2.4 ENZYMES Flashcards
What is an enzyme?
- Biological catalysts made of globular proteins that speed up rate of metabolic reactions by lowering activation energy (via a different pathway)
Give an example an intracellular enzyme
- Catalase in the liver breaking down hydrogen peroxide into oxygen and water
Give an example of an extracellular enzyme
- Trypsin in the small intestines hydrolyses proteins
Describe the active site of enzyme
- An indented area complementary to a substrate molecule as a result of folding and bonding in the proteins tertiary structure
What is a catabolic reaction?
- A reaction that breaks down substrates
What is an enzyme-substrate complex?
- 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)
what is an enzyme-product complex?
- 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)
Describe the lock and key model
- 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
Describe the induced fit model
- 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
Draw an activation energy graph to show the action of enzymes
(EXOTHERMIC LAYOUT)
Define the optimum temperature for an enzyme
- The temperature at which they catalyse a reaction at the maximum rate
Explain the effect of increased temperature on an a mixture containing enzymes and substrates
- 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
Define activation energy
- The minimum amount of energy required for reactants to start forming products
Explain how high temperatures result in enzyme denaturation in regards to 3D tertiary structure and the effect on rate of reaction
- 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
Explain how high temperatures effect an enzymes primary structure
- NO EFFECT on primary structure
- Because heat does not break peptide bonds between amino acids
Draw a rate-temperature graph and label the optimum temperature/maximum rate of reaction
State the equation to determine rate of reaction for an enzyme
Explain what the temperature coefficient Q₁₀ tells us
- The increase in the rate of reaction when the temperature is increased by 10°C
State the formula for temperature coefficient Q₁₀
State what the value of Q₁₀ is for most reactions and explain what this means
- 2
- This means for every 10°C increase in temperature, the rate of reaction is doubled (x2)
Define acid
- A proton donor when they dissociate in aqueous solution
Define buffer
- A substance that minimised changes in pH on small additions of acid or alkali
Explain how pH effects the shape of an enzyme in terms of 3D tertiary structure and the effect on rate of reaction
- 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
State the effect of slight/extreme pH on the reversibilty of an enzymes active site
- 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)
Draw a rate-pH graph and label the optimum pH/maximum rate of reaction
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
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
State how cells regulate their metabolism in terms of enzymes
- Enzyme synthesis and enzyme degradation
Explain why initial rate of reaction is the fastest
- Initial rate gives maximum rate of reaction because:
- At the start,
