1. UNIT 2 Chapter 6: A Tour of the Cell Chapter 7: Membrane Structure & Function Chapter 8: An Introduction to Metabolism

2. The Chemistry of Life is Organized into Metabolic Pathways  The sum total of all an organism’s chemical reactions is its metabolism Catabolism: breakdown of molecules, releases energy Catabolism: breakdown of molecules, releases energy Anabolism: construction of molecules, stores energy Anabolism: construction of molecules, stores energy  Bioenergetics is the study of how organisms manage their energy resources

3.  Metabolism is highly complex and numerous metabolic pathways exist  Definitions Kinetic energy Kinetic energy Potential energy Potential energy Chemical energyChemical energy

4. Living Systems are Subject to Two Laws of Thermodynamics  Thermodynamics is the study of energy transformations First Law of Thermodynamics: energy cannot be created or destroyed First Law of Thermodynamics: energy cannot be created or destroyed Second Law of Thermodynamics: energy transformation must make the universe more disordered Second Law of Thermodynamics: energy transformation must make the universe more disordered Entropy: a measure of disorder or randomnessEntropy: a measure of disorder or randomness

5.  Order can be increased locally, but there is an unstoppable trend towards randomization in the universe Increased entropy usually in the form of heat Increased entropy usually in the form of heat Heat is the most random state of energy Heat is the most random state of energy  Organisms do not violate the 2 nd law Light energy or chemical energy goes in, and convert that energy into mostly heat Light energy or chemical energy goes in, and convert that energy into mostly heat Living organisms possess relatively low entropy compared to the universe Living organisms possess relatively low entropy compared to the universe

6. Free Energy  Free energy is a system’s energy available to do work  Reactions are considered spontaneous if  G is negative  If  G = 0, the reaction is at equilibrium  G = G final – G start

7. Metabolism and Metabolic Disequilibrium  Exergonic reactions release energy and occur spontaneously  G is negative  G is negative C 6 H 12 O 6 + 6 O 2  6 CO 2 + 6 H 2 O + energyC 6 H 12 O 6 + 6 O 2  6 CO 2 + 6 H 2 O + energy  Endergonic reactions store energy and are non-spontaneous  G is positive  G is positive

8.  In natural (living) systems, equilibrium is not reached

9. ATP (Adenosine TriPhosphate)  In most cases, ATP is the immediate source of energy for cells

10.  The third phosphate group can be hydrolyzed to produce ADP, a phosphate group and energy (7.3kcal/mole of ATP) (7.3kcal/mole of ATP)

11.  Energy coupling is a common “tactic” used by cells to power endergonic reactions using exergonic ones Phosphate group hydrolyzed from ATP used to phosphorylate another molecule Phosphate group hydrolyzed from ATP used to phosphorylate another molecule  ATP can be regenerated by cells very rapidly Working muscle cells use ~10million ATP molecules per second Working muscle cells use ~10million ATP molecules per second

12. Enzymes Work to Speed Reaction Rates  Enzymes are biological catalysts that lower the energy of activation (E A ) for a reaction  Enzymes are not altered by the reaction They are free to catalyze again They are free to catalyze again

13. Enzymes are Designed to Work in Specific Reactions  A given enzyme will only work on one type of substrate Substrate will bind to active site of protein Substrate will bind to active site of protein Lactase Lactase Lactose + H 2 O  Glucose + Galactose

14. Enzyme Activity  Enzymes are proteins, and therefore are subject to denaturation Enzymes possess optima – conditions at which they function best Enzymes possess optima – conditions at which they function best Temperature and pHTemperature and pH Some enzymes require cofactors (inorganic substances) or coenzymes (organic substances) to promote catalytic activitySome enzymes require cofactors (inorganic substances) or coenzymes (organic substances) to promote catalytic activity

15.  Some molecules prevent enzyme activity by binding to the enzyme Competitive inhibition: inhibiting molecule binds to active site, preventing substrate from binding Competitive inhibition: inhibiting molecule binds to active site, preventing substrate from binding Non-competitive inhibition: inhibiting molecules bind elsewhere on the enzyme, which alters the enzymes conformation and the active site Non-competitive inhibition: inhibiting molecules bind elsewhere on the enzyme, which alters the enzymes conformation and the active site

16. Metabolic Control  Allosteric enzymes can be activated or deactivated by an activator or inhibitor They bind to allosteric site on enzyme They bind to allosteric site on enzyme  Most allosteric enzymes are comprised of multiple polypeptides

17.  Enzymes can be inhibited by the products they create Feedback inhibition Feedback inhibition  In multiple subunit enzymes, cooperativity can amplify the enzyme’s response to substrates END

18. Cell Membranes & Phospholipids Phospholipids constitute cell membranes and their fatty acid tails determine membrane fluidity Unsaturated tails increase fluidity, saturated tails decrease fluidity Temperature also plays a role:

19. Cholesterol also influences membrane movement Reduces membrane fluidity Warm: phospholipids move freely Cool: tight packing of phospholipids - solidify Cells can alter the lipid composition of their membranes to suit environmental needs

20. Fluid Mosaic Model Membranes possess a variety of different proteins embedded in the phospholipid bilayer

21. There are two main types of membrane proteins: peripheral and integral (transmembrane) Peripheral proteins are not embedded in the membrane itself, they are bound to proteins found in the membrane

22. The Role of Proteins in Membranes Proteins help provide structure and support for cells They also perform numerous other functions

23. Cell-to-cell recognition is achieved by integral proteins and the carbohydrates bound to them Membrane carbohydrates usually branched oligosaccharides Cells can be distinguished from one another

24. Membrane’s Molecular Organization Allows for Selective Permeability Molecules and ions are constantly moving across cell membranes Oxygen, carbon dioxide, sugars, amino acids, ions (K +, Na +, Ca 2+, Cl - ) Passage is not indiscriminate, membranes are selectively permeable Dependent upon interaction with hydrophobic core of membrane Transport proteins may assist molecules across membrane

25. Some Transport Across a Membrane Does Not Require Energy Transport across a membrane may occur without energy (passive) or energy may be required (active) Diffusion is the simplest form of passive transport Requires a concentration gradient to occur

26. Even though a concentration gradient may exist, some molecules may not be able to pass through the membrane Facilitated diffusion involves the use of a transport protein Some simply provide channels for molecules Others change conformation to move molecules

27. Active Transport Requires Energy Cells sometimes need to move molecules against their concentration gradients Active transport requires the cell to “spend” some of its energy, usually in the form of ATP Sodium/Potassium pump (Na + /K + pump) 3 Na + move out, 2 K + move in

28. Sodium/Potassium Pump

29. Osmosis Osmosis is the passive diffusion of water across a selectively permeable membrane Concentration differences in solutions required Higher concentration of solutes = hypertonic Lower concentration of solutes = hypotonic Hypotonic and hypertonic are relative terms Ex. Human cells are hypertonic to distilled water, but they are hypotonic to sea water If no concentration differences exist, solutions are isotonic

30. In the case of osmosis, the type of solutes present does not matter – only the total amount of solutes Osmosis will continue until both solutions are isotonic END