Enzymes/Proteins Flashcards
Primary structure of a protein
The sequence of amino acids in the polypeptide chains.
The secondary structure of proteins
The way the chain of amino acids of the polypeptide is folded.
It is held by hydrogen bonds.
The tertiary structure of proteins
The way the whole molecule is folded.
It is held by ionic and disulphide bonds.
The quaternary structure if proteins
It is a number of polypeptide chains linked together.
It is often associated with non-protein groups to make a protein.
Test for proteins (Buiret)
Add sodium hydroxide solution
Then add copper sulphate and mix
If a protein is present it turns purple.
Enzymes
They are globular proteins. They are biological catalysts so they speed up reactions but are not used up. They lower the activation energy needed to start a reaction, so the reaction can start at a lower temperature.
Active site
It is the place where the substrate binds to.
The active site of enzymes is a specific shape.
Only substrates that are the right shape will bind and form enzyme-substrate complexes.
This explains why enzymes only catalyse one reaction.
The lock and key model
The active site does not change shape as it is fixed.
The active site is complementary to the substrate before binding.
The induced fit model
The active site is not complementary to the substrate.
The active site changes shape when the substrate binds to it as it is flexible.
The change in active site shape allows the substrate to fit and form enzyme-substrate complexes by distorting the bonds.
Amino acids
Amino acids make up proteins.
They have a central carbon, amino group (NH2), carboxyl group (COOH), hydrogen atom (H) and R group (varies).
Amino acids join to mate dipeptides or polypeptides.
A condensation reaction forms a peptide bond between the C atom of one amino acid and the N of the other.
They can be broken by a hydrolysis reaction.
Effects of increasing temperature on enzymes
It increases rate of reaction to a point because it gives particles kinetic energy to move. This means it can form more enzyme-substrate complexes. This is at about 45 degrees.
Effect on enzymes when temperature is too high
The enzyme denatures because the binds holding the tertiary structure are broken.
This changes the shape of the active site of the enzyme.
This means fewer enzyme-substrate complexes can be formed.
More enzyme molecules denature as temperature increases more.
Effects of pH on enzymes
Each enzyme has an optimum pH.
A change in pH can denature the enzyme.
Bonds holding the tertiary structure are broken.
Active site changes shape.
Fewer/no enzyme-substrate complexes.
More extreme the pH the more enzymes denature.
Effects of increasing the concentration of the substrate on enzymes
It increases the rate of reaction to a point.
This is until all the active sites are full.
This provides the maximum amount of enzyme-substrate complexes.
Competitive inhibition
The inhibitor is a similar shape to the substrate/complementary to the active site.
It binds with the active site of the enzyme.
This prevents the substrate binding with the active site meaning fewer/no enzyme-substrate complexes.
