Term
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Definition
| accepts 2 electrons and 1 proton |
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Term
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Definition
| accepts 2 protons and 2 electrons |
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Term
| 3 ways to regenerate NAD+ |
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Definition
1. pyruvate to lactate
2. pyruvate to acetaldehyde to ethanol
3. pyruvate to acetyl CoA followed by further oxidation |
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Term
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Definition
1. occurs in microorganisms and higher micororganisms under anaerobic conditions
2. enzyme lactate dehydrogenase reduces pyruvate to lactate
3. net results: Glucose + 2 Pi + 2 ADP + H+--> 2 lactate + 2 ATP + 2 H2O
4. NAD+ and NADH do not appear in this reaction, but since they are regenerated, this allows glycolysis to proceed under anaerobic condition
Also – lactate will be converted in into lactic acid, dropping overall cellular pH! |
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Term
| pyruvate to acetaldehyde to ethanol |
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Definition
1. yeasts and micro-organisms
2. enzyme pyruvate decarboxylase, decaroxylates pyruvate (CO2 is generated)
3. enzyme alcohol dehydrogenase reduces acetaldehyde to ethanol, allowing NADH to be oxidized to NAD+ |
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Term
| net result of glucose to ethanol |
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Definition
| Glucose + 2 Pi + 2 ADP ----> 2 Ethanol + 2 CO2 + 2 ATP + 2 |
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Term
| exapliain the absence of NAD+ and NADH from the net results |
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Definition
1. NAD+ and NADH are enzymatic co-factors.
Although, NAD+ and NADH do not appear in this reaction, they are crucial intermediates. And more importantly, there is no net oxidization or reduction taking place thus glycolysis can continue |
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Term
| how does glucose enter glycolysis? |
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Definition
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Term
| how does fructose enter glycolysis? |
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Definition
| write pathway on slide 35 |
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Term
| how does galactose enter glucose? |
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Definition
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Term
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Definition
| cleaved by sucrase in to fructose and glucose |
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Term
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Definition
| cleaved by lactase generating Glucose and Galactose |
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Term
| Regulatory mechanisms of glycolysis |
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Definition
1. allosteric inhibition (binding at a site other than active)
2. Regulation by phosphorylation
3. transcriptional reguation |
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Term
| glycolysis regulation (skeletal vs. liver tissue) |
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Definition
The liver is focused on the whole body’s level of glucose and ATP
The muscle cells only care about themselves |
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Term
| similarities for glycolysis regulation in skeletal muscles and liver |
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Definition
| regulated at the same irreversible steps, specifically the following ATP consuming enzymes: Phosphofructokinase, Hexokinase, and Pyruvate Kinase |
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Term
| PFK--structure related to regulation |
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Definition
| 1. has 4 catalytic sites and 4 allosteric sites |
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Term
| skeletal muscles--ATP and AMP regulation |
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Definition
1. High ATP levels cause the four allosteric sites to be bound by ATP, leading to less PFK activity (sigmoidal curve on graph)
2. When ATP levels are low, and AMP levels are high: AMP will bind the allosteric sites, increasing PFK activity (hyperbolic curve on graph) |
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Term
| skeletal muscles--pH regulation of PFK |
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Definition
1. Excess lactic acid can cause a drop on pH
2. this lower pH environment will cause ATP to bind to PFK, reducing its activity
3. the method is meant to reduce the damage from lactic acid, by reducing the rate of glycolysis which would make more lactic acid |
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Term
| why is PFK regulation the control point for glycolysis? |
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Definition
| 1. PFK produces fructose 1,6 biphosphate which is only destined for glycolysis. No other pathways. The conversion of fructose 6-phospahte to fructose 1,6 biphosphate is a committed step towards glycolysis. |
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Term
| why is hexokinase not the control point for glycolysis? |
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Definition
| 1. hexokinase produce glucose-6-phosphate, which can enter into glycolysis or used in glycogen formation |
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Term
| skeletal muscle--regulation of hexokinase |
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Definition
1. Ultimately, a build-up of glucose 6-phosphate will shut off hexokinase.
2. This buildup is due to a build-up of fructose-6-phosphate, since the two structures can be converted into one another and exist at equilibrium
3. The build-up of fructose 6 phosphate is a result of high ATP levels inhibiting PFK. |
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Term
| skeletal muscle--regulation of pyruvate kinase |
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Definition
Turns phosphoenolpyruvate into pyruvate
Inhibited by ATP and Alanine (synthesized one step after pyruvate)
Negative feedback [check]
Fructose-1-6-Bisphosphate enhances its activity (positive feedback) |
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Term
| Liver--roles and regulations |
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Definition
1. ATP regulated similarly to skeletal muscles
2. pH regulation is not an issue because lactate is not produced in the liver
3. maintains blood glucose levels
4. stores glycogen
5. detoxifies alcohol, metabolizes drugs, emsulsifies fats and lipids |
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Term
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Definition
| citrate, ATP, and F-2,6-BP (blood glucose monitoring) |
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Term
| L-PFK regulation--ATP and Citrate |
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Definition
1. (L) PFK is inhibited by high levels of ATP, same as in muscle tissue.
