Some problems for this section can be found on the worksheet for this week. These can be used for credit.
To understand the basic energy rules, view the slideshow which is on D2l (it is also linked here)
Enzymes: First watch this video and answer the questions. Do not click on the “next” button when prompted, the video will advance automatically here.
https://edpuzzle.com/embed/media/55836053ddd82e833b378cbe
Know what substrates are and how they relate to enzyme catalyzed reactions.
Example what is the substrate in this enzyme catalyzed reaction described in the video?
The substrate is the reactant (or reactants) in a reaction involving an enzyme. The reactant fits into the active site of an enzyme which in this reaction is trypsin. Note that the enzyme is shown above the arrow. Doing this helps remind you that the enzyme is not changed by the reaction. One enzyme can do many reactions (like a machine)
Know how enzymes catalyze biological reactions, specifically their effects on activation energy and their mechanism of action.
View this activity
This shows how enzymes speed up reactions: They can get molecules closer to each other and in the right orientation.
Another concept in how enzymes speed up reactions is activation energy. Imagine you have a homework assignment due next week. You could do it now, or you could put it off until right before it is due. The activation energy is the energy needed to get the process started. Note that the homework might take you an hour whether you do it now or later. The activation energy is just what it takes to get started. Enzymes decrease activation energy as shown in the diagram below.
By Originally uploaded by Jerry Crimson Mann, vectorized by Tutmosis, corrected by Fvasconcellos – en:Image:Activation2.png, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=1407225
Note that that the ΔG (The overall energy) does not change whether or not the enzyme is present. Enzymes also have no effect on the equilibrium of a reaction; adding an enzyme does not shift the reaction to the left or right. It does change how quickly the reaction reaches equilibrium.
Know what active and allosteric sites are.
We have already mentioned active sites, they bind to the substrate(s) of a reaction. Some enzymes also have allosteric sites. These do not bind to substrates but they bind to compounds that can turn on (activators) or turn off (inhibitors) an enzyme.
One example is important in insulin control of blood sugar. There is an enzyme that converts glucose to glycogen. This enzyme only works when insulin is present (this is when you just ate a meal; your body wants to convert the glucose you ate to glcyogen to store for later. When insulin binds to insulin receptor a chain reaction occurs (like the following dominoes shown here)
In the reaction an enzyme called a kinase becomes active and kinases add phosphates to other proteins some of which are enzymes. Adding a phosphate to the enzyme which turns glucose to glycogen makes it active. The phosphate is added to an allosteric site which is not near the active site. However, when the phosphate is added, the enzyme changes it shape into an active form. This is shown here
By aussiegall – [1], CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=4428411
Note that some compounds can inhibit by binding to the allosteric site and some can activate an enzyme by binding to an allosteric site as illustrated in this video
[youtube https://www.youtube.com/watch?v=WAZXqhtduFw]
Know what competitive and non-competitive inhibition is and how it relates to active and allosteric sites.Know how one can distinguish these inhibitors
Many drugs can inhibit enzyme function by binding to the active site. Here is an example
The key point here is that the inhibitor binds very strongly to the active site preventing the substrate from binding. Because both the inhibitor and substrate bind to the same site, the binding is said to be competitive. If the concentration of substrate increases, the inhibitor is less effective.
Non-competitive inhibitors bind to the allosteric site. Adding more substrate has no effect on allosteric inhibitors since the inhibitor changes the active site to be “closed”.
Know what feedback inhibition is and how it can be used to control amino acid synthesis.
http://www.powtoon.com/embed/ehIHXeADNit/
Do Problem #7, page 161.
