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MALIK ALQUB MD. PHD.BIOENERGETICS1st Law of ThermodynamicsThe First Law of Thermodynamics states that energy cannot be created or destroyed but only changes forms. In the introductory activity chemical energy in our bodies was changed to mechanical energy in our arms. Friction caused some of this mechanical energy to be changed to noticeable heat energy in our hands. 2nd Law of ThermodynamicsThe Second Law of Thermodynamics states that at every energy transfer some portion of the available energy is degraded to heat which moves to cooler objects.

Applications of Thermodynamics1-1

Power plantsThe human bodyAir-conditioningsystemsAirplanesCar radiatorsRefrigeration systemsHigh energy vs. Low energy state

High energy Low energy Transition stateHigh energy vs. Low energy state

Intial stateFinal stateTransition stateG is negativeG; free energy changeG= final energy state intial energy stateorG= low energy state high energy statethenChange in free energy is negative (G is negative)Thats meanThere is a net loss of energy (exerogenic)

High energy vs. Low energy state

Transition stateIntial stateFinal stateG is positiveG; free energy changeG= final energy state intial energy stateorG= high energy state low energy statethenChange in free energy is positive (G is positive)Thats meanThere is a net gain of energy (endergonic)

Exergonic reactionsChemical processes that release energy to its surroundingsDownhill processes

Endergonic reactionsChemical processes that store or absorb energy Uphill processes

G; free energy changeCoupled Reactions

Coupled Reactions

EnzymesAre highly specific protein catalystsAccelerate the forward and reverse reactionsAre neither consumed nor changed in the reactionpH and temperature dramatically affect enzyme activity

Coenzymes Complex nonprotein organic substances facilitate enzyme action by binding the substrate with its specific enzyme Coenzymes are smaller molecules than enzymesMany vitamins serve as coenzymes, e.g. riboflavin and niacinEnzyme ActivityThe properties of enzymes related to their tertiary structure. The effects of change in temperature, pH, substrate concentration, and competitive and non-competitive inhibition on the rate of enzyme action

HOW ENZYMES WORK

Enzymes are ORGANIC CATALYSTS. A CATALYST is anything that speeds up a chemical reaction that is occurring slowly. How does a catalyst work?

The explanation of what happens lies in the fact that most chemical reactions that RELEASE ENERGY (exothermic reactions) require an INPUT of some energy to get them going. The initial input of energy is called the ACTIVATION ENERGY

EnzymesAn enzyme is a biological catalystThe pockets formed by tertiary and quaternary structure can hold specific substances (SUBSTRATES). These pockets are called ACTIVE SITES. When all the proper substrates are nestled in a particular enzyme's active sites, the enzyme can cause them to react quickly Once the reaction is complete, the enzyme releases the finished products and goes back to work on more substrate.

The activity of enzymes is strongly affected by changes in pH and temperature. Each enzyme works best at a certain pH and temperature,its activity decreasing at values above and below that point. This is because of the importance of tertiary structure (i.e. shape) in enzyme function and forces, e.g., ionic interactions and hydrogen bonds, in determining that shape.

Optimum ConditionThe effects of change in temperature. Temperature: enzymes work best at an optimumt emperature.

Below this, an increase in temperature provides more kinetic energy to the molecules involved. The numbers of collisions between enzyme and substrate will increase so the rate will too.

Above the optimum temperature, and the enzymes are denatured. Bonds holding the structure together will be broken and the active site loses its shape and will no longer workThe effect of change in pH.pH: as with temperature, enzymes have an optimum pH. If the pH changes much from the optimum, the chemical nature of the amino acids can change.

This may result in a change in the bonds and so the tertiary structure may break down. The active site will be disrupted and the enzyme will be denatured. The effect of change in concentrationEnzyme concentration: at low enzyme concentration there is great competition for the active sites and the rate of reaction is low. As the enzyme concentration increases, there are more active sites and the reaction can proceed at a faster rate.Eventually, increasing the enzyme concentration beyond a certain point has no effect because the substrate concentration becomes the limiting factor.

