Bio 178 Lecture 12 Biological Membranes & Energy

Reading Chapters 6 & 8 Quiz Material Questions on P 124 & 158 Chapters 6 & 8 Quiz on Text Website (

Outline Biological Membranes ð Membrane Transport Energy and Metabolism

Endocytosis (Cntd.) Receptor Mediated Endocytosis (RME) 1. Specific molecules bind to specific receptors in the PM. 2. These accumulate in coated pits (clathrin). 3. The clathrin then causes a vesicle to form (only when the target molecule binds to the receptor)  endocytosis. Example - LDL (low density lipoprotein) Means of transportation of cholesterol. When cholesterol is required for membranes the LDL is taken up by RME. Hypercholesterolemia - LDL receptors lack tails  LDL not taken up by RME  cholesterol remains in blood  atherosclerosis.

Receptor Mediated Endocytosis

Exocytosis Utilization of a membrane to transport material out of a cell. Example - Secretion

Active Transport Description Movement of substances up their concentration gradient. Requires input of energy. Utilizes protein carriers in the memrane. Function Allows the cell to have a higher intracellular than extracellular concentration of the transported substance.

Types of Active Transport Can be classified according to whether the use of energy is direct or indirect. Direct Energy Use - Na + -K + Pump Example Maintains a higher intracellular [K + ] but lower [Na + ] than the extracellular environment. Ions pumped up concentration gradient using energy directly from ATP. Carrier protein undergoes conformational changes to transport 3 Na + out for every 2 K + pumped in.

Sodium-Potassium Pump Speed per carrier = 300 Na + /S

McGraw-Hill Video: Sodium-Potassium Pump

Sodium-Potassium Pump(Cntd.) Functions Maintain resting potential (-70 mV) of the cell and thus allows action potentials to occur. Driving force for coupled transport. Indirect Energy Use - Coupled Transport Example Coupled transport uses the energy stored in the concentration gradient of a different molecule.

Coupled Transport (Cntd.) Example - Glucose Transport Energy Input Required because glucose is large, polar, and usually has a higher intracellular than extracellular concentration Mechanism Na + /K + pump results in a concentration gradient that allows Na + to diffuse back into the cell using a carrier protein. Glucose also binds to this carrier protein to enter the cell against its concentration gradient (  using energy indirectly derived from the Na + /K + pump).

Coupled Transport of Na + and Glucose

Coupled Transport (Cntd.) Symport Protein transporting different materials in the same direction. Antiport Protein transporting different materials in the opposite direction, eg. Na+ with Ca 2+. Countertransport

Symport and Antiport Mcgraw-Hill video

Membrane Transport

Energy Definition Capacity to do work. Kinetic Energy Energy of motion. Potential Energy Stored energy.

Potential and Kinetic Energy

Thermodynamics The study of energy transformations. Measurement of Energy Kilocalorie (kcal) = 1000 cal 1 cal  Heat needed to raise the temperature of 1g water 1  C. First Law of Thermodynamics The total energy of the universe is constant - it cannot be created or destroyed, it can only be transferred or transformed.

Thermodynamics (Cntd.) Heat Measure of the random motions of molecules. The energy available to do work decreases with time - it dissipates as heat. Second Law of Thermodynamics The entropy of the universe is increasing. Entropy A quantitative measure of disorder. Summary of the Laws of Thermodynamics The quantity of energy in the universe is constant but the quality is decreasing.

Energy and Redox Reactions Reducing Power In redox reactions energy is passed with an electron. How much energy does an electron possess? Dependent on distance from the nucleus. Can be boosted to a higher energy level by light.

Free Energy (G) The amount of energy available to break bonds and form new bonds. Change in free energy (∆G) Endergonic Reactions +∆G  Products contain more energy than reactants. Not spontaneous. Exergonic Reactions -∆G  Products contain less energy than reactants. Usually spontaneous.

Endergonic and Exergonic Reactions