Enzymes-What are they and How do they work? 9/17 Don’t forget to work on the problems at end of yesterdays notes! It is good for 10 points! What happens to Keq in a complicated rxn? What happens when we run out of energy? What is an activation energy? What is an enzyme? What do enzymes do and under what conditions? How do enzymes stabilize the intermediate? What is Michaelis-Menton Kinetics?

What happens to Keq when the number of product or reactant molecules in a reaction is not 1:1? Simple Old Fashion Rxn: Hexokinase Glucose + ATP  G-6-P + ADP Keq = [G-6-P][ADP]/[Glucose][ATP] Complicated Reaction? Example catalase H2O2 + H2O2  2 H2O + O2 Keq= products/reactants or keq= [O2]/ [H2O2]2 ….. Note: product or reactant concentrations are now factored to the n-th power or (P)n !!!! Remember that water is ignored because its presence in the solution is 56 M This won’t be on tests but might be useful on a GRE exam!

If the disorder of the universe is constantly increasing, how do cells continue to survive? Cells live if they have energy! Cells get energy from the sun, chemosynthesis or other cells/cell-products! Heterotrophs use other organisms! Cells store energy: fats, carbohydrates and proteins What happens when cells die or get injured? 1) ATP supply too low! 2) Pumps don’t work! 3) Ions flow in/out! 4) Water flows in and cells swell/become fragile! 5) Cell may incur temporary OR permanent damage! Correlation of fish removed from water? Correlation to person experiencing a stroke?

What happens to energy during a chemical reaction What happens to energy during a chemical reaction? ATP Pi + ADP What is an activation energy? Why do enzymes speed up reactions? 1) Activation energy must be overcome for Rxn to proceed! 2) Enzymes lower Activation energy! 3) Enzymes stabilize transition state! 4) Enzymes make it easier to get to energy YIELDING phase of rxn! ATPase ATP ADP + Pi + Energy

What is an enzyme (….-ase)? Enzymes are proteins! (very rarely RNA) Amino acids use specific charges at the active site to stabilize the transition state! Stabilization “lowers” activation energy! A stabilized transition state makes it easier for a reaction to rapidly proceed to products! Enzymes are called “CATALYSTS” Enzymes often require co-enzymes or prosthetic groups for activity! Each enzyme has a specific set of conditions where it has the most efficient function! Conditions Affecting Enzymes: pH, Temperature, ions around it, etc!

There are 20 different amino acids to chose from in a protein There are 20 different amino acids to chose from in a protein. Peptide bonds link the A.A. together in chains! These are the charges that line active sites on enzymes.

What do enzymes do? Enzymes make 99% of our reactions possible! Enzymes like carbonic anhydrase increase reaction rates by up to a 36 X 106 times!!! Enzymes are tightly controlled by the cell! HOW?????? Enzymes are controlled with respect to access to coenzymes, pH, temperature, transcription, translation, chemical modification and by inhibitors/stimulants! How might drugs work????? Enzymes have group and substrate specificity!

Classic: Environmental pH and Temperature turn enzymes On/Off or they can permanently disable (denature) an enzyme. Enzyme have “OPTIMAL” conditions for function!

Two models have been proposed for how enzymes function: The older ‘Lock and Key’ and newer ‘Induced Fit’ Models. Induced Fit at the active site leads to substrate activation by the amino acids and prosthetic groups (if present) of the enzyme!

There are two classic ways that enzymes function as a “substitute” binding site to stabilize the intermediate: Nucleophilic (e-) or Electrophilic (p+) substitution, where an electron or proton is given to the target to promote substrate modification/cleavage.

The active site of carboxyl peptidase (a digestive enzyme) uses a zinc ion (prosthetic group) to orient/stabilize a target protein so it can be cleaved precisely between glycine-tyrosine peptide bonds.

In this example the digestive enzyme chymotrypsin is breaking the peptide bond on its substrate into two pieces (products)! This is done by stabilizing the formation of an acyl-intermediate that is temporarily attached to the enzyme itself!

Enzymes can catalyze reactions where a reactant turns into a product, they can also do “activities” such as carry oxygen or move glucose across a membrane. Classic Examples of “enzymes” that do not have a reactant and product: 1) Hemoglobin in a erythrocyte 2) Albumin in plasma 3) Na+/K+-ATPase 4) Acetycholine receptor on a neuron Any or all of these can be effected by inhibitors Any or all of these can be effected by temeprature, pH and other factors

Why does hemoglobin release more oxygen in active muscle and pick up more oxygen in a pH basic lung????????? Bohr Effect The shift in the oxygen binding curve to the right means less oxygen will be attached to the hemoglobins in an acidic region! So oxygen leaves the hemoglobin and can be delivered to where it is needed most! ↑Carbon dioxide and ↑Temperature have similar effects.

If the Hb is not bound by oxygen you will appear cyanotic (bluish) If the Hb is not bound by oxygen you will appear cyanotic (bluish)! Remember that only a tiny amount of oxygen can dissolve directly in blood! (see bottom yellow line) The more hemoglobin you have in your blood, the more oxygen your blood can deliver (that simple)! If the tissues are warmer or more acidic, the oxygen is more likely to leave the hemoglobin so it can be used in this tissue (that simple). Shift occurs if pH↓ or Temp. ↑