Enzymes, 2.4 Flashcards
What are enzymes and what is their role?
Biological catalysts. Speed up metabolic reactions
What is the turnover number?
The number of reactions an enzyme can catalyse per second
What type of proteins are enzymes?
Globular
Why is the structure of an enzyme important?
Determines its function
What is substrate?
A molecule on which an enzyme acts
What is the active site?
Area on an enzyme which is complementary to the substrate molecule.
How can the shape of an active site be altered?
Increase in temperature. Change in pH.
What are enzymes inside the cell called?
Intracellular
What are enzymes outside the cell called?
Extracellular
Describe the function of lactase
Breakdown of milk, sugar and lactose intolerance glucose and galactose. Lactose intolerant = don’t produce lactase.
What is the function of catalase?
Breakdown of hydrogen peroxide to water and oxygen. Hydrogen peroxide is toxic but is a by product of some reactions
What is a cofactor for?
Addition of a non-protein to an enzyme before they can catalyse
What is a prosthetic group?
A cofactor for which is permanently bound - covalent bonds. Part of its 3D shape
What is an example of a prosthetic group?
Enzyme carbonic anhydrase - catalysed CO2 and H2O to carbonic acid
What are coenzymes?
Organic molecules that bind temporarily transferring a chemical group when required. They are chemically changed after and need to be recycled.
Give an example of a coenzyme
B3 - needed for respiration and energy to grow
Describe the Lock and Key Hypothesis.
- Substrate identifies active site of enzyme
- Substrate fits into the enzymes active site
- Temporary hydrogen bonds hold them together
- Substrate is broken into smaller product molecules that leave the active site
Describe the Induced Fit Hypothesis..
- Shape of the active site is complementary to the shape of the substrate
- Enzyme modules itself around the substrate
- Intermolecular forces bind
- Product will be a different shape and will detach
What is an advantage of enzymes?
Lower activation energy. When molecules collide they need to collide with sufficient energy to cause a reaction
What is the effect of increasing the temperature on enzymes?
Molecules gain energy and move faster, increases the chance of collisions and the energy with which molecules collide. Rate of reaction increases.
What is the optimum temperature?
When the rate of reaction is at its maximum. After this the enzyme denatures.
Why does an increase in temperature denature an enzyme?
Breaks the weak bonds in the enzyme which hold the tertiary structure together. Active site changes shape. Change is irreversible.
What is meant by the temperature coefficient Q10?
Increase in the rate of a process when the temperature rises by 10degrees
What is Q10?
Rate of reaction at (T+10) / rate of reaction (T)
What does the pH show?
Whether a substance is acid, alkali or neutral.
What is a buffer?
Resists changes in pH
Why will a change in the pH affect n enzyme?
- Hydrogen ions causes changes in pH
- Excess hydrogen ions will interfere with hydrogen bonds and change the shape
- Less substrate will be able to bind - rate of reaction slowed.
What is the optimum pH?
pH at which the rate is at its maximum - after this the enzyme is disrupted
Describe the effect of substrate concentration?
- As substrate concentration increases so does the rate of reaction
- Can binds to active sites, more complexes formed, more product formed
What has happened when the rate of reaction has reached its maximum rate concerning substrate concentration?
All the active sites will be occupied so more substrate will not be able to successfully collide.
What is the effect of enzyme concentration?
- As enzyme concentration increases so does the rate
- More active sites available, more successful collisions, more product formed
- At a point there will be no further increase as there will be no more substrate.
Why is the initial rate of reaction the fastest?
At the start there is the most substrate - higher chance of collisions
Define inhibitor
Substance that slows down the rate of a reaction by affecting the enzyme
What are the two types of inhibitor?
Competitive and non-competitive.
Describe how competitive inhibitors work?
- Have a similar shape to enzyme substrate
2. They compete directly with substrate to form an enzyme-inhibitor complex
What does the amount of inhibition depends on in competitive inhibitors?
The concentrations of inhibitor and substrate.
How do non-competitive inhibitors work?
- Binds to the allosteric site and disrupts the tertiary structure
- Active site is no longer complementary to the substrate
- Substrate can no longer bind
How does the amount on inhibitor effect the rate of reaction in non-competitive inhibition?
More inhibitor the greater the degree of inhibition
Why does enzyme activity need to be controlled?
Can be dangerous eg multiple sclerosis.
How do we regulate metabolic pathways?
With enzyme inhibition
How does enzyme inhibition regulate metabolic pathways?
- End product acts as a regulator - end product inhibition
- High amount of product
- Will bind non-competitively to an enzyme in the pathway
- When amount of product decreases inhibition ends
What is an example of an inhibitor?
Toxins/Venoms - block enzymes. Cyanide - inhibits aerobic respiration. Snake venom - inhibits AChE, causes paralysis.
What can we use to stop anti freeze? And why?
Alcohol. Reduces the rate of reaction which breaks down anti freeze. Competitive inhibitor.
