Energy and Metabolism Chapter 6

6.1 The Flow of Energy in Living Systems Energy-capacity to do work Kinetic-energy of motion Potential-stored energy Energy has many forms: 1.Mechanical 2.Heat 3.Sound 4.Electric current 5.Light 6.Radioactive radiation Study of energy is thermodynamics; unit of measure =kilocalorie=1000 calories. Calorie is the amount of heat required to raise 1g of water 1 0 C.

6.1 cont’d Oxidation-Reduction Oxidation-atom or molecule loses electrons (it is said to be oxidized) Reduction-atom or molecule gains electrons (it is said to be reduced) Reactions always take place together because they are transferring energy from one molecule to another.

6.2 Thermodynamics Laws of Thermodynamics-govern all energy changes in the universe. 1 st Law of Thermodynamics-states that energy cannot be created or destroyed it can only change from one form to another. Ex: lion eating a gazelle; lion is transferring some of the potential energy in gazelle’s tissues to his own body. Lion will store as potential energy and later convert it to kinetic energy. During the conversions, some energy is lost as heat, but is constantly replaced by the sun. 2 nd Law of Thermodynamics-the disorder (entropy) in the universe is continuously increasing; disorder is more likely than order. Ex: your messy room seems to happen with little energy; but getting in back in order requires energy.

6.2 cont’d Entropy-measure of disorder of a system (with every energy change, increasing amount of entropy) Free energy-the amount of energy actually available to break and subsequently form other chemical bonds. (energy available to do work) G = H – TS G= free energy H= enthalpy-energy contained in molecules chemical bonds T= temperature (K= 0 C + 273) S= entropy

6.2 cont’d When chemical reactions occur under conditions of constant temp, pressure and volume-as most biological reactions do-there is a change in free energy. In some reactions, the change in free energy is positive; these types of reactions do not proceed spontaneously because they require energy. They are endergonic. (H is higher than S) In some cases the change in free energy is negative; these reactions proceed spontaneously because they release free energy. They are exergonic. (T S) is greater than the change in H (enthalpy) Why haven’t all reactions that release energy occurred? Activation energy-extra energy required to destabilize bonds and initiate reaction. Reactions with a large activation energy tend to proceed more slowly Activation energies are not constant; can be influenced by a catalyst. Catalysts can only reduce activation energy, making reaction proceed faster.

6.3 ATP: The Energy Currency of Cells Phosphate groups repel one another-bonds are unstable –when broken 7.3 kcal/mole is released. Liberated phosphate usually attaches temporarily to an intermediate molecule, then it is usually released as an inorganic phosphate. ATP will drive endergonic reactions

6.3 ATP ATP-chief energy currency in all cells; adenosine triphosphate 1. making sugars 2. supplying activation energy for chemical reactions 3. actively transporting substances across membranes 4. moving cells through their environment 5. growth

6.4 Enzymes: Biological Catalysts Enzymes-proteins that catalyze reactions in living organisms. Lower activation energy so reaction can happen faster Ex: H 2 O + CO 2  H 2 CO 3 Without enzyme = 200 molecules/hour With enzyme carbonic anhydrase = 600,000 molecules/sec How does it work? 1.Most enzymes are biological proteins that have pockets called active sites 2.Substrates bind at these active sites 3.Amino acids on side of enzyme interact with the substrate by stressing a particular bond; thus lowering activation energy. Animation: How Enzymes Work

8.2 Enzymes Multi-enzyme complex-several enzymes catalyzing different steps in a sequence of reactions loosely bonded together. Advantages: 1.The product of one reaction can be delivered to the next enzyme without releasing it. 2.Possibility of unwanted side reactions is eliminated. 3.All reactions can be controlled as one unit. RNA as a catalyst (ribozymes) intramolecular-catalyze reactions on themselves intermolecular-act on other molecules 1.Chip out unnecessary sections from RNA copies of genes 2.Prepare ribosomes for protein synthesis 3.Facilitate replication of DNA within mitochondria

8.2 Factors That Affect Enzymes 1.Temperature-an increase in temperature will increase an enzyme-catalyzed reaction up to the temperature optimum C-40 0 C optimum for most enzymes; then they will denature 2. pH-ionic interactions hold enzymes together; sensitive to H+ concentrations 6 to 8 optimum for most enzymes; then they will denature (pepsin retains its shape in a pH of 2) 3. Inhibitors-substances that bind to an enzyme to decrease activity a. competitive-inhibitor competes with the substrate for the same binding site. b. noncompetitive-bind to substrate somewhere other that the active site. (allosteric site-chemical on/off switch) Tutorial 6.2 Allosteric Regulation of Enzymesl

8.2 Factors cont’d 4. Coenzymes-non protein organic molecules; shuttle energy in the form of H+ form one enzyme to another. Ex: NAD + + e-  NADH; H is then transferred to another molecule.

6.5 Metabolism: The Chemical Description of Cell Function Metabolism- total of all chemical reactions carried out by an organism Anabolism-reactions that expend energy to make or transform chemical bonds Catabolism-reactions that harvest energy when chemical bonds are broken. Biochemical pathways-reactions in which the product of one reaction becomes the substrate in the next. Evolution of pathways 1.F + G  H 2.E  F + G  H 3.C  D  E  F + G  H Regulation- feedback inhibition-the end product of the pathway binds to an allosteric site on the enzyme that catalyzes the first reaction in the pathway. Animation: Feedback Inhibition of Biochemical Pathways