Proteins & Enzymes Flashcards
What do all proteins contain?
contain the elements Nitrogen (N), Carbon (C), and Hydrogen (H) and oxygen (O). Some also contain sulphur (S)
Structure of amino acids
R groups can be:
Positively charged +
Negatively charged -
Hydrophilic* attracted to water
Hydrophobic* repelled by water
Describe how a peptide bond is formed between two amino acids to form a dipeptide
- Condensation reaction
- Between amine and carboxyl
- Forms peptide bond
Number of peptide bonds
The number of peptide bonds in the chain will be one less than the total number of amino acids originally joined together
Protein Structure
- Polymer of amino acids;
- Joined by peptide bonds;
- Formed by condensation reactions
primary structure:
number and sequence of amino acids in a polypeptide chain
secondary structure:
way the polypeptide chain folds or coils into alpha helixes or/and beta pleated-sheets. The secondary structure is held together by WEAK hydrogen bonds between each amino acid
tertiary structure:
further folding of the polypeptide chain into a specific complex 3D shape.
3 different bonds:
1. WEAK HYDROGEN BONDS (between H and O)
2. IONIC BONDS, also weak bonds, which form between oppositely charged R groups.
3. DISULPHIDE BRIDGES, Strong bonds between R groups containing -SH groups
quaternary structure:
two or more polypeptide chains joined together
Haemoglobin has 4 polypeptide chains.
This is a GLOBULAR, functional protein.
Collagen has 3 polypeptide chains.
This is a FIBROUS, structural protein.
Describe & explain how you could use the biuret test to distinguish a solution of enzyme, lactase, from a solution of lactose
Add Biuret reagent to both solutions
Lactase enzyme will give a purple colour
Because Lactase is a protein;
Lactose reducing sugar will remain blue
How do enzymes increase the rate of reaction
lowering the activation energy needed for a chemical reaction.
They do this by distorting the bonds in the substrate during the formation of an ENZYME SUBSTRATE COMPLEX
LOCK & KEY MODEL
- The active site is rigid and does not change shape
- The substrate binds to the enzymes active site
- The substrate fits exactly into the active site – they are complementary
- Products are formed and no longer fit into the active site, so is released
- The enzyme is free to take part in another reaction
Sucrase does not hydrolyse lactose.
Use your knowledge of the way in which enzymes work to explain why
- Lactose has a different shape
- Does not bind to active site of enzyme
- The substrate and the enzyme active site are not complementary;
- No ES complexes form
Induced Fit Model
- The substrate enters the enzymes active site and binds to it Forming the ESC
- The binding of the substrate molecule induces the change in the shape of the active site.
- The ‘slight’ change in shape of the specific 3D tertiary structure of the active site, distorts the bonds within the substrate molecule which lowers the Ea of the reaction.
- When substrate leaves, the active site returns to its original shape
Describe one way that the lock and key model is different from the induced fit model
- Active site does not change shape
- substrate is
- complementary
An enzyme catalyses only one reaction. Explain why.
- Enzyme has active site is a specific shape;
- Only one substrate binds
When a pathogen causes an infection, plasma cells secrete antibodies which destroy this pathogen.
Explain why these antibodies are only effective against a specific pathogen
- Antigens have specific tertiary structure;
- Antibody is complementary to antigen
- Antibody-antigen complex forms
Describe how a change in the base sequence of the DNA coding for an enzyme may result in a non-functional protein.
- Change in primary structure changes
sequence of amino acids; - Hydrogen bonds and Ionic bonds and Disulphide bonds form in different positions;
- Alters the tertiary structure of the enzyme
- No Enzyme-Substrate complexes can be formed
Factors affecting Enzyme action: Temperature
If the temperature is increased, beyond the optimum, then the atoms have more kinetic energy. This causes the weak Hydrogen bonds and ionic bonds to break, this causes a change in the specific tertiary structure, which may change the shape of the active site.
no longer be complementary to the enzymes substrate, meaning less enzyme substrate complexes can be formed.
The enzyme is denatured and can no longer catalyse any chemical reactions.
