Enzymes Flashcards
Chemical agents that speed up chemical reactions without being consumed
Catalysts
Chemical agents that speed up chemical reactions without being consumed (Catalysts in biomolecules)
Enzymes
Chemical reaction involves
breaking or forming a bond
Changing one molecule into another generally involves
contorting the starting molecule into a highly unstable state before the reaction can proceeed
To reach the contorted state, molecules need to absorb
Energy — Activation Energy (supplied with thermal energy)
What does the energy do?
The energy accelerates the reactant molecules and collides more often causing the breakage of a bond.
When molecules absorb enough energy,
the reactant molecule goes into an unstable condition called a transition state
What comes after the transition state?
Atoms settle into more stable bonding arrangement as energy is released into their surroundings. Molecules return to the stable shape and lower energy.
[ToF] Can too much heat kill the cell?
Ye
How does an enzyme catalyze a reaction?
by lowering the Energy Activation barrier, enabling the reactant molecules to absorb enough energy to reach the transition state even at moderate temperatures.
The reactant an enzyme acts on
Substrate
Forms after enzymes bind to its substrate
Enzyme-substrate Complex
Summary of catalytic action of enzymes
Enzyme + Substrate <-> Enzyme-substrate complex <-> Enzyme + products
Typically a pocket or groove on the surface of the enzyme where catalysis occurs
Active site
Formed by only a few amino acids, with the rest of the protein molecule providing a framework that determines the shape of the active site
Active site
[ToF] Enzymes are stiff structures locked into a given shape
False
The tightening
of the binding after initial contact; the shape change that makes the active site fit even more snugly around the substrate
Induced fit
Process of catalysis
- Substrate enters the active site, enzyme changes shape to fit it
- Substrates are held in the active site by weak interactions (hydrogen bonds/ionic bonds)
- Active site lowers activation energy and speeds up the reaction
- Substrates are converted into products (wahhaha binubugbog)
- Products are released
- Active sites are available for more molecules
Components of an enzyme
Cofactor (co-enzyme, metal ions, prosthetic groups), Apoenzymes, Holoenzymes
Nonproteins that help mediate enzymatic reactions. They serve as nucleophiles, mediate covalent catalysis, form electrostatic interactions with the substrate, and stabilize the transition state.
Cofactors
Bind to the enzyme and remove electrons/protons/chemical groups from the substrate
Cofactors
Loosely-bound organic cofactors that may assume the role of hydrogen acceptors [Nicotinamide adenine dinucleotide (NAD), Adensonine Triphosphate (ATP)]
Co-enzyme
Tightly-bound inorganic/organic cofactors (Heme, biotin, flavin, iron sulphides, copper, and ubiquinone)
Prosthetic groups
Inorganic such as the metal atoms zinc, iron, and copper in ionic form
Metal ions
No associated cofactors
Apoenzymes
Complete enzymes
Holoenzymes
Model that suggests that enzymes are rigid (cannot change) [maling model lmfaoo]
Lock and key model
Suggests that enzymes are flexible, and can change to accommodate substrates
Induced fit model
Characteristics of Enzymes
- Specific
- Reusable (into the same chemical reactions)
- Flexible
Limit catalysts/enzymes and prevent them from doing their jobs
Inhibitors
In which an inhibitor competes with substrate for binding to an active site. When it occupies said active site, it forms an enzyme-inhibitor complex and the enzyme cannot react until the inhibitor dissociates.
Competitive Inhibition
They have a structure similar to the substrate, but they are unreactive.
Competitive Inhibitors
Example of competitive inhibitor
Statins - a class of drugs that reduces cholesterol levels. They are inhibitors of the enzyme HMG-CoA
reductase. HMG-CoA reductase is the enzyme that synthesizes cholesterol from lipids
In which an inhibitor binds to an enzyme at a location other than the active site. In some cases, these inhibitors physically block the normal active site or change the shape of the enzyme molecule entirely, deforming the active site. Involves negative feedback.
Noncompetitive inhibition
In which inhibitors bind only to the substrate-enzyme complex. Common in reactions involving two or more substrates or products. Products leave the active site less easily, slowing the reaction
Uncompetitive Inhibition
Factors affecting enzyme activity
Temperature, pH, substrate concentration, enzyme concentration
Relationship between Enzyme Activity and Temperature
The higher the temperature, the faster the reaction (substrates and active sites collide more frequently)
Relationship between Enzyme Activity and pH
The optimal pH value for enzymes is between pH 6-8.
Exceptions include pepsin that works at a low pH, and trypsin in more alkaline parts of the intestine that are more denatured.
Relationship between Enzyme Activity and Substrate Concentration
Increasing substrate concentration also increases the rate of reaction until all enzymes have bound
Relationship between Enzyme Activity and Enzyme Concentration
Increasing enzyme concentration will speed up the reaction as long as there is substrate available to bind to. Once all of the substrate is bound, the reaction will no longer speed up because additional enzymes will have nothing to bind to.