2. A build-up of citrate indicates a backed up TCA cycle; and enhances ATP-mediated inhibition of (L) PFK |
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Term
| (L) PFK regulation--F-2,6-BP |
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Definition
1. a signaling molecule that helps the liver respond to high levels of blood glucose
2. Glucose in blood will be converted to F-6-P then F-1,6 BP.
3. High levels of F-6-P create F-2,6-BP generation
4. F-2,6-P then activates PFK, activating glycolysis, and subsequent consumption of the high amount of blood glucose
5. F-2,6-BP massively increases PFK’s enzyme velocity, even in the presence of small concentrations. Any time it sees substrate, will act on it! |
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Term
| F-2,6-BP's affect on ATP regulation |
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Definition
F-2,6-BP diminishes the inhibitory effect of ATP on PFK activity.
Increasing amounts of F-2,6-BP changes the sigmoidal curve to a hyperbolic curve, indicating an increase in PFK activity.
ATP, acting as a substrate, initially stimulates the rxn (remember, enzyme is a kinase!), however as [ATP] increases, ATP allosterically inhibits PFK (notice the drop in velocity over 1 mM ATP).
Increasing amounts of F-2,6-BP increases the tolerable levels of ATP at which PFK is highly active, effectively countering ATP’s inhibitory effect.
At 1 micromol F-2,6-BP, the enzyme pretty much ignores ATP levels |
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Term
| F-2,6-BP's affect on citrate regulation |
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Definition
| Citrate enhances the binding of ATP to PFK. So since F-2,6-BP says ignore ATP levels, citrate’s presence here wouldn’t matter |
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Term
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Definition
Has high affinity for glucose and is inhibited by G6P
Product of its reaction primarily goes to glycolysis |
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Term
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Definition
Only exists in the liver and serves as a blood glucose monitor.
Has low affinity for glucose and isn’t inhibited by G6P
Product of glucokinase primarily goes to glycogen and fatty acid synthesis
Only plays a role when the brain and muscles are satiated with ATP
Has a higher Km than hexokinase (k-1+k2/k1) |
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Term
| what allows glucokinase to monitor blood sugar? |
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Definition
GK low affinity allows the brain and muscles to get first dibs on glucose in the body
when these two major consumers of glucose are satiated with ATP, will glucokinase activity become a factor |
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Term
| Pyruvate kinase--muscle vs. liver |
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Definition
| 1. enzymes are similarly regulated, but again, the L (liver form) is responsive to the blood-glucose level |
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Term
| Pyruvate kinase--phosphorylation |
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Definition
1. glucagon signals low blood sugar levels
2. cAMP cascade
3. phosphorylates liver pyruvate kinase
4. reduces liver consumption of glucose, and allows brain and allows brain and muscle to have more glucose |
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Term
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Definition
| 1. cancer cells show and over expression of GLUT1 and GLUT3, which are transporters for mammalian tissue in basal glucose uptake. |
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Term
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Definition
You can use many different isotopes with different half-lives. F18 has a half-life of about an hour. F18 displaces an OH group on glucose. Now you have labeled (fluoridated) glucose that you have the patient ingest. It enters through glucose transporters to get transported into glucose-6-phosphate. When a cell ingests glucose, it phosphorylates it so it can’t leave! So this tags the cancer cells.
Bombard O18 (a heavy isotope) with high energy protons. If one proton is accepted it becomes fluoride 18 which is an unstable molecule. One of the high energy protons will leave, a positron, and it will interact with an electron. This sends 2 waves in either direction from the annihilation event location. If you have multiple annihilation events in a cell, you can image where they are all occurring. This is the heat map image on the PET scan. |
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Term
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Definition
Converts non-carbohydrate precursors into something glycolysis can metabolize
If you’re starving, the liver will start consuming AAs, glycerol, whatever I can to make glucose via gluconeogenesis
Occurs primarily in the liver and kidney (mostly liver)
Ensures that the brain and the RBC have a steady supply of glucose
Glycerol section of fatty acid can be sliced out so it can become glucose in the liver. (The fatty acids go into the TCA cycle.) |
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Term
| glycerol conversion to DHAP |
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Definition
DRAW
Glycerol can be converted into DHAP, which then enters glycolysis
Glycerol → Glycerol Phosphate [Glycerol Kinase]
Glycerol Phosphate → DHAP [Glycerol Phosphate Dehydrogenase]
DHAP can either continue down becoming pyruvate, or be turned into glucose |
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Term
| gluconeogenesis--The Cori cycle |
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Definition
1. pyruvate for gluconeogenesis comes from the lactate generated by muscles.
1. Muscle cells consumes glucose, generate 2 ATP with pyruvate
2. converts pyruvate to lactate to regenerate NAD+
3.Lactate travels through the blood to the liver and lactate is converted into pyruvate and then to glucose via gluconeogenesis.