Substrate concentration: at a low substrate concentration there are many active sites that are not occupied. This means that the reaction rate is low. When more substrate molecules are added, more enzyme-substrate complexes can be formed. As there are more active sites, and the rate of reaction increases.Eventually, increasing the substrate concentration yet further will have no effect. The active sites will be saturated so no more enzyme-substrate complexes can be formed.

Competitive and non-competitive inhibitionInhibitors slow down the rate of a reaction. Sometimes this is a necessary way of making sure that the reaction does not proceed too fast, at other times, it is undesirable

Reversible inhibitors:

Competitive reversible inhibitors: these molecules have a similar structure to the actual substrate and so will bind temporarily with the active site. The rate of reaction will be closer to the maximum when there is more real substrate, (e.g. arabinose competes with glucose for the active sites on glucose oxidase enzyme).Non-competitive reversible inhibitors: these molecules are not necessarily anything like the substrate in shape. They bind with the enzyme, but not at the active site. This binding does change the shape of the enzyme though, so the reaction rate decreases.Irreversible inhibitors:

These molecules bind permanently with the enzyme molecule and so effectively reduce the enzyme concentration, thus limiting the rate of reaction, for example, cyanide irreversibly inhibits the enzyme cytochrome oxidase found in the electron transport chain used in respiration. If this cannot be used, death will occur

Enzyme Kinetics Equation

v0 = kcat[ES]Vmax = kcat [E]totalThe maximum velocity Vmax occurs when the enzyme is saturated -- that is, when all enzyme molecules are tied up with S, or [ES] = [E]total. Thuslet v0 be the initial velocity of the reaction. the appearance of the product P in solution Enzyme Kinetics EquationRate of formation of [ES] = k1[E][S].

Rate of consumption of [ES] = k-1[ES] + kcat [ES]. During the initial phase of the reaction, as long as the reaction velocity remains constant, the reaction is in a steady state, with ES being formed and consumed at the same rate. During this phase, the rate of formation of [ES]Enzyme Kinetics Equation

k-1[ES] + kcat[ES] = k1[E][S] So in the steady state,Rate of formation Rate of consumption Enzyme Kinetics Equation

k-1[ES] + kcat[ES] = k1[E][S] (k-1 + kcat) [ES] = k1 [E][S]

OR

(k-1 + kcat)/k1 = [E][S]/[ES]Enzyme Kinetics Equation

To simplify , the kinetic constants by defining them as Km Km = (k-1 + kcat)/k1 (k-1 + kcat)/k1 = [E][S]/[ES]Km= [E][S]/[ES]Enzyme Kinetics Equation

and then express [E] in terms of [ES] and [E]total.[E] = [E]total - [ES] Km= [E][S]/[ES]Km = ([E]total - [ES]) [S]/[ES]Enzyme Kinetics Equation

Km = ([E]total - [ES]) [S]/[ES]First multiply both sides by [ES] [ES] Km = [E]total[S] - [ES][S] Then collect terms containing [ES] on the left: [ES] Km + [ES][S] = [E]total[S] Enzyme Kinetics Equation

[ES] Km + [ES][S] = [E]total[S] Factor [ES] from the left-hand terms: [ES](Km + [S]) = [E]total[S] and finally, divide both sides by (Km + [S]): [ES] = [E]total [S]/(Km + [S]) Michaelis-Menten Equationv0 = kcat[ES]Vmax = kcat [E]total[ES] = [E]total [S]/(Km + [S]) v0 = kcat[E]total [S]/(Km+[S])v0 = Vmax [S]/(Km + [S])Effect of [substrate] on RX VelocityEEEEEEEsubstrateEEEEEEsubstrateEEEEEEEsubstrateEEffect of [substrate] on RX VelocityEEEEEEEEsubstrate enzymzsEEEEEEEVmaxEEEEEESaturationEffect of [substrate] on RX Velocityv0 = Vmax [S]/(Km + [S])

Hyperpolic shapeEffect of [substrate] on RX Velocity

123[S] >>> Km, the velocity of reaction is constant and independent of [S]

[S]