Glycolysis Flashcards
Give the affinity, tissues expressed and important note about GLUT 1
Tissue: All, RBC
Affinity: high [1mM ]
Important note: basal uptake of glucose
Give the affinity, tissues expressed and important note about GLUT 2
Tissue: Liver , pancreas, intestine
Affinity: low affinity [15-20mM]
Important Note: liver uptakes excess glucose, pancreas regulates insulin
Give the affinity, tissues expressed and important note about GLUT 3
Tissue: brain
Affinity: highest
Important note: high affinity basal uptake of glucose
Give the affinity, tissues expressed and important note about GLUT 4
Tissue: Muscles, heart and fat
Affinity : 5mM
Important note: regulated by insulin
What are the typical blood glucose levels
5mM
Explain the process of the glucose going from intestinal lumen to bloodstream (use as much detail as possible)
- High salt concentrations drive glucose into the epitheal cells via Na+ glucose symporter
- As this continues it builds high concentration of glucose inside the epithelial cells
- The high concentration of glucose with drive GLUT 2 uniporter to activate
- There is a downhill efflux of glucose out of the cell into the blood stream
- Na K+ ATPase will be drive 3 NA out of the out of the cell and 2 K+ inside of the cell making a concentration gradient
Describe the activity of GLUT 4 via the binding of insulin
- Insulin bind to its receptor which triggers a series a reactions
- One of the kinases will activate the GLUT 4 vesicle which moves it to the membrane of the cell AND activates phosphatase (PP-1)
- Phosphatase then dephosphorylates which increases the activity of glycogen synthase and decreases the activity of glycogen phosphorylase
What transporter in increased in endurance athletes?
GLUT 4
What does phosphatase do?
Dephosphorylates which increases the activity of glycogen synthase and decreases activity of glycogen phosphorylase
What enzyme opposes phosphatase?
Glucagon A kinase
What are some uses of glucose?
- used in the cell wall
- stored as glycogen
- backbone of nuclei acids
- used as pyruvate
How is NADPH produced?
Via reductive biosynthesis
What is the catabolic fate of pyruvate?
Pyruvate gets turned into ACoA via ox. Then to CO2 + water
What are the anabolic fates of pyruvate?
Lactate and ethanol
What is fermentation
Anaerobic breakdown of nutrient molecules without NET oxidation
What role Does phosphorylation play in the preparatory phase of glycolysis?
- Keeps the glucose molecule inside the cell therefore it can’t go out via a transporter
- it also destabilizes glucose
- decrease glucose concentration so that more can go inside the cell
Describe the first step of glycolysis (use as much detail as possible)
Glucose + ATP <— hexokinase + Mg+ –> Glucose-6-phosphate + ADP + H+
-phosphate/ phosphoryl transfer
-coupled reaction
- product inhibition
What enzyme catalyze the first reaction in glycolysis
Hexokinase, the first ATP investment
What’s the difference between a phosphate and a phosphoryl transfer
Phosphate: OPO2-/3
Phosphoryl: PO2-/3
Why does ATP bond to the catalytic site unless glucose it there?
So it does catalyze the phosphoanhydride bond, water is now gone so it isn’t in the reactive
What are isozymes?
Different enzymes that catalyze the same reaction
What are the key features of hexokinase
- Ubiquitous
- less specific
- high affinity therefore low km therefore hyperbolic shape
- product inhibition
What transport is hexokinase most like
GLUT 1
What are the key features of glucokinase
- liver and pancreas
- low affinity therefor high km therefore sigmoidal
- regulated by compartmentalization/ regulatory proteins
What transporter is glucokinase most like
GLUT 2
Describe the release of insulin in the pancreas
- Glucose enters the beta cells via the GLUT 2 channel
- Glucose is converted to pyruvate which produces CO2 and undergoes respiration in the mitochondria
- ATP is produced which inhibits the release of K+ via the ATP K+ channel t
- This causes depolarization which changes the voltage of the cell
- Change in voltage cause Ca2+ voltage gated channel to allow Ca+ into the cell which stimulates insulin to be released via exocytosis
What regulates the pancreatic beta cells
Glucose
Describe the regulation of glucokinase in the liver
- Glucose enters the hepatocyte via the GLUT 2 channel
- The increase in glucose (or increase in fructose-1-phosphate) activated glucokinase
- Conversion of glucose to glucose-6-phosphate follows
- Subsequent steps of glycolysis follow
How is glucokinase inactivated?
Glucokinase binds to glucokinase regulatory protein which transport GK into the nucleus where it can’t catalyze reactions
Need increased glucose or fructose-1-phosphate to activate again
What can happen to G-6-P in the heptocyte?
- Fills glycogen stores first
- Can be used for pyruvate which can be used in other reactions
What does glucosephosphate isomerase do?
Converts glucose-6-phosphate into fructose-6-phosphate by opening up the 6 member ring, doing a isomerization then closing the ring
What is the second step of glycolysis?
