Proteins Making Chemical Reactions Possible Enzymes Proteins Making Chemical Reactions Possible

Energy and chemical reactions Most chemical reactions require energy to begin - the energy required to start a chemical reaction is called activation energy.

What are enzymes? Enzymes are proteins which reduce activation energy allowing chemical reactions to occur in living things

Enzymes reduce activation energy

Enzymes Act as Biological Catalysts Catalysts are inorganic molecules that speed up chemical reactions - catalysts remain unchanged by the reaction that they speed up. -one molecule of catalyst can catalyze (start) many chemical reactions Enzymes speed up reactions in living things -enzymes are not changed by the reaction they speed up - one molecule of enzyme can catalyze (start) many reactions

Active Site Enzymes have an area called an active site. - the active site is where the chemical reaction occurs

The Shape of the Enzyme Determines Function The active site of the enzyme fits with only one type of molecule known as the substrate. Substrate is the molecule that the enzyme acts on. The fact that the active site can only accept one type of substrate is known as enzyme specificity

Enzyme Reactions Catalase + 2H2O2 ES Catalase + 2H2O + O2 Written as : Enzyme + Substrate ES Enzyme + Product - ES refers to the enzyme substrate complex, the time when the substrate joins with the active site. Example Catalase + 2H2O2 ES Catalase + 2H2O + O2 enzyme substrate enzyme enzyme product product substrate complex

Two Ideas About Enzyme Action Lock & Key Model Induced Fit Model

Lock & Key Model Substrate fits into the active site like a key into a lock The enzyme puts stress on the bond which reduces the amount of energy needed to break apart the substrate The products of the reaction leave and make the enzyme available for more substrate

Induced Fit Model Substrate doesn’t quite fit into the active site Substrate causes (induces) the enzyme to change shape – allows the substrate to fit into the active site Enzyme stresses bonds on substrate

Enzymes can build molecules Substrate molecules can only bond one way. Substrate molecules fit into the active site in the best position to bond Once in the active site, the molecules of substrate join

Enzyme Inhibitors Inhibitors control the rate of enzyme activity - if there is too much of an enzyme’s product, inhibitors can slow or even stop an enzyme’s activity Two types of Inhibition - Competitive - Non Competitive

Competitive Inhibition The inhibitor is a molecule that can occupy part of the active site While the inhibitor is in the active site, substrate can’t bind with the enzyme – inhibitors compete with the substrate for the active site inhibitor competes with substrate inhibitor blocks the active site

Noncompetitive Inhibition The inhibitor binds with the enzyme at a site away from the active site. Inhibitor causes enzyme to change shape – prevents substrate from entering the active site Inhibitor binds with enzyme Enzyme changes shape keeps substrate from active site

Feedback Inhibition Enzymes are often part of a series of reactions called a biochemical pathway - the product of one enzyme acts as the substrate for another enzyme -the final product – acts as an inhibitor for the first enzyme in the pathway - this stops the pathway and the production of the end-product stops as well

Feedback Inhibition When the concentration of the end-product drops to a low level, inhibition ends and the enzyme pathway resumes operation The end-product of the pathway is used for other purposes As the end-product is used, its concentration drops

Co-Enzymes and Co-factors Co-enzymes and Co-factors are molecules that help certain enzymes to catalyze a reaction - co-enzymes and co-factors often act as carriers of electrons, atoms or functional groups needed to complete a reaction.

Co-Enzymes and Co-Factors - while they bind to an enzyme’s active site, and participate in the reaction, they are not changed by the reaction and aren’t considered substrates. - Co-enzymes are organic molecules and include: NAD, NADP, FAD, vitamin B 1, vitamin B 6, and vitamin B 12 - Co-factors are inorganic molecules and include dietary minerals like zinc, iron, copper & potassium

Denatured Enzymes Enzymes are proteins and if they are exposed to extremes of temp or pH lose their shape - if a protein loses its shape, it loses its function - a protein that loses its shape is said to be denatured - if an enzyme is denatured, substrate can’t enter the active site extreme temp or pH

Common Enzymes Amylase - breaks down starch Catalase – breaks down H2O2 DNA polymerase – joins DNA nucleotides to build DNA Lipase – break apart fats Lactase – breaks apart lactose – milk sugar Protease- breaks apart protein molecules -What does –ase in a molecules’ name imply?

Vocabulary for Enzyme Excitement Enzyme Competitive Inhibition Activation energy Non Competitive Inhibition Catalyst Denatured Protein Active site Feedback Inhibition Substrate Biochemical Pathway Enzyme specificity co-enzyme/co-factor Lock & Key Model Induced Fit Model Enzyme inhibitor