1. Introduction to Metabolism
Ch. 8 – AP Biology

2. Metabolism
Definition – The totality of an organism’s chemical processes
An organism’s chemical reactions are arranged into intricately branched pathways
Metabolic pathway
Alters molecules by a series of steps.
Each step is selectively accelerated by a particular enzyme

3. Catabolic Pathways
Result in the breakdown of complex molecules into simpler compounds.
Example: Cellular respiration
Glucose is broken down into CO2 and H2O
Energy that was stored in the chemical bonds of glucose becomes available to do work for the cell.

4. Anabolic Pathways
Pathways that consume energy to build complicated molecules from simpler molecules
Example: making proteins from amino acids
Example: Photosynthesis

5. Organisms are Energy Transformers
The ability to do work.
Two Types of Energy
Kinetic
Energy of motion
Example: light
Potential
Stored energy
Possessed by matter because of its location or structure
Chemical energy – especially important in biology
Transformation of energy from kinetic to potential and back again is essential to life.
Living things do this all the time!

6. Thermodynamics The study of energy transformations
Organisms are open systems
They absorb energy from the environment
They release heat into the environment

7. Laws of Thermodynamics
1st Law of Thermodynamics
Energy can be transformed, but it cannot be created or destroyed
2nd Law of Thermodynamics
Energy transformation increases the entropy of the universe
Entropy = measure of disorder or randomness
Example of entropy: heat
In most energy transformations, ORDERED forms of energy are converted to HEAT
Conversion of energy to different forms does NOT violate 1st law.
Order of life does NOT violate the 2nd Law.
Entropy of the UNIVERSE, as a whole, is increasing in spite of the order that living things maintain…at least for a while.
QUANTITY of energy in the universe is constant;
QUALITY of energy is not.

8. Free Energy Spontaneous change
Change that can occur without outside help
Can be harnessed to perform work
Causes stability of a system to increase
Unstable systems tend to change to become more stable
A process can occur spontaneously ONLY if it increases the entropy of the universe.

9. Free Energy Definition Symbol
Portion of a system’s energy that can perform work when temperatures are uniform in the system
Symbol G

10. G is a measure of a system’s instability
Concept of Free Energy helps us determine if a process can occur spontaneously.
G is a measure of a system’s instability
It’s tendency to change to move to a more stable state.
Systems that are rich in energy are unstable
More complex molecules are rich in energy and therefore, unstable.
Those systems that tend to change spontaneously to a more stable state are those that have high energy and thus low entropy.
In any spontaneous process, the G of a system DECREASES
Change in G would be negative.

11. Free Energy and Chemical Reactions
As a chemical reaction moves toward equilibrium, free energy of the reactants and products decreases.
Free energy INCREASES when the reaction is moved away from equilibrium.
At equilibrium, change in G = 0
At equilibrium, a chemical reaction performs NO work.
A process is spontaneous and CAN perform work when it is SLIDING TOWARD equilibrium
Movement AWAY from equilibrium is NONspontaneous and occurs ONLY with the help of an OUTSIDE ENERGY source.

12. Exergonic Reactions Energy outward
Proceeds with a net release of free energy
Change in G is negative
CELLULAR RESPIRATION

13. Endergonic Reaction Energy inward STORES free energy in molecules
Change in G is positive
NONspontaneous
PHOTOSYNTHESIS
If a chemical process is EXERGONIC in one direction, it must be ENDERGONIC in the reverse direction.

14. Cells at equilibrium… Are DEAD.
Thus, it is advantageous to sustain DISequilibrium
Product of one reaction is not allowed to accumulate, but instead becomes a reactant in the next step along some metabolic pathway.

