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Energy:
the capacity to do work
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-kinetic energy:
the energy of motion
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-potential energy:
stored energy
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Energy can take many forms:
- mechanical electric current
- heat light
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Most forms of energy can be converted to
heat energy.
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Heat energy is measured in
kilocalories.
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One calorie =
the amount of heat required to raise the temp of water by 1oC
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1 kilocalorie (kcal) =
1000 calories
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Potential energy stored in
chemical bonds can be transferred from one molecule to another by way of electrons.
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oxidation:
loss of electrons
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reduction:
gain of electrons
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First Law of Thermodynamics –
- energy cannot be created or destroyed
- -energy can only be converted from one form to another
- For example:
- sunlight energy chemical energy
- photosynthesis
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Second Law of Thermodynamics:
- disorder is more likely than order
- entropy: disorder in the universe
- The 2nd Law of Thermodynamics states that entropy is always increasing.
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Free energy:
- the energy available to do work
- -denoted by the symbol G (Gibb’s free energy)
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enthalpy:
- energy contained in a molecule’s chemical bonds
- free energy = enthalpy – (entropy x temp.)
- G = H - TS
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Chemical reactions can create changes in free energy:
DG = DH - T DS
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When products contain more free energy than reactants –
DG is positive.
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When reactants contain more free energy than products –
DG is negative.
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Chemical reactions
can be described by the transfer of energy that occurs
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endergonic reaction:
- a reaction requiring an input of energy
- - DG is positive
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exergonic reaction:
- a reaction that releases free energy
- - DG is negative
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activation energy:
- extra energy needed to get a reaction started
- -destabilizes existing chemical bonds
- -required even for exergonic reactions
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catalysts:
substances that lower the activation energy of a reaction
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ATP = adenosine triphosphate
-the energy "currency" of cells
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ATP structure:
- -ribose, a 5-carbon sugar
- -adenine
- -three phosphates
- ATP stores energy in the bonds between phosphates.
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Phosphates are highly negative, therefore:
- -the phosphates repel each other
- -much energy is required to keep the phosphates bound to each other
- -much energy is released when the bond between two phosphates is broken
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When the bond between phosphates is broken:
- ATP ADP + Pi
- energy is released
- ADP = adenosine diphosphate
- Pi = inorganic phosphate
- This reaction is reversible.
- The energy released when ATP is broken down to ADP can be used to fuel endergonic reactions.
- The energy released from an exergonic reaction can be used to fuel the production of ATP from ADP + Pi.
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Enzymes:
- molecules that catalyze reactions in living cells
- -most are proteins
- -lower the activation energy required for a reaction
- -are not changed or consumed by the reaction
- Enzymes interact with substrates.
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substrate:
molecule that will undergo a reaction
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active site:
- region of the enzyme that binds to the substrate
- Binding of an enzyme to a substrate causes the enzyme to change shape, producing a better induced fit between the molecules.
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Multienzyme complexes offer certain advantages:
- 1. The product of one reaction can be directly delivered to the next enzyme.
- 2. The possibility of unwanted side reactions is eliminated.
- 3. All of the reactions can be controlled as a unit.
- Not all enzymes are proteins.
- Certain reactions involving RNA molecules are catalyzed by the RNA itself.
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ribozymes:
- RNA with enzymatic abilities
- For example, the ribosome is a ribozyme.
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Enzyme function is affected by its environment.
- Factors that can change an enzyme’s 3-dimensional shape can change its function.
- -for example, pH, temperature, regulatory molecules
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Temperature
- -enzyme activity may be increased with increasing temp, up to the temp optimum
- -temperatures too far above the temp optimum can denature the enzyme, destroying its function
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pH –
most enzymes prefer pH values from 6 to 8.
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Inhibitors
are molecules that bind to an enzyme to decrease enzyme activity.
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-competitive inhibitors
compete with the substrate for binding to the same active site
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-noncompetitive inhibitors
bind to sites other than the enzyme’s active site
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Allosteric enzymes
- exist in either an active or inactive state.
- -possess an allosteric site where molecules other than the substrate bind
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allosteric inhibitors
bind to the allosteric site to inactivate the enzyme
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allosteric activators
bind to the allosteric site to activate the enzyme
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Metabolism:
all chemical reactions occurring in an organism
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Anabolism:
chemical reactions that expend energy to make new chemical bonds
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Catabolism:
chemical reactions that harvest energy when bonds are broken
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Some enzymes require additional molecules for proper enzymatic activity.
These molecules could be:
- -cofactors:
- usually metal ions, found in the active site participating in catalysis
- -coenzymes:
- nonprotein organic molecules, often used as an electron donor or acceptor in a redox reaction
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Biochemical pathways
- are a series of reactions in which the product of one reaction becomes the substrate for the next reaction.
- Biochemical pathways are often regulated by feedback inhibition in which the end product of the pathway is an allosteric inhibitor of an earlier enzyme in the pathway.
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