Download BY 330 Spring 2015Worksheet 4 Name the substrate ligand and

BY 330 Spring 2015
Worksheet 4
1. Name the substrate ligand and product for the enzyme pyruvate kinase.
Name one regulatory ligand that will increase the Michaelis constant of this
enzyme.
Substrate ligand – phosphoenol pyruvate
Product – pyruvate
ATP, alanine are examples of regulatory ligands that will increase the
Michaelis constant
2. What are the three pathways that glucose-6-phosphate can take if there is
excess glucose in the cell and the energy charge is stable? What additional
pathway can it take if the energy charge in the cell is too low?
OMIT
3. What is the most powerful modulator of phosofructokinase and how does it
originate and work?
Fructose-2,6-bisphosphate – turns on PFK (positive modulator). Made
from fructose-6-phosphate (PFK2 catalyzes this reaction and glucose-6phosphate turns PFK2 on).
4. How are alanine and citrate important during glycolysis, even though they
are not present in the formal pathway?
Alanine – negative modulator of pyruvate kinase  if there is a lot of
alanine (a lot of amino acid) in the cell and not much sugar, cell will
burn the alanine and save the sugar/glycolysis for later.
Citrate – negative modulator of PFK  if there is a lot of citrate, the
Krebs cycle is active and the cell does not need to go through glycolysis
to produce any more pyruvate
5. Describe and explain energy charge and how it is important to the cell.
Energy charge is the normal amounts of ATP, ADP, and AMP the cell
would like to maintain to have normal processes occur. Usually, the
levels of ATP are high while the levels of ADP and AMP are lower,
respectively. (The graph Dr. Watts drew might help to explain this). It is
important to maintain a normal energy charge, otherwise the cell will
need to make more energy. For example, if the levels of ATP in the cell
decrease and the levels of ADP and AMP increase, the cell will need to
use glycolysis to make more ATP and get itself back towards a normal
energy charge.
6. What is the law of mass action? Which enzymes do not follow this law and
how do they work?
BY 330 Spring 2015
Worksheet 4
The law of mass action describes enzymes that can work in more than
one direction. Whichever direction the equilibrium lies, is the direction
that enzyme will work in. For example, if there is too much product
present, these enzymes will work in reverse and if there is too much
substrate present, the enzyme will work in the forward direction.
Hexokinase, pyruvate kinase, and phosphofructokinase do not follow
this law. They are rate-limiting enzymes, which means that they will
only work in the forward direction.
7. If 10 molecules of isocitrate are converted to succinate in the Krebs cycle,
how many molecules of NADH will be produced? AcetylCoA? CO2? GTP?
FADH2? Show the cycle.
(I won’t show the cycle here, but it comes straight from your notes.
Make sure you include sites of energy, NADH, and FADH2 production in
your drawing).
NADH – 20
AcetylCoA – 0
CO2 – 20
GTP – 10
FADH2 - 0
8. Which three enzymes in the Krebs Cycle lead to the production of NADH?
Isocitrate dehydrogenase, alpha-ketogutarate dehydrogenase, and
malate dehydrogenase
9. If 12 molecules of glucose are catabolized to malate, how many FADH2 are
produced?
24
10. The Km of phosphofructokinase is 0.2. What happens to this value when
citrate binds? Glucose-6-phosphate? ATP? Fructose-2,6-bisphosphate?
Alanine?
Citrate – increases
Glucose-6-phosphate – decreases
ATP – increases
Fructose-2,6-bisphosphate – decreases
Alanine – no change as alanine only modulates pyruvate kinase, not PFK
11. What reaction occurs in between glycolysis and the Krebs Cycle? How much
NADH and CO2 are produced here for 6 molecules of glucose? What enzyme
catalyzes this reaction?
Pyruvate dehydrogenase reaction or the oxidative phosphorylation of
pyruvate; For 6 glucose – 12 NADH, 12 CO2; pyruvate dehydrogenase
catalyzes this reaction
12. Can acetylCoA enter the Krebs Cycle directly? What has to bind to it and what
product is produced? What enzyme is used for this reaction?
BY 330 Spring 2015
Worksheet 4
No, acetylCoA must be escorted by oxaloacetate. AcetylCoA +
oxaloacetate = citrate. Citrate synthase catalyzes this reaction
13. Give two examples of regulation that occurs during the Krebs Cycle.
Dr. Watts gave three examples:
ATP is a positive modulator for isocitrate dehydrogenase.
Succinate is a negative modulator for citrate synthase.
Oxaloacetate is a negative modulator for succinate dehydrogenase.