1. An introduction to metabolism
Chapter 3
An introduction to metabolism

2. Metabolism and Energy
The sum of all the reactions that take place in our cells.
Reactions require ENERGY
Energy is the ability to do work (cellular work)
Different types of energy
Chemical, Electrical, Mechanical, Light, Thermal
Each form of energy can be converted to other forms
Energy can exist in two states
Kinetic energy
Occurs as a result of motion (molecules, ions moving in solution)
Potential energy
Stored within an object (chemical bonds, glucose)

3. Energy Obeys Laws The First Law of Thermodynamics Photosynthesis
The total amount of energy in any closed system is constant.
Energy cannot by created or destroyed; it can only be converted from one form to another.
If a physical system gains an amount of energy, another physical system must experience a loss of energy of the same amount
Photosynthesis
Sunlight converts to chemical energy
Cellular Respiration
Convert chemical energy into mechanical energy (muscle contraction)

4. Conversion of Energy Depends on Combustion of methane (CH₄)
Breaking and formation of chemical bonds in a chemical reaction
Energy is absorbed when breaking bonds
Energy is released when forming bonds
Combustion of methane (CH₄)
Mole
6.022 x 10²³ of atoms of a certain element
Gives each element on the periodic table its certain atomic mass
1 mol of carbon dioxide
1 mol of methane
2 mol of oxygen
2 mol of water

5. Bond Energy Measure of the strength or stability of a covalent bond.
Measured in (kJ/mol)
Different amounts of energy are required to break different types of bonds
Activation Energy
The minimum amount of energy needed to break bonds and start a chemical reaction (match needed to start combustion reaction)

6. Chemical Reaction
Activation energy required
Reaches transition state
Temporary condition in which bonds in the reactants have reached breaking point and new bonds are ready to form in products.
Two types
Exothermic reaction
Net release of energy
Endothermic reaction
Net absorption of energy
BEabsorbed – BEreleased = Net energy released/absorbed

7. Energy Obeys Laws The Second Law of Thermodynamics Entropy
In every energy transfer or conversion, some of the useful energy in the system becomes unusable and increases the entropy of the universe.
Entropy
A measurement of disorder in a system
Always increases whenever there is a chemical reaction
Increases when
Solids react to form liquids or gases
Liquids react to form gaseous products
Total number of product molecules is greater than the total number of reactant molecules

8. Spontaneous vs Non-Spontaneous Change
Predict whether a chemical reaction will occur without the continuous input of additional energy
Spontaneous
Will continue to occur on its own (lit match)
No additional energy required
Three Factors to determine whether a reaction will happen spontaneously (favourable)
Energy changes - exothermic changes – release of energy
Entropy – increase
High temperatures
Non-spontaneous
Will not continue to occur on its own (boiling pot of water)
Additional energy is required
Factors determining whether a reaction will not happen (not favoured)
Energy changes – endothermic – absorption of energy
Entropy decreases – increasing order
Low temperatures

9. Favoured vs Not Favoured

10. Gibbs Free Energy Energy that is not lost during a reaction
Represented by the symbol G
Applies to both chemical and physical processes
Always a reduction in the amount of free energy after completion of process
Responsible for (living organisms)
Synthesis of molecules
Reproduction
Movement
Represented by
∆G = Gfinal state – Gintitial state

11. ∆G = Gfinal state – Gintitial state
Difference in the free energy of the final state of molecules to the free energy of the initial state
Negative values (-∆G) (spontaneous)
Free energy of products is less than free energy of reactants
Gives off free energy
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O ∆G = kJ/mol glucose oxidized
Exergonic reaction – releases free energy
Positive values (+∆G) (non-spontaneous)
Free energy of products is more than free energy of reactants
Must gain free energy to occur
This reaction cannot happen on its own
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ ∆G = kJ/mol glucose formed
Endergonic reaction – requires energy

