Enzymes Flashcards
(38 cards)
What are immobilised enzymes?
Enzymes that are fixed to an inert matrix over which the substrate molecules move.
State the two main ways enzyme immobilisation can be achieved.
1) Entrapment- held inside a gel, e.g. silica gel
2) Micro-encapsulation- trapped inside a micro-capsule, e.g. alginate beads
Define metabolism
The sum of all the enzyme controlled chemical reactions taking place
State the two main types of reactions that make up metabolism.
Anabolic and catabolic reactions
What is anabolism?
A set of metabolic pathways that synthesise complex molecules from smaller, simpler molecules.
What is catabolism?
A set of metabolic pathways that breakdown complex molecules into smaller, simpler molecules.
What is an enzyme?
• A biological catalyst used to speed up the rate of intracellular and extracellular biochemical reactions
• Not used up or permanently altered
What is an intracellular enzyme?
An enzyme that acts within cells, e.g. catalase.
What is an extracellular enzyme?
An enzyme is secreted by cells and functions outside of cells, e.g. amylase.
What is the active site of an enzyme?
A region on an enzyme that is complementary to the shape of a specific substrate. The substrate binds and the reaction takes place.
Why is an active site described as ‘specific’?
• The 3D structure of each enzyme (including the active site) is unique due to the presence of different side chains and branches
• Only specific substrates complementary to the active site can bind
Define activation energy
The minimum amount of energy required for a reaction to take place.
What is catalysis?
• An increase in the rate of a chemical reaction using a catalyst (such as an enzyme)
• The catalyst lowers the activation energy of the reaction
Describe the ‘lock and key’ model.
1) Substrate(s) and the active site of the enzyme come into contact
2) Substrate(s) binds, enzyme-substrate complex forms
3) Reaction takes place, product(s) formed in an enzyme-product complex
4) Product(s) released from the active site. The active site is now free to bind to another substrate
What is the induced fit hypothesis?
A model of enzyme action which states that once a specific substrate binds to the active site, the enzyme undergoes subtle conformational changes. This puts a strain on the substrate, lowering the activation energy for the reaction.
What factors affect the rate of an enzyme-controlled reaction?
• Temperature
• pH
• Substrate concentration
• Enzyme concentration
Explain how increasing temperature above the optimum affects the rate of an enzyme-controlled reaction.
• Temperature increases above the optimum
• Increased vibrations break hydrogen and ionic bonds in tertiary structure
• Active site changes shape, enzyme is denatured
• No more enzyme-substrate complexes can form
• Rate of reaction decreases
How does temperature effect the rate of enzyme-controlled reactions?
• As temperature increases molecules have more KE
• Molecules move faster and collide more frequently
• More enzyme-substrate complexes form
• Rate of reaction increases
• Rate peaks at the optimum temperature
How does pH affect the rate of enzyme-controlled reactions?
• Enzymes have an optimum pH
• pH shifts from the optimum
• Hydrogen and ionic bonds in the tertiary structure are altered
• Interaction of polar and charged R-groups changes
• Active site changes shape, enzyme is denatured
• Rate of reaction decreases
What is a buffer?
A molecule that maintains a constant pH in a solution when small volumes of acid (H+) or base (OH-) are added.
How does substrate concentration affect the rate of an enzyme-controlled reaction?
If an enzyme concentration is fixed, the rate of reaction increases proportionally to the substrate concentration.
Once all active sites become full, the rate of reaction remains constant (graph plateaus)
Enzyme concentration is a limiting factor
How does substrate concentration affect the rate of an enzyme-controlled reaction?
If an enzyme concentration is fixed, the rate of reaction increases proportionally to the substrate concentration.
Once all active sites become full, the rate of reaction remains constant (graph plateaus)
Enzyme concentration is a limiting factor
How does enzyme concentration affect the rate of an enzyme-controlled reaction?
If substrate concentration is fixed, the rate of reaction increases proportionally to the enzyme concentration.
When all of the substrate occupy active sites, the rate of reaction plateaus
(substrate concentration is a limiting factor)
How does enzyme concentration affect the rate of an enzyme-controlled reaction?
If substrate concentration is fixed, the rate of reaction increases proportionally to the enzyme concentration.
When all of the substrate occupy active sites, the rate of reaction plateaus
(substrate concentration is a limiting factor)