4. Glucose enters the bloodstream and the muscle can use it again.
To turn pyruvate into glucose, you need to consume 6 ATP
Recover 2 ATP through glycolysis |
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Term
| barriers to gluconeogenesis |
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Definition
the net ΔG of glycolysis is highly negative due to the three ATP-consuming, essentially irreversible steps.
Gluconeogenesis overcomes these irreversible steps by using a different enzyme – as irreversible means that the same enzyme is highly unlikely to perform the reverse reaction
Glycolysis as a whole has a very negative ΔG. To overcome the irreversible steps favorable energy generated by HK, PFK, and PK there needs to be 3 reverse reactions: |
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Term
| Gluconeogenesis reverse reactions |
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Definition
1. Pyruvate to PEP, using enzyme pyruvate carboxylase
2. Fructose 1,6 biphosphate to Fructose 6 phosphate, using enzyme Fructose 1,6-bisphosphatase
3. Glucose-6-phosphate to glucose, using enzyme glucose-6-phosphatase |
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Term
| Pyruvate to phosphoenolpyruvate |
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Definition
DRAW
1. Pyruvate carboxylase is only within the mitochondria (compartmentalization!) – and mediates the formation of oxaloacetate from pyruvate
2. Oxaloacetate is shuttled out of the mitochondria as malate, and is oxidized back into oxaloacetate by NAD+
3. Oxaloacetate is converted into PEP by phosphoenolpyruvate carboxykinase (PEPCK) |
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Term
| Why does pyruvate have to be carboxylated, then decarboxylated/phosphorylated to regenerate PEP |
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Definition
| If we were to take a pyruvate and jam a phosphate onto it, it would require 31 kJ of energy. It’s highly unfavorable! The reason gluconeogenesis goes thru this seemingly roundabout way of using 2 enzymes, one that carboxylates and one that decarboxylates and adds a phosphate group, the overall delta G of this reaction is just .8 kJ. That’s how it gets over this unfavorable reaction! |
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Term
| Three steps of pyruvate to phosphoenolpyruvate |
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Definition
Pyruvate → Oxaloacetate [Pyruvate Carboxylase]
Carboxylates
(Oxaloacetate→Malate to get out of mitochondria, then Malate→Oxaloacetate in cytoplasm via oxidation) [enzymes not listed]
Oxaloacetate→ Phosphoenolpyruvate (PEP) [PEPCK] |
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Term
| Fructose 1,6 Bisphophate → Fructose-6-Phosphate |
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Definition
[Fructose 1,6 Bisphosphatase]
This is pretty straightforward:
This enzyme is allosterically regulated (last section)
The enzyme dephosphorylates it |
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Term
| Glucose-6-phosphate → Glucose |
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Definition
[glucose-6-phosphatase]
Glucose transporters on the plasma membrane of the liver cell only recognize glucose!! Not G6P! G6P won’t get pumped out by liver cells, you need to turn it into glucose. This is the final step in the path.
The liver and kidneys, given their role in monitoring blood glucose have the enzyme glucose-6-phosphatase:
compartmentalized into the ER
mediates the generation of free glucose via dephosphorylation
glucose is then pumped into the cytoplasm where it can be transported out of the liver and kidney and into the blood. |
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Term
| Glucose-6-Phosphate Complex: |
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Definition
1. A transporter takes the G6P into the lumen of the ER, where the phosphatase is embedded in the membrane, it dephosphorylates it
2. two different transporters pump out [phosphate] and another pumps out glucose.
3. This glucose can now get pumped out by normal glucose transporters and go into the bloodstream & do its thing |
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Term
| net reaction for pyruvate to glucose |
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Definition
| 2 pyruvate + 4 ATP +2 GTP +2 NADH +6 H20----> glucose + 4 ADP + 2 GDP + 6 Pi + 2 NAD+ + 2 H+ |
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Term
| Pyruvate to Glucose Key Steps: |
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Definition
Pyruvate -> PEP
Fructose 1,6 Bis -> Fructose 6 P
Glucose 6 Phosphate -> Glucose
Everything else is just the reverse of glycolysis! |
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Term
| glycolysis vs. gluconeogenesis |
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Definition
| The things that turn glycolysis on are the things that turn gluconeogenesis off! |
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Term
| bifunctional enzyme phosphofructokinase2 (PFK2) |
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Definition
1. regulates liver sensitivity to blood glucose
2. FBPase is phosphatase domain
3. PFK2 is the kinase domain |
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Term
| PFK2 in low blood glucose conditions |
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Definition
1. pancreas releases glucagon
2. glucagon triggers protein kinase A release
3. PKA phosphorylates PFK2, inactivating PFK2
4. FBPase2 domain is activated and dephosphorylates F-2,6-BP, producing F6P
5. This will lower PFK activity and shut liver glycolysis down |
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Term
| PFK 2 in high blood glucose conditions |
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Definition
1. pancreas releases insulin
2. Insulin triggers the release of phosphoprotein phosphatase (PPP)
3. the PFK2 domain will be dephosphorylated, becoming activated
4. PFK2 will convert F-6-P, to F-2,6-BP
5. PFK will be activated, and liver glycolysis will occur, removing glucose from the blood |
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