Enzymes Flashcards
(22 cards)
Why are enzyme inhibitors necessary?
- In many biological processes, enzymes function in a negative feedback loop. In this loop, the product of the enzyme will inhibit the enzyme once enough product has been made in order to stop the enzyme from producing more product than what is needed.
- Excess product can be potentially damaging, it is also wasteful.
- The reaction still produces enough product to sustain necessary metabolic requirements.
How do competitive inhibitors function?
- Competitive inhibitors compete with the substrate for the active site. The inhibitor molecule has a similar shape to the substrate molecule. When the inhibitor binds, it occcupies the active site without causing a reaction.
- Mostly reversible, bind temporarily. Aspirin is an exception.
What is the effect of increasing the substrate concentration in a reaction with a competitive inhibitor?
- Increases the rate of reaction.
- The substrate molecules will outcompete the competitive inhibitor.
How do non-competitive inhibitors function?
- They do not bind to the active site. The inhibitor molecule can bind to the allosteric site.
- Causes the tertiary shape of enzyme to change, so AS changes shape.
- The substrate is no longer able to bind to form an enzyme-substrate complex as it is no longer complementary.
- Can be permanent or reversible.
What is the effect of increasing the substrate concentration on a reaction with a fixed quantity of non-competitive inhibitor?
- No increase on the rate of reaction.
- They do not compete for the AS.
What is an example of an intracellular enzyme?
Catalase, catalyses the break down of hydrogen peroxide to oxygen and water.
Why are enzymes required in the body?
They allow reactions to occur at lower temperatures which would otherwise not be safe/possible in the body.
What two enzymes are involved in starch digestion?
- Amylase hydrolyses starch into maltose. (salivary glands)
- Maltase converts maltose into alpha-glucose. (small intestine)
Is trypsin intra or extracellular?
Extracellular, secreted with pancreatic juices into small intestine.
Do competitive inhibitors limit the original Vmax?
- No, provided a high enough substrate is added, the original Vmax can still be reached.
Are statins competitive or non-competitive inhibitors?
They are competitive inhibitors of an enzyme involved in the synthesis of cholesterol. Used to reduce blood cholesterol concentrations.
Is aspirin competitive or non-competitive?
It irreversibly binds to the active site of COX enzymes, preventing the synthesis of prostaglandins and thromboxane - responsible for pain and fever respectively.
What is an example of end-product inhibition?
- PFK is an enzyme responsible for the addition of a second phosphate group to glucose during glycolysis.
- PFK is inhibited by ATP, so when ATP conc is high, less glucose is acted on by PFK.
What inorganic cofactor does amylase require to digest starch?
- Chloride ion.
How are most coenzymes derived?
From vitamins
What coenzyme is synthesised form vitamin B3?
NAD (used in respiration)
What coenzyme is synthesised form vitamin B5?
Coenzyme A
What ion forms an important part of carbonic anhydrase?
- Zn 2+ ions
How are most enzymes produced?
- As an inactive form - inactive precursor enzymes.
- This occurs particularly with enzymes which can cause damage within the cells synthesising it or the tissues where they are released, or when an enzyme only needs to be activated under certain conditions.
How are precursor enzymes activated?
- Often need to undergo a tertiary shape change, often to the active site.
- This can be achieved by the addition of a cofactor or the action of a protease.
What are precursor proteins called? What are they called after activation?
- apoenzymes
- holoenzymes after activation
What are enzymes called which are activated by a change in pH or temperature? What is an example?
- proenzymes or zymogens.
- Inactive pepsinogen is converted into pepsin by the pH of the stomach, protecting body cells against the digestive action of pepsin
