Enzymes as Biological Catalysts Flashcards
What do enzymes do?
Speed up the rate at which a reaction reaches equilibrium
Do enzymes affect the position of equilibrium?
No
What are enzymes made of?
Mostly proteins but some types of RNA (ribozymes`) can also be catalysts
What conditions are optimal for enzymes?
Body temperature, aqueous solution and neutral pH
What is specificity in relation to proteins?
Each enzyme has a limited range of substrates. Some can distinguish stereoisomers
What is enzyme potency?
Each enzyme can convert many substrate molecules into product per second
What happens at a reaction’s transition state?
The reaction takes place really rapidly which is unstable for the reactants
How do enzymes affect the transition state?
They bind to the reactants and make it stable, also reducing the activation energy by providing alternative pathways
What is the transition state?
The reaction intermediate species which has the greatest free energy hence why it is unstable
What causes glycogen storage disease?
It is an enzyme deficiency that results in failure of glycogen to enter the transition ‘phosphorylated’ state and so there is defective glycogen synthesis/breakdown
What are the symptoms of glycogen storage disease?
Hypoglycaemia, hepatomegaly (liver swelling), skin and mouth ulcers, bacterial/fungal infection and bowel inflammation/irritability
What is the treatment for glycogen storage disease?
Slow release glucose meal and feeding little and often to mimic glycogen conversion to glucose
What is a cofactor?
Metal ions (inorganic) which many enzymes depend on for catalytic activity
What do cofactors form with enzymes?
Metal co-ordination centre in the enzyme - metalloprotein
What is a coenzyme?
An organic molecule which many enzymes depend on for catalytic activity
What do coenzymes do?
Mostly associate with the coenzyme transiently and change charge or structure during the reaction but are regenerated eg VITAMINS
What are tightly bound coenzymes called?
Prosthetic groups
What is an enzyme without a cofactor called?
Apoenzyme
What is an enzyme with a cofactor called?
Holoenzyme = apoenzyme + cofactor
What do cofactors do?
Stabilise transition states
Where does the substrate bind in the enzyme?
Active site - a cleft or crevice that contains amino acids essential for catalytic activity for highly specific reactions
What is the lock and key model?
Active site of the unbound enzyme is complementary to the shape of the substrate
What is the induced fit model?
Binding of the substrate induces a conformational change in the enzyme resulting in complementary fit
What are isozymes?
Isoforms of enzymes - they catalyse the same reaction but have different properties and structure
Where are isozymes synthesised?
During different stages of foetal and embryonic development
Where are isozymes present?
In different tissues and in different cellular locations
In lactate dehydrogenase what are the 2 subunits and what do they do?
H (heart) - promotes aerobic respiration
M (muscle) - promotes anaerobic respiration
What is the role of creatine kinase?
It is a dimeric protein which binds to the muscle sarcomere. M form is produced in skeletal muscle (MM), B form is produced in brain (BB) and the heart produces both types = heterodimer (MB). Brain type in blood suggests stroke/tumour, whilst heart type suggests heart attack.
What is the role of enzyme activation by phosphorylation?
Can convert enzymes to active or inactive forms by protein kinases - fast, reversible and found in all cells - especially in energy generation
What are zymogens?
Inactive precursors of an enzyme
What happens in irreversible covalent modification to regulate enzyme activity?
Results in activation of enzymes. Zymogens are irreversibly transformed into active enzymes by cleavage of a covalent bond
What are some examples of digestive enzymes?
Trypsin, chymotrypsin, carboxypeptidase A and B, elastase, pepsin and phospholipase
What are some examples of blood coagulation factors?
Factors VII, IX, X, XI, and XIII, kallikrein and thrombin
What are some examples of enzymes in blood clot dissolving?
Plasminogen, and plasminogen activator
What are some examples of enzymes involved in programmed development?
Chitin synthetase, cocoons and collagenase
