Chapter 8 - Energy, Enzymes and Metabolism Flashcards
Catabolism
Subset of metabolic reactions where molecules are broken down; release of energy from the breakdown into the subunits
Anabolism
Subset of metabolic reactions where simple molecules/smaller units are combined to create complex molecules; requires an input of energy
Metabolism
The sum total of all the chemical reactions occurring in a biological system at a given time
Energy coupling
Energy production reactions of catabolism are used to drive the energy requiring reactions of anabolism; anabolic reactions utilize the stored energy in molecules such as ATP, NADH, NADPH, FADH2; catabolic reactions release energy that is then stored in molecules such as ADP, NAD+, NADP+ and FAD
Energy
Capacity to do work or the capacity for change
Potential Energy
Energy stored as chemical bonds, concentration gradients or electric charge imbalances
Kinetic Energy
The energy of movement
First law of thermodynamics
Law of conservation of energy; energy of the universe is constant; energy cannot be created or destroyed, energy can only be transformed from one type to another
Second law of thermodynamics
All energy transfers or transformations make the universe more disordered (increases entropy); no energy transformation is 100% efficient, some energy is lost to disorder; overall, the universe increases disorder
Gibbs Free Energy, G
The portion of a system’s energy that is able to perform work when T (temperature) is uniform throughout a system; change in G is a measure of instability of a system, high G = unstable
Spontaneous reaction
Can occur without assistance; reaction will move forward without assistance; increases the stability of a system; -G
Non-spontaneous reaction
Can only occur if energy is added; reaction cannot move forward without outside intervention; decreases the stability of a system; +G
Exergonic/Exothermic reactions
Catabolic reactions; net release of free energy; -G; spontaneous; stability of system increases; reactants have more energy than products
Endergonic/Endothermic reactions
Anabolic reactions; requires energy from its environment; +G; non-spontaneous; stability of system decreases; reactants have less energy than products
ATP
Adenosine triphosphate; the source of energy for cellular work; can hold and transfer free energy
ATP hydrolysis
Exergonic reaction that involves the breakdown of ATP and a release of free energy; ATP releases a large amount of energy when it undergoes phosphorylation: donates a terminal phosphate group to another molecule to activate the molecule; yields G: -7.3 kcal/mol under standard conditions
ATP formation
Endergonic reaction that requires free energy to form ATP; cells add an inorganic phosphate to ADP to form ATP; G = +7.3 kcal/mol
Energy coupling cycle
If a negative delta G, then the energy provided by ATP is sufficient to move a reaction forward (-G = more energy released); each ATP molecule undergoes about 10,000 cycles of synthesis and hydrolysis a day
Enzyme
Biological catalyst (most are proteins) that speeds up the rate of reaction by reducing the activation energy requirement, but is not altered by the reaction, meaning that the catalyst ends up in the same chemical condition before and after the reaction; enzymes are specific to one type of reaction and interact with specific reactants (aka substrates)
Activation energy
The amount of energy needed to initiate a reaction; amount of energy needed to change reactants into unstable molecular forms called transition state intermediates to initiate a reaction
Transition state
To get the bonds into a state that allows them to break, the molecule must be contorted (deformed, or bent) into an unstable/high energy state; activation energy is added to molecules to transform the molecules into an unstable state to initiate the reaction
Where does the activation energy come from?
To speed up a reaction in a living system, an enzyme lowers the energy barrier by bringing the reactants close together
Substrate
Reactants that bind to the active site of the enzyme
Active site
Sequestered site on the enzyme where the reaction is more favored to move forward; the 3D shape of the enzyme determines the specific types of substrates that can bind to the active site
Enzyme-substrate complex
Binding of a substrate to the active site of an enzyme; held together by hydrogen bonds, electrical attraction or covalent bonds
How do enzymes help a reaction move forward?
Orientation of the substrate: aligns the molecules to bind, initiating the reaction and creating products at a faster rate; induces strain in the the bonds of the substrates, putting it in a reactive transition state; temporarily adds chemical groups that make the substrate more reactive or prone to build or break
Induced fit
Enzyme changes shape when it binds the substrate, which alters the shape of the active site, improving the catalytic ability of the enzyme and providing favorable conditions for the reaction to move forward
Prosthetic groups
Non-protein enzyme partners that are non-amino acid groups bound to enzymes: ie. heme, FAD
Inorganic cofactors
Non-protein enzyme partners that are ions (Cu, Zn, Fe) permanently bound to enzyme
Coenzymes
Non-protein enzyme partners that are small carbon-containing molecules that are not permanently bound; moves from enzyme to enzyme adding or removing chemical groups from the substrate; ie. ATP, coenzyme A, NAD
Maximum rate of catalyzed reaction
The higer the concentration of substrate, the faster the rate of reaction; however; once the number of enzymes are satured with substrates, the reaction rate levels off; nothing is gained by adding more substrate, because no free enzyme molecules are left to act as catalysts
Irreversible enzyme inhibitors
Inhibitors that covalently bind to certain side chains at the active site of the enzyme; permanently inactivates the enzyme by destroying its ability to interact with its normal substrate
Enzyme inhibitor
Chemicals that bind to enzyme that slow down the rates of reactions; reduces enzyme activity
Competitive inhibitors
Inhibitors that are similar enough to the enzyme’s natural substrate competes for the active site, binding non-covalenty to the active site; reduces the amount of output of the reaction; prevents the substrate from entering the active site
Uncompetitive inhibitors
Enzyme inbitors that bind to the enzyme-substrate complex after the subtrate binds to the active site; prevent products from being released from the active site
Noncompetitive inhibitors
Enzyme inhibitors that bind to the enzyme at a location other than the active site that alters the shape of the enzyme; the conformation change either inactivates the active site or reduces the rate of product formation
Allosteric regulation
An effector molecule (activator or inhibitor) binds to an allosteric site (not an active site), inducing the enzyme to change shape; an activator binds to an allosteric site, allowing the enzyme to take proper shape for substrate binding; an inhibitor binds to an allosteric site changing the shape of the enzyme, disabling the active site
Allosteric enzyme
Quaternary protein where the active site is on the catalytic subunit and the activators and inhibitors bind to the regulatory subunits
Allosteric enzyme rate of reaction
Rate of reaction is very sensitive to substrate concentration; after the substrate binds to the first active site, there is a change in the quaternary structure and other sites become more likely to bind to substrates, speeding up the reaction
Feedback inhibition
When an end product of a reaction is in high concentration, some of the end product binds to an allosteric site on the commitment step enzyme, causing the enzyme to become inactive/shut down; the end product acts as a noncompetitive inhibitor
Isozyme
Enzyme that catalyzes the same reaction but have different optimal properties (such as temperature of pH)
