Enzymes Flashcards
what are enzymes?
- biological catalysts
- globular proteins so soluble
enzymes catalyse reactions at which level?
- at cellular level e.g. respiration
- at whole organism level e.g. digestion in mammals
enzymes affect what?
- structure e.g. involved in collagen production (important protein in connective tissue of animals)
- function e.g. respiration
What is an intracellular enzyme?
enzymes that work inside cells
e.g. catalase
Catalase
- H2O2 - hydrogen peroxide is a toxic by-product of several cellular reactions. can kill cells if left to build up.
- Catalase works inside cells to catalyse breakdown of H202 to harmless 02 and H20
What is an extracellular enzyme?
works outside cells
e.g. Amylase and Trypsin
Amylase
- works in digestive system and is found in saliva
- secreted in the mouth by cells in salivary glands
- catalyses hydrolysis of starch into maltose (sugar) in the mouth
Trypsin
- works in digestive system and is produced by pancreas
- secreted in small intestine
- catalyses hydrolysis of peptide bonds (turns big polypeptides to smaller polypeptides)
What is a catalyst?
substance that speeds up chemical reactions without being used up in reaction
What is an active site?
- enzymes have active site with specific shape
- it is part of enzyme that substrate molecules bind to
- the specific shape of active site is determined by enzymes tertiary structure.
- active site is only formed by a few amino acids and is usually a cleft/depression
What must happen for an enzyme to work?
a substrate with a complementary shape to the enzyme’s active site must bind to it.
if substrate shape is not complementary, reaction will not be catalysed so enzymes work with only few substrates
What is the lock and key hypothesis?
- substrate with a complementary shape to the active site binds to it forming enzyme-substrate complex.
- substrate changes into product but is not released from enzyme forming enzyme-product complex.
- products are released and the enzyme remains unchanged after the reaction.
What is the induced fit hypothesis?
- As substrate binds to active site, active site changes shape, slightly to fit substrate more closely together
- enzyme-substrate complex forms and the bond son the substrate are strained so more likely to react.
- substrate is held in the active site by temporary bonds between substrate and R-groups of amino acids.
- enzyme-product complex forms and product is released
What is activation energy?
- it is the certain amount of energy that needs to be supplied to the chemicals before the reaction will start
- often provided as heat
What do enzymes do to activation energy?
- enzymes reduce activation energy needed so reactions happen at a lower temperature than they could without enzymes.
- they speed up the rate of the reaction