MOLECULAR BIOLOGY: ENZYMES Flashcards
Describe the function of enzymes in catalyzing biological reactions
Enzymes are catalysts, which are things that increase the rate of a reaction, but does not get used up during the reaction. Structure determines function. A change in structure => a change in function.
List important biological reactions catalyzed by enzymes
Metabolism, DNA synthesis, RNA synthesis, protein synthesis, digestion
Explain reduction of activation energy (diagram)
Enzymes decrease the activation energy (Ea) of a reaction by lowering the energy of the transition state. Enzymes increase the rate of a reaction by decreasing the activation energy. Enzymes will increase the rate constant, k, for the equation rate = k[A][B]. Enzymes do NOT change the Keq of a reaction. Enzymes do not change Keq because it lowers the activation energy for BOTH forward and reverse reactions. Enzymes will make the reverse reaction go faster also. Enzymes do not change ΔG, the net change in free energy. Enzymes affect the kinetics of a reaction, but not the thermodynamics.
Explain enzyme-substrate specificity
Enzyme-substrate interactions occur at the enzyme’s active site. Enzyme-substrate specificity derives from structural interactions. Lock and key model: rigid active site. Substrate fits inside the rigid active site like a key. Induced fit model: flexible active site. Substrate fits inside the flexible active site, which is then induced to “grasp” the substrate in a better fit. Enzymes can be specific enough to distinguish between stereoisomers.
Enzymes can be protein or RNA. Which are most made of in the body?
Almost all enzymes in your body is made of protein.
What is the most important RNA enzyme?
The most important RNA enzyme in your body is the ribosome.
Enzyme structure derives from 4 levels.
Primary: this is the sequence of the protein or RNA chain. Secondary: this is hydrogen bonding between the protein backbone. Examples include alpha helices and beta sheets (backbone H-bonding). For RNA, this is base pairing. Tertiary: this is the 3-D structure of the enzyme. This involves -R group interactions and spatial arrangement of secondary structure. Quaternary: when more than 1 chain is involved. When you hear about “dimers”, “trimers”, “tetramers”, “oligomers”, that’s quaternary structure.
What does heat and extreme pH do to enzymes?
Heat and extreme pH denatures enzymes by altering their structure.
Describe Feedback inhibition
The product of a pathway inhibits the pathway. For example, hexokinase, the first enzyme in glycolysis, is inhibited by its product glucose-6-phosphate.
Describe competitive inhibition
An inhibitor competes with the substrate for binding to the active site. Competitive inhibition increases the amount of substrate needed to achieve maximum rate of catalysis. Competitive inhibition does NOT change the maximum possible rate of the enzyme’s catalysis. You can overcome competitive inhibition by providing more substrate.
Describe Non-competitive inhibition
An inhibitor binds to an allosteric site on the enzyme to deactivate it. The substrate still have access the active site, but the enzyme is no longer able to catalyze the reaction as long as the inhibitor remains bound. Non-competitive inhibition decreases the maximum possible rate of the enzyme’s catalysis. Non-competitive inhibition does NOT change the amount of substrate needed to achieve the maximum rate of catalysis. You can’t overcome non-competitive inhibition by adding more substrate.
