the capacity to do work
the energy of motion
Energy can take many forms:
- mechanical electric current
- heat light
Most forms of energy can be converted to
Heat energy is measured in
One calorie =
the amount of heat required to raise the temp of water by 1oC
1 kilocalorie (kcal) =
Potential energy stored in
chemical bonds can be transferred from one molecule to another by way of electrons.
loss of electrons
gain of electrons
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
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.
- the energy available to do work
- -denoted by the symbol G (Gibb’s free energy)
- energy contained in a molecule’s chemical bonds
- free energy = enthalpy – (entropy x temp.)
- G = H - TS
Chemical reactions can create changes in free energy:
DG = DH - T DS
When products contain more free energy than reactants –
DG is positive.
When reactants contain more free energy than products –
DG is negative.
can be described by the transfer of energy that occurs
- a reaction requiring an input of energy
- - DG is positive
- a reaction that releases free energy
- - DG is negative
- extra energy needed to get a reaction started
- -destabilizes existing chemical bonds
- -required even for exergonic reactions
substances that lower the activation energy of a reaction
ATP = adenosine triphosphate
-the energy "currency" of cells
- -ribose, a 5-carbon sugar
- -three phosphates
- ATP stores energy in the bonds between phosphates.
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
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.
- 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.
molecule that will undergo a reaction
- 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.
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.
- RNA with enzymatic abilities
- For example, the ribosome is a ribozyme.
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
- -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
most enzymes prefer pH values from 6 to 8.
are molecules that bind to an enzyme to decrease enzyme activity.
compete with the substrate for binding to the same active site
bind to sites other than the enzyme’s active site
- exist in either an active or inactive state.
- -possess an allosteric site where molecules other than the substrate bind
bind to the allosteric site to inactivate the enzyme
bind to the allosteric site to activate the enzyme
all chemical reactions occurring in an organism
chemical reactions that expend energy to make new chemical bonds
chemical reactions that harvest energy when bonds are broken
Some enzymes require additional molecules for proper enzymatic activity.
These molecules could be:
- usually metal ions, found in the active site participating in catalysis
- nonprotein organic molecules, often used as an electron donor or acceptor in a redox reaction
- 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.