1. Enzymes & Metabolism: Part 1 Unit 5

2. Metabolism is the sum of an organism’s chemical reactions
Metabolism arises from interactions between molecules within the cell

3. A metabolic pathway begins with a specific molecule and ends with a product
Each step is catalyzed by a specific enzyme

4. ENZYMES THAT WORK TOGETHER IN A PATHWAY CAN BE
Concentrated in specific location
Covalently bound in complex
Soluble with free floating
intermediates
Attached to a membrane in sequence
Biochemistry Lehninger

5. CATABOLIC PATHWAY (CATABOLISM) Release of energy by the breakdown of complex molecules to simpler compounds EX: digestive enzymes break down food
ANABOLIC PATHWAY (ANABOLISM) consumes energy to build complicated molecules from simpler ones EX: linking amino acids to form proteins
E.g.: Hydrolysis
E.g.: Dehydration Synthesis

6. Forms of Energy ENERGY = capacity to cause change
Energy exists in various forms (some of which can perform work)
Energy can be converted from one form to another

7. KINETIC ENERGY – energy associated with motion
HEAT (thermal energy) is kinetic energy associated with random movement of atoms or molecules
POTENTIAL ENERGY = energy that matter possesses because of its location or structure
CHEMICAL energy is potential energy available for release in a chemical reaction

8. THERMODYNAMICS = the study of energy transformations
Organisms are open systems
OPEN system energy + matter can be transferred between the system and its surroundings

9. The First Law of Thermodynamics
= energy of the universe is constant
Energy cannot be created or destroyed
CONSERVATION OF ENERGY

10. The Second Law of Thermodynamics
During every energy transfer or transformation
entropy (disorder) of the universe INCREASES
some energy is unusable, often lost as heat (endotherms)

11. ORGANISMS are energy TRANSFORMERS!
Second law of thermodynamics
First law of thermodynamics
Chemical
energy
Heat
CO2
H2O
ORGANISMS are energy TRANSFORMERS!
Spontaneous processes occur without energy input; they can happen quickly or slowly
For a process to occur without energy input, it must increase the entropy of the universe

12. Free-Energy Change (G) can help tell which reactions will happen
∆G = change in free energy ∆H = change in total energy (enthalpy) or change in heat
∆S = entropy (disorder) T = temperature
∆G = ∆H - T∆S
Only processes with a negative ∆G are spontaneous
Spontaneous processes can be harnessed to perform work

13. Exergonic and Endergonic Reactions in Metabolism
EXERGONIC reactions (- ∆G)
Release energy
are spontaneous
ENDERGONIC reactions (+ ∆G)
Absorb energy from their surroundings
are non-spontaneous

14. A cell does three main kinds of work:
ATP powers cellular work by coupling exergonic reactions to endergonic reactions
A cell does three main kinds of work:
Mechanical (cilia, muscle contractions)
Transport (movement of molecules)
Chemical (making polymers)
In the cell, the energy from the exergonic reaction of ATP hydrolysis can be used to drive an endergonic reaction
Overall, the coupled reactions are exergonic

15. Reactants: Glutamic acid
LE 8-11 P i P
Motor protein
Protein moved
Mechanical work: ATP phosphorylates motor proteins
Membrane
protein
ADP
ATP + P i P P i
Solute
Solute transported
Transport work: ATP phosphorylates transport proteins P
NH2 +
NH3
Glu + P i
Glu
Reactants: Glutamic acid
and ammonia
Product (glutamine)
made
Chemical work: ATP phosphorylates key reactants

16. Energy to charge ATP comes from catabolic reactions
ATP (adenosine triphosphate) is the cell’s renewable and reusable energy shuttle
Energy to charge ATP comes from catabolic reactions
Adenine
Phosphate groups
Ribose

17. Energy for cellular work provided by the loss of phosphate from ATP
Energy from catabolism
(used to charge up ADP into ATP
ADP + P i

18. hydrolysis Endergonic reaction:
DG is positive, reaction is not spontaneous
NH2 +
NH3
DG = +3.4 kcal/mol
Glu
Glu
Glutamic
acid
Ammonia
Glutamine
Exergonic reaction:
DG is negative, reaction is spontaneous
ATP +
H2O
ADP P +
DG = –7.3 kcal/mol i
hydrolysis
Coupled reactions:
Overall DG is negative;
Together, reactions are spontaneous
DG = –3.9 kcal/mol

19. Every chemical reaction between molecules involves
bond breaking and bond forming
ACTIVATION ENERGY = amount of energy required to get chemical reaction started
Activation energy is often supplied in the form
of heat from the surroundings
IT’S LIKE PUSHING A
SNOWBALL UP A HILL . . .
Once you get it up there,
it can roll down by itself

20. The Activation Energy Barrier
LE 8-14
The Activation Energy Barrier A B C D
Transition state A B EA
Free energy C D
Reactants A B
DG < O C D
Products
Progress of the reaction

21. CATALYST = a chemical agent that speeds up a reaction without being consumed by the reaction
ENZYMES = biological catalysts Most enzymes are PROTEINS Exception = ribozymes (RNA)

22. ENZYMES work by LOWERING ACTIVATION ENERGY;
Course of
reaction
without
enzyme EA
without
enzyme
EA with
enzyme
is lower
Reactants
Free energy
Course of
reaction
with enzyme
DG is unaffected
by enzyme
Products
Progress of the reaction
ENZYMES work by LOWERING ACTIVATION ENERGY;

23. ENZYMES LOWER ACTIVATION ENERGY BY
Orienting substrates correctly
Straining substrate bonds
Providing a favorable microenvironment
Enzymes change ACTIVATION ENERGY but NOT energy of REACTANTS or PRODUCTS

24. ENZYMES Most are proteins Lower activation energy Specific
Shape determines function
Reusuable
Unchanged by reaction
Image from:

25. The REACTANT that an enzyme acts on = SUBSTRATE
Enzyme + substrate = ENZYME-SUBSTRATE COMPLEX
Region on the enzyme where the substrate binds = ACTIVE SITE
Substrate held in active site by WEAK interactions (ie. hydrogen and ionic bonds)

26. LOCK & KEY Active site on enzyme fits substrate exactly
TWO MODELS PROPOSED
LOCK & KEY Active site on enzyme fits substrate exactly
INDUCED FIT Binding of substrate causes change in active site so it fits substrate more closely