12. Exergonic vs Endergonic
Every type of cell in every organism continuously carries out thousands of these reactions

13. Coupled Reactions
Transfer of energy from an exergonic reaction to an endergonic reaction
Free energy from exergonic reaction drives endergonic reaction
When combined free energy is released and both reactions occur spontaneously
A → B + C ∆G = - 5 kJ/mol D + E → F ∆G = +4 kJ/mol

14. Catabolic vs Anabolic Two types of pathways Catabolic Anabolic
Complex molecules are broken down into simpler compounds
Release free energy
-∆G
Anabolic
Build complicated molecules from simpler molecules
Consumes free energy
+ ∆G

15. ATP Adenosine triphosphate
Supplies energy that powers nearly every cellular function
Energy “currency”

16. Where Does Energy From ATP Come From?
Consists of
Nitrogenous base (adenine)
5 carbon sugar (ribose)
3 phosphate groups
Free energy comes from the three negatively charges phosphate groups

17. Hydrolysis of ATP Catabolic reaction
Phosphate group is broken off using water
Two products formed
Adenosine diphosphate (ADP)
Inorganic phosphate (Pi)
H⁺ released into solution
ATP + H₂O → ADP + Pi ∆G = kJ/mol

18. ATP and Energy Coupling
Release of a phosphate group (ATP) attaches itself to a reactant molecule - phosphorylation
Molecule gains free energy becoming more reactive
Enzyme brings ATP molecule and reactant molecule together – allow for transfer of phosphate group

19. Regeneration of ATP
ATP molecules must be generated for cells to keep functioning
Cells generate ATP by combining ADP with Pi
Reaction called ATP synthesis
Requires free energy
Where do we obtain energy to create ATP?
Food
Breakdown of carbohydrates, fats proteins
All are sources of free energy

20. ATP Cycle
ATP is hydrolyzed and resynthesized at least 10 million times per second in our cell

21. Enzymes and Activation Energy
Metabolism in organisms would be slow if enzymes were not present
Just because a reaction can proceed on its own does not mean that it will proceed.
Speed at which a reaction occurs is increased by enzymes
Almost all enzymes are proteins
RNA molecules can also function as enzymes
Only function of enzyme
Lower the potential energy level of the transition state.
Catalyzed reactions written with enzyme name above reaction arrow
Name of enzyme ends in “-ase” and is usually based on substrate

22. What Provides Activation Energy for A Chemical Reaction?
Thermal Energy – combustion reactions
Combustion of propane
A small spark is enough energy for some reactants to overcome the activation barrier
Increase in temperature is bad in biology
Destroy structural components of some proteins and DNA
Speed up all of the reactions in a cell

23. Enzymes Lower Activation Energy

24. How do Enzymes Reduce Activation Energy?
Important – Substrate molecules need to be in transition state for a reaction to proceed.
Enzymes can achieve this in 3 different ways
Bring molecules together (a)
Expose reactant molecules to altered charge environments (b)
Active site contains ionic groups with (+) or (-) charges
Change the shape of the substrate (c)
Weakens its chemical bonds reducing energy required to break them (induced fit model)

25. Food as Fuel
C –H bonds
Position of electrons to atomic nuclei of carbon and hydrogen
Electrons are approx equidistant from two small nuclei (high energy)
Farther away an electron is from the nucleus the more potential energy it has
Size of nucleus affects
potential energy
Electrons are more strongly
attracted to a larger nucleus than
a smaller one

26. Energy Changes During Oxidation
Oxidation of glucose (exergonic)
Transfer of electrons to O₂
Controlled oxidation
Cells are able to capture more free energy and produce less waste thermal energy
Occurs through a series of enzyme-catalyzed reactions
Energy released transfers to energy-carrying molecules

27. Energy Carriers Dehydrogenases (Class) NAD⁺
Facilitate transfer of high-energy electrons from food molecules
NAD⁺
Nicotinamide adenine dinucleotide
Important in metabolic processes
Remove two hydrogen atoms from a substrate molecule
NAD⁺ becomes reduced to NADH
Other H⁺ is released into cytosol
Facilitate the synthesis of ATP