ACS BIOCHEMISTRY EXAM – OBU Latest Graded A+

Separation of Organelles / Fractionation of Cells - ANSWER Differential Centrifugation 1. Tissue Homogenization 2. Low speed centrifugation (whole cells, nuclei, membrane) 3. Medium speed centrifugation (mitochondria, lysosomes, peroxisomes) 4. High speed centrifugation (microsomes -fragments of ER) 5. Very high-speed centrifugation (soluble proteins) Isopycnic Centrifugation - ANSWER Sucrose-Density (components separated by density) Interactions occur... - ANSWER because of the electrostatic properties of molecules. - these properties can involve full, partial or momentary charges Examples of electrostatic interactions - ANSWER dipole-dipole interactions hydrogen bonds ionic interactions van der Waals interactions Hydrophobic Interactions... - ANSWER entropy, not an attraction between hydrophobic molecules The special properties of water... - ANSWER derived from its polarity and hydrogen bonding - overall polarity is due to polar bonds and shape Entropy & 2 Critical Processes that involve Water - ANSWER 1. Dissolving of highly ordered solids (salts) - entropy of some of the water is decreased, but the entropy of the ions is greatly increased 2. The hydrophobic effect - there is no strong attraction between hydrophobic molecules (van der Waal's only) - there is no repulsion between hydrophobic molecules and water Aggregation of H-bonds in water is driven by - ANSWER entropy change of water (decrease) - it can also drive other reactions such as enzyme-substrate interaction Ion Product Constant - ANSWER [H+][OH-] = Keq [HOH] = 1.0 x 10^-14 Equilibrium Constant - ANSWER Keq = [H+][OH-]/[HOH] 2 Applications of pH - ANSWER 1. Controlling pH with buffers 2. How pH (protonation) affects weak interactions of molecules (charge and ability to form H-bonds) pKa = - ANSWER -log Ka pKa definition - ANSWER pH at which half of the acid is ionized. titration curves reveal the pKa of weak acids - is a measure of affinity for protons a high pKa constitutes... - ANSWER it takes a high pH (lots of OH-) to remove the H+ from the acid - the acid has a high affinity for H+ - if the pKa is high, it has a HIGH affinity (want) to grab onto H+, because of the large amount of OH- Significance of Buffering - ANSWER 1. Homeostasis 2. This phenomenon is very important for biochemical activity - many reactions depend on the state of protonation of particular functional groups A buffer is made... - ANSWER from a weak acid and its conjugate base Henderson-Hasselbalch Equation - ANSWER pH = pKa + log ([A-]/[HA]) (unprotonated over protonated) Decent Buffering occurs... - ANSWER within around 1 pH unit of pKa (ration of A/HA is between 1/10 or 10/1 Buffering of Blood - ANSWER blood is primarily buffered by the bicarbonate system (CO2/HCO3-) but also by phosphoric acid system (H2PO4-/H3PO4) The hydration of CO2 (middle equilibrium) is greatly enhanced by the enzyme... - ANSWER carbonic anhydrase Carbonic anhydrase - ANSWER raises H+ conc in RBC's, therefore affecting the ionization of hemoglobin side chains which affects O2 binding and release How will breathing rate affect the CO2/HCO3- equilibrium? - ANSWER excessive breathing creates a low level of CO2 in the blood - if CO2 levels increase, the brain tells the lungs to increase rate and depth of breathing to bring the levels down Shallow or slow breathing... - ANSWER will eventually cause elevated blood CO2 levels, equilibrium to shift to the right, the H3O+ conc. increases and pH drops Inside cells buffering is achieved by... - ANSWER phosphate ions and amino acid side chains on proteins Non-polar, aliphatic R groups - ANSWER glycine, alanine, proline, valine, leucine, isoleucine, methionine