Lesson 2: Energy and Enzymes Flashcards
What is a chemical reaction?
Occurs when atoms have enough energy to combine or change bonding partners
What is metabolism?
The SUM TOTAL of all chemical reactions
How do metabolic reactions involve energy changes?
1) An input of energy is needed to build things (like macromolecules) -> think condensation
2) Energy is generated when things (like macromolecules) are broken down -> think hydrolysis
What is energy?
The capacity to do work, or the capacity for change
What are the two types of metabolism?
Anabolic and catabolic reactions
What is an anabolic reaction?
Complex molecules are MADE from simple molecules; energy is required (ex: condensation reactions)
What is a catabolic reaction?
Complex molecules are BROKEN DOWN to simple ones; energy is released (ex: hydrolysis reactions)
How are catabolic and anabolic reactions linked?
Catabolic pathways produce subunits and releases energy that can be used for anabolic pathways
What is free energy (G)?
The usable energy for work
What is an exergonic reaction?
Reactions that release free energy (- delta G). They are spontaneous
ex: catabolism (hydrolysis reactions)
What is an endergonic reaction?
Reactions that consume free energy (+ delta G). They are non-spontaneous
ex: anabolism (condensation reactions)
What are more characteristics of an exergonic reaction?
- High energy state to a low energy state (energetically favorable)
- The free energy of the reactants is HIGHER than the
free energy of the products (- delta G)
What are more characteristics of an endergonic reaction?
Low energy state to a high energy state (energetically unfavorable)
- The free energy of the reactants is LOWER than the
free energy of the products (+ delta G)
The activation energy for an endergonic reaction is MUCH LARGER than for an exergonic reaction. Therefore, this reaction must be coupled to an exergonic reaction to overcome the energy barrier
What is the activation energy?
The amount of energy required to start the reaction (activation energy must be added for the molecule to reach the TRANSITION STATE)
- higher activation energy -> slower the reaction
- lower activation energy -> faster the reaction
What is the transition state?
As the reaction goes from reactants to products, the molecules must be contorted into an unstable higher energy state (which is the the TRANSITION STATE)
What are enzymes?
Enzymes are primarily proteins and they are highly specific.
They serve as catalysts that lower the activation energy (energy barrier) for reactions, specifically exergonic reactions. Therefore, they increase the rate of chemical reactions.
What determines the specificity of an enzyme?
The 3-D shape and composition of the enzyme determines the specificity (noncovalent interactions allow the enzyme to bind its substrate/reactant)
How do enzymes reduce the activation energy?
By providing the framework in which reactions can take place. They stabilize the structure of the transition state.
Note: Enzymes can increase reaction rates by 1 million to 10^17 times
What is another function of an enzyme?
Many enzymes participate directly in the catalytic process. Enzymes can form or break chemical bonds.
ex: amylase, sucrase, lactase, or maltase can break down carbohydrates
What are the steps for how enzymes work?
1) Substrate binds to enzyme
2) Substrate is converted to products
3) Products are released
4) Active site is available for another substrate
- Enzyme is left completely unchanged (enzyme can be used over and over)
Can enzymes overcome the activation energy for an endergonic reaction?
No, the activation energy is too large and MUST be coupled with an exergonic reaction.
Note: enzymes can still stabilize the transition state and break/form bonds in endergonic reactions.
What is reaction coupling?
The activation energy for an endergonic reaction is too large and cannot occur UNLESS it is coupled to an exergonic reaction. This results in a NEGATIVE net free-energy change for the pair of reactions.
Describe the steps of reaction coupling.
1) If you want to form a polymer, the reaction must be coupled with an exergonic reaction or it will not occur.
2) ATP hydrolysis (ATP –> ADP + P) is an example of an exergonic reaction that will power the energetically unfavorable condensation reaction.
3) ACTIVATION STEP: ATP can transfer a phosphate group to the reactants to produce a high-energy intermediate. The reaction will now become energetically favorable since we are going from a high energy to low energy state.
4) CONDENSATION STEP: This high energy intermediate reacts with the other reactant to form the product.
What is ATP?
ATP is a nucleotide and stands for adenosine triphosphate
- An active cell must produce millions of molecules of ATP per second
- An ATP is typically consumed within a second of its formation
- Each ATP molecule undergoes about 10,000 cycles of synthesis and hydrolysis every day!
How is ATP an activated carrier?
ATP transfers and captures free energy through ATP hydrolysis and condensation
What are two characteristics of ATP that account for the free energy released?
1) Phosphate groups have negative charges and repel each other – the energy needed to get them close enough to bond is stored in the P~O bond.
- Therefore, when you remove a phosphate group. All
this energy needed to keep them close together will be
released.
2) The free energy of the P~O bond is much higher than the energy of the O~H bond that forms after hydrolysis.
- After you remove a phosphate group, it becomes a P-O-
H bond which is more energetically favorable, therefore
energy is released.
How is ATP hydrolysis reversible?
Cells often use the energy released from ATP hydrolysis to fuel the regeneration of ATP from ADP + P
