75 WJEC Biology AS Level - Marianne Izen - 2nd Edition (1.4 Enzymes And Biological Reactions) Flashcards
Where are enzymes made?
Enzymes, like other proteins, are made inside cells.
Where do enzymes act?
There are three distinct sites where they act:
- Extracellular
- Intracellular, in solution
- Intracellular, membrane-bound
How do enzymes act extracellularly?
Enzymes are secreted from cells by exocytosis.
They then catalyse extracellular reactions.
Give an example of extracellular enzyme action in the human being?
Amylase, made in the salivary glands, moves down the salivary ducts to the mouth.
It then breaks down carbohydrates.
Give an example of extracellular enzyme action in microorganisms?
Saprotrophic fungi and bacteria secrete amylases, lipases and proteases on to their food.
These enzymes then digest it.
The organisms then absorb the products of digestion.
How do enzymes act intracellularly, in solution?
Intracellular enzymes act in solution inside cells.
Give examples of intracellular enzymes acting in solution.
Enzymes that catalyse glucose breakdown in glycolysis, a stage of respiration in solution in the cytoplasm
Enzymes in solution in the stroma of the chloroplasts catalyse the synthesis of glucose.
How do enzymes act intracellularly, being membrane bound?
Intracellular enzymes may be attached to membranes and then act.
Give examples of how enzymes act intracellularly, being membrane bound.
Enzymes on the cristae of mitochondria and the grana of chloroplasts, where they transfer electrons and hydrogen ions in ATP formation.
What is an enzyme-substrate complex?
An enzyme acts on its substrate, with which it makes temporary bonds at the active site, forming an enzyme-substrate complex.
What happens to the enzyme-substrate complex once the reaction is complete?
When the reaction is complete, products are released, leaving the enzyme unchanged and the active site ready to receive another substrate molecule.
What does the unique shape of the active site mean?
The unique shape of the active site means that an enzyme can only catalyse one type of reaction.
Other molecules, with different shapes, will not fit.
What do you mean by enzyme specificity?
‘Enzyme specificity’ means that an enzyme is specific for its substrate.
Describe the lock and key model of enzyme action.
‘Enzyme specificity’ means that an enzyme is specific for its substrate.
This concept gave rise to ‘the lock and key theory’: the substrate is imagined fitting into the active site as a key fits into a lock.
The shapes of lock and key are specific to each other.
Draw a diagram of the enzyme substrate complex
