Transcript Step 1: Hexokinase

Announcements
• Reading for today on glycolysis: pp. 221-234
• Homework due today: Problems 8-5, 8-7
– In both problems, use the favorable free energy change of ATP hydrolysis
to drive the unfavorable transport of solute up its concentration gradient
on a per mole basis.
• Reading for Wednesday, Feb. 21 on fermentation and TCA cycle:
236-241, 248-258
• Reading for Friday, Feb. 23 on integration of metabolism: 258-262
• Reading for Monday, Feb. 26 on respiration: 265-271
• Homework due Monday, Feb. 26: Problem 9-5
– Convert all concentrations to M, and your answer will be in M.
– Don’t worry about [H+] – use equations as given in problem.
– Determine [glucose] at equilibrium (ΔG’ = 0); then a concentration greater
than this will favor production of G6P.
• Wednesday, Feb. 28 on respiration: 271-283
• Friday: Exam 2 on Days 12-22, 99 points, 33 m/c questions.
– Note Exam 3 will be worth 81 points.
Outline/Learning Objectives
CHO metabolism
A.Metabolic reactions
and ATP
B.Oxidation-reduction
reactions
C.Glycolysis
After reading the text, attending
lecture, and reviewing lecture
notes, you should be able to:
• Describe the roles of ATP/ADP
and NAD+/NADH in biological
reactions.
• Summarize the purpose and
place, reactants and products,
critical enzymes, and net yield
of glycolysis.
• Calculate free energy changes
associated with glycolysis.
• Summarize the products, control
steps, etc. of glycolysis.
Catabolic and Anabolic
Metabolic Pathways
Catabolic (degradative)
• Glycolysis, fermentation
• TCA cycle, electron
transport, oxidative
phosphorylation
• Glycogenolysis
• Fatty acid oxidation
• Amino acid degradation
Anabolic (synthetic)
• Gluconeogenesis
• Glycogen synthesis
• Fatty acid synthesis
• Amino acid synthesis
ATP is an energy intermediate
Donates Phosphate;
Hydrolysis is exergonic
Accepts Phosphate;
Synthesis is endergonic
Oxidation and Reduction
• Oxidation: gives up e– Dehydrogenation: gives up H+
• Reduction: accepts e– Hydrogenation: accepts H+
• Redox reactions
– Usually involve 2 e-, 2 H+ in the cell
– Catalyzed by dehydrogenases
NAD+ accepts, NADH donates e-
NAD+/NADH is an
intermediate e- acceptor/donor
• Its redox reaction is coupled to another redox
reaction in metabolic pathways:
NADH + H+
 NAD+ + 2e- + 2H+
Acetaldehyde + 2e- + 2H+
 ethanol
Acetaldehyde + NADH + H+  ethanol + NAD+
This fermentation reaction is catalyzed by alcohol
dehydrogenase.
Final e- Acceptors
• Glycolysis, fermentation
(NAD+ )
– No net oxidation of glucose
• Aerobic respiration
O2
– Complete oxidation of glucose using O2 as final eacceptor: ½ O2 + 2 H+ + 2 e-  H2O
• Anaerobic respiration
S, H+, Fe3+
– Complete oxidation of glucose using something other
than O2 as final e- acceptor.
• Glycolysis is the central catabolic pathway and
first part of aerobic respiration:
Oxidation of Glucose
C6H12O6 + 6 O2  6 CO2 + 6 H2O
Go’ = -686 kcal/mol
• In bomb calorimeter, the large
EA of this rxn is overcome by
heat of fire.
• In the cell, a series of reactions
with small EA is overcome by
body temperature and
enzymes.
• Purpose: convert chemical
bond energy of glucose to
chemical bond energy in ATP
Glycolysis Problems
2-88
2-89
2-90
2-93
Energetics of Glycolysis
1 M cellular
Conc., Conc.,
pH=7 pH=7
STEP
REACTION
ΔGo’
ΔG’
1
GLC + ATP → G6P + ADP + H+
-4.0
-8.0
2
G6P → F6P
+0.4
-0.6
3
F6P + ATP → F1,6BP + ADP + H+
-3.4
-5.3
4
F1,6BP → DHAP +G3P
+5.7
-0.3
5
DHAP → G3P
+1.8
+0.6
6
G3P + Pi + NAD+ → 1,3BPG + NADH + H+
+1.5
-0.4
7
1,3BPG + ADP → 3PG + ATP
-4.5
+0.3
8
3PG → 2PG
+1.1
+0.2
9
2PG → PEP + H2O
+0.4
-0.8
10
PEP + ADP +H+ → PYR + ATP
-7.5
-4.0
The table above shows free energy change values in kcal/mol
for the concentrations of intermediates in red blood cells. The
overall ΔG’ from glucose to pyruvate is about -20 kcal/mol.
Glycolysis Summary
• Cytoplasmic
• Catabolism of:
– carbohydrates  G6P, F6P
– fats: glycerol  DHAP
– some amino acids  pyruvate
•
•
•
•
Cost = 2 ATP, Gain = 4 ATP, Net Gain = 2 ATP
Reduced Coenzymes: 2 NADH + H+
End product: pyruvate (CH3COCOO-)
Control steps: irreversible reactions 1, 3, and 10