2.4 ENZYMES Flashcards
1
Q
What is an enzyme?
A
- Biological catalysts made of globular proteins that speed up rate of metabolic reactions by lowering activation energy (via a different pathway)
2
Q
Give an example an intracellular enzyme
A
- Catalase in the liver breaking down hydrogen peroxide into oxygen and water
3
Q
Give an example of an extracellular enzyme
A
- Trypsin in the small intestines hydrolyses proteins
4
Q
Describe the active site of enzyme
A
- An indented area complementary to a substrate molecule as a result of folding and bonding in the proteins tertiary structure
5
Q
What is a catabolic reaction?
A
- A reaction that breaks down substrates
6
Q
What is an enzyme-substrate complex?
A
- An enzyme molecule with a substrate molecule temporarily joined to its active site by non-colavent forces (e.g van der waals/hydrogen bonding/ionic bonding/hydrophobic interaction)
7
Q
what is an enzyme-product complex?
A
- An enzyme molecule with a product molecule temporarily joined to its active site by non-colavent forces (e.g van der waals/hydrogen bonding/ionic bonding/hydrophobic interaction)
8
Q
Describe the lock and key model
A
- Complementary enzyme and substrate molecules have kinetic energy
- When they collide, an enzyme-substrate complex forms
- Substrate molecule is either broken down into product or built up into product
- Enzyme-product complex forms
- Product released from active site and enzyme catalyses another substrate
9
Q
Describe the induced fit model
A
- Complementary enzyme and substrate molecules have kinetic energy
- When they collide the active site side chain/R-groups change shape slightly so substrate can bind for effectively to the enzymes active site
- An enzyme-substrate complex forms
- Substrate molecule is either broken down into product or built up into product
- Enzyme-product complex forms
- As the product has a slightly different shape from the substrate molecule, they detach from the active site
- Enzyme catalyses another substrate
10
Q
Draw an activation energy graph to show the action of enzymes
A
(EXOTHERMIC LAYOUT)
11
Q
Define the optimum temperature for an enzyme
A
- The temperature at which they catalyse a reaction at the maximum rate
12
Q
Explain the effect of increased temperature on an a mixture containing enzymes and substrates
A
- Enzyme and substrate molecules gain kinetic energy so move faster
- Thus, more frequent successful collisions with sufficient energy to overcome activation energy
- Rate of formation of enzyme-substrate complexes increases so rate of reaction also increases
13
Q
Define activation energy
A
- The minimum amount of energy required for reactants to start forming products
14
Q
Explain how high temperatures result in enzyme denaturation in regards to 3D tertiary structure and the effect on rate of reaction
A
- Heat = KE = molecues vibrate
- This breaks the weak forces that hold the tertiary structure of the enzymes active site
- Active site changes shape, substrate cannot fit in effectively
- Rate of reaction decreases
- More heat means the active site shape changes irreversibly, no longer complementary
- The reaction cannot be catalysed as 3D shape is destroyed
15
Q
Explain how high temperatures effect an enzymes primary structure
A
- NO EFFECT on primary structure
- Because heat does not break peptide bonds between amino acids
16
Q
Draw a rate-temperature graph and label the optimum temperature/maximum rate of reaction
A
17
Q
State the equation to determine rate of reaction for an enzyme
A
18
Q
Explain what the temperature coefficient Q₁₀ tells us
A
- The increase in the rate of reaction when the temperature is increased by 10°C
19
Q
State the formula for temperature coefficient Q₁₀
A
20
Q
State what the value of Q₁₀ is for most reactions and explain what this means
A
- 2
- This means for every 10°C increase in temperature, the rate of reaction is doubled (x2)
21
Q
Define acid
A
- A proton donor when they dissociate in aqueous solution
22
Q
Define buffer
A
- A substance that minimised changes in pH on small additions of acid or alkali
23
Q
Explain how pH effects the shape of an enzyme in terms of 3D tertiary structure and the effect on rate of reaction
A
- When acid is added, protons are attracted to and cluster around negative areas (e.g R-groups) of the enzyme, which alters the charge
- This interferes with the tertiary structure by interfering with the hydrogen bonds and ionic bonds of the active site
- Shape of active site changes so substrate cannot fit in effectively so rate of reaction decreases
24
Q
State the effect of slight/extreme pH on the reversibilty of an enzymes active site
A
- Slight pH changes alter the active site reversibly (can be restored if optimum pH is restored)
- Extreme pH changes alter the active site perminantly (thus its denatured)
25
Draw a **rate-pH** graph and label the **optimum pH/maximum rate** of **reaction**
26
Explain the effect of **substrate concentration** on **rate** using a **rate-substrate concentration graph**
- As **concentration** of **substrates increase** the **rate** of **reaction** also **increases**
- Because, more **enzyme-substrate complexes** form
- So more **enzyme-product complexes** form
- So more **product molecules** are formed
- **Substrate concentration** is the **limiting factor** because as it **increases**, **rate increases**
- Once the **maximum rate** is reached, **substrate concentration** no longer is the **limiting factor** because adding **more doesnt increase rate** of **reaction**
- This is because **all enzymes active sites** are occupied with **substrate molecules**
- **Another factor** is the **limiting factor** now
27
Explain the effect of **enzyme concentration** on **rate** using a **rate-enzyme concentration graph**
- As **enzyme concentration increases** more **active sites** become **available**
- More **frequent successful collisions** between the **enzyme molecules** and **substrate molecules**
- More **enzyme-substrate complexes** form
- So more **product molecules** are formed so **rate** of **reaction increases**
- **Enzyme concentration** is the **limiting factor** because as it **increases**, **rate increases**
- If the **substrate concentration** is **fixed/limited** all the **substrates** will be **occupying** an **active site** or have been released as **products**
- Therefore, **substrate concentration** now becomes the **limiting factor**
28
State how cells **regulate** their **metabolism** in terms of **enzymes**
- **Enzyme** **synthesis** and **enzyme degradation**
29
Explain why **initial rate** of **reaction** is the **fastest**
- **Initial rate** gives **maximum rate** of **reaction** because:
- At the start,
