Enzymes as biological catalysts Flashcards
What do enzymes do?
They are catalysts that speed up chemical reactions and make up the process of metabolism.
They speed up the rate at which a reaction reaches equilibrium
What characteristics define all enzymes?
Catalysts Proteins Efficient Specific Potent - each enzyme molecule can convert many substrate molecules into product per second
What must enzymes pass to allow the reaction to occur?
Activation energy barrier
What is the transition state?
The transition state is the reaction intermediate species which has the greatest free energy
How do enzymes reduce the activation energy?
They provide an alternative reaction pathway
What is a cofactor?
A small metal ion molecule that increases the enzymes catalytic activity
What is a coenzyme?
A small organic molecule that increases the enzymes catalytic activity
What do metal cofactors form in the centre of an enzyme?
A metal co-ordination centre called a metalloprotein
What do coenzymes change during the course of the reaction?
Their charge or structure
What is a prosthetic group?
A tightly bound coenzyme
What is an apoenzyme?
An enzyme without a cofactor
What is a holoenzyme?
An enzyme with a cofactor
What are some examples of a cofactors?
Zinc, Iron, Copper, coenzymes such as ATP, NAD and FAD
What do many vitamins function as?
Coenzymes
What is an example of an enzyme that shows induced fit?
Hexokinase which changes shape as glucose binds to the active site, ATP is a co-substrate
What are some examples of active sites?
The three pancreatic protrases that contain reactive serine residue which catalyse the hydrolysis of peptides
What 2 factors affect enzyme activity?
Temperature and pH
What is an isoenzyme?
An isoform of an enzyme that catalyses the same reaction but has different properties and structure
When can different isoenzymes be synthesized?
Foetal and embryonic development
Different tissues
Different cellular locations
What is an example of an isoenzyme?
Lactate dehydrogenase which when containing 2 subunits in the heart promotes anaerobic respiration but when in muscle promotes anaerobic respiration
What is an example of reversible covalent modification?
Phosphorylation
What are phosphorylation reactions carried out by?
Kinases and dephosphorylation carried out by phosphatases
What does the irreversibel covalent modification result in?
Irreversible activation of enzymes
What is a zymogen?
An inactive precursor of an enzyme that is irreversibly transformed into an active enzyme by the cleavage of a covalent bond
