2.4 - Enzymes Flashcards
1
Q
What are enzymes?
A
- Enzymes are biological catalysts
- They are proteins with a complicated tertiary/quaternary structure
- They work by lowering the activation energy for a reaction, this speeds it up
- They are not used up from this method
2
Q
What is an example of an exothermic reaction that could be catalysed by enzymes?
A
- Enzymes can catalyse the reaction of reactants being turned into products
- This reaction releases energy so is exothermic and is catabolic as it is splitting the reactants into multiple products
- Enzymes can reduce the activation energy needed for the reaction, in turn speeding the reaction up, up to 10 to the power of 12 times
3
Q
What are the two models for enzyme action?
A
- The lock and key model
- The induced fit model
4
Q
What is the process of the lock and key model?
No change in shape
A
- Complimentary substrates bind to the enzymes active site
- This creates an enzyme-substrate complex
- The substrates are then released as the product and the enzyme is left unchanged
5
Q
What is the process of the induced fit model?
Temporary change in shape
A
- Substrates bind to the enzymes active site, temporarily changing the shape of the active site to fit the substrates
- This creates an enzyme-substrate complex
- The substrates are then released as the product and the active site of the enzyme then returns to its original shape
6
Q
What is meant when an enzyme is described as working intracellularly?
A
- When the enzyme works within the cell.
- For example: Catalase which takes H2O2 (Hydrogen peroxide) which is often made from respiration and must be broken down inside of the cell into H2O + O2 as it is toxic
7
Q
What is meant when an enzyme is described as working extracellularly?
A
- When the enzyme works outside of the cell
- For example: Pepsin is a protease enzyme which works in the stomach outside of the cell for digestion
- Also fungi is extracellular as the mycelium grows and releases the enzyme outside of the cell which digests the material outside of the fungal hyphae and allows the fungi to absorb the nutrients back in
8
Q
What are cofactors?
A
- Non proteins substances that must be present for some enzymes to work
- For example: Prosthetic groups & Co enzymes
9
Q
How do prosthetic groups work to allow enzyme activity?
A
Prosthetic groups are permanently bound to the enzyme, For example: FAD
10
Q
How do co enzymes work to allow enzyme activity?
A
Co enzymes are temporarily bound to the enzyme, often they are ions such as:
- Zn2+ for carbonic anhydrase
- Cl- for amylase
11
Q
What is an anabolic reaction?
A
Joining things together
12
Q
What is an catabolic reaction?
A
Splitting things apart
13
Q
What do hydrogenase enzymes do?
A
Add hydorgen
14
Q
What do decarboxylase enzymes do?
A
Take away carboxylic acid group or a Co2 molecule
15
Q
What does peptidyl transferase do? (From translation)
A
Peptidyl transferase catalyses the addition of amino acids to the growing polypeptide chain in protein synthesis by building peptide bonds
16
Q
What is the optimum temperature for enzymes?
A
37°C (Same as body temperature in humans)
17
Q
What is an extremophile and how would their enzymes be adapted to suit their environment?
A
- An extremophile is a bacteria that lives in a bubbling hot spring
- The enzymes would be adapted to survive the hot temperatures
- This means the optimum temperatures for the enzymes inside the bacteria would be higher than the optimum temperature for normal enzymes (37°C)
18
Q
How is enzyme activity affected as temperature rises towards optimum?
A
- As temperature increases, the kinetic energy for the particles increases so they are more active
- This means that there is a greater chance of collisions
- This means more substrates will bind to their complimentary active sites
- Therefore more enzyme-substrate complexes are being formed as temperature is rising towards the optimum
19
Q
How is enzyme activity affected as temperature increases above the optimum?
A
- As the temperature goes above the optimum it causes the enzyme to denature
- This means the proteins 3D structure is disrupted and will be unravelled (Denatured) due to the very high kinetic energy causing the particles to move rapidly
- The denaturing will:
- Break the hydrogen bonds
- Disrupt the hydrophobic interactions inside & the hydrophilic interactions outside the protein on the surface
20
Q
How is the denaturing of proteins shown in eggs when they are being cooked?
A
- When an egg is uncooked the globular proteins are ravelled so the egg white is transparent as light can pass between the gaps
- However when the egg is cooked, the albumin proteins denature and they unravel so the strands tangle, stopping light from passing through the egg so the egg appears white
21
Q
What does denaturing an enzyme cause?
A
-The active site will no longer be complimentary to the substrates as the shape is caused to change
22
Q
What does the Q10 equation aim to work out?
A
If we increase the temperature by 10°C what happens to the rate of reaction
23
Q
What is the normal Q10 coefficient in enzymes?
A
2, so as the temperature increases by 10°C it causes the rate of reaction to double
24
Q
What is the equation to work out the Q10 coefficient?
A
Rate of reaction at T + 10°C/Rate of reaction at T = (Normally) 2
25
What is PH measuring?
The concentration of H+ ions
26
How can PH affect enzymes?
The concentration of H+ ions can affect the 3D structure of the protein
27
How does concentration of H+ ions (PH) affect the structure of the protein?
