Biology 1202B Lecture Notes - Catabolism, Endergonic Reaction

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Bioenergetics: the study of energy in living systems and the organisms that utilize it.
Potential Energy:
- Energy that matter occupies because of it's location, arrangement, or position
- Energy of position
- Ex: Water behind a dam; chemical energy (gas)
Kinetic Energy:
- Energy in the process of doing work
- Energy of motion
-Ex: Heat; Light energy
First Law of Thermodynamics:
- Energy cannot be created or destroyed but only converted to other forms
- The amount of energy in the universe is constant
Second Law of TD:
- All energy transformations are inefficient because every reaction results in entropy and the loss of usable energy
as heat
- Entropy: the amount of disorder in a system
Biological Work:
- Free energy - that part of a system's total energy that can perform work when the temp. is uniform as in a living
- Free energy is represented by G (G is two components: H [system's total energy] and S [the entrpoy of the
system]; G=H-TS [T-degreesKelvin=degreesC+273])
- Measures energy that is no longer available to perform useful work within the current environment
- Can also be understood as the 'quality' of heat flowing between two bodies
Biological Work
- The change in free energy in a system changing from one state to another is symbolized by DeltaG (Delta =
change) [Delta is the triangle]
- DeltaG=G final state - G initial state
- DeltaG= DeltaH - TdeltaS
- Change in free energy between reactants and products
Endergonic Reactions
- Chemical reaction that requires a net input of energy; Ex: photosynthesis
- DeltaG>0
- Requires free energy from surroundings
Exergonic Reactions
- Chemical reactions that releases energy; Ex: Cellular respiration
- DeltaG<0
- Spontaneous reactions
- Net release of free energy
Coupled Reaction
- Allows life to overcome its energetic barriers
- Use of an exergonic process to drive an endergonic one
Redox Reactions
- Chemical reactions that involve the transfer of 1 or more electrons from one reactant to another
- Electron transfer called: oxidation-reduction or redox reactions
- Donor=reducing agent (oxidized)
- Acceptor= oxidizing agent (reduced)
Cellular Metabolism
- The sum total off the chemical activities of all cells
- Endergonic + exergonic reactions
- Ex: anabolic and catabolic pathways
Anabolic Pathway
- metabolic reactions which consume energy (endergonic) to build complicated molecules from simpler
- Ex: photosynthesis
Catabolic Pathway
- Metabolic reactions which release energy (exergonic) by breaking down complex molecules in simpler
- Ex: Cellular respiration
- Anabolic reactions = synthesis reactions
- Catabolic reactions = breakdown reactions
- Anabolic + catabolic = metabolism
- Endergonic reactions (anabolic) - delta G > 0 (i.e. photosynthesis)
- Exergonic reactions (catabolic) - delta G < 0 (i.e. mitochondrial respiration)
ATP and Enzymes
- Biological organic molecules are composed of subunits (building blocks)
- Monomers combined to make polymers
- Very large organic molecules are called macromolecules
Common combining reaction
- Exchange reaction called dehydration synthesis (removal of an H2O)
- Reverse reaction is hydrolysis
How Does ATP Work?
- By direct chemical transfer of a phosphate group (phosphorylation)
- The exergonic hydrolysis of STP is coupled with the endergonic processes by transferring a phosphate group to
another molecule
- Transfer phosphate group from ATP to another molecule, changes its free energy so that what was an
endergonic reaction (up) becomes an exergonic reaction (down) - this is energy coupling
Chemistry in Cell
- Cell: reactants and products in the same space; chemicals interact by random collisions (total space must be
- Spontaneous reations can occur very slowly
- Enzymes spped up reactions
- Catalyst: changes rate of reaction without being consumed (i.e. enzymes)
- Chemical reactions b/t molecules, bonds must be broken (requires energy) and bonds must be made (releases
- Initial energy required to break bonds in the activation energy (EA)
- Bonds break only when molecules have absorbed enough energy to become unstable
- Chemical reactions b/t molecules involve both bond breaking and bond forming
- In exergonic reactions, the reactants must absorb energy from their surroundings, the free energy of activation or
activation energy (EA), to break bonds (this energy makes reactants unstable, increases the speed of the reactant
molecules and creates more powerful collisions)
- not only is the EA released back into the surroundings, but even more energy is released with the formation of
the new bonds
- EA - amount of energy necessay to push the reactants over an energy barrier
- At the summit, the molecules are at an unstable point, the transition state
- The difference b/t free energy of the products and the free energy of the reactants is the delta G
- For some processes, the barrier is high and the thermal energy provided by room temp is sufficent to reach the
transition state
- In most cases, EA is higher and a significant input of energy is required
- The laws of TD would seem to favour the breakdown of proteins, DNA, and other complex molecules
- Enzyme speed reactions by lowering EA
- Enzymes do not change delta G
- Enzymes are substrate specific
- A substrate is a reactant which binds to an enzyme
- When a substrate or substrates binds to an enzyme, the enzyme catalyzes the conversion of the substrate to
the product
- Enzymes - mechanisms to lower EA and speed a reaction
- Rate that a specific # of enzymes converts substrates to products depends on part on substrate concentraions
- Low substrate concentraion, an increase in substrate speeds binding to available active sites (however, there is a
limit to how fast a reaction can occur)
- At some substrate soncentrations, the active sites on all enzymes are engaged, called enzyme saturation
- The only way to increase productivity at this point is to add more enzyme molecules
- Inhibitors prevent enzymes from catalyzing reactions (competitive inhibition - same site binding) (Noncompetitive
inhibition - binds elsewhere but causes the shape of the active site to change)
- Feedback inhibition - metabolic pathway is truned off by its end product - end product acts as an inhibitor
Enzyme facts:
- Typically large proteins
- Sustrate binds to active site
- Lowers EA
- Suffix ase
- Many enzymes require cofactors