Unit 4: Bioenergetics, ATP, and Enzymes Flashcards
State the laws of thermodynamics
First: Energy can’t be created or destroyed
Second: Energy transformations always result in an increase in entropy
Describe
Entropy
Chaos
Randomness
Unusable energy
The opposite of free energy
Describe
Free energy
Measure of instability
Usable energy
The opposite of entropy
Explain
ΔG
Changes in free energy that occurs over the course of a chemical reaction
-ΔG = the system (molecules in the reaction) has LOST free energy == exergonic
+ΔG = the system has GAINED free energy == endergonic
What is a positive ΔG?
Increase in free energy in a system
More energy in PRODUCTS than REACTANTS
Endergonic == Energy absorbed into system
What is negative ΔG?
Decrease in free energy in a system
More energy in REACTANTS than PRODUCTS
Exergonic == Energy released into environment
Define / briefly describe
Spontaneous
Exergonic
Reactions that are energetically favorable
NOT THE SAME AS “FAST”!!!
How can endergonic reactions happen?
Endergonic reactions REQUIRE energy from another source
Often “coupled” with exergonic reactions
So long as exergonic reaction RELEASES more energy than endergonic ABSORBS, the pair of reactions will still be possible
What are the types of activities cells do that require energy?
Chemical work: Coupling an exergonic reaction with an endergonic one to allow the endergonic reaction to happen
Transport: Establishing concentration gradients (which increases order / decreases entropy)
Mechanical: Moving cell parts / cytoskeleton
Describe
Energy coupling
Pairing of an exergonic reaction (releases energy!) with an endergonic one (which couldn’t happen without an input of energy from environment)
What is this molecule?
Adenosine triphosphate (ATP)
What is this part of ATP called?
A phosphate group
Specifically, the third phosphate, which is broken off when ATP -> ADP
What is this part of ATP called?
Phosphate
This is the 2nd phosphate (counting from sugar); still present in ADP
What is this part of ATP called?
Ribose
Reminder: Nucleotides contain a pentose / 5-carbon sugar, which is ribose here
What is this part of ATP called?
Adenine
Reminder: Nucleotides contain a nitrogenous base, which is adenine here
What is this part of ATP called?
Adenosine
(Ribose + Adenine)
How is ATP “used”?
ATP → ADP + Pi
The last phosphate breaks off, leaving ADP behind.
ADP and Pi contain WAY less free energy (are more stable / less reactive)
This energy is released, which can be used to do cell work
How is ATP made?
General - *not specifically asking what mechanisms are used to make ATP!
ADP + Pi → ATP
Energy must be supplied to build ATP, which has more free energy than ADP and phosphate do separately
What processes can provide the energy necessary for regenerating ATP?
Cellular respiration and photosynthesis
Define
Reaction Rate
The speed at which reactants are converted to products
Define
Catalyst
A chemical that:
1. Speeds up the rate of a chemical reaction
2. Is not used up during the reaction
Can catalysts alone make endergonic reactions happen?
NO!
Catalysts speed up reactions that would otherwise happen more slowly
BUT they don’t make reactions happen that otherwise wouldn’t be able to
Define
Enzyme
Biological molecules that act as catalysts
- Usually (but not always) proteins
- Encoded by our cells’ DNA
Define
Activation Energy
The energy that is required to break reactants / make them enter an unstable state so that they are able to react / form products
Define
Transition state
Molecular structure that is highly unstable (and thus can react)
How does activation energy limit the rate of reactions?
High activation energy: Requires system to absorb a LOT of energy, making the reaction less likely to occur -> SLOWER
What do enzymes do to the rate of reactions?
-Increase rate (more product / faster) by
-Lowering activation energy
Define
Substrate
A molecule that binds to the enzyme’s active site
The reactant of an enzyme-catalyzed reaction
Describe
Enzyme Structure
Protein (usually)
Folded polypeptide, which has an ACTIVE SITE (area where substrate bind), and potentially other sites (ALLOSTERIC SITES) for other molecules to bind
How do enzymes increase activation energy?
They don’t.
They lower them.
haha. i tricked you. or not.
How do enzymes lower activation energy?
Possible ways:
* Stress bonds, making them more likely to reach transition state
* Act as a template to place substrates together and in correct orientation
* Produce a small microenvironment where the reaction is more suitable to react
How do enzymes affect ΔG of a reaction?
They don’t.
What type of reaction?
Exergonic
-ΔG
Identify letters a through e
a: energy in the reactants
b: activation energy without enzyme
c: activation energy with an enzyme
d: ΔG
e: energy in the products
Identify letters a through e
a: energy in the reactants
b: activation energy without enzyme
c: activation energy with an enzyme
d: ΔG
e: energy in the products
What kind of reaction is this?
Endergonic (+ΔG)
Define
Denaturation
The permanent loss of 3D shape of a molecule
In proteins/enzymes: Loss of tertiary and quaternary structure
How does denaturation affect an enzyme’s ability to catalyze reactions?
Small changes to shape: slight lessening of catalytic ability
Complete denaturation: enzyme does not function
What conditions may cause an enzyme to denature?
Very high temperatures (above optimal)
Acidic conditions (below optimal pH)
Basic conditions (above optimal pH)
T/F: All enzymes have the same optimal conditions
FALSE!!!
Each enzyme has a specific optimal temp, pH, etc and range at which it will work
Each enzyme is best suited for the environment in which it evolved
Describe the effect of cold temperatures on enzyme-catalyzed reactions, and why.
Low temp = low molecular motion = fewer collisions
Reactions slow in cold reactions
Describe the effect of high temperatures on enzyme-catalyzed reactions, and why.
High temp = high molecular motion = more collisions
BUT
high temperatures and excess thermal energy can cause hydrogen bonds (in tertiary and quaternary structure of protein) to break
If the enzyme denatures, then the enzyme-catalyzed reaction rate plummets/stops
Describe the effect of pH variations on enzyme-catalyzed reactions, and why.
Proteins are stabilized by hydrogen and ionic bonds (among others)
These bonds are influenced by proton (H+) concentration
Very low pH = high concentration of H+
Very low pH = low concentration of H+
If pH strays from optimal, the enzyme can denature and stop functioning
Define
Cofactors
Nonprotein structures (atoms, ions, or molecules) that bind to enzymes and are necessary for proper catalytic function
Two types of cofactors
Vitamins (organic molecules) and minerals (inorganic, usually ions)
Define
Active Site
Part of enzyme where substrate binds
* Lock and key model describes active site as perfectly complementary to substrate
* Induced fit model describes active site and substrate as somewhat complementary, but binding leads to a better fit
Define
Enzyme inhibition
Methods of irreversibly or reversibly stopping or slowing an enzyme’s activity
What is the importance of enzyme inhibition?
It ensures only necessary enzymes are functioning
Ex: If one enzyme is involved in polymerizing amino acids into proteins, while another was involved in hydrolyzing proteins into amino acids, it’d be kind of stupid to have them both functioning simultaneously!
Describe
Competitive Inhibition
A molecule (not the substrate) binds to active site of enzyme, blocking correct substrate from binding
Increasing concentration of substrate can reduce effect of competitive inhibitor
Describe
Noncompetitive inhibition
A molecule (not the substrate) binds to an area other than the substrate, causing a change to the enzyme that prevents binding to the substrate
Increasing the substrate concentration does NOT reduce the effect of the noncompetitive inhibitor
A type of allosteric regulation
Define
Allosteric regulation
Controlling an enzyme’s function by having a molecule attached to a part of the enzyme other than the active site
Define
Allosteric site
A part of an enzyme (other than the active site) where a molecule can bind, which changes the shape of the active site
