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Lecture 2

water, pH, buffers and membranes

significance of water -where most proteins work - abundant molecule in cell ~60-90% - transport of nutrients, enzymes catalyzed rxns of metabolism and transfer of chem energy happens there - polar. interact w other molecules of h2o and non h2o -solvent/reactant
Because water is polar, it can form H-bonds with other water molecules in a tetrahedral array
H bonds very weak, non-covalent bonds, hydrogen and N O or S
describe the amount of H bonds in the three states of water - Solid, every possible H bond - liquid, 20-30% H bonds - Gas, 0% H bonds. Covalent bonds still intact
List 4 properties of water 1. High boiling and melting pts 2. surface tension- waters cant interact "up"=sideways interactions 3. H bonds cause ice to be less dense than liquid water and float 4. high specific heat 5. high heat of vaporization
specific heat vs heat of vaporization specific heat- heat/energy needed to raise temp of 1g of water 1C heat of vaporization- amount of heat needed to cause a change to gas
how does water dissolve ionic and polar molecules? - part of water interacts with + part and +part of water interacts with - part of molecule
uncharged polar substances ___________ dissolve in water can
hydrophobic effect weak noncovalent interaction where hydrophobic molecules to come together and aggregate when put in water to reduce surface area
what noncovalent bonds/interactions are there? briefly explain each 1. charge-charge (electrostatic) interactions: ion-ion(A+B-), ion-dipole(Na+Cl- in water), dipole-dipole (2 polar molecules) 2. hydrophobic interactions- nonpolars aggregating 3. Van der Waals- close enough, bond 4. Hydrogen bonds- H with N O or S
why are weak noncovalent interactions important? additive force in the structure and folding of molecules. They are integral to normal functioning of the body as well as diseases
where do Van der Waals work? in all molecules, they operate at an optimal distance. As atoms move closer together, energy will rise due to electron-electron repulsion
nonpolar noncharged biomolecules interact with eachother by electrostatic forces
what makes covalent bonds stronger than non-covalent? the sharing of electrons
Non polar interactions are ___________ in an aqueous environment and ___________________ in a non polar environment strengthened, weakened
polar interactions are ___________ in an aqueous environment and ___________________ in a non polar environment weakened, strengthened
why does water tend to ionize? H+ and OH- ions have a short lifetime
equilibrium constant of wate r keq=([H+][OH-])/[H2O]=Kw=1x10^-14
pure water is neutral meaning it has equal number of H+ and OH- ions which is 1x10^-7
pH/pOH formula pH= -log[H+] pOH= -log[OH-] both added should equal 14
equilibrium constant for the dissociation of a proton from an acid in water is called acid dissociation constant Ka=([H+][A-])/[HA]
can be used to talk about the change in degree of ionization of an acid pKa=-logKa
mixture of weak acid and conjugate base of that acid that resists changes in pH buffer
practical buffering zone pKa + or - 1pH
henderson hasselbalch equation pH=pKa+log ([A-]/[HA])
buffers work best at pH which they are 50% dissociated
what changes blood pH from normal? metabolism, it produces ~20 moles of acid per day (as CO2, lactate, "ketone bodies")
how does the body get rid of excess acid? exhaling CO2 (lungs, fast) excreting H+ (kidneys, slow) NH4+
not being able to rid the blood of excess H+ can lead to acidosis
how is acidosis life threatening - affects protein structure - affects molecular interactions essential to life (depend on pH)
how can pH affect biological processes? molecular interactions depend on pH which affects molecular charge 1. enzyme-substrate (inactive enzyme) 2. receptor-ligand 3. Hb+O2 <--> Hb[O2]4+3H+ low pH increases Hb release of O2 by mass action 4. transmembrane pH gradient affects Na+ gradient
explain how the bicarbonate buffer system of the blood works 1. hydration of CO2 catalyzed by carbonic anhydrase to produce H2CO3 (unstable) 2. rapid, nonenzymatic dissociation of H2CO3 to H+ and HCO3- which act as buffer system in RBCs. Free protons affect O2 binding affinity
what lowers blood pH? how does body respond? CO2 as a byproduct of oxidative metabolism increasing rate of breathing to expel CO2 raising blood pH again
normal pH of blood? 7.35–7.45
how does blood always stay prepared for a stressor that lowers pH? by having a bicarbonate that is normally about 20x that of CO2 in the blood.
pka of carbonic acid 6.1
how to find blood pH? pH=6.1+log ([HCO3-]/[pCO2x 0.03])
Created by: rusulali97



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