module 2.1.4 - enzymes Flashcards
what type of protein is an enzyme
globular protein
what is the role of enzymes
act as catalysts to metabolic reactions in living organisms, which means they usually speed up metabolic reactions
- so that they occur at a reasonably fast pace even at body temperature
are required to build all the structures of the body (e.g. the cytoskeleton of a cell can be built up and reduced by enzyme activity), as well as to control the activity of the body
write an example of an intracellular and what it does
catalase
- converts hydrogen peroxide to oxygen and water
what is an intracellular protein
working inside cell
what is an example of extracellular proteins and what it does
amylase and trypsin
- released into the digestive system
what is an extracellular protein
working outside cell
what is 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
comment on the specificity of enzymes
refers to its ability to catalyse just one reaction or type of reaction. only one particular substrate molecule will fit into the active site of the enzyme molecule
comment on the lock and key hypothesis
the shape of the active site is caused by the specific sequence of amino acids. this produces a specific tertiary structure — the three-dimensional shape of the molecule
explain how enzymes catalyse reactions (comment of activation energy)
enzymes can speed up the rate of a reaction at body temperature
- they lower the activation energy required for the reaction to occur
what is activation energy
the amount of energy required to set off the reaction and break the bonds in the substrate molecule
explain 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
explain the course of an enzyme controlled reaction
substrate is complementary in shape to the enzyme’s active site, therefore the substrate enters the enzyme’s active site, combining to form the enzyme–substrate complex (ESC)
- destabilises and strains the bonds in the substrate, forming the enzyme product complex. The product is finally leaves the active site and the enzyme is then free to take up another substrate molecule
describe and explain the effect of pH on enzymes
All enzymes have an optimum pH — the pH at which they work best. Therefore, 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.
This affects the tertiary structure of the molecule and so alters the shape of the active site. 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. The higher the percentage of enzymes that are denatured, the slower the rate of reaction will be
describe and explain the effects of temperature on enzymes
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