1. An Introduction to Metabolism
Chapter 6

2. Metabolism The totality of an organism’s chemical reactions.
Metabolic Pathway: begins w/ a specific molecule, it is modified by enzymes until the end product is created
Catabolic: breaking down (degradative)
C6H12O6 + 6O2  6CO2 + 6 H2O + energy (ATP + heat)
Anabolic: Consume energy (build materials)
synthesis of protein from amino acids
Enzyme 1
Enzyme 2
Enzyme 3 A B C D
Reaction 1
Reaction 2
Reaction 3
Starting molecule
Product

3. Forms of Energy Potential: energy of position or structure
Chemical energy: stored in chemical bonds
Kinetic: movement perform work, by moving matter
Heat or thermal energy: random movement of particles KMT
Light energy
Energy animation.swf
Energy changed to heat is not usable (to do work) by living organisms

4. Thermodynamics 2nd Law 1st Law
Every E transfer or transformation increases the entropy (randomness) of the universe
Energy lost as heat is only usable if it is warming the organism, most goes to waste
Living systems increase entropy of surroundings
1st Law
E can be transferred and transformed but neither created nor destroyed
Photosynthesis and eating are huge energy transfers!
1st Law
2nd Law

5. Free Energy Enthalpy: Change in energy in a system
Entropy: Measure of disorder of a system
Free Energy (G): Energy available to do work
Random molecular motion (heat) can’t be recovered to do work = NOT USEFUL
Enthalpy –Temp (change in entropy)
- G is spontaneous, increases entropy of the universe
+G is non spontaneous, decreases entropy of universe (requires input of energy)

6. Free Energy: ΔG = ΔH- TΔS Free energy = enthalpy (total energy) change- temperature x entropy change
- ΔG are spontaneous, is exergonic: cellular respiration
+ ΔG are endergonic: photosynthesis
ΔG = ΔGfinal – ΔGinitial a negative result is spontaneous since less free energy exists in the products!
Reaching equilibrium means death, no work being done

7. Biological sources of Free Energy
ATP
ATP is a high-energy molecule: when it breaks down into adenosine diphosphate (ADP) and inorganic phosphate (Pi), it releases free energy that can be used to drive biological processes
Proton Motive Force
Movement of H+ ions across a membrane creating an electrochemical gradient

8. Cellular work Mechanical work – movement (Cilia & Flagella)
Transport work – molecules across membranes against concentration gradients
Chemical work – endergonic chemical reactions
Cells use exergonic reactions to drive endergonic reactions
9 + 2 Microtubule arrangement
Na+/K+ pump
Photosynthesis

9. ATP Structure
Ribose sugar bonded to adenine w/ 3 phosphates attached to the sugar
Phosphates can be broken off by hydrolysis
Phosphorylation: The inorganic phosphate is then transferred to other molecules (changes the reactivity of the other molecule). ENERGY is released
ΔG = -7.3 Kcal/mol ATP + H20  ADP + Pi
Adenine
Phosphate groups
Ribose

10. Fig. 8-10 + ∆G = +3.4 kcal/mol Glutamic acid Ammonia Glutamine
NH2
NH3 +
∆G = +3.4 kcal/mol
Glu
Glu
Glutamic
acid
Ammonia
Glutamine
(a) Endergonic reaction 1
ATP phosphorylates
glutamic acid,
making the amino
acid less stable. P +
ATP +
ADP
Glu
Glu
NH2 P 2
Ammonia displaces
the phosphate group,
forming glutamine.
NH3 + + P i
Glu
Glu
Figure 8.10 How ATP drives chemical work: Energy coupling using ATP hydrolysis
(b) Coupled with ATP hydrolysis, an exergonic reaction
(c) Overall free-energy change

11. ATP Cycle & Regeneration of ATP from ADP
The E to rephosphorylate ADP to become ATP comes from the cell’s catabolic reactions. ΔG = kcal/mol
ATP
H2O
Energy for cellular
work (endergonic,
energy-consuming
processes)
Energy from
catabolism (exergonic,
energy-releasing
processes)
ADP + P i

12. Progress of the reaction
Enzymes:
Enzymes: Speed up reactions that happen anyway: CATALYST
Enzyme Animation.swf
Enzymes are: Proteins, usually end in ase: sucrase, lactase, catalase, pepsin (huh?)
Enzymes: Lower activation energy, The E necessary to start a rxn
Enzymes: DO NOT change the ΔG
Progress of the reaction
Products
Course of
reaction
without
enzyme
Reactants
with enzyme EA
EA with
is lower
∆G is unaffected
by enzyme
Free energy
Figure 8.15

13. Enzymes & Substrates Substrate: Molecule that enzyme acts on
Enzyme-substrate complex: Enzyme bound to the reactant it works on
Active Site: Area on the enzyme where the substrate binds
Induced Fit: The enzyme changes shape to hold the substrate with weak bonds (H bonds or Ionic bonds)
How it works:
Template to bring substrates together
“stretches” substrate and stresses its bonds
Changes environmental conditions of substrate

14. Conditions that affect Enzyme Activity
pH: pH’s that are too high or too low denature the protein (enzyme), most work in pH of 6-8 (pepsin is an exception in stomach pH of 2)
Temperature: Enzymes have an optimal temperature, above this the protein denatures
Cofactors: inorganic substance bound to enzyme for enzyme to work
Coenzyme: organic molecule required for enzyme to function

15. Enzyme Inhibition Competitive Inhibition: Noncompetitieve Inhibitors
Bonds to active site, prevents substrate from binding
Reversible: mimic substrate
Irreversible: CO + hemoglobin
Noncompetitieve Inhibitors
bind to enzymes and change the conformation of the active site so a substrate can no longer bind.

16. Allosteric Regulation
Allosteric regulation occurs when a regulatory molecule binds to a protein at one site and affects the protein’s function at another site

17. Enzyme Regulation
Feed back inhibition – turns off a metabolic pathway when enough product has accumulated
Products act as allosteric inhibitors when in excess.
When the products are used up the enzyme is no longer inhibited and free to catalyze more reactions.

18. Enzyme Concept Check Inhibition pathways Allosteric Pathways
Describe the Vocabulary word in each box, and give an example of that pathway. To summarize, describe how enzymes affect the activation energy and the ΔG of a reaction.