Enzymes Flashcards
(31 cards)
What type of protein is an enzyme, and what structural feature is responsible for its specificity?
Enzymes are globular proteins with a specific tertiary structure.
What is the role of the enzyme’s active site?
The active site on the enzyme is the region that binds to a specific substrate.
Why are enzymes highly specific in their action?
Enzymes are highly specific due to the shape of the active site and their tertiary structure.
What determines the tertiary structure of an enzyme?
The tertiary structure is determined by its primary structure — the amino acid sequence
What can affect an enzyme’s tertiary structure?
The enzyme tertiary structure can be affected by pH, temperature, and mutation.
What happens if an enzyme’s tertiary structure changes?
The active site changes, so the substrate no longer binds leading no enzyme-substrate complex and the enzyme is denatured.
What is an enzyme?
An enzyme is a biological catalyst that speeds up chemical reactions without being used up.
What types of metabolic reactions do enzymes catalyse? Give one example of each.
Enzymes catalyse metabolic reactions:
• Intracellular (e.g. respiration inside cells)
• Extracellular (e.g. digestion in mammals)
Explain how enzymes affect both structure and function in organisms.
Enzymes affect structure (e.g. collagen production) and function (e.g. respiration).
How do enzymes lower the activation energy of reactions?
Enzymes lower the activation energy By forming an enzyme-substrate complex, they:
Bring molecules close together — reducing repulsion for binding
And Strain bonds — making bonds easier to break
Describe the Lock and Key model of enzyme action.
The lock and key model of the enzyme action is when the substrate fits exactly into the active site, like a key into a lock. This explains specificity.
What is the Induced Fit model and why is it preferred?
The induced fit modal states the active site changes shape slightly to fit the substrate perfectly. It explains greater specificity and how enzymes hold/break substrates more efficiently.
Explain how temperature affects enzyme activity.
• As temperature rises, molecules gain kinetic energy.
• This means that enzyme and substrate molecules move faster and collide more frequently with more energy.
• As a result More frequent and successful collisions increase the rate at which enzyme-substrate complexes form, so the rate of reaction increases.
If the temperature gets too high, it starts to affect the bonds that hold the enzyme’s 3D shape (like hydrogen and ionic bonds). • These bonds begin to break, causing the enzyme to denature. • When an enzyme denatures, its active site changes shape, so it no longer fits the substrate — this prevents enzyme-substrate complexes from forming. Decreasing enzyme reaction rapidly
What is the optimum temperature for enzymes in humans?
Approximately 37°C.
How does pH affect enzyme activity?
• Each enzyme has an optimum pH.
• Too far from optimum = H⁺/OH⁻ ions interfere with ionic/H-bonds → tertiary structure changes → denaturation
What is the optimum pH for pepsin and where is it found?
Pepsin has a pH 2 and found in the stomach
How does enzyme concentration affect the rate of reaction?
Increasing enzyme concentration increases the rate of reaction because there are more active sites available to form enzyme-substrate complexes. However, if the substrate becomes the limiting factor, further increases in enzyme concentration will have no effect on the rate.
How does substrate concentration affect the rate of enzyme activity?
As substrate concentration increases, more substrate molecules collide with enzyme active sites.
• This leads to more frequent formation of enzyme-substrate complexes, increasing the rate of reaction.
• Up to a saturation point (all active sites full) Eventually, every enzyme active site is occupied, meaning adding more substrate no longer increases the rate.
• Over time, substrate gets used up → rate decreases
Describe how competitive inhibitors affect enzyme activity.
• competitive Inhibitor is similar to substrate and binds to active site
• Blocks substrate therefore enzymes-substrate complexes can’t form
• Can be overcome by increasing substrate concentration
How does substrate concentration affect the rate of enzyme activity?
• ↑ substrate = ↑ rate (more enzyme-substrate complexes form)
• Up to a saturation point (all active sites full)
• Over time, substrate gets used up → rate decreases
Describe how non-competitive inhibitors affect enzyme activity.
• Inhibitor binds away from active site → changes active site shape
• Substrate no longer binds
• ↑ Substrate has no effect on inhibition
Describe an experiment to measure product formation by catalase.
• Catalase breaks H₂O₂ → O₂ + H₂O
• Measure volume of O₂ (e.g. gas syringe or displacement of water)
• Control temp (water bath), pH (buffer)
• Repeat + calculate mean rate = volume/time
• Use negative control (no enzyme)
Describe an experiment to measure product formation by catalase.
• Catalase breaks H₂O₂ → O₂ + H₂O
• Measure volume of O₂ (e.g. gas syringe or displacement of water)
• Control temp (water bath), pH (buffer)
• Repeat + calculate mean rate = volume/time
• Use negative control (no enzyme)
Describe how to measure starch breakdown by amylase.
• Mix starch + amylase
• Every 10 sec, place a drop into iodine on a spotting tile
• Blue-black = starch present, Orange = no starch
• Time how long until iodine no longer changes colour
• Repeat using different enzyme concentrations
• Can also test pH (use buffer) or substrate concentration
