Enzymes Flashcards
what is the role of enzymes?
Enzymes are globular proteins.
They act as catalysts to metabolic reactions in living organisms, which means they lower the activation energy required for the reaction to occur.
describe intracellular and extracellular enzymes
Enzymes may be intracellular (working inside cells), such as catalase which converts hydrogen peroxide to oxygen and water. Alternatively, enzymes may be extracellular (working outside cells), such as the digestive enzymes amylase and trypsin, which are released into the digestive system.
what are some of the properties of enzymes
- the molecule has a three-dimensional shape — its tertiary structure
- part of the molecule is an active site that is complementary to the shape of the substrate molecule
- each enzyme is specific to the substrate
- there is a high turnover number
- they have the ability to reduce the energy required for a reaction to occur
- their activity is affected by temperature, pH, enzyme concentration and substrate concentration
- the enzyme is left unchanged at the end of the reaction
How does pH affect enzyme activity?
they will not work as quickly at a pH outside their optimum range.
This is because the hydrogen ions that cause acidity affect the interactions between R groups in the tertiary structure of the enzyme, so hydrogen and/or ionic bonds may break.
The shape will no longer be complementary to the shape of the substrate molecule, so the enzyme substrate complex will no longer form, meaning that the enzyme is denatured.
describe the lock and key hypothesis
Only one particular substrate molecule will fit into the active site of the enzyme molecule. This is because of the shape of the active site- a tertiary structure specific to the substrate
describe the induced fit hypothesis
The active site of an enzyme molecule does not have a perfectly complementary fit to the shape of the substrate.
When the substrate moves into the active site, it interacts with the active site and interferes with the bonds that hold the shape of the active site.
As a result, the shape of the active site is altered to give a perfect fit to the shape of the substrate.
This changes the shape of the active site, which also affects the bonds in the substrate, making them easier to make or break (and therefore reducing the activation energy).
How does temperature affect enzyme activity? (6 marker)
Each enzyme has an optimum temperature at which it is most active. This temperature is often 37°C (in mammals), but it may be different in other organisms.
At low temperatures (0–45°C), the activity of most enzymes increases as temperature rises.
At low temperatures, the molecules have little kinetic energy.
They collide infrequently with the substrate molecules and activity is reduced.
As temperature rises, the molecules gain more kinetic energy.
They collide more frequently with the substrate molecules and are more likely to have sufficient energy to overcome the required activation energy.
Therefore, activity increases.At higher temperatures, the increased kinetic energy causes the enzyme to vibrate, causing vibration within the protein molecule, so hydrophilic and hydrophobic interactions, as well as hydrogen bonds and ionic bonds in the tertiary structure break.
This changes the 3D structure/conformation of the protein, so the enzyme loses its shape, becoming denatured.
The active site no longer fits the shape of the substrate and activity reduces quickly to zero.
How does enzyme concentration affect enzyme activity?
more enzyme molecules = more active sites
greater likelihood of collisions between the enzyme and the substrate molecules.
More interactions per second mean a higher rate of reaction.
As the enzyme concentration increases, so does the rate of reaction.
How does substrate concentration affect enzyme activity?
If the substrate concentration is high, there is a greater chance of successful collisions between the enzyme active sites and substrate molecules, forming enzyme substrate complexes and thus resulting in higher product formation. As the substrate concentration increases, so does the rate of reaction.
If the number of enzyme molecules is limited, the rate of reaction plateaus once all the enzyme active sites are fully occupied as enzymes are working at maximum rate.
Therefore further increases in substrate concentration will have no effect as enzyme concentration will then be the limiting factor.
what are coenzymes?
Coenzymes are larger organic substances that take part in the reaction. They usually transfer other reactants between enzymes
what are examples of coenzymes?
coenzyme A, which takes part in aerobic respiration, and NAD, which is involved in transporting hydrogen atoms to the inner mitochondrial membrane.
Coenzyme A and NAD are both made from the B vitamins.
what are cofactors?
inorganic substances, usually metal ions.
They increase rate of catalysis by binding to the active site of the enzyme so that the enzyme-substrate complex forms more quickly and easily.
what are examples of cofactors?
Cl– in amylase and Zn2+ as a prosthetic group in carbonic anhydrase.
what are inhibitors?
substances that reduce the rate of reaction and fit into a site on the enzyme.
what is a competitive inhibitor?
have a shape similar to the shape of the substrate and complementary to the shape of the active site.
They fit into the active site, stopping the substrate molecules fitting in.
This reduces the number of available active sites.
