1. Action of Enzymes Flashcards
What is a catalyst
A chemical that speeds up the rate of reaction & remains unchanged & reusable at the end of the reaction
What are enzymes
Enzymes (a protein molecule) speed up chemical reactions by acting as biological catalysts
They catalyse metabolic reactions - both at a cellular level (eg. respiration) & for the organism as a whole (eg. digestion in mammals)
Role of enzymes
Speed up chemical reactions that would otherwise require high temps/pressures, extremes of pH & high concentrations of reactants - all factors that would kill the organism
- Life is completely dependent on enzymes
- Enzymes are more specific than chemical catalysts & so do not produce unwanted by-products & rarely make mistakes
3.
What can enzymes affect
Enzymes can affect:
- STRUCTURES in an organism (eg. enzymes are involved in the production of collagen, an important protein in the connective tissue of animals)
AS WELL AS
- FUNCTIONS (like respiration)
Enzyme action can be…
Intracellular - within cells
OR
Extracellular - outside cells
Intracellular enzyme example
Catalase:
- Hydrogen peroxide (H2O2) is the toxic by-product of several cellular reactions. If left to build up, it can kill cells.
- Catalase is an enzyme that works inside cells to catalyse the breakdown of hydrogen peroxide to harmless oxygen (O2) & water (H2O).
Extracellular enzyme example
Amylase:
- Amylase works outside cells in the human digestive system.
- Its found in saliva, & its secreted into the mouth by cells in the salivary glands. It catalyses the hydrolysis of starch into maltose in the mouth.
What type of proteins are enzymes
Globular proteins
Structure of enzymes
- Enzymes have an active site, which has a specific shape. The active site is the part of the enzyme that the substrate molecules (the substance that the enzyme interacts with) binds to
- The specific shape of the active site is determined by the enzyme’s tertiary structure
- For enzymes to work, the substrate must fit into the active site (its shape must be complementary). If the substrate shape doesnt match the active site, the reaction wont be catalysed. This means enzymes work w very few substrates (usually one).
What is activation energy
In a chemical reaction, a certain amount of energy needs to be supplied to the chemicals before the reaction will start.
Its often provided as heat.
Enzymes and activation energy
- Enzymes reduce the amount of activation energy that’s needed, often making reactions happen at a lower temp than they could w/o an enzyme.
This speeds up the rate of reaction. - When a substrate binds to an enzyme’s active site, an enzyme-substrate complex is formed. Its the formation of this that lowers the activation energy
Why does the formation of an enzyme-substrate complex lower activation energy
- If 2 substrate molecules need to be joined, attaching to the enzyme holds them close tg, reducing any repulsion between the molecules so they can bond more easily.
- If the enzyme is catalysing a breakdown reaction, fitting into the active site puts a strain on bonds in the substrate. This strain means the substrate molecule breaks up more easily.
see pg42 for graph of activation energy & enzymes
What is the ‘Lock and Key’ model
Enzymes only work with substrates that fit their active site. Early scientists came up with the ‘Lock and Key’ model.
This is where the substrate fits into the enzyme’s active site in the same way that a key fits into a lock.
see pg43 for dia
How did the ‘Induced Fit’ model come about
- Scientists soon realised that the ‘Lock and Key’ model didnt give the full story.
- The enzyme & substrate do have to fit tg in the first place, but new evidence showed that the enzyme-substrate complex changed shape slightly to complete the fit.
- This locks the substrate even more tightly to the enzyme. Scientists modified the old ‘Lock and Key’ model & came up w the ‘Induced Fit’ model
What is the ‘Induced Fit’ model
- The “Induced Fit’ model helps to explain why enzymes are so specific & only bond to one particular substate
- The substrate doesn’t only have to be the right shape to fit the active site, it has to make the active site change shape in the right way as well.
see pg43 for dia
