Exam 2: Energy and Enzymes Flashcards
In what 2 circumstances do reactions take place?
- Reactants collide in precise orientation
- Reactants have enough kinetic energy to overcome repulsion b/t the electrons that come in contact during bond formation (activation energy)
What is energy?
The ability to promote change or do work
2 forms of energy
kinetic and potential
Kinetic energy is associated with…
Movement
Potential energy is associated with…
Structure/location
Chemical energy
energy in molecular bonds, form of potential energy
=> structure of a molecule determines potential energy
First Law of Thermodynamics
Energy cannot be created or destroyed, but can be transformed
Second Law of Thermodynamics
Transfer of energy from one form to another INCREASES THE ENTROPY of a system => as entropy increases, there is less energy available for organisms to use
Where do electrons have high potential energy
In outer electron shells
Formula for free energy change
ΔG=ΔH-TΔS
ΔG
Change in free energy
ΔH
Change in total energy (enthalpy)
T
Temperature in Kelvin
ΔS
Change in entropy
ΔG > 0
endergonic
ΔG < 0
exergonic
Which type of reaction occurs spontaneously?
exergonic
Which type of reaction is thermodynamically favored?
Exergonic
How can you conduct an endergonic reaction?
Couple it with an exergonic reaction
What are 2 ways in which energetic coupling occurs?
- Transfer of high energy electrons
- Transfer of a phosphate group
What are 3 examples of coupled reactions?
- Redox reactions: electron transfer
- Electron carriers: NADH and FADH2 both receive high energy electrons to deliver to the right places
- ATP driven reactions: include high energy electrons
What are redox reactions?
Reactions that involve transfer of electrons
The more CH bonds…
The more reduced it is
The less CH bonds…
The more oxidized it is
Reduced molecules have higher or lower potential energy?
Higher, gains a proton
oxidized molecules have higher or lower potential energy?
Lower, loses a proton
What is NADH
Electron carrier; has reducing power (can give its electrons)
Why does ATP have high potential energy
The 3 negatively charged phosphate groups are very close together
What is phosphorylation
Transferring a phosphate group
What does the hydrolysis of ATP result in
ADP and inorganic phosphate
Is hydrolysis endergonic or exergonic
Exergonic, the entropy (disorder) of the products is higher
What happens to the energy released during ATP hydrolysis?
It is transferred to a protein during phosphorylation and usually causes a change in the protein’s shape
3 factors affecting reaction rates
- concentration of reactants
- temperature
- catalysts
How does concentration of reactants affect reaction rates?
Higher reactant concentration => higher opportunity for interaction
How does temperature affect reaction rates?
Heat causes molecules to move more rapidly and collide => speeds up reaction times
Cold causes molecules to move more slowly and collide less => slows reaction times
How do catalysts affect reaction rates?
They help to trigger reactions (important biological catalysts are enzymes)
What is induced fit?
Enzyme undergoing a conformational change when substrates bind to active site
What 2 functions do enzymes perform?
- Bring substrates together in precise orientation so electrons involved in the reactions can interact
- Lower activation energy
What is activation energy?
Amount of free energy required to reach transition state i.e. start a reaction
Enzymes can catalyze in 3 different ways:
- bring substrates closer and in proper orientation
- strain the substrate
- control the chemistry of the active site
While enzymes can speed up reactions,
they cannot make reactions spontaneous i.e. they only act on exergonic reactions
Steps of enzyme catalysis
- Initiation
- Transition state facilitation
- Termination
Initiation
Reactants bind to active site in specific orientation => enzyme-substrate complex
Transition state facilitation
interactions between enzyme and substrates lowers activation energy
Termination
Products released, enzyme unchanged
What 2 things limit rate of catalysis? What does this mean?
- Substrate present
- Enzyme available
=> enzymes are saturable
What does it mean for an enzyme to be saturated?
The max # of substrates are present/all active sites are occupied by the substrate
What is velocity on an enzyme graph?
Moles of product formed per second
Vmax
Max rate of moles of product formed per second in reaction
When enzyme is saturated, reaction can’t proceed any quicker (horizontal asymptote)
Km
Substrate concentration at half of Vmax
What does a lower Km indicate?
More efficient enzyme b/c it achieves half of its Vmax consuming less substrate concentration
2 types of enzyme inhibitors
Competitive, Non-competitive
Which enzyme inhibitor binds to the active site? What does this do?
Competitive, interferes with active site so substrate cannot bind
Which enzyme inhibitor doesn’t bind to the active site? What does this do?
Non-competitive, changes shape of enzyme so substrate cannot bind
Vmax and Km of enzyme when competitive inhibitor is present
Same and higher
Vmax and Km of enzyme when non-competitive inhibitor is present
Lower and same
Allosteric regulation
When a noncompetitive inhibitor activates or deactivates the enzyme
Cofactor
Inorganic ions that temporarily bind to enzyme for proper function
Coenzyme
Hold onto certain things for an enzyme to make catalysis smoother, example is NADH
Prosthetic group
Small molecule permanently attached to the enzyme
How are enzymes affected by the environment?
Most enzymes function maximally in a narrow range of temp and pH => may denature outside of that range
Metabolic pathway
Series of reactions, each step catalyzed by a different enzyme; sum of catabolic and anabolic pathways
Feedback inhibition
When an enzyme in a pathway is inhibited by the product of the reaction sequence, feedback inhibition occurs; how your cell knows when to stop
