Regulating enzyme function Flashcards
What are the different types of regulation of enzyme activity?
Short term
Long term
What are the different types of short term regulation of enzyme activity?
Changing substrate and product concentration
Changing enzyme conformation
How can enzyme conformation be changed?
Allosteric regulation
Proteolytic cleavage
Chemical modification
What are the different types of long term regulation?
Change in rate of protein synthesis
Change in rate of protein degradation
What are isoenzymes?
Catalyse same reaction
but have different structure and hence different kinetic properties
What is an example of changing product concentration regulating enzyme activity?
Product inhibition
What is product inhibition?
Product of a reaction inhibits the forward reaction
What are the two different states of allosteric enzymes?
Tense state, T state
Relaxes state, R state
What is the affinity of allosteric enzymes in the T state for their substrate?
Low affinity
What is the affinity of allosteric enzymes in the R state for their substrate?
High affinity
What shape does a graph of x axis-substrate concentration against y axis-reaction velocity for allosteric enzymes take?
Sigmoid curve
Why does a graph of x axis-substrate concentration against y axis-reaction velocity for allosteric enzymes take a sigmoid curve shape?
Enzyme initially in T state
binding of substrate is hard
After first substrate has bound, enzyme converted to R state
binding of substrates is easy
What do allosteric activators do?
Bind to enzyme
increase proportion of enzymes in R state
What do allosteric inhibitors do?
Bind to enzyme
increase proportion of enzymes in T state
What is an example of a chemical group commonly added to/removed from enzymes?
Phosphate group
What type of enzyme is responsible for adding phosphate groups to enzymes?
Protein kinases
Where do protein kinases get the phosphate group from?
Terminal phosphate of ATP
What type of enzyme is responsible for removing phsophate groups from enzymes?
Protein phosphatase
What type of reaction is involved in removing phosphate groups from enzymes?
Hydrolysis
Why is phosphorylation effective at regulating enzyme function?
Adds negative charges
A phosphate group can make hydrogen bonds
Rate of phosphorylation/dephosphorylation can be adjusted
Allows for amplification
What is an enzyme cascade?
Series of reactions
each catalysed by an enzyme
How do enzyme cascades give amplification?
Each enzyme can catalyse many reactions
producing many product molecules
What is reciprocal regulation?
Same signal activates one enzyme
inhibits another enzyme
What is the purpose of reciprocal regulation?
Activate one pathway, inhibit another pathway
these pathways are usually opposites of one another
What is a zymogen?
Inactive form of enzyme
How are zymogens converted into active enzymes?
Through the action of another active enzyme
What is the initial form of digestive enzymes?
Zymogens
How are digestive enzyme zymogens activated?
Proteolytic cleavage by other active enzymes
What is the enzyme largely responsible for activating digestive enzyme zymogens?
Trypsin
What inhibits trypsin?
Pancreatic trypsin inhibitor
What is a1-antitrypsin?
Plasma proteins
inhibits range of proteases
What is the molecular cause of emphysema?
Defect in a1-antitrypsin
What does a defect in a1-antitrypsin cause in emphysema?
Elastase in lungs is not inhibited
digests elastin in lungs
What is the target of short term regulation of enzyme activity?
Enzymes already present in cell
What is the target of long term regulation of enzyme activity?
Change enzyme amount in cell
How does short term regulation differ from long term regulation in terms of time?
Long term takes longer to have effect
and lasts longer
