Potential and Kinetic energy: cheetah at rest and running Chapter 8 Introduction to metabolism Potential and Kinetic energy: cheetah at rest and running

Use of Energy by Cells One property of living things above all makes them seem almost miraculously different from nonliving matter: they create and maintain order, in a universe that is tending always to greater disorder. to create this order, the cells in a living organism must perform a never-ending stream of chemical reactions.

Cell Metabolism is Organized by Enzymes The chemical reactions that a cell carries out would normally occur only at much higher temperatures than those existing inside cells. For this reason, each reaction requires a specific boost in chemical reactivity. This requirement is crucial, because it allows the cell to control each reaction – enzymes catabolic reactions anabolic reactions

Biological Order is Made Possible by the Release of Heat Energy from Cells The universal tendency of things to become disordered is a fundamental law of physics – the second law of thermodynamics In the universe, or any isolated system (a collection of matter that is completely isolated from the rest of the universe), the degree of disorder only increases (quantified and expressed as entropy)

High Energy (Low Entropy) Low Energy (High Entropy) Entropy is measure of disorder Cell and Organismal Biology 2009

Super cells? So cells might appear to defy the second law of thermodynamics – by surviving, growing, and forming complex organisms How? The answer is that a cell is not an isolated system, it takes in energy from its environment in the form of food, or photons from the sun (or even, from inorganic molecules alone) and uses this energy to generate order within itself. During all of these energy conversions some of the energy is converted into heat  increases surrounding entropy

First Law of Thermodynamics First law of thermodynamics – states that energy can be converted from one form to another, but that it cannot be created or destroyed.

Laws of Thermodynamics First Law Energy can neither be created nor destroyed, it can only change from one form to another Second Law Disorder in the Universe is increasing (i.e. entropy is increasing) Entropy is measure of disorder

Unfavorable reactions Cells are chemical systems that must obey all chemical and physical laws. Although enzymes speed up reactions, they cannot by themselves force energetically unfavorable reactions to occur. Therefore ezymes directly couple energetically favorable reactions, which release energy and produce heat, to energetically unfavorable reactions, which produce biological order.

Figure 8.5 The relationship of free energy to stability, work capacity, and spontaneous change Molecule moves from complex to simple-lower E Diffusion- like sodium/glucose cotransport Paper-burn it to release heat, lower free energy. Sugar- do the same to produce CO2 and water. Respiration can do the same with more control Combustion

Figure 8.6 Energy changes in exergonic and endergonic reactions Exothermic Endothermic G<0, energy released (exothermic) G>0, energy must be supplied (endothermic) Sugar to CO2 and water Gibbs free energy G Change in free energy G Coupled reactions

Figure 8.8/8.9 The structure and hydrolysis of ATP  Molecule most involved in supply of energy for reactions and movements From breakdown of sugar Negative phosphates repel therefore high energy

Figure 8.10 Energy coupling using ATP hydrolysis

Figure 8.11 How ATP drives cellular work

Figure 8.14 Energy profile of an exergonic reaction Even exergonic reactions don’t always occur spontaneously-just as well EA is activation energy Transition state is very unstable/high energy therefore unlikely. Eg 5 bonded carbon

Figure 8.15 Enzymes lower the barrier of activation energy Lower Ea by stabilizing transition state

Enzymes Powerful and specific catalysts S+E ES EP E+P Unstable/high energy Lysozyme- relatively slow- 1/sec- Used lysozyme in the lab earlier in semester

Mechanisms of enzyme action Increase local concentrations of substrates Strain bonds to increase likelihood of reaction (induced fit) Form covalent intermediates Stabilize transitional state of reaction Cell and Organismal Biology 2009

Figure 8.16 The induced fit between an enzyme and its substrate Highlights how enzymes work-next slide Hexokinase

Figure 8.18 Environmental factors affecting enzyme activity Why does temperature and pH affect enzymes? Why?

Regulation of Cyclin Dependent Kinase by phosphorylation Regulation of Enzymes Regulation of Cyclin Dependent Kinase by phosphorylation Substrate protein is also phosphorylated

Figure 8.19 Inhibition of enzyme activity Regulation of Enzymes Competitive inhibitor Allosteric- binding of a small molecule to the enzyme causes conformation change that then affects the activity of the enzyme Allosteric inhibitor

Figure 8.20 Allosteric regulation of enzyme activity Allosteric inhibitors and activators Cooperativity

Figure 8.21 Feedback inhibition End-point inhibition

Multiple feedback systems typical of biochemical systems

Mechanisms to increase efficiency of enzyme systems Pyruvate dehydrogenase Cooperativity Binding of substrate to one subunit increases the likelihood of other binding

Mechanisms to increase efficiency of enzyme systems Pathway organization Pathways and clusters

Figure 8.22 Organelles and structural order in metabolism Mechanisms to increase efficiency of enzyme systems Organelles are large scale organizers of pathways