2.1.4 - ENZYMES Flashcards
What is an enzyme?
A biological catalyst (speeds up chemical reactions without being used up in the reaction itself)
GLOBULAR PROTEINS
What is an active site?
The area of the enzyme where the reaction with the substrate takes place
State an example of an intracellular enzyme
- Catalase breaks down hydrogen peroxide into harmless oxygen and water
- Hydrogen peroxide is the toxic by-product of several cellular reactions (if built up, can kill cells)
State an example of an extracellular enzyme
- Amylase and Trypsin work in the human digestive system
- Amylase in saliva catalyses the hydrolysis of starch into maltose
Trypsin catalyses the hydrolysis of peptide bonds - turning big polypeptides into smaller ones (which get broken down into amino acids by other enzymes)
Describe the ‘Lock and Key’ model
- Enzymes only work with complementary substrates that fit their active site
Describe the ‘Induced Fit’ model
- The substrate binds to the active site + active site changes shape to fit the substrate more closely
What is an enzyme-substrate complex?
A molecule formed when an enzyme comes into perfect contact with its complementary substrate
Explain why enzymes are so specific.
- Different enzymes have different shapes active sites, determined by their tertiary structures since they’re proteins
- For the enzyme to work, the substrate has to fit into the active site (be complementary)
List factors affecting enzyme activity
- Enzyme concentration
- Substrate concentration
- pH
- Temperature
Explain temperature as a factor affecting enzyme activity
- Rate of reaction increases up to optimum temperature
- Even if higher than optimum temperature, rate of reaction will begin to decrease and enzymes will denature
Explain pH as a factor affecting enzyme activity
- All enzymes have an optimum pH
- Most work best at pH 7
- Above + below optimum pH, rate of reaction will decrease
Explain enzyme concentration as a factor affecting enzyme activity
- Rate of reaction increases as enzyme concentration increases as there are more active sites for substrates to bind to
- However, after a certain point, rate of reaction will plateau + won’t increase simply because even if you add more enzymes, there aren’t any more substrates to bind to them
Explain substrate concentration as a factor affecting enzyme activity
- Rate of reaction increases as substrate concentration increases as more enzyme-substrate complexes are formed
- However, beyond a certain point the rate of reaction no longer increases as enzyme concentration becomes the limiting factor
What is an inhibitor?
A substance which slows down or stops a reaction by affecting the binding of substrates to enzymes
- reversible or irreversible
- competitive or non-competitive
What is a reversible inhibitor?
reversible inhibitors bind to the active site through hydrogen bonds and weak ionic interactions –> don’t bind permanently
What is an irreversible inhibitor?
irreversible inhibitors include heavy metal ions (e.g. mercury + silver) which cause disulphide bonds within the protein structure to break (changes shape of active site)
What is a competitive inhibitor?
Similar in shape to substrate molecules
They compete with substrate molecules to bind to the active site - but no reaction takes place
They just block the active site so substrates cant bind
What is a non-competitive inhibitor?
Bind to enzyme away from active site and instead at ALLOSTERIC SITE
- Causes enzyme’s active site to change shape so substrates can no longer bind to it
What is a cofactor?
- Some ions require inorganic ions to function properly
- They help the enzyme and substrate bind together
- Aren’t used up or changed in any way (don’t participate in the reaction)
What is a coenzyme?
- Larger organic (carbon-containing) cofactors
- Participate in the reaction + changed by it (like a second substrate)
- Can carry chemical groups or electrons between enzymes
- VITAMINS AREA SOURCE OF COENZYMES
Give an example of a cofactor.
- Chloride ions act as a cofactor for amylase
- For amylase to break starch down into maltose, chloride ions must be present
What is a prosthetic group?
A cofactor that is tightly bound to an enzyme + permanent
Give an example of a prosthetic group.
Haemoglobin contains a prosthetic haem group which contains iron permanently bound to the molecule, which serves as a means of binding oxygen
