enzymes Flashcards
What are enzymes?
Biological catalysts that interact with
substrate molecules to facilitate
chemical reactions. Usually globular
proteins
Why are enzymes
important?
The allow reactions to happen quickly without extreme conditions (e.g. high temperatures and pressures) that are not possible in living cells because they would damage the cell components
What is a substrate?
A substance used, or acted on, by
another process or substance, e.g. a
reactant in an enzyme-catalysed
reaction
What is anabolism?
Anabolic reactions of metabolism that construct molecules from smaller units. These reactions require energy from the hydrolysis of ATP, and are catalysed by enzymes
What is catabolism?
Catabolic reactions of metabolism that break molecules down into smaller units. These reactions release energy, and are catalysed by enzymes
What is metabolism?
The sum of all of the different
reactions and reaction pathways
happening in a cell or organism
What is meant by ‘Vmax’?
Maximum initial velocity or rate of an
enzyme-catalysed reaction
Describe the mechanism of
enzyme action
Enzymes help the molecules collide
successfully, and therefore reduce
the activation energy required
What is the active site of an
enzyme?
An area within the tertiary structure of the enzyme that has a shape that is complementary to the shape of a specific substrate molecule. This allows the enzyme to bind to a substrate with specificity
What is the ‘Lock and Key
Hypothesis’ of enzyme
action?
In the same way that only the right key will fit into a lock, only a specific substrate will ‘fit’ the active site of an enzyme Enzyme + Substrate —> ESC —> Enzymes + Products
How does the enzyme act
on the substrate in the Lock
and Key Hypothesis?
• The substrate and enzyme molecules each have KE and are constantly moving randomly • If a substrate molecule successfully collides with an enzyme molecule, an ESC forms • The substrate is held in such a way by the enzyme that the right atom-groups are close enough to react • The R-groups within the active site of the enzyme will also interact with the substrate forming temporary bonds • These put strain on the bonds within the substrate, which also helps the reaction along • The substrate is converted into the product, an EPC formed, and then the products leave the enzyme
What is the ‘Induced Fit
Hypothesis’?
Modified lock and key explanation
for enzyme action: the active site of
the enzyme is modified in shape by
binding to the substrate
How does the enzyme act
on the substrate in the
Induced Fit Hypothesis?
• The active site of the enzyme changes shape slightly as the substrate enters to fit it better • An ESC is formed, and noncovalent R-group interactions (e.g. hydrogen bonds, ionic attractions, van Der Waals forces and hydrophobic interactions) bind the substrate molecule to the enzyme’s active site • This can weaken bonds in the substrate, lowering the activation energy for the reaction • The substrate is converted into the product forming an EPC • As the product molecules have a slightly different shape from the substrate molecule, they detach from the active site
What are intracellular
enzymes? (Give an example)
Enzymes that act within cells • Hydrogen peroxide is a toxic product of many metabolic pathways • Enzyme catalase break it down into O2 and H2O quickly, preventing its accumulation • Found in both animal and plant tissues
What are extracellular
enzymes?
Enzymes that act outside the cell that made them (in some organisms e.g. fungi, they work outside the body) • The substrates for intracellular enzymes (e.g. nutrients) are large molecules that can’t enter the cell directly though the cell membrane • Extracellular enzymes are released from cells to break down the large nutrient molecules into smaller molecules in the process of digestion
Describe the process of the
digestion of starch
1. Starch polymers are broken down into maltose (disaccharide) by amylase which is produced by the salivary glands and the pancreas. It’s released in saliva into the mouth, and in pancreatic juice into the small intestine 2. Maltose is broken down into glucose (monosaccharide) by maltase in the small intestine
Describe the process of the
digestion of proteins
Trypsin is a protease that catalyses the digestion of proteins into smaller peptides which can be broken further into amino acids by other proteases • It’s produced in the pancreas and released with the pancreatic juice into the small intestine, where it acts on proteins
Why does increasing the
temperature initial increase
the rate of reaction?
If a reactant mixture containing enzyme and substrate molecules is heated: • Both types of molecule will gain KE and move faster • This will increase the rate of successful collision • The rate of formation of ESCs increases and the rate of reaction increases, increasing the number of EPCs per second, up to a point
