3.1.4 - Proteins

What is the structure of an amino acid?

What is type of amino acid is formed via by the condensation reaction of two amino acids and what is the bond between them?

• Dipeptide

• Peptide bond

What is the primary structure of a protein?

The specific sequence of amino acids held by peptide bonds

After the primary structure of a protein is formed, where does it go and why?

The Golgi body to be packaged into the secondary structure of a protein

What is the secondary structure of a protein?

The sequence of amino acids folding to make either an α helix or a β pleated sheet held together by hydrogen bonds

Where do hydrogen bonds form on a secondary structure of a protein?

Between the carboxyl group of one amino acid and the amine group of another

What is the tertiary structure of a protein?

The further folding of the secondary structure forming a unique 3D shape held together by ionic and hydrogen bonds and disulphide bridges

What is the quaternary structure?

A protein made up of more than one polypeptide chain

What is the importance of the primary structure?

If an amino acid is in a different sequence the bonds that will form in the tertiary structure will have a different location resulting in a different 3D shape

What is the test and positive result for a protein?

• Add biuret

• Positive result = solution turns blue to purple

What are enzymes?

Proteins with a 3D tertiary structure

What is the function of enzymes and how do they do this?

They catalyse reactions by lowering the activation energy

How is the active site specific?

Due to the specific folding in the tertiary structure of the protein

What is formed after a substrate and enzyme bind together?

An enzyme-substrate complex

Describe the induced fit model

• The substrate enters the active site of the enzyme and is not fully complimentary

• The active site changes shape slightly to mould around the substrate and become complimentary to one another

• When the E-S complex occurs it puts strain on the bonds and lowers the activation energy

• The products are removed and the enzyme active site returns to its original shape

What are 5 factors that affect enzymes?

• Temperature

• pH

• Inhibitors

• Substrate concentration

• Enzyme concentration

How does temperature affect enzymes?

• If too low, not enough kinetic energy for successful collisions between enzyme and substrate

• If too high, enzymes denature and E-S complexes can’t form

How does pH affect enzymes?

If too acidic or too alkali that will interfere with the charges in the amino acids in the active site denaturing the enzyme causing less E-S complexes

How do substrate and enzyme concentration affect rate?

• If there are too few substrates then reaction will be slower as there will be fewer collisions

• If there are too few enzymes then active sites will become saturated and therefore unable to work faster

How do competitive inhibitors lead to fewer E-S complexes being formed?

They have a similar shape to the substrate and can bind to the active site preventing the substrate from binding with the enzyme therefore less E-S complexes

What happens to competitive inhibitors when more substrate is added?

The substrate will out-compete the competitive inhibitor knocking them out of the active site

How do non-competitive inhibitors lead to fewer E-S complexes?

They bind to the allosteric site which causes the active site to change shape meaning the substrate is no longer complimentary therefore less E-S complexes

What happens to the maximum rate of reaction when there is a high substrate concentration but competitive inhibitors are present?

It has the same maximum rate of reaction as no inhibitors