Enzymes Flashcards
Features of enzymes
Globular proteins - Highly folded & coiled
They have a specific tertiary structure
They are Biological catalysts
They lower the activation energy of a chemical reaction
What is the active site?
A small hollow depression made up of a small number of amino acids
Enzyme Specificity
Enzymes are specific
- A single substrate
OR
- A specific bond
What does the tertiary structure of enzymes determine
Determines the shape and electrostatic charge of the active site
Contains : hydrogen,ionic and sometimes disulphide bonds
What is activation energy
The minimum energy required for a chemical reaction to take place
How do enzymes lower the activation energy? simple
The enzyme bends the bonds that need to be broken for the reaction to occur
What are the enzyme models?
Lock and Key model
Induced fit model
Lock and key model
1) Substrate collides with active site of enzyme and becomes attached (enzyme-substrate complex forms)
2) Enzyme catalyses breakdown of substrate
3) Products released from active site
What is an enzyme substrate complex?
Temporary bonds between the amino acids (active site) and the substrate molecule
What is the induced fit model?
shape of the enzymes active site and its substrate are not exactly complementary
BUT
when the substrate enters the active site a conformational change (change of shape occurs which induces catalysis
Induced Fit Model Steps
1) The substrate enters the enzymes active site, forming an enzyme-substrate complex
2) Enzyme undergoes a conformational change
3) This caused the conversion of substrate into product
4) this forms and enzyme product complex
5) the product is realised from the enzymes active site
How do enzymes lower the activation energy?
- Active site is slightly flexible
- Substrate interacts active site, changing its shape
- This strains bonds in the substrate molecule
- Makes them more likely to break
Induced fit relating to lowering the activation energy
1) Enzyme-Substrate complex forms
2) Active site changes shape so its complementary to the substrate which bends the bonds in the substrate
3) Reduces activation energy
What is the active site
Part of an enzyme where substrate molecules bind and undergo chemical reaction
What is an enzyme?
A tertiary structure protein that lowers the activation energy and acts as a biological catalyst
What factors affect enzyme activity?
1) Substrate concentration
2) Enzyme concentration
3) Temperature
4) pH
Substrate Concentration
-Substrate conc increases, ROR increases
because there are more substrate molecules to fill the enzymes active site
- More frequent collisions so more E-S complexes formed
- Saturation point reached - all the enzymes active sites are occupied with substrate molecules
- So, adding more substrate molecules won’t have any effect on the ROR
- The reaction is going as fast as possible = Vmax
- Only way the reaction can go any faster is by increasing enzyme concentration
Substrate conc/ ROR graph
1) ROR high at the start - lots of active sites available to bind to the substrate
2) Reaction continues - many of the active sites become occupied so rate of product reaction increases at a slower rate
3) Once all the actives sites are occupied the rate levels off = Vmax
4) Enzyme conc is now the limiting factor
Enzyme concentration
•Enzyme conc increases - ROR increases
- because more active sites available to bind to substrate molecules
•More frequent collisions = more E-S complexes formed
• Point reached where all substrates are bound to an enzyme so increasing enzyme conc won’t increase the ROR
Enzyme conc/ Rate of enzyme catalyses reaction graph
- Enzyme coc increases = ROR increases
because more enzymes = more active sites available to bind to substrate molecules - Substrate available = rate will continue to increase
- All substrates will be bound to an active site so the ROR plateaus
- substrate conc is now the limiting factor
Temperature
- Low temp = slow ROR , because enzyme and substrate have low amounts of kinetic energy
- won’t be many collisions = reduced formation of ES complexes
- Temp increases = increased number of collisions = more ES complexes formed = ROR
Temp too high = hydrogen bonds break within the protein causing it to unravel and denature
Enzyme denatured = active site changes shape
This means they can’t bind to their substrate = decreases ROR
Temperature/ROR graph
Increase temp = Increased kinetic energy
= more ES complexes formed
Then optimum temp
the. enzyme denatured
Enzyme denaturation
- Hydrogen and Ionic bonds broken
- Loss of tertiary structure
- Altered shape of active site/Active site not complementary to substrate
- Less ES complexes formed
pH
each enzyme has its own optimum pH
- deviations in pH from the optimum changes the charges in the amino acids in the active site
- This affects the ionic bonding in the tertiary structure
- Deviations in pH can also break hydrogen bonds in the tertiary structure
- This causes the enzyme to change shape and denature
- This decreases the ROR as the pH deviates from the enzymes optimum