- Increasing H+ ions (Decreasing PH) it interacts with the negative charges in the helix, this replaces the interactions holding the chain together
- Therefore this disruption of the hydrogen bonds can cause the 3D structure of the chain to change
28
How does concentration of H+ ions (PH) affect the activity of the protein?
- Slight changes of the PH away from the optimum can reduce activity of the enzyme as it temporarily changes the shape of the active site so that it is no longer completely complimentary to the substrate
- Large PH changes can denature the enzyme, permanently changing the shape of the active site so that it is no longer complimentary to the substrate
29
What is the digestive, protease enzyme, trypsin's optimum PH?
-PH 7.5 as it works in the small intestine so is slightly alkaline due to the bile
30
What is the digestive, protease enzyme, pepsin's optimum PH?
- PH 2 as it works in the stomach with hydrochloric acid
- This is because the enzyme has evolved to be stable at low PH's
- The enzyme expects there to be a high concentration of H+ ions so the structure has a lot of negative charges
31
How is the rate of reaction affected by the concentration of substrates?
-If substrate concentration increases the rate of
reaction increases and more ESC's are formed
-This is only until the limiting factor becomes available active sites (All of the active sites are occupied)
-This then means that the rate of reaction doesn't increase anymore and it plateaus
32
How is the rate of reaction affected by the concentration of available active sites?
- If the number of enzymes active sites increases the rate of reaction increases and more ESC's are formed
- This is only until the limiting factor becomes the concentration of substrates
- This then means that the rate of reaction doesn't increase anymore and it plateaus
33
How does a competitive inhibitor affect the rate of reaction?
- A competitive inhibitor will decrease the rate of reaction
- This is because competitive inhibitors can temporarily bind to the active site of the enzyme and stop the binding of substrates
- However if substrate concentration increases it means the substrates are more likely to beat the competitive inhibitor and bind to the active site before it
- This is because there would be a much larger number of substrates compared to the one competitive inhibitor trying to bind to the active site
- The maximum rate of reaction that would be reached without a competitive inhibitor can still be reached with one, when the substrate concentration increases so much so, that the ratio of substrate to inhibitor is high enough for substrates to consistently form ESC's with the enzymes
34
How does a non-competitive inhibitor affect the rate of reaction?
- A non-competitive inhibitor will also decrease the rate of reaction
- This is because non-competitive inhibitors can bind to the allosteric site of the enzyme and change the shape of the enzymes active site
- This means that the active site is no longer complimentary to the shape of the substrates so the substrates are unable to bind and form enzyme-substrate complexes
35
How does a non-competitive inhibitor work?
- A non-competitive inhibitor will bind to the allosteric site of an enzyme
- They do not compete with the active site of the enzyme, with substrates that also aim to bind to it
- However they do change the shape of the enzyme and the enzymes active site because of the binding to the allosteric site
- This means that the active site is no longer complimentary to the shape of the substrates so the substrates are unable to bind and form enzyme-substrate complexes
36
Why does an increase in substrate concentration not increase reaction rate in the presence of non-competitive inhibitors?
- The non-competitive inhibitors cause the active sites of the enzymes to change shape
- This means that no matter how many substrates there are, they wont be able to bind to the enzymes as they are not complimentary to the active sites on the enzymes that have changed shape due to the non-competitive inhibitors
- Therefore, the substrates are not directly competing with the non-competitive inhibitor, so increasing the substrate concentration will not increase the rate of reaction
37
How would an experiment be set up to measure the rate of reaction and how it is affected by enzymes?
-Set up a conical flask with a substrate and pieces of living tissues containing the enzyme catalase
-Connect the bung to a delivery tube leading to a gas syringe to measure the volume of oxygen produce (cm^3)
-Work out the rate of reaction via the rate of oxygen produced using the gas syringe
-Rate of reaction =
Oxygen produced (cm^3) / Time (mins)
38
How would the experiment be manipulated to measure how reaction rate would be affected by the concentration of substrates?
- Change the percentage of the concentration of the substrate
- For example: The percentage of the substrate (H2O2) used would change
39
How must this experiment be controlled?
- The volume of the substrate used
- The size of the tissues containing the enzyme catalase
- The type of tissue
- The mass of the tissue
- The surface area of the tissue
40
What is the independent variable in this experiment?
The concentration of the substrate (%) is changed
41
What are the expected findings from this experiment?
- The volume of oxygen produced will increase rapidly at the start as time increases
- This is until it plateaus after a bit as the oxygen cannot any increase any further
- This is due to there not being any more available enzymes to form enzyme-substrate complexes
42
How is the rate of reaction measured using a graph?
-Plot a tangent and measure the change in y (The volume in cm^3) / the change in x (The time in minutes, seconds or hours)
43
What is end-product inhibition?
- End-product inhibition is when the final product inhibits an enzyme involved in the initial reactions
- At the end of the metabolic pathway, the final product may be able to inhibit the enzyme responsible for catalysing the initial reaction
- This causes the whole metabolic pathway to stop
