Mod 7 Flashcards
Glycogen
- Glucose storage
- Highly branched structure with one reducing end, and several non-reducing ends
- Alpha-1,4 linear, alpha-1,6 branched
Glucose residues simultaneously removed from non-reducing ends providing rapid surge of glucose when needed
Carb storage
- Stored as glycogen in our muscle and liver
- Once glycogen stores full, excess carbs converted to fat for storage
Break down of glucose (order)
First glycolysis
- Can occur in anaerobic conditions
- In humans results in lactate productions, in yeast ethanol due to fermentation
Then pyruvate dehydrogenase reaction and the citric acid cycle
General glycogen breakdown enzyme
Glycogen phosphorylase
- Phosphorolysis using Pi releases glucose-1-phosphate
- Phosphoglucomutase enzyme then converts it to glucose-6-phosphate
General glycogen synthesis enzyme
Glycogen synthase
- Uses UTP for energy
UTP -> UDP + Pi
Synthesis of glycogen from glucose-1-phosphate
Allosteric regulation of GS and GP
GS activated by high concentrations of glucose-6-phosphate
GP activated by high AMP concentration (signals low ATP)
Covalent regulation of GS and GP
GP:
- Kinase phosphorylates it = converts to active form
- Phosphatase dephosphorylates it = converts back to inactive
GS:
- Opposite of GP
Hormones that phos or dephos
Insulin stimulates dephosphorylation by the phosphatase
Glucagon and epinephrine stimulate phosphorylation by the kinase
Glycogen metabolism → insulin
- In response to elevated glucose levels in bloodstream
- Signals circulating glucose to be taken up into tissues to be used for energy or to be stored for later use
Insulin binds to receptor at cell surface
Phosphorylates
Causes activation of GS and inactivation of GP
Glycogen metabolism → glucagon
- Counter-regulatory to insulin
- Released when glucose levels in blood drop , signals glucose release from the liver glycogen stores
Dephosphorylates
Inactivates GS, activates GP
Glycolysis overall reaction
glucose to pyruvate
Glucose enters the cell from the bloodstream, then oxidized to provide useable ATP energy
sum of 10 rxns
glucose + 2ADP + 2Pi + 2NAD+
–>
2 pyruvate + 2ATP + 2 NADH
6-carbon glucose splits in two = 2 3-carbon pyruvate molecules, etc.
What is special about reactions 1 and 3 of glycolysis
- Targets for the control of flux through glycolysis
- Associated with a large change in free energy
- Considered irreversible
- Good points of regulation
Glycolysis Step 1
Catalyzed by enzyme hexokinase
End-product inhibition by product glucose-6-phosphate
Glycolysis Step 3
Catalyzed by enzyme phosphofructokinase
End-product inhibition by high [ATP] and citrate
Also allosterically up-regulated by metabolite fructose-2,6-bisphosphate
End-product inhibition
End products of a reaction feedback and inhibit flux through an enzyme
Allosteric regulation
a mechanism where a regulatory molecule (effector) binds to a protein at a site other than the active site, causing a conformational change that alters the protein’s activity, either enhancing or inhibiting it
Fermentation
a pathway that produces ATP with no net oxidation of carbon
NAD+ must be regenerated to continue glycolysis
aerobic = done using ETC
anaerobic = other reactions
Where does lactate fermentation occur
Occurs in microorganisms, some eukaryotic cells (ex. muscle during intense exercise)
makes muscles sore
How does lactate fermentation occur
Enzyme lactate dehydrogenase oxidizes NADH,
reducing pyruvate to lactate,
and regenerating NAD+
for glycolysis to continue
Where does ethanol fermentation occur
Occurs in yeast and other microorganisms
How does ethanol fermentation occur
In yeast, ethanol is produced rather than lactate during fermentation
Regenerates NAD+ and allows glycolysis to continue
Lactate and ethanol fermentation net reactions
Lactate
glucose + 2 ADP + 2 Pi
–>
2 lactate + 2 ATP
Ethanol
glucose + 2ADP + 2Pi
–>
2 ethanol + 2 CO2 + 2 ATP
How many molecules ATP does anaerobic fermentation produce? glycolysis?
both 2!
Gluconeogenesis
what + where + what’s converted
De novo synthesis of glucose when glycogen stores low
In liver an a bit in kidneys
Some amino acids, some citric acid cycle intermediates, and lactate = can be converted to oxaloacetate then to glucose through gluconeogenesis
Is gluconeogenesis the reverse of glycolysis
not exactly
Three non-equilibrium reactions with large changes in free energy in glycolysis are bypassed
Is gluconeogenesis energetically favourable or costly
costly
- uses 4 ATP
- but glycolysis only produces 2 ATP
requires energy input
liver can make glucose when glycogen stores run out, at a cost of 6 ATP / glucose
Gluconeogenesis reaction
2 pyruvate + 4 ATP + 2 GTP + 2 NADH
–>
glucose + 4ADP + 2 GDP + 6Pi + 2 NAD+
Glycolysis vs gluconeogenesis
Steps 1, 3, and 10
(in glycolysis)
Catalyzed by glucokinase, phosphofructokinase, and pyruvate kinase
Irreversible reactions
By-passed by glucose-6-phosphatase, fructose bisphosphatase, PEP carboxykinase and pyruvate carboxylase
Regulation of step 3: glycolysis vs gluconeogenesis
Conditions favour the synthesis of either fructose-6-phosphate or fructose-1,6- bisphosphate, but never both at the same time
Glycolysis forms fructose-1,6-bisphosphate
- using phosphofructokinase
- activated by AMP and fructose-2,6-bisphosphate
Gluconeogenesis forms fructose-6-phosphate
- using fructose bisphosphate
- inhibited by high concentrations of AMP and fructose-2,6-bisphosphate
Pentose phosphate pathway
Glucose broken down to generate NADPH for reductive processes such as fat synthesis
- Also provides ribose-5-phosphate for the synthesis of nucleotides
Pentose phosphate pathway net reaction
3 glucose-6-phosphate + 6 NADP+
–>
2 fructose-6-phosphate + glyceraldehyde-3-phosphate (taken away for glycolysis)
+ 3 CO2 + 6 NADPH
