M5 - Lesson 3: Enzyme Activity and Inhibition Flashcards
The substrate must fit into the active site the way a key fits into a lock. With the substrate at, the active site, a chemical reaction occurs that involves breaking or forming bonds of the substrate.
Lock-And-Key Model
What are the two modes of enzyme activity?
Lock-And-Key Model
Induced-fit Theory
The substrate induces the active site to take on a shape complementary to the shape of the substrate molecule.
Induced-fit Theory
The products that form are no longer attracted to the active site and leave the enzyme. The enzyme goes on to catalyze the same reaction with other substrate molecules.
Lock-And-Key Model
What are the two ways of Lock-And-Key Model Hypothesis?
Structurally - substrates that don’t fit won’t react;
Chemically - substrates that are not chemically attracted to the active site won’t be able to react.
The substrate may induce the enzyme to take on a shape that matches the substrate.
Induced-fit Theory
What are the induced-fit model that is better explains enzyme activity?
Attraction
Reaction (conformational change)
Release (enzyme reverts to original shape)
Formation of an enzyme-substrate complex as an intermediate species provides an alternative pathway, with lower activation energy, through which a reaction can occur.
The Mechanism of Enzyme Action
The active site has a fixed geometric shape. Only a substrate with a matching shape can fit into it.
Lock-and-Key Model
The active site has a flexible shape that can change to accept a variety of related substrates. Enzymes vary in their degree of specificity for substrates.
Induced-Fit Model
The action of many poison and drugs is due to their ability to inhibit specific enzymes.
Inhibition of Enzyme Activity
Type of inhibition in which a substrate and an inhibitor compete for the active site on the enzyme. They are so similar in structure that the enzyme binds to the inhibitor by mistake.
Reversible Competitive Inhibiton
As long as the competitive inhibitor occupies the active site, no reaction of the substrate can take place.
Reversible Competitive Inhibiton
TRUE OR FALSE
However, we can reverse non-competitive inhibition by adding more substrate that competes with the inhibitors for the active site, The addition of large amounts of substrate can completely reverse the inhibition.
FALSE
reverse competitive inhibition
- Has a structure similar to substrate
- Occupies active site
- Competes with substrate for active site
- Has effect reversed by increasing substrate concentration
A competitive inhibitor
Example of competitve inhibition
Overcoming Alcoholism
It interfere with active site of enzyme so substrate cannot bind
Competitive Inhibition
It changes shape of enzyme so it cannot bind to substrate
Non-competitive Inhibition
An inhibitor that won’t fit;
Allosteric site causing a conformational change in the active site; the substrate cannot attach to react
Non-competitve
An inhibitor that is blocked;
Active site and prevents the substrate from entering
Competitive
it competes with aldehyde oxidase and prevents the acetaldehyde from being converted to acetic acid
Antabuse (disulfiram)
Resulting in a strong feeling of nausea and other strong hangover symptoms - a good detergent from drinking.
Acetaldehyde
Administered as a daily pill, so its efficacy relies on the patients motivation.
Antabuse
What are the other examples of competitive inhibition?
a. Ethanol as antidote in Methanol Poisoning
b. Antihistamines
Type of inhibition wherein it binds to enzyme, at a site other than the active site. Its structure does not resemble that of the structure. When attaches to an enzyme, it alters the three-dimensional structure of the enzyme as well as the shape of the active site.
Reversible Non-Competitive Inhibiton
It does not compete for the active site, adding more substrate will no reverse inhibiton.
Reversible Non-Competitive Inhibiton
- Does not have a structure like substrate
- Binds to the enzyme but not active site
- Changes the shape of enzyme and active site
- Substrate cannot fit altered active site
- No reaction occurs
- Effect is not reversed by adding substrate
A noncompetitive inhibitor
Inhibits the enzymes that forms cells walls of bacteria, destroying the bacterium.
Penincilin
Causes blood vessels to narrow, increasing blood pressure.
ACE
What is the meaning of ACE?
Angiotensin-Converting Enzyme
Inhibitors are given to those with high blood pressure to prevent ACE’s synthesis from its zymogen.
ACE (Angiotensin-Converting Enzyme)
Protease is an essential enzyme that allows the virus to make copies of itself
HIV
Protease inhibitors interfere with this copying, decreasing the virus population in the patient.
HIV
A type of inhibition of enzyme activity which occurs when a functional group in the active site or a co factor required for the activity of the enzyme is destroyed or modified.
Irreversible Inhibition
This is also a non-competitive inhibition; does not have a structure similar to the substrate; cannot be removed from the protein without destroying it.
Irreversible Inhibition
What are the 3 Examples of Irreversible Inhibition?
Nerve Gases
Poisoning of Heavy Metals (Hg, Pb, Ag)
Penincillin
An enzyme that catalyzes a reactions taking place at the juncture of nerve cells and also necessary for normal transmission of nerve impulses
Cholinesterase
Occurs naturally in poisons and venoms; combine with the -OH group on a serine molecule that is vital to the active site of the cholinesterase enzyme. When this happens, the enzyme loses its ability to transmit nerve impulses. That is why animals poisoned by nerve gases become paralyzed.
Nerve Gases
These are toxic because they bind irreversibly with free -SH functional groups on enzymes.
Poisoning of Heavy Metals (Hg, Pb, Ag)
Is an antibiotic that kills bacteria because it irreversibly binds to glycopeptide transpeptidase for the synthesis of a bacterial cell wall.
Penincillin
