Mcat biochem Basics PDF

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Professor: Dr. Heather Tienson-Tseng
MCAT Biochem...

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Ch 3 | Basics of Biochemistry Wednesday, April 7, 2021

12:23 PM

Thermodynamics ΔG=ΔH−TΔS ΔH=ΔE+PΔV -

E represents bond energy of the products or reactants in a system P is pressure V is volume ○ In biological systems, ΔH=ΔE because change in volume is zero

(liquid/aqueous environment) - Negative ΔG = exergonic reaction - Positive ΔG = endergonic reaction ○ Only occur with energy input § Driven by reaction coupling to exergonic processes - Negative ΔH = exothermic reaction - Positive ΔH = endothermic reaction ΔGo'=-RTlnK'eq -

Where ΔGo' is a standardized form of gibbs free energy change when all solutes except H+ are 1M and pH is 7 ○ Used at biological conditions ○ R is given on MCAT ○ Keq' is [Ceq][Deq] / [Aeq][Beq}

ΔG=ΔGo'+RTlnQ -

If you have ΔGo' value (usually given) you can calculate the ΔG for this reaction in a human with the concentrations in the human cell This equation shows that a reaction with an unfavorable Gibbs Free Energy change at standard conditions can be made to occur spontaneously by altering the concentrations (adding more reactants)

Kinetics & Enzymes -

The study of reaction rates All reactions proceed through an unstable transition state reached by adding the activation energy Ea ○ Enzymes function as an on/off switch in the body to help mediate the free energy and direct it to certain processes ○ Enzyme catalysts function by stabilizing the transition state § They make this high energy state of existence less unfavorable to be in

Oxidation & Reduction -

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Identify oxidation by: ○ Gain of oxygen atoms ○ Loss of hydrogen atoms ○ Loss of electrons Identify reduction by: ○ Loss of oxygen atoms ○ Gain of hydrogen atoms ○ Gain of electrons In photosynthesis, glucose is oxidized into carbon dioxide and oxygen is reduced into water

Acids & Bases -

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Be able to identify Bronsted Lowry acids and bases ○ Easy: where did the protons go? Be able to identify Lewis acids and bases ○ Look at what compound formed covalent bons (accepted electrons) vs. which compound donated electrons/covalent bonds § Ex. Hemoglobin binding to oxygen - oxygen is the base and Fe is the acid The larger the Ka or Kb, the stronger the acid or base The smaller the pKa or pKb, the stronger the acid or base

Bicarbonate Buffer System

CO2 + H2O H2CO3 H+ + HCO3-

Resists changes in pH ○ During exercise, when lactic acid causes H+ levels to rise, more carbonic acid is produced, then more CO2 and H2O are expelled...