Glucose-6-phosphate gets converted to fructose-6-phosphate thru the enzyme phosphoglucose isomerase, reversible reaction
What enzyme is used in 3rd step in glycolysis?
Fructose-6-phosphate + ATP gets converted into fructose-1,6-bisphosphate + ADP + H+ via phosphofructokinase-1
Phosphoryl transfer
Coupled reaction
What does phosphofructokinase-1 do?
Catalyzes reaction fructose-6-phosphate to fructose-1,6-bisphosphate with Mg
Which step is the committed step if glycolysis ?
Conversion of fructose-6-phosphate to fructose-1,6-bisphosphate
Why is PFK-1 seen as the committed step?
Other steps are either reversible or glucose-6-phosphate can be used in other reaction such as making glycogen or pentose phosphate pathway
How many ATP are yielded during the Energy investment stage of glycolysis
None, 2 are used
What happens in the 4th step of glycolysis?
Fructose-1,6-bisphosphate is cleaved at carbon 3/4 via aldolase to produce Dihyroxyacetone phosphate (DHAP) and glyceraldehyde phosphate (GAP)
What does Aldolase do?
It converts fructose-1,6-bisphosohate into DHAP and GAP
What enzyme is used 5th step in glycolysis? Why type of reaction is this
Converting DHAP into GAP via triose phosphate isomerase
IRREVERSIBLE rxn
What is the balanced energy equation for the energy investment stage of glycolysis?
Glucose + ATP —> 2 GAP + 2 ADP 2 H+
What/ How is GAP converted into its product
- GAP is converted in 1,3-bisphosphoglcerate through the enzyme glyceraldhyde-3-phosphate dehydrogenase (reversible)
- ## Transfer of the Hydrogen on GAP to NAD+ to produce NADH and an inorganic phosphate transfer onto GAP
What are the different energy rich intermediates in glycolysis
1,3-Bisphosphoglycerate and phosphoenolpyruvate
Recall the energy recovery stage of glycolysis ( include all important enzymes/ reaction types etc)
- Glyaldehyde-3-phosphate gets converted to 1,3 BPG via enzyme glycealdhyde3phosphate dehydrogenase
NAD+ gets oxidized and phosphate gets added - 1,3 BPG gets converted into 3-phosphoglycerate + ATP via phosphoglycerate kinase doing a SLP
- 3-phosphoglyceate gets converted into 2-phosphoglycerate via an phosphoglycerate mutase
- 2-phosphoglycerate gets converted into PEP
- PEP gets converted into pyruvate and ATP via pyruvate kinase
What is the equation for glycolysis
1 glucose + 2 ADP + 2Pi —> 2 pyruvate + 4 ATP + 2 NADH + H + H2O
How is 2,3-bisphosphoglycerate created and what is it’s significance?
- 1,3 phosphoglycerate get converted into 2,3 Bisphosphoglycerate via phosphoglycerate kinase
- 2,3 Bisphosphoglycerate stabilizes the T state in deoxyhemoglobin to make it easier to offload oxygen in the muscles
Where can galactose enter into the glycolysis pathway?
Can enter where there is G6P, via galactokinase
Where can fructose enter into the glycolysis pathway?
In the muscle: fructose-6-phosphate, hexokinase
In the liver: GAP, fructokinase
How does fructose enter a hepatocyte?
Fructose is converted into fructose-1-phosphate via fructokinase due to a phosphate transfer
What does fructose-1-phosphate indicate
Well feed state
How is galactose converted to be used for glycolysis
- Galactose is converted to galactose-6-phosphate via galactokinase which under goes SLP
- Galactose-6-phosphate + UDP glucose create UDP-galactose and glucose-1-phosphate
- Glucose-1-phosphate is then isomerased to glucose 6 phosphate to glycolysis
- UDP-galactose is epimerased to for UDP-Glucose to release the cycle
Provide an explaination as to how PFK-1 is an allosteric enzyme?
PFK-1 exists in 2 states, T state and R state. Also has 2 binding sites (substrate and allosteric)
T state is stabilized when ATP binds to allosteric site, making the enzyme inactive (Low affinity for ATP)
F6P preferentially binds to stabilize R state
What are activators of PFK-1?
F6P + AMP + F2,6BP
What inhibits PFK-1
ATP
Why is AMP a more sensitive indicator than ADP
There’s lower amount of it in the cell therefore changes are more significant
What does PFK-2
Convert Fructose6phosohate to fructose2,6bisphospate
How is PFK-2 regulated in the liver?
Insulin increases activity and glucagon decrease’s activity
How is PFK-2 regulated in the skeletal muscles?
Allosteric regulators
Activators of pyruvate kinase
F1,6BP, feed forward activation
What inhibits pyruvate kinase
Acetyl coa
Glucagon (only in liver)
ATP
Explain the regulation of pyruvate kinase in the liver
Pyruvate kinase is in its inactive form when phosphorylated to be activated you need to dephosphorylate by
PP.
To then inactive you need to phosphorylate
What activates AMPK
High levels of AMP
What happens when AMPK is phosphorylated?
Switches from ATP consumption to ATP production
