Energy, ATP, and Enzymes. Energy The ability to do work, that is, to move matter against opposing...
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Transcript of Energy, ATP, and Enzymes. Energy The ability to do work, that is, to move matter against opposing...
Energy, ATP, and Enzymes
Energy The ability to do work, that is, to move
matter against opposing forces such as gravity and friction Kinetic energy- energy of motion Potential energy- stored energy, the capacity
to do work
Thermodynamics Study of energy transformation The First Law of Thermodynamics- energy can be
transferred and transformed, but it can neither be created nor destroyed The total energy of the universe is constant Mass is a form of energy
The Second Law of Thermodynamics- every energy transfer or transformation increases the entropy of the universe There is trend toward randomness Energy must be spent to retain order- this spending of
energy usually releases heat, increases the entropy elsewhere
Free Energy- the portion of a system’s energy that can perform work
It’s called “free” energy because this is the energy which can perform work, not because there is no energy cost to the system
Exergonic Reaction- a process with a net release of free energy Sometimes called spontaneous, but that doesn’t mean that it
will occur rapidly
Endergonic Reaction- a process which absorbs free energy from the surrounding
Most synthesis are endergonic
Energy Coupling- use of exergonic process to drive an endergonic process
The free energy released from the exergonic process is absorbed by the endergonic process
Types of Cellular Work Mechanical- beating of cilia, muscle
contractions, etc. Transport- pumping of molecules and
ions across a plasma membrane against their concentration gradient, etc.
Chemical- pushing endergonic reactions that would not occur spontaneously
ATP- Power to Drive Cellular Work Adenosine triphosphate – a close
relative to Adenine, a nucleotide found in DNA Contains 3 phosphate groups connected to
each other in sequence The bonds can be broken by hydrolysis
When the terminal phosphate bond is broken, a molecule of inorganic phosphate (Pi) is formed
This forms adenosine diphosphate, ADP + Pi
This generates free energy, which can be used by the cell to do work
ATP
Enzymes and Chemical Reactions Catalyst- a chemical agent that changes the
state of a reaction without being consumed in the reaction
Substrate- reactants in an enzyme-catalyzed reaction
Intermediate- compounds formed between initial reactants and products (i.e. enzyme-substrate complex)
Products- products Cofactors- helpers for enzymes Energy Carriers- sources of quick energy
(ATP)
Enzymes are protein catalysts 99% of all enzymes are proteins Speed up reactions Work for both forward and reverse
reaction They can become saturated They are highly selective
How Energy Relates to Reaction Initial State transition state final state
Substrate must overcome an energy barrier to react and form the products
An enzyme lowers the energy barrier, thus speeding up the reaction
http://www.uic.edu/classes/bios/bios100/lectures/enzymes01.html
Lock and Key Hypothesis There is only one active site which precisely
fits the reactants (more or less)
Enzymes are Substrate Specific Enzymes bind to the substrate or substrates when
there are two or more reactants Catalytic action of the enzyme converts the
substrate(s) to product(s) Enzymes can distinguish its substrate from similar
molecules and even isomers of the same molecules
Only a restricted region of the enzyme molecule actually binds to the substrate- active site This is not perfect- as enzyme and substrate come
together, a small conformation change occurs so that the action site fits even more snugly around the substrate Induced Fit
http://www.uic.edu/classes/bios/bios100/lectures/enzymes02.html
A Cell’s Physical and Chemical Environment Affect Enzyme Activity
Temperature: a measure of molecular motion As temp increases, reaction rate will increase However, as temp increases, the molecular
motion of the enzyme also increases Enzyme’s active site may become unstable and
function poorly Bond maintaining 2o, 3o, and 4o structure of
protein collapse denatured
Temperature optimum- temperature at which enzyme exhibits peak performance
pH- a measure of [H+] – acidic or basic pH optimum- peak performance at a certain pH Extreme pH, enzyme may denature
Cofactors A non-protein enzyme helper Aid in enzyme catalytic function May be inorganic (Zn or Cu) or organic coenzymes Stabilize transition state Most vitamins are coenzymes
Most Enzymes are Regulated1. Competitive Inhibition Other molecules is “competing” for space on the active site Interfere with substrate binding…slow down reaction rate
2. Allosteric Regulation Regulatory molecules (ligands) may bind to a location
other than the active site allosteric site Allosteric activation- shape change make active site
available Allosteric deactivation or non-competitive inhibition-
shape change makes active site unavailable
3. Feedback Inhibition (Negative Feedback) When the product of a pathway acts as an
inhibitor of the pathway Prevents too much buildup of product Provides a mean of self-regulating in a system