CHAPTER 9 - ENZYMES Flashcards
What is an Exergonic reaction?
energy is being released
What is an Endergonic reaction?
Energy is being absorbed
What is Activation energy?
When the input of energy is needed to bring the reactants to the peak of their energy.
Why is activation energy needed to get the reaction started?
Because it takes energy to bring reactant molecules together and to break chemical bonds before new chemical bonds can be made and the final products (and energy) released.
What is happening as we approach the peak of an energy diagram?
The reactants (2 H2 + 1 O2) form an activated complex (H4O2): an unstable configuration of the reactant atoms that briefly exists before the final, more-stable products (2 H2O) are formed.
What are some ways in which enzymes can be regulated?
-Don’t express the gene (i.e. don’t transcribe it) in cells that don’t need it!
e.g. express pepsin in gastric glands of stomach, but NOT in brain cells!
-Don’t activate the enzyme until it’s needed (e.g. pepsin is synthesized and released as inactive pepsinogen, which is activated to pepsin by the acidic environment of the
stomach, where it digests dietary protein from your food)
-Most enzymes have a narrow pH optimum (e.g. pepsin is active in the acidic stomach
but inactive in the duodenum, where the pH is much less acidic, and trypsin is active).
-Most enzymes have optimal temperatures (e.g. Siamese cats have a very heat-
the sensitive enzyme that produces more pigment at more excellent body parts)
What does a competitive inhibitor do?
-If it permanently blocks the active site – no reaction
-If it temporarily blocks – will compete with reactants to bind, and slows reaction.
What does an allosteric inhibitor do?
that binds to an allosteric site, thus changing the shape of
the active site and decreasing/preventing binding of enzymes to reactants
Describe 8+ ways that one could theoretically decrease pepsin activity in a stomach.
1) Lower the temperature (so that even the smaller EA provided by pepsin isn’t available)
2) Heat up the stomach enough to denature pepsin (destroy its higher-level structure)
3) Shut down parietal cells in gastric pits, which pump hydrogen ions into the stomach.
4) Neutralize the acid in the stomach with basic chemicals, to increase the pH.
5) Make the stomach even more acidic with strong acids, to denature pepsin
6) Add competitive inhibitor
7) Add an allosteric inhibitor
8) Mutate the gene’s promoter to decrease transcription of pepsinogen.
9) Mutate the gene’s coding sequence, so the resulting protein is inactive.
10) Take away all dietary protein, so pepsin has nothing to interact with, etc. etc.