15. ATP and Cellular Work Cells do three kinds of work
Mechanical
Moving stuff – cilia for example
Transport
Moving molecules against concentration gradient
Chemical
Pushing of reactions that would NOT occur spontaneously
ATP is the immediate source of energy that powers cellular work

16. ATP
Adenosine Triphosphate

17. Hydrolysis of ATP
Breaking of bonds between the phosphate groups of the ATP “tail”
Energy is released
Molecules of ADP and Pi (inorganic phosphate) are left behind
EXERGONIC
Change in G is – 7.3 Kcal/mol
Phosphate bonds are NOT unusually strong – in fact, they are fragile
All 3 phosphate groups are negatively charged
Triphosphate tail is like a loaded spring
ADP and Pi are more stable than ATP

18. ADP and Pi are Renewable
ATP is made from the ADP and Pi that result when ATP is used by the cell
If ATP were NOT recyclable in this way, humans would have to consume their body weight in ATP each day.
The regeneration of ATP from ADP and Pi is endergonic
+7.3 kcal/mol are required
Cellular Respiration is the process that makes the energy to regenerate ATP
Energy is RELEASED from the breakdown of a GLUCOSE molecule to do this

19. ATP and Pi are Renewable

20. ENZYMES
Just because a reaction is spontaneous, does NOT mean it is fast.
Many chemical reactions happen so slowly that they are imperceptible.
Enzymes are CATALYSTS.
Speeds the rate of a chemical reaction without being consumed in the reaction

21. Activation Energy Initial energy required to get a reaction started
Initial energy required to break bonds
Acts as a barrier that must be overcome in order for the reaction to occur
Someone has to push the boulder off the top of the mountain in order for it to fall.
Heat is one way to provide activation energy
Speed up movement of molecules
Increase collisions; stress bonds
However, heat is BAD for cells
Enzymes LOWER activation energy without increasing temperature

22. Activation Energy

23. ENZYMES Substrate – substance upon which the enzyme acts
The substrate will undergo change to become product
The enzyme remains unchanged
Can be used again and again

24. Fit of Enzymes with Substrates
Enzymes are complexly shaped
Active site
Region of enzyme that interacts with substrate
Shape of active site is critical to function
Induced fit
Enzyme fits substrate like a clasping handshake
Enzyme is induced by substrate to change its shape to fit the substrate precisely/snugly
Not rigid like a key and lock

25. Enzyme Action Enzyme-substrate complex forms
Substrate is held at the active site by
hydrogen bonds; ionic bonds, etc.
Induced fit between enzyme and substrate occurs
Enzymes catalyze reactions in a variety of ways
Stress bonds of substrate making them easier to break
Bringing two or more substrates together making it more likely they will bond
Enzyme releases products
Enzyme will go on to act again and again
1000 molecules/sec!
An enzyme is saturated when it is catalyzing the maximum number of reactions it can
Only way to speed reaction would be to add more enzyme

26. Enzyme Action

27. Affects of Environment on Enzymes
Denature – enzyme loses its shape
Shape is CRITICAL to function
If misshapen, the enzyme will not work
Factors that denature enzymes
Increase in Temperatures pH
There are others….
Other environmental factors may not denature enzymes, but still affect their ability to catalzye
Decrease in Temperature
Lowers speed of molecules
Lowers number of collisions
Lowers rate of reaction

28. Cofactors Nonprotein “helpers” of enzymes
Molecules that help enzymes do their jobs
Inorganic
Metal atoms – zinc, copper, iron
Organic
Coenzymes - vitamins

29. Enzyme Inhibitors
A chemical that specifically and selectively inhibits a particular enzyme
Helps control enzyme activity

30. CONTROL OF METABOLISM Metaboic Pathways
Also called biochemical pathways
The product of one reaction becomes the reactant for the next reaction until the needed product is made
Many steps
Each step is catalyzed by a particular enzyme
These pathways can be controlled by
Switching on and off the genes that encode specific enzymes (genetic control)
Regulating the activity of enzymes once they are made (focus of our study now)

31. Allosteric Enzymes Enzyme has two active sites
“normal” active site that interacts with substrate
2nd active site (or receptor region) that binds with some molecule that affects activity of the enzyme itself.
2nd site may be used to inhibit or stimulate an enzyme’s activity

32. Feedback Inhibition
End product of a biochemical pathway acts as inhibitor of an enzyme within the pathway
Switches OFF the metabolic pathway
Prevents the cell from wasting chemical resources if the product of the pathway is already in good supply

33. Cooperativity Enzymes can also be stimulated to go to work
Cooperativity amplifies the response of an enzyme to its substrate

34. Organelles help to ORDER metabolism
Enzymes are often isolated from different parts of the cell by the organelles that contain them
Helps control sequence of chemical reactions
Keeps incompatible processes separated
Allows for more efficient reaction results