2.4 Enzymes Flashcards
What are the physical features of enzymes?
- Globular proteins- Spherical with lots of alpha helix
- Generally soluble in water due to R groups
- Biological catalysts
What is the definition of activation energy?
- Minimum amount of energy required for a reaction to take place
How do enzymes work?
Reduce activation energy through complimentary fit between enzyme and substrate.
What is the induced fit hypothesis?
That there is a change in shape of the enzyme in response to a substrate binding
What are the steps of the induced fit hypothesis?
- Substrate collides with active site
- Enzyme molecule;e changes shape slightly so active site fits more closely around substrate
- Enzyme substrate complex formed **
- Destabilises substrate producing product
- Enzyme product complex formed
What is meant by the term ‘anabolic reactions’?
Build up larger molecules e.g. protein synthesis
What are catabolic reactions?
Break down larger molecules
What are intracellular enzymes?
Act within cells e.g. synthesis of polymers
What are extracellular enzymes?
Make substrates outside of cells
Released from cells
What do extracellular enzymes allow for?
Use of polymers
Single cell use it to absorb glucose
How is starch digested?
Starch polymers are broken down into maltose by amylose in saliva
Maltose is broken down into glucose in small intestine
How are proteins digested?
Trypsin is a protease which catalyses digestion of proteins into smaller peptides
Broken down further into amino acids
Trypsin is produced in pancreas
What is the effect of temperature on enzymes?
Kinetic energy causes bonds to vibrate
More likely to collide successfully
What happens to enzymes if temperatures goes to high?
Bonds vibrate too much and break causing enzymes to lose 3D shape and denature
What does denature mean?
Enzyme has permanently changed shape
What are thermophiles?
Living organisms adapted to withstand hotter temperatures?
Enzymes are more stable and more resistant to change
What are cryophiles?
Enzymes that function in very cold environments.
Enzymes have more flexible structures and are less stable
What is the effect of pH on enzymes?
H + ions interact with polar groups and charged R groups where bonds break and substrate no longer fits active site
What is renaturation?
Where if pH of solution returns to optimum enzymes will return to original shape
What is V max?
Maximum rate of reaction
All active sites are occupied by substrate particles
What is the effect of increasing substrate concentration?
- Increases number of collisions between enzymes and substrate
- Increases number of enzyme substrate complexes which in turn increases rate of reaction
How can V max be increased?
Increasing the limiting reactant or temperature e
What is the effect of increasing enzyme concentration?
- Increases number of active sites available
- Increases number of enzyme substrate complexes increasing rate of reaction
What is an inhibitor?
Any substance/molecule that slows down the rate of an enzyme controlled reaction by affecting the enzyme molecule
What are competitive inhibitors?
- Similar shape to substrate
- Occupy active site to form enzyme-inhibitor complexes
- number of enzyme substrate complexes decreases causing rate to decrease
- Most don’t bind permanently
What are non competitive inhibitors?
- Bind elsewhere on the enzyme at the allosteric site
- Affects tertiary structure
- Level of inhibition depends on concentration of inhibitor
- Many bind permanently
- Used in insecticides
What is an allosteric site?
Another binding point on an enzyme
What is end product inhibition?
Product of one reaction is an inhibitor to the enzyme that produced it
What are co-factors?
Non protein components
Bind temporarily at allosteric site
Obtained from diet e.g. Fe +
What are co-enzymes?
- Organic co-factor
- Many derived from vitamins e.g. NAD
- Carry chemicals between enzymes.
What are prosthetic groups?
- Also a cofactor
- Bind permanently
How are enzymes activated?
- Need a change in tertiary structure
- Can be activated either by co factors or a change in pH
