1. Enzymes (B7)

3. Characteristics (B.7.1)
globular proteins that act as biological catalysts
lower the activation energy
speed up reactions (up to 108 – 1012 faster) to a rate that is useful by the cell
each enzyme reacts (temporarily binds) with a specific molecule in the reactants called a substrate
have no effect on (ΔG) of a given reaction
can be catabolic (break molecules down) or anabolic (build molecules up)

4. Compare inorganic catalysts vs. enzymes (B.7.2)
both speed up reactions by providing an alternative pathway of lower activation energy
neither changes the position of equilibrium or yield of the reaction
enzymes are highly specific for their substrate, whereas inorganic catalysts are often non-specific and can catalyze several reactions
enzymes have an optimum temperature and are denatured at high temperatures, whereas inorganic catalysts are much less a affected by the conditions and generally work well at high temperatures

5. Substrate concentration and enzyme activity B.7.3
substrate concentration – as substrate concentration increases, the probability of enzyme colliding with substrate increases and therefore increases rate of reaction
enzyme saturation is reached when all active sites on the enzyme are engaged

8. Vmax and Michaelis constant (Km) graphs B.7.4

9. the curve when the rate for an enzyme saturated with substrate is known as the maximum velocity (Vmax)
is the maximum rate at which an enzymatic reaction is occurring
Vmax varies from one enzyme to another and is dependent on reaction conditions such as temperature and pH

11. Michaelis constant (Km)
this is the concentration of substrate when the rate is equal to one half Vmax
enzymes with low Km
indicates that it has a high affinity for a substrate, as only a small concentration of substrate is needed for the reaction to proceed at half its maximum velocity
enzymes with high Km
indicates that the enzyme has less affinity for the substrate, as a large concentration of substrate is needed to reach half Vmax

12. needs higher concentration
already at ½ velocity
at low concentration
needs higher concentration
to reach ½ velocity

14. Mechanism of enzyme action (B.7.5)
Induced-Fit Animation
enzymes contain an active site which is a specific location on the enzyme where reactions occur
generally, a given enzyme is able to catalyze only a single chemical reaction or, at most, a few reactions involving substrates sharing the same general structure
enzyme and substrate meet by random motion of molecules and connect

15. the “connection” is made by weak ionic and hydrogen bonds between areas on the substrate and enzyme
the enzyme undergoes slight change in shape bringing reactive amino acid R-groups in the enzyme closer to the substrate (this is called induced fit) which can lower the activation energy by:
physically stressing the substrate which helps break the bonds
sometimes changes pH within the active site
even can temporarily covalently bond with the substrate
the entire reaction from binding to release occurs thousands to millions times a second

20. Mechanisms of Enzyme Control (B.7.6)
two common ways of interference:
competitive
noncompetitive inhibition

22. 1. Competitive Inhibition
molecule that is similar to the usual substrate binds to the active site of the enzyme instead of the substrate
adding more substrate helps (increase the rate) since there is increased competition for the active sites by the substrate

23. Figure 2. Normal activity of an enzyme substrate complex (2A)
Figure 2. Normal activity of an enzyme substrate complex (2A). Herbicide binding to the enzyme and preventing normal action (2B). The enzyme in a herbicide resistant plant that can't bind with the herbicide (2C).

25. 2. Noncompetitive Inhibition
chemical binds to the enzyme at area other than the active site
this alters the enzyme’s shape enough so the substrate doesn’t fit well, or at all, and therefore the rate of reaction slows down or stops
adding more substrate does not help (increase the rate) since the active site is non-functional

27. Enzyme Activity (B.7.7)
enzymes can become denatured (changes shape, and substrate is no longer functional)
heavy metal ions – poison enzymes especially by reacting with S-H groups
pH – each enzyme has an optimal pH at which they perform
temperature – body temp. (37°C ideal for humans)
extreme heat will denature proteins