1.4.2 Many proteins are enzymes Flashcards
What is an enzyme?
A globular protein that acts as a biological catalyst by speeding up the rate of a chemical reaction.
How do enzymes speed up the rate of a chemical reaction?
They provide an alternative pathway for the reaction, one with a lower activation energy.
What is activation energy?
The minimum amount of energy required for a reaction to occur.
What is the induced fit model?
The enzyme structure is not rigid; the active site changes shape to fit the substrate, putting strain on the substrate to weaken bonds and lower activation energy.
Are enzymes globular or fibrous proteins?
Globular.
What determines the 3D structure of enzymes?
The order and sequence of amino acids.
When does an enzyme-substrate complex form?
When the substrate binds with the active site.
What holds enzyme-substrate complexes together?
Temporary bonds that form.
What is specificity in regards to enzymes?
One enzyme has a small number of substrates due to the exact molecular fit between the substrate and active site.
How does the active site of an enzyme cause a high rate of reaction?
The enzyme-substrate complex puts strain on the bonds in the substrate, making them easier to break, which reduces activation energy.
How do high temperatures affect enzyme activity?
They break many H bonds, altering the shape of the active site and making it harder for the enzyme to form an enzyme-substrate complex.
How can changes in pH affect enzyme activity?
Excess H+ or OH- ions change interactions between amine and carboxyl groups, influencing H bonds in the active site and reducing successful collisions.
How can changes in pH denature the enzyme?
It further changes the shape of the active site, preventing enzyme-substrate complexes from forming.
Where do competitive inhibitors bind?
The active site.
What must competitive inhibitors be like to bind to the active site?
They must be complementary to the active site and similar in shape to the substrate.
Are competitive inhibitors permanently bound to the active site?
No.
How can the effects of a competitive inhibitor be overcome?
By increasing the substrate concentration.
Where do non-competitive inhibitors bind to an enzyme?
The allosteric site.
Can non-competitive inhibitors be a different shape to the substrate?
Yes, they don’t have to be complementary to the active site.
Does increasing substrate concentration overcome the effects of a non-competitive inhibitor?
No.
How do non-competitive inhibitors work?
They alter the shape of the active site, changing the tertiary structure, so the substrate is no longer complementary to the active site.
Where do coenzymes bind to?
The active site.
Are coenzymes involved in the reaction?
No.
Are coenzymes chemically altered/used up in the reaction?
No.
Are coenzymes a non-protein substance?
Yes.
Are cofactors involved in the reaction?
Yes.
Are cofactors temporarily modified in the reaction?
No.
Where do cofactors bind?
The active site.
Are cofactors a non-protein substance?
Yes.
Describe the induced-fit model of enzyme action.
Substrate binds to the active site, active site changes shape to distort bonds in the substrate, reducing activation energy.
How does a competitive inhibitor decrease the rate of an enzyme-controlled reaction?
The inhibitor has a similar shape to the substrate, fits/binds to the active site, preventing/reducing enzyme-substrate complex formation.
Explain how the active site of an enzyme causes a high rate of reaction.
It lowers activation energy, the induced fit causes the active site to change shape, and the enzyme-substrate complex causes bonds to form/break.
How does the formation of an enzyme-substrate complex increase the rate of reaction?
It reduces activation energy due to stress on bonds.
How does a decrease in temperature affect the rate of an enzyme-controlled reaction?
Molecules move less, reducing the chance of collision.
(a) In humans, the enzyme maltase breaks down maltose to glucose.
This takes place at normal body temperature.
Explain why maltase:
* only breaks down maltose
* allows this reaction to take place at normal body temperature.
- Tertiary structure
- Active site complementary to substrate
- Description of induced fit;
- lowers activation energy
- forms enzyme-substrate complex;
Descibe competitive and non- competitive inhibition of an enzyme. (5marks)
- reduce binding of enzyme to substrate/ preventing formation of ES complex
competetive- inhibitor similar shape to substrate - Binds to AS of enzymes
- can be overcome by more substrate
Non -comp
- inhibitator binds to siter on enzyme other than active site
- prevents formation of active site/ changes shape of active site
Describe one similarity and one difference between the induced fit model of enzyme activity and the lock and key model.
sim
- substrate binds to AS
- enzyme substrate complexes formed
diff
As changes shape, but doesn’t change in lock and key
AS not complimentary to substrate with induced fit, but is complementary in lock and key
Describe the structural nature of enzymes
globular proteins
specific tertiary structure
complementary to substrates
substrates bind to active site of enzymes
Difference between competitive and non competitive inhibitors
competitive - bind the active site of enzymes, blocking substrate form binding
Non competitive inhibitors - bind to different site on enzyme - causing a conformational change that alters the shape of the active site
Digestive enzymes
active site, specific teriratry structure, can only bind to, form enzymes substrate complexes
Discuss the induced fit model of enzyme substrate interaction
substrates collide with enzymes active site
form an enzyme substrate complex
induces slight changes in shape of active site
making it more complementary to the substrate
which facilitates the reaction
Explain how enzymes reduce the activation energy of reactions
binds substrate to active site
straining the bonds in the substrates
allows their conversion into products
Explain the relationship between substate concentration and enzyme activity
increase substrate conc increases rate of reaction
as more enzyme substrate collisions
there is a max rate when all active sites are occupied
enzymes saturation
How does enzyme concentration affect reaction rate?
increasing enzyme conc increase rate
as there are more enzymes available to catalyse substrate molecules
are instantly converted to products
How does temperature affect the rate of enzyme controlled reactions?
increasing temp initially increases rate of reaction by providing more kinetic energy for successful enzyme substrate collision
optim temp - enzymes denature
decreasing the rate as the active site loses its complementary shape
pH
-log10 (H+)
