enzymes Enzymes have unique optimal temperature and/or optimal pH where they work best e.g. protease work best at acidic pH (present in the stomach)

Enzymes There are many different types of enzymes, each one specific to a specific job – Names are usually associated with its job, usually ending with ‘ase’ e.g. Enzyme in our saliva is amylase to break down amylose and amylopectin (starch) into simple sugars

Enzymes Components of an enzyme-reaction – Substrate: the reactant which the enzyme acts on Enzymes bind to substrate to convert it into a product – Active site: the location where the substrate binds Active sites are specific for a particular substrate

Enzymes Induced Fit Model: After a substrate binds to the active site, the enzyme slightly changes shape to better accommodate the substrate

Enzymes Weak bonds with the R-groups of the amino acids in the active site hold the substrate in place Enzymes lower the activation energy by binding substrates together in the correct orientation and by applying stress to the substrate’s bonds, reducing the amount of thermal energy that must be absorbed to achieve transition state Active sites can also provide suitable microenvironments for particular reactions (e.g. can provide alternate pH levels depending on the amino acids present in the active site)

Enzymes Once the reaction is complete the product is released from the enzyme and the enzyme is free to accept another substrate and conduct the reaction again – Referred to as Catalytic Cycle

Enzymes Sometimes enzymes require the presence of additional molecules to catalyze the reaction – Coenzymes: organic molecules that assist an enzyme – Cofactors: metal ions that assist the enzyme Either of these may bind to active site or substrate e.g. vitamins are coenzymes

Enzymes Enzyme activity can be regulated Activator: molecule that binds to allosteric site of an enzyme to keep it active or cause increase in activity Allosteric site: site on enzyme that is not the active site but allows interaction with molecules to change activity

Enzymes Enzyme activity can be regulated Inhibitors: chemicals that interfere with enzyme function Competitive Inhibition: Could bind to active site, preventing substrate from entering (thus “competing” with substrates for active sites) Noncompetitive Inhibition: Could bind to allosteric site which changes the shape of the enzyme, causing the active site to change, preventing substrate from binding

Enzymes Enzyme activity can be regulated Biochemical reactions usually occur in pathways (multi-step reactions to change reactant into product) Feedback inhibition: the final product is an inhibitor of the enzyme that catalyzes the reaction

Homework Pg 42 #1, 3-12