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

2. 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.

3. 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

4. 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)

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

6. 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

7. 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.

8. 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

9. 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.

10. 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

11. 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

12. 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

13. Figure 8.10 Energy coupling using ATP hydrolysis

14. Figure 8.11 How ATP drives cellular work

15. 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

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

17. 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

18. 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

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

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

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

22. 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

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

24. Figure 8.21 Feedback inhibition
End-point inhibition

25. Multiple feedback systems typical of biochemical systems

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

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

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