1. Introduction to Energy in a Cell
Unit 3 – Energy in a Cell
Introduction to Energy in a Cell

2. Energy Can be defined as the ability to do work.
Types of energy can include:
1. Light
2. Sound
3. Electricity
4. Heat
5. Chemical
Energy can transform in our body. The food that we eat gives us the energy to move, maintain body temperature, make new chemicals, maintain cells in our body, and much more.

3. How do organisms get energy?
Heterotrophs: are organisms that are not able to make their own food. They must get it from somewhere else (where it is already made). Examples: animals, fungi, bacteria, protists.
Autotrophs: are organisms that are able to make their own food. Plants use the energy from the sun to make carbs through photosynthesis.

4. Thermodynamics and Energy
First law of thermodynamics: energy can neither be created nor destroyed. It can only change forms.
Ex. Solar energy  chemical energy (sun to food)
Second law of thermodynamics: all conversions of energy produce some heat, which is not useful energy. This thermal energy is lost to the atmosphere.

5. Entropy
Entropy is a measure of disorder or randomness of a system. (The greater the disorder in the system the greater the entropy)
A system tends to become more random, and not more ordered.
Heat is one form of disorder. The more heat generated during energy conversions, the more the entropy of the system. For example, when you exercise, your body gives off heat. Heat is a waste energy. Not all of the energy is used for muscle contraction; some will be wasted as heat.

6. Entropy
Similarly, when energy is transferred, it is not all usable. Some of the energy is lost to the surroundings.
Ex. When an owl eats a mouse, the owl gains some energy from the mouse, and some is lost to the surroundings in the form of heat.

7. Entropy

8. Reactions
In terms of energy, we will discuss two types of reactions, exothermic and endothermic.
Exothermic reactions are those that release energy. Energy that is stored in chemical bonds is released when those bonds are broken.
Some of this chemical energy is usable, and some is lost as heat, light, or sound.
Products have less energy than the reactants.

9. Reactions
Endothermic reactions require an addition of energy from an external source.
Products have more energy than the reactants (stored in bonds).
Photosynthesis is an endothermic reaction (sun light input needed to make carbs.)
sunlight + 6CO2(g) + H2O(l) = C6H12O6(aq) + 6O2(g)

10. Cellular Metabolism
The sum of endothermic and exothermic reactions in our cells is our cellular metabolism.
Where does the energy come from for reactions in our body?
ATP (adenosine triphosphate)

11. Cellular Metabolism
Energy is stored in the phosphate bonds of ATP, and becomes released and usable when these phosphate bonds are broken.
ATP + water  ADP + P + energy
ADP can then be re-phosphorylated into ATP, re-enabling it to do work.

12. Activation Energy
This is the energy required to start or initiate a reaction.
Ex. A lit match, heat from a bunsen burner, etc.
This activation energy is the reason that reactions do not all occur spontaneously.
For example, molecules in our body (such as ATP), do not break down spontaneously.

13. Enzymes
Globular protein catalysts that help control metabolic reactions. They permit low temperature reactions by reducing the activation energy.
They can control the speed of a reaction.

14. Enzymes
Enzymes remain unchanged after the reaction and can be used again and again.
They do their task by bringing substrate molecules together. Their folded surfaces act as molds or active sites for trapping molecules and aligning them to cause the reaction.
Each kind of enzyme recognizes, binds and alters only specific reactants.

15. Enzymes

16. Enzymes http://www.youtube.com/watch?v=V4OPO6JQLOE

17. Factors affecting rate of reactions
1. Temperature – reaction rate increases as temp. increases. Molecules move faster, and collide more frequently.
Rates often peak at 37°C because at higher temperatures, enzymes are denatured and lose their function.
High fevers are dangerous for this reason.

18. Factors affecting rate of reactions
2. pH ranges – acids and bases denature proteins. The result is a loss of the active site on the protein.

19. Factors affecting rate of reactions
3. Concentration of substrate molecules – The greater the number of molecules, the more collisions and thus a higher reaction rate.
This only increases until the number of substrate molecules outnumber available enzymes.
4. Inhibitors – molecules with shapes similar to active sites on enzymes and similar to the shape of the substrate. This molecule can bind to the enzyme and inhibit its function.
Ex. Poison – cyanide.

20. Other factors affecting reaction rates
Cofactors (inorganic metal ions such as iron, magnesium or zinc) or
Coenzymes (organic compounds composed of vitamins or vitamin derivatives)
– help enzymes bind to substrate molecules when they do not fit the active site.
They alter the active site so they can fit together.
Competitive inhibitors – molecules that have a shape similar to a specific enzyme, which permits it to bind to the active site.

21. Other factors affecting reaction rates
Non-competitive inhibitor – does not bind to the active site, but binds to the enzyme on another site and changes its shape. This inhibits function.
Inhibitors block chemical reactions.

22. Other factors affecting reaction rates
Allosteric activity – change in the protein enzyme caused by the binding of a molecule to the regulatory site of the enzyme.
Feedback inhibition is an example of allosteric activity. The final product of a pathway binds to the regulatory site of an enzyme, which causes a change in the active site. This inhibits further reactions.