We are both correct, but following different models for enzyme-substrate interaction.
I believe in the lock and key model, where a substrate is in a fixed shape (the lock), and the enzyme also has a specific shape, which functions as a key. This model depends on both substrate and enzyme having very particular shapes, that only fit together. My roommate believes in the induced fit model, the metaphor for which is the hand in glove. The glove is the substrate – it is loosely in the shape of a hand, but does not fully take “hand shape” until the hand, or enzyme, is inside it.
This model says the enzymes and substrates are not perfectly shaped for each other initially, but when the enzyme meets the substrate, the enzyme’s active site changes to fit the substrate due to a large number of weak interactions at the active site. Both models work, and are used in biochemistry, so we are both right – but should learn the other model. If K=1 then ?G? = 0If K>1 then ?G? < 0If K<1 then ?G? > 0Overall free energy of a reaction is important for understanding enzyme function, because free energy helps to dictate whether or not a reaction takes place at all. Enzymes facilitate speedier reactions by lowering the activation energy needed to form a transition state. If the delta G is negative, the reaction will occur spontaneously and exergonically. Transition state analogs are compounds that mimic the transition state created by the enzyme. They are chemically similar and bind to the substrate, but the enzyme cannot interact with them. Due to these properties, they can be used as inhibitors by preventing the enzymes binding to the substrates.
When the enzymes bond to the substrate, they lower the activation energy required to form the transition state. The weak bonds between the active site of the enzyme and the substrate helps the transition state to form with less energy needed. Products are synthesized faster because it is easier for intermediates to reach the transition state using enzymes. Both models of allosteric regulation contain two forms of the enzyme: T (tight, inactive) and R (relaxed, active). In the concerted model, or the “all or nothing” model, says that generally, proteins in solution will be in the T state. When a substrate binds to a subunit of an enzyme, immediately all of the subunits convert to the R, active state.
Analogous to a light switch that controls many lights in the same room, if you touch it and move it to the on position, all of the lights in the room will turn on at once. In the sequential model, binding the subunit of an enzyme to the substrate will change that subunit from T to R, but will not immediately change the others. Instead, a second binding to the substrate will change the state of the next subunit. Each subunit needs to bind to the substrate in order to change states, so it happens one at a time, and not all at once as in the concerted model.The Michaelis-Menten equation is an equation that shows the relationship between the concentration of the substrate and the velocity of the reaction. The graph is an asymptote, which initially looks linear but begins to level out, and never reaches Vmax.
The equation: V0 = VmaxS / (KM + S) Vmax is the maximum velocity possible, when the substrate concentration is maxed out. It is never reached on the graph. KM is called the Michaelis constant. It shows the concentration of the substrate when the reaction velocity is half of Vmax.
S is the molar concentration of the substrate. V0 is the initial velocity (moles/time) Competitive inhibitors have no effect on Vmax, but increase KM. Uncompetitive inhibitors lower KM and Vmax.
Noncompetitive inhibitors lower Vmax and do not have an effect on KM. Both competitive and noncompetitive inhibitors resemble the substrate, but noncompetitive inhibitors do not. Competitive inhibitors can be overcome by substrate concentration, but the other two cannot. All three have reversible inhibition. Competitive inhibitors bind at the active site on the substrate, uncompetitive inhibitors bind to the E-S complex, and with noncompetitive inhibition, the enzyme binds to both the substrate and the inhibitor, and the resulting E-S-I complex can’t make the product.