Chapter 3 Study Questions (Part 2) Flashcards
many enzymatically catalyzed reactions are reversible, except for… (2)
- reactions that have very large negative Gibbs free energy values
- reactions that involve ATP
all steps in glycolysis that do not involve ATP are…
reversible
which steps in glycolysis are reversible? why?
those that don’t involve ATP. because of where phosphate is located on ATP.
what are three reasons that cells do not store ATP?
- not stable (doesn’t last long)
- less energy dense than glucose (1:1 vs. 1:32)
- absorbs a ton of water, cell swells to unhealthy size.
what are the different energy sources used by the cell to produce ATP?
carbohydrate
fatty acids
proteins
what do we store carbohydrates as?
glycogen
what do we store fatty acids as?
triglycerides
what do we store proteins as?
we don’t store it
which energy source provides the most energy?
lipids, because they are the most energy dense.
what are the two models of enzyme catalysis?
lock and key (we don’t use)
induced fit
what is the induced fit model of enzyme catalysis? why do we use it?
not fit exactly, induced fit. explains how the reaction can keep going.
what is the lock and key model of enzyme catalysis?
doesn’t explain how the reaction can keep going
how can an enzyme break a chemical bond without requiring an input of energy?
charges pull in different directions, changes the bond angles.
thus the enzyme falls out because there is no longer complementarity.
charged attractions distort conformation, so no ATP is used.
what is the difference between a substrate and a ligand?
just as a ligand reacts with a receptor, a substrate bonds with an enzyme.
they bind to cause a change, change shape, and pop out when we want it to stop
compare and contrast allosteric and covalent regulation of enzyme activity
A: - 1 catalytic/active site, substrate binds and is modified
- 1+ regulatory site: anything else can bind there and it changes the catalytic site
C: attach phosphate group by covalent bond
name an example of an allosteric enzyme
glycogen phosphorylase
which effector molecules modulate glycogen phosphorylase activity?
AMP and ATP
how does AMP affect glycogen phosphorylase enzyme activity? ATP?
AMP: increased AMP means we want more ATP, increases enzyme activity
ATP: increased ATP means we want less enzyme activity, less AMP
which enzyme regulates glycolysis?
phosphofructokinase (PFK)
what is the role of PFK? how is it regulated?
regulate glycolysis. allosterically regulated.
effect of AMP on PFK activity
enhances
effect of ATP on PFK activity
inhibits
PFK: if ATP levels are high…
how does that affect the catalytic site?
the energy level is good, so the cell doesn’t need to run glycolysis as much.
promote access to catalytic site
PFK: if AMP is high…
how does that affect the catalytic site?
energy level is low so the cell wants to speed up the rate of glycolysis.
discourage access to catalytic site.
in glycolysis, why is glucose phosphorylated? (2)
- keeps it in the cell. by adding phosphate, glucose is no longer recognized by the glucose transporter.
- maintains concentration gradient. by adding phosphate, there is still more glucose outside the cell than inside, because what’s inside isn’t glucose.
why is glucose-6-phosphate isomerized to fructose-6-P?
fructose-6-P is more symmetrical. 2 3C molecules.