1. Chapter 8 Introduction to Metabolism

2. Think Tank Question…
Using the concepts of energy, entropy, and metabolism answer the following:
Does the concept of evolution violate the 2nd law of thermodynamics? Explain.
It would appear the answer is yes since organisms get more complex…but…SEE ANSWERS ON SLIDE

3. Metabolism
Metabolism is the sum of all of the chemical reactions in a biological organism
A metabolic pathway is a series of defined steps resulting in a certain product, each step catalyzed by an enzyme
Catabolic pathway – release energy by breaking down complex molecules into simpler compounds; energetically “downhill”; example – cellular respiration
Anabolic pathway – consume energy to build complicated molecules from simple ones; energetically “uphill”; example - photosynthesis
The energy released from a catabolic pathway is stored and used to complete an anabolic pathway

4. Energy Energy – the capacity to cause change or do work
Kinetic energy – energy of motion
Potential energy – stored energy, the energy in an object currently not moving

5. Thermodynamics
Thermodynamics – the study of energy transformations that occur in a collection of matter
1st law – energy can be transferred and transformed, but cannot be created or destroyed
2nd law – every energy transfer or transformation increases the entropy of the universe
Entropy is a measure of randomness or disorder in the universe
Disorder = randomness caused by the thermal motion of particles; the energy is so dispersed it is unusable.

6. Back to the tank… Does evolution violate the 2nd law??? NOPE.
The construction of complex molecules (metabolism) generates disorder.
Life requires as constant input of energy to maintain order.

7. The Laws of Thermodynamics

8. Free Energy Free energy – the energy available to do work
ΔG = ΔH - T ΔS ; the Gibbs-Helmholtz equation
ΔG = the change in free energy, the maximum amount of usable energy that can be harvested
ΔH = enthalpy or total energy in biological systems
T = temperature in Kelvin
ΔS = change in entropy
Significance
Indicates the maximum energy available to do work
Indicates whether a reaction will occur spontaneously or not
At equilibrium ΔG = 0

9. Reaction types Exergonic Endergonic
Chemical products have less free energy than the reactants
Energetically downhill
Spontaneous
Loses free energy
ΔG is negative
- ΔG is the max amount of work the reaction can perform
Endergonic
Products have more free energy than reactants
Energetically uphill
Non-spontaneous
Requires energy
ΔG is positive
+ ΔG is the minimum amount of work required to drive the reaction

11. Applying Concepts…
REACTION
REACTANTS
PRODUCTS ΔG
Hydrolysis of sucrose
Sucrose + H2O
Glucose + Fructose
7.0
Triglyceride attachment
Glycerol + fatty acid
Monoglyceride
3.5
Photosynthesis
6CO2 + 6H2O
Glucose + 6O2
686
The table shows some reactions and the absolute values of their associated free energy changes (ΔG).
For each reaction, would you expect ΔG to be positive or negative?
Which reactions will be spontaneous? Explain your answers.
Hydrolysis of sucrose = negative free energy and therefore spontaneous (Hint: from complicated to less complicated molecules – catabolic reaction); more disorder with the glucose and the fructose. The glycosidic bond between the two monosaccharides in sucrose creates more order.
Triglyceride attachment = positive and therefore NOT spontaneous
Photosynthesis = positive and therefore NOT spontaneous (requires energy)

12. Cellular Work
ATP powers cellular work by coupling exergonic and endergonic reactions
Cell conducts 3 main types of work: mechanical, transport, and chemical
ATP – Adenosine triphosphate

13. ATP Hydrolysis Breaking of the bonds between phosphate groups
ATP + H2O  ADP + Pi
ΔG = -7.3 kcal/mol or kJ/mol (under standard conditions

14. Energy Coupling Example

15. How ATP Performs Work

16. Regeneration of ATP
Organisms at work are constantly using ATP, but ATP can be regenerated with the addition of a phosphate to ADP
Requires energy; ΔG = +7.3 kcal/mol or kJ/mol

17. Enzymes
Enzyme – biological catalysts or catalytic protein (a chemical agent that speeds up a reaction without being consumed by the reaction)
All reactions require an initial investment of energy for starting a reaction called the activation energy (EA)
Enzymes reduce this activation energy

18. How Enzymes Work

19. Induced Fit Model Substrate – enzyme reactant
Active site – pocket or groove on enzyme that binds to substrate
Enzyme substrate complex – enzyme flexes and molds to the shape of the substrate
Analogy = baseball and a catchers mitt

20. Induced Fit Model

21. Enzyme Specificity
Enzymes function in a very specific range of environmental conditions including temperature and pH
Some enzymes require ions or other molecule partners:
Cofactors – inorganic nonprotein helpers, ex: zinc, iron, copper
Coenzymes – organic cofactors, ex: vitamins

22. Enzyme Inhibitors
Competitive inhibitors – block active site, direct competition with substrate
Noncompetitive inhibitors – bind away from the active site, not in direct competition with substrate

23. Allosteric Regulation
Allosteric regulation can be described as any case in which a protein’s function at one site is affected by the binding of a regulatory molecule to a separate site
Activation, inhibition, and cooperativity

24. Feedback Inhibition
In feedback inhibition a metabolic pathway is switched off by the binding of its end product to an enzyme that acts early in the pathway

25. Applying Concepts… The Scenario:
In the boy’s locker room a bacteria is found growing on some old socks made of a synthetic polymer.
You make a protein extract from the bacteria and isolate the probable enzyme that can cleave the monomers from the polymer.
You also synthesize a dipeptide glycine-glycine to test as a possible inhibitor of the enzyme.

26. RATE OF POLYMER CLEAVAGE
Applying Concepts…
EXPERIMENT
CONDITION
RATE OF POLYMER CLEAVAGE 1
No enzyme
0.505 2
Enzyme
825.0 3
Enzyme pre-boiled at 100 C
0.520 4
Enzyme + RNA
799.0 5
Enzyme + dipeptide
0.495
Explain the results of each experiment.
How do you think the dipeptide works? How would you test your hypothesis?