Enzymes and all that Flashcards
(24 cards)
What do enzymes do?
Make a reaction more kinetically favorable (lower activation energy) but cannot effect G or thermodynamics
What are cofactors
metal ions or small molecules that bind to the active site and help stabilize the catalysis (usually using charges to stabilize)
What are coenzymes
organic, larger molecules that bind to the active site to help carry something to the catalysis (acetyl groups usually)
Why are enzymes regulated in the cell
metabolic pathways need to be regulated to maintain cell health and preserve energy
example: glycolysis could be in progress to glycogen breakdown could be happening in the cell, leaving a net energy loss
Ways enzymes are regulated: Covalent Modification
attachment (covalently) or breaking bonds to inhibit or inactivate an enzyme for a period of time
methylation (addition or subtraction of a methyl group)
acetylation (addition or subtraction of an acetyl group)
Glycosylation (addition or subtraction of a sugar)
Ways enzymes are regulated: Proteolytic Cleavage
an enzyme that is formed in an inactive form (formally called zymogens) and needs to be covalently modified when needed to function
Ways enzymes are regulated: Allosteric Regulation
binding of a molecule to a site other than the active site, an allosteric site, to change the enzyme to increase of decrease catalysis
Ways enzymes are regulated: Feedback Inhibition
downstream products in a series of enzymes and reactions in tandon inhibit or increase upstream reactions
important in glycolysis
ATP- inhibitor
AMP- activator (molecule indicating use of ATP)
Enzyme Kinetics
study of the formation of products from substrates in the presence of an enzyme
V =?
reaction rate= moles of product formed/ per second
[S]= ?
concentration of substrate
Vmax = ?
reaction rate when enzyme is saturated (enzyme is fully used and adding more substrate does not change reaction rate)
Km = ?
substrate concentration [K] when the reaction rate is at half of its maximum (Vmax)
What Km means
A high Km shows low affinity between enzyme and substrate
A low Km shows high affinity between enzyme and substrate
How do enzymes exhibit cooperativity
When working in tandem with one another, enzymes can change their affinity for substrate based on the reactions of other enzymes
Positive cooperativity- the binding of a substance to one subunit increases the affinity of other subunits for the substrate
Negative cooperativity- the binding of a substance to one subunit decreases the affinity of other subunits for the substrate
What is the difference between a regular saturation kinetics graph and a sigmoidal kinetics (positive cooperativity) graph
similarities- x axis (independent) is substrate concentration for both, y axis (dependent) is reaction rate for both, both have a vmax showen where adding more X does not effect the Y
differences- the cooperativity graph has a S (sigmoidal) shape indicating low affinity for substrates until a subsrate binds to one unit and increases affinity while the traditional has a linear portion until the enzyme is beginning to become saturated
Competitive inhibition
molecules compete to bind to the active site with the substrates
leads to lower affinity= lower Km
reversible if more substrate is added = no change in Vmax
Competitive inhibition effect on Michaelis graph
linear before Vmax hit
Noncompetitive inhibition
molecules binding to allosteric site to slow or prevent catalysis but affinity for substrate is not changed meaning Km= same
Nonreversible= Vmax lowered
Noncompetitive inhibition effect on Michaelis graph
Vmax lowered, same curve shape but plateaus earlier
Uncompetitive inhibition
molecule that binds to the allosteric site after the substrate and enzyme have bound together and change the conformation of enzyme to decrease its ability to catalyze the substrate
cannot bind unless substrate is already bound= higher affinity= lower Km
prevents enzyme and substrate from detaching= alters catalytic capability= lower Vmax
Uncompetitive inhibition effect on Michaelis graph
Overall shifts left and plateaus farther down (lower Km and Vmax)
Mixed type inhibition
Mixed type inhibition effect on Michaelis graph
