C1.1 Enzymes and Metabolism Flashcards
What are enzymes?
Globular proteins that acts as biological catalysts that speed up chemical reactions in the body.
They can be recycled as they are never “used up” in reactions
What is metabolism? What is the role of enzymes in metabolism?
Metabolism is the sum of all chemical reactions occuring in an organism.
- enzymes control metabolism
- lower activation energy of reactions
- provide alternative pathways
- increase the collisions
- occur when substrates are dissolved in water
- enzyme can move if in fluid
Anabolic and catabolic reactions
Enzymes as globular proteins with an active site for catalysis
How do enzymes work? What is the name of this model?
- Enzymes are specific to substrates (reactants)
- Enzymes have active sites that are specific to the substrate (match physically and chemically)
The Induced Fit Model:
- As substrate binds to enzyme to form enzyme substrate complex, the active site changes slightly
- enhances catalytic activity
- enzyme returns to previous shape after reaction
What happens to the active site of an enzyme when it undergoes denaturation?
The active site becomes distorted and loses its substrate specificity.
It is unable to catalyse reactions and this is usually irreversible
What is enzyme immobilization? What is the point of it?
It is when the enzymes are unable to move and so they stay in one place after reactions.
Used commercially so the enzyme doesn’t have to be removed from the product.
What is most necessary for a substrate molecule and an enzyme’s active site to come together?
Movement and collision of the enzyme and substrate.
What happens to enzymes when you increase the amount of substrate?
An increase in enzyme activity until the point of saturation where they work at their maximum rate and plateau after that.
What is the overall metabolic activity controlled by?
- rate of enzyme production and breakdown
- inhibitors
- enzyme interaction with products
What are metabolic pathways? What are the types of pathways?
Pathways are a series of reactions from a starter molecule/precursor to an end product.
Each reaction is catalyzed by a different enzyme.
Cyclical pathways:
The reactant becomes the product
Non-cyclical/linear:
reactant is different from the product
What are anabolic reactions?
Reactions that build up a product
- condensation reactions
- photosynthesis
What are catabolic reactions?
Reactions that break down a product
- hydrolysis
- cell respiration
What are intracellular and extracellular metabolic reactions?
Intracellular:
- occur in the cell
- e.g: DNA replication, cellular respiration
Extracellular:
- occur outside the cell
- e.g: digestive enzymes in the intestines
What is the efficiency of metabolic reactions?
They are not 100% efficient:
- energy is released as heat
(especially in respiration)
What are endotherms and ectotherms?
Endotherms:
warm blooded
control their own body temp
Ectotherms:
cold blooded
rely on external sources for heat
What is denaturation?
The permanent or temporary change in 3D shape and protein structure due to the breaking of bonds.
Causes a change in active site and inability to catalyze reactions.
What factors change rate of enzyme activity?
- Temperature
- pH
- Substrate/enzyme concentration
How does pH affect enzymes?
Outside of optimum pH, enzymes denature if pH is too far from ideal.
How does temperature affect enzymes?
Activity increases as temp increases until optimum is reached. After optimum enzymes denature due to breaking of bonds.
How does concentration of enzymes/substrate affect their activity?
Higher concentration increases activity up until a maximum when it plateaus.
What are inhibitors? What types of inhibition are there?
Substances that prevent or reduce enzyme activity.
- Competitive inhibition
- Non-competitive inhibition
- Feedback inhibition
- Mechanism based inhibition
What is competitive inhibiton?
When a substance competes with a substrate for the active site, as they are chemically similar.
The inhibitor binds to the active site, blocking substrates from binding.
The rate will slow down but will eventually reach the same point.
Higher inhibition rate decreases the rate of reaction but the same amount of enzymes are still available.
They can be outcompeted if there are more substrates.
E.g: statins (lower cholesterol)
What is non-competitive inhibition?
WHen a substance binds to the allosteric site of an enzyme (not the active site).
This changes its shape and stops the enzyme from functioning.
This is reversible.
What is feedback inhibition?
When the inhibitor is produced in a metabolic pathway.
The product becomes an inhibitor of the first enzyme in the pathway.
Used to stop the cell from making unnecessary products and conserve energy.
This acts as a non-competitive inhibitor.
E.g: Isoleucine
What is mechanism based inhibition?
When a substrate analogue (molecule) forms covalent bonds with the active site.
This is an irreversible inhibition.
The substrate analogue is changed by the enzyme after bonding and forms a stable inhibitor-enzyme complex.
e.g: Penicillin
Explain how penicillin is a mechanism based inhibitor:
Penicillin is an antiobiotic that kills bacteria by binding with the enzymes that form links in bacterial cell walls.
By forming a stable inhibitor-enzyme complex, the cell walls burst from the pressure as they are not linked together.
They do not affect us as we do not have cell walls.
Explain antibiotic resistance:
DNA mutations can change the shape of an enzyme’s active site.
If bacteria aren’t completely killed off, the bacteria can mutate and pass on plasmid DNA through conjugation.
This renders penicillin ineffective in inhibiting the enzymes.
Resistance can happen when antibiotic rounds are not completed.
What is substrate specificity?
Enzymes are specific to the substrates they bind to
