Metabolism & Energy  Metabolism – sum of an organism’s chemical reactions  Two Main Types of Metabolic Pathways: Catabolic Pathways: breaking down molecules to release energy (downhill) Ex. Cellular Respiration Anabolic Pathways: uses energy to build complex molecules from simple molecules (uphill) Ex. Photosynthesis  Energy released from catabolic pathways, drive anabolic pathways.

Energy  Energy – the ability to do work Ability to rearrange a collection of matter Various Types – kinetic, potential, light, chemical, etc.  1 st Law of Thermodynamics: energy can be transformed and transferred, but it cannot be created or destroyed Aka – energy of the universe is constant  2 nd Law of Thermodynamics: every energy transfer/transformation makes the world more disordered (more entropy)

Energy Continued – 2 nd Law of Thermodynamics  As living things perform chemical reactions that do work some forms of energy are converted to heat  Heat can only do work if there is a temperature difference (heat will flow from a warmer to cooler area)  Temperature is uniform in cells, so no work can be performed by the heat that is released during chemical reactions Ex. Rooms with lots of people get warm  This leads to entropy (more disorder or randomness) The more randomly arranged a collection of matter is, the greater its entropy Gases have more entropy than liquids and liquids have more entropy than solids

Gibbs Free Energy  ΔG = ΔH – T ΔS  Where…. ΔG = total available energy ΔH = change in enthalpy  Enthalpy = total energy in a system T = temperature in Kelvin ΔS = change in entropy  Entropy = measure of the disorder in a system

Spontaneous Reactions  Increase the entropy (disorder) of the universe  Occur without an input of energy  Exergonic  Are reactions that can occur on their own  Examples:  Water flowing downhill  Cellular Respiration

Chemical Reactions & Energy  Exergonic Reactions: 1) Net release of free energy 2)Occur spontaneously 3)ΔG < 0  Endergonic Reactions: 1) Absorbs free energy 2) Non-spontaneous 3) ΔG > 0

Cellular Respiration vs. Photosynthesis  Cellular Respiration ΔG = -686 kilocalorie or -686 Calories  Photosynthesis ΔG = 686 kilocalorie or 686 Calories Prove these numbers with Gibbs Free Energy Prove these numbers with Gibbs Free Energy

ATP: The Energy Molecule  ATP is the fuel that powers work in cells b/c it links exergonic reactions to endergonic reactions  ATP helps cells do…. 1) Chemical Work: dehydration synthesis or hydrolysis 2) Mechanical Work: muscle contraction 3) Transport Work: active transport

Energy: ATP Structure  Made up of… 1) Adenine 2) Ribose 3) Three phosphate groups  Have like charges so they repel each other  Bonds b/w phosphates are unstable  Energy of repulsion is stored in the bonds that hold the phosphates together

ATP Structure

ATP & Cellular Reactions  ATP is constantly broken down and re-made  Making ATP (from ADP & P)  endergonic +7.3 kilocalories  Breaking ATP down  exergonic -7.3 kilocalories  ATP is like a rotating door through which energy is passed as it moves from catabolic to anabolic pathways.  The energy temporarily stored in ATP drives almost all cellular work!!!

ATP Cycle

More About ATP…..  Transferring a P from ATP (forming ADP) to another molecule transfers energy  The molecule receiving the P, and hence energy, is PHOSPHORYLATED  Nearly all endergonic reactions require less energy that provided by the cleavage of ATP  Most cells have only a few seconds supply of ATP at any given time

Living Systems & 2 nd Law of Thermodynamics  Living systems do not violate the 2 nd law of thermodynamics Which states that entropy increases over time  Order is maintained by coupling cellular processes that increase entropy (exergonic) with those that decrease entropy (endergonic) ATP Cycle

Living Systems & 2 nd Law of Thermodynamics  Energetically favorable reactions, such as ATP  ADP + P, are exergonic  The energy released from this reaction can be used to maintain or increase order in a system by being couple with reactions that have a positive free energy change (endergonic)

How is Free Energy Used by Living Organisms?  Chemical Reactions Dehydration synthesis – makes polymers Hydrolysis – breaks down polymers  Body temperature regulation Endothermy: using thermal energy made by chemical reactions to maintain the homeostasis of body temperature Ectothermy: use external thermal energy to regulate and maintain body temperature

How is Free Energy Used by Living Organisms?  Reproduction/Raising Offspring Seasonal reproduction in plants  Excess Acquired Free Energy vs Free Energy Used Results in energy storage or growth  Insufficient Required Free Energy vs Free Energy Used Loss of mass, and, eventually, death

Enzymes  Definition: Proteins that speed up the rate of a chemical reaction Have a 3-D shape conferred by their primary, secondary, tertiary, and quaternary structure -- let’s review those!  Can build (dehydration synthesis) or break down (hydrolysis)

Enzyme, Substrate & Active Site – What’s the Relationship?  Enzyme – catalyst  Substrate – molecule(s) the enzyme is working on  Active Site – area where the enzyme and substrate fit together Shape is essential to function!

Enzymes & Energy  E A (Activation Energy)  Energy required to break bonds in the reactants Enzymes act to lower the activation energy

Enzymes & Activation Energy

How Do Enzymes Lower Activation Energy?  Active sites hold onto and put stress on the substrate (molecule the enzyme if working on)  Bonds are broken  Less energy is needed to achieve the transition state

Enzymes & Activation Energy  If there was no barrier of activation energy  proteins, DNA & other molecules would spontaneously decompose  Enzymes can only lower activation energy; they CANNOT cause a rx’n to occur that would not occur spontaneously

Enzyme Characteristics  Specific  Binds to a substrate based on shape recognition  Substrate binds to the active site by induced fit  active site is slightly flexible, but clasps tightly when the enzyme and substrate meet.  Reusable  can be used over & over

The Catalytic Cycle of Enzymes Substrate is converted into products Products leave; Active Site is open Enzyme and substrate meet; Held together by weak bonds

Enzyme Action

What Factors Affect Enzyme Activity?  1) Temperature Above optimal temp – enzyme denature (lose their shape) – Explain why.

What Factors Affect Enzyme Activity?  2) pH Every enzyme has an optimal pH Pepsin is found in the stomach (acidic) while trypsin is found in the small intestine (slightly basic)

What Factors Affect Enzyme Activity?  3) Substrate Concentration At some point, every enzyme is saturated with substrate and the reaction cannot proceed any faster

What Factors Affect Enzyme Activity?  4) Cofactors: helper(s) to the enzyme; may bind to the active site OR bind loosely & reversibly along with the substrate

What Factors Affect Enzyme Activity?  Another cofactor example

What Factors Affect Enzyme Activity?  5) Enzyme Inhibitors: inhibits the substrate from binding to the active site… A. Competitive Inhibitors – resemble substrate structure and compete for a place in the active site B. Noncompetitive Inhibitors – Binds to a part of the enzyme away from the active site  changes enzyme shape

Competitive vs. Noncompetitive Inhibitors

Enzymes & Allosteric RegulationAllosteric Regulation  Allosteric Regulation: an enzyme can change b/w 2 conformational shapes due to activators or inhibitors

Feedback Inhibition & Cooperativity  Feedback Inhibition: Metabolic pathway is turned on and off by its product; the end product acts to inhibit the enzyme that catalyzes the reaction  Cooperativity: A mechanism where one substrate may prime an enzyme to accept additional substrate molecules more easily

Denatured?  What does it mean if an enzyme has been denatured?  How does an enzyme become denatured?

Denaturation  Explain how changes in the following affect an enzymes function: temperature, pH, salt concentration