Bio 178 Lecture 12Biological Membranes & Energy

http://www.cellsalive.com/channels.htm

Reading

• Chapters 6 & 8

Quiz Material

• Questions on P 124 & 158

• Chapters 6 & 8 Quiz on Text Website (www.mhhe.com/raven7)

Outline• Biological Membranes 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

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

Active TransportDescription

• 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 TransportCan 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 TransportEnergy InputRequired 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.)SymportProtein transporting different materials in the same direction.

Antiport

Protein transporting different materials in the opposite direction, eg. Na+ with Ca2+.

Countertransport

Symport and Antiport

Mcgraw-Hill video

Membrane Transport

EnergyDefinitionCapacity to do work.

Kinetic Energy

Energy of motion.

Potential Energy

Stored energy.

Potential and Kinetic Energy

ThermodynamicsThe 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.)HeatMeasure of the random motions of molecules.

The energy available to do work decreases with time - it dissipates as heat.Second Law of ThermodynamicsThe entropy of the universe is increasing.

EntropyA quantitative measure of disorder.

Summary of the Laws of ThermodynamicsThe quantity of energy in the universe is constant but the quality is decreasing.

Energy and Redox ReactionsReducing PowerIn 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