Today: -Poster Discussion - Metabolism and Energy -Enzymes -Lab Preview -Photosynthesis Preview?

Metabolism Metabolism = all an organism’s chemical reactions An emergent property!

Metabolism Overview Notice that this is an open system!

Energy: Capacity to Do Work 1. Kinetic Energy- energy of movement 2. Potential Energy- energy due to location/structure 3. Chemical Energy- result of arrangement of atoms in molecules (potential energy in disguise!!)

First Law of Thermodynamics Energy can be transferred and transformed, but not created or destroyed. What has Escher done??

Second Law of Thermodynamics Every energy transfer increases the ENTROPY of the universe

Thermodynamics The quantity of energy in the universe is constant, but the quality is not!

Life is Ordered… Does this violate the second law of thermodynamics?

Life is Ordered… No! Life exists at the expense of free energy.

Free Energy (G) Ordered states (at left) have high free energy, or energy available to do work Ordered states (at left) have high free energy, or energy available to do work Disordered states (high entropy) have low free energy. Disordered states (high entropy) have low free energy.

Free Energy (Spontaneity) H = Total Energy T= Temperature in degrees Kalvin (K= o Celsius +273) S = Entropy So G is a measure of Instability! Free Energy = Portion of a system’s energy that can perform work when temperature is uniform throughout the system Free Energy = Available Energy!

More on Free Energy delta G = G final state – G starting state For a process to occur spontaneously, the system must either lose energy (decrease H) or lose order (increase S) This results in a negative value for

Free Energy (G) in Metabolism Metabolic reactions can be classified as either: EXERGONIC “Energy Outward” Negative delta G Spontaneous ENDERGONIC “Energy inward” Positive delta G Not Spontaneous! OR

Closed Systems Reach Equilibrium:

Organisms are Open Systems! = “Metabolic Disequilibrium”

Revisiting ATP

ATP does work by phosphorylating intermediates. Phosphorylation usually makes a molecule less stable/more reactive.

Example:

Glucose Metabolism & Efficiencies

Enzymes The Chemistry of Life is driven by more than Thermodynamics! This is a spontaneous (negative delta G) reaction! So… 1. Why doesn’t table sugar break down into glucose and fructose in our kitchens? 2. Why does sucrose break down so easily in organisms?

Activation Energy

Enzymes Lower Activation Energy Barrier

Enzymes: Key Features Biological Catalysts- Enzymes can increase the rate of a reaction, but does not change the delta G! Biological Catalysts- Enzymes can increase the rate of a reaction, but does not change the delta G! Enzymes are specific, and typically only recognize one particular substrate Enzymes are specific, and typically only recognize one particular substrate Substrates interact with active sites on the enzyme as described by the induced fit model Substrates interact with active sites on the enzyme as described by the induced fit model Enzymes are affected by their environment Enzymes are affected by their environment

Reminder: Enzymes Are Just Proteins! Proteins are composed of chains of amino acids

Reminder: Enzymes Are Just Proteins!

Enzyme Function

Enzymes: Induced Fit

An Enzyme’s ACTIVITY is generally OPTIMIZED for its Environment How does this arise??

Many Enzymes Require COFACTORS: Vitamin C (ascorbate) is a Cofactor The hydroxylation of proline residues in collagen requires ascorbate. The hydroxylation of proline residues in collagen requires ascorbate. Vitamin C is, therefore, required for the maintenance of normal connective tissue as well as for wound healing. Vitamin C is, therefore, required for the maintenance of normal connective tissue as well as for wound healing. Vitamin C also is necessary for bone remodeling due to the presence of collagen in the organic matrix of bones. Vitamin C also is necessary for bone remodeling due to the presence of collagen in the organic matrix of bones.

Enzymes: Regulation Enzymes: Regulation Enzyme Inhibitors- Molecules that selectively inhibit the activity of specific enzymes Competitive Inhibitors Block substrates from entering active site Noncompetitive Inhibitors Bind to another region of the enzyme, changing the shape of the enzyme and limiting or preventing its activity

Enzyme Inhibitors Normal Function Noncompetitive Inhibition Competitive Inhibition

Cool Things To Do With Enzyme Inhibitors: Design Drugs Figure: COX 1 and 2 : The cyclo-oxygenase systems by drdoc on-line ©

Other Mechanisms: Allosteric Regulation Regulatory molecules may bind weakly to an allosteric enzyme, changing its shape and function

Other Mechanisms: Allosteric Regulation

Allosteric Regulation Often Explains Feedback Inhibition:

One Last Mechanism: Cooperativity The binding of one molecule of substrate to an allosteric enzyme may trigger a favorable conformational change in the other subunits

Next: Designing your Enzyme Experiment!

Designing Your Experiment: Lab 4

Oxidation of Catechol (catalyzed by Catecholase) Our Model System: Factors that might affect the rate of this reaction?

How will we know if our enzyme is working and/or affected by its environment?

Introducing Your Reagents: “Potato Juice” = Enzyme Solution!

Thinking About Good Experimental Design What is a ‘control’? What does it tell me about my experiment? What is a ‘control’? What does it tell me about my experiment? What would a good control be for this experiment? What would a good control be for this experiment? With your lab group, complete the Prelab Sheet: 1)Identify factors that might affect enzyme function (generate hypotheses!) 2)Decide which factor you would like to test 3)Design your experiment!

New: PHOTOSYNTHESIS Brainstorm: 4 Things We Know About Photosynthesis 4 Questions About Photosynthesis Why is Photosynthesis important??