Paper 1 - Proteins and Enzymes Flashcards
What are proteins?
Polymers made up of one or more chains of amino acid monomers
Amino acid structure
amino group - side chain - carboxyl group
What is a dipeptide ?
2 amino acids joined together with a peptide bond in a condensation reaction
Fibrous proteins
- Long, thin molecules
- insoluble in water
- parallel chains + many cross linkages = long fibres
- strong + stable
- eg. Keratin in hair
Globular proteins
- Compact
- soluble in water
- e.g. Enzymes, antibodies, haemoglobin etc
Test for proteins
- Add a few drops of biuret solution
2.it present-colour change of pale blue to lilac
Primary structure of a protein
The sequence of amino acids in the polypeptide
Secondary structure of a protein
- Polypeptide chain coils into an alpha helix
- Polypeptide chain folds into a beta pleated sheet
- hydrogen bonds
Tertiary structure of a protein
Folding of the secondary structure into a specific 3D shape = functional properties
- disulphide, ionic, hydrogen bonds
Quaternary structure of a protein
More than one polypeptide chain eg. Hb
What are enzymes?
Globular proteins that act as biological catalysts
Lock and Key Model
Substrate (key) is complimentary to the active site (lock) so they bind perfectly
Induced fit model
The active site mould itself around the substrate and then becomes fully complementary = strain on the substrate and its bonds and lowers the energy needed to break the bonds
Immobilised enzymes
Enzymes that have been trapped into an inert matrix which prevents them from moving
- Makes recovery and reuse of enzymes easier
- Ensures that the enzymes doesn’t contaminate the final product
- Allows for continuous processes
- Offers enzyme stability in temp. and pH = greater efficiency
What are the factors affecting enzyme action?
- Temperature
- pH
- Substrate concentration
- Enzyme concentration
Temperature on Enzyme Action
Higher temperature:
- increase in kinetic energy of enzyme + substrate molecules
- collide with enough energy more frequently
- increases rate of reaction
Explain denaturation
When optimum temperature is reached, hydrogen bonds break → changes tertiary structure of enzyme → alters shape of active site → substrate will no longer fit the active site ( no longer complimentary)
pH on Enzyme Action
- Increase / decrease = decrease in rate of enzyme activity
- H+ ions affect the hydrogen + ionic bonds in enzymes which hold the tertiary structure
→ change in shape of active site
→ enzyme is no longer complimentary to the substrate
→ no ES complexes form
Define pH
Concentration of hydrogen ions present in a solution
pH = -log10 H+
Substrate concentration on Enzyme Action
As more substrate is added, all active sites become occupied - rate is at maximum = enzyme saturated → line plateaus
Substrate conc is no longer a limiting factor
Enzyme concentration on Enzyme Action
As the conc increases, there are more active sites available to form ES complexes = rate of reaction increases
All substrates become occupied = enzymes in excess - free ones with no substrate to bind to
Competitive inhibitors
Similar shape to substrate so can bind to the active site→ presents the substrate from entering it = no ES complexes formed
Non-competitive inhibitors
Attach themselves to the allosteric site → altering the shape of the active site → substrate = no longer complimentary → no ES complexes formed
