1.6 Regulation of Metabolic Pathways Flashcards
(167 cards)
1
Q
What is the difference between a catabolic and anabolic pathway?
A
Anabolism is building up complex molecules from simple ones and catabolic is taking a high energy nutrient and breaking it down into low energy products, from complex to simple
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Q
A
3
Q
A
4
Q
Name this molecule
A
ATP
5
Q
Name this molecule
A
Coenzyme A
6
Q
What is the equation for Coenzyme A going from a thioester to a thiol?
A
7
Q
Where is CoA used in metabolism?
A
- CoA functions in acyl transfer reactions where X is an acetyl, acetoacetyl or other group which is transferred to another molecule.
- Acetyl-CoA is central to metabolism; used in Krebs cycle, fatty acid synthesis/oxidation etc.
- Acetoacetyl-CoA is used in the switch to “ketone bodies” during starvation
8
Q
Name this molecule
A
NAD+ and NADH
9
Q
What are the different forms of Nicotinamide Adenine Dinucleotide?
A
- NAD+ is the oxidised form; NADH is the reduced form
- NADP+ and NADPH are phosphorylated forms
10
Q
How does the wavelength absorbance of NADH compare to NAD+?
A
Oxidised red curve absorbs light weakly but reduced form absorbs strongly at 340 nm
11
Q
Name this molecule
A
FAD or Flavin adenine dinucleotide
12
Q
What are the different forms of FAD?
A
FAD is the oxidised form; FADH2 is the (fully) reduced form
13
Q
What is the equation for cellular respiration?
A
Glucose + 6O2 → 6CO2 + 6H2O
14
Q
What is the first reaction of the preparatory phase of glucose?
A
The phosphorylation of glucose
Where glucose is converted to glucose-6-phosphate
15
Q
What enzyme catalyses the conversion of glucose to glucose-6-phosphate in the first reaction of the preparatory phase of glycolysis?
A
- The conversion of glucose to glucose-6-phosphate is catalyzed by HEXOKINASE in most tissues and GLUCOKINASE in the liver.
- First IRREVERSIBLE reaction of GLYCOLYSIS
16
Q
What can be said about the delta Go of the first reaction in the preparatory phase of glucose?
A
It has a delta Go of -16.7 kj/mol which means it is favourable under standard conditions, and with there being a high concentration of glucose it is quite favourable
17
Q
What is the second reaction in the preparatory phase of glycolysis?
A
It is the isomerisation of glucose-6-phosphate to fructose-6-phosphate
18
Q
What enzyme is used in the second reaction of the prepatory phase of glucose?
A
The conversion of glucose-6-phosphate to fructose-6-phosphate is catalysed by phosphohexose isomerase
19
Q
What can be said about the delta Go of the second reaction of the prepatory phase of glucose?
A
It has a delta Go of 1.7 which means it is small and positive under standard conditions. In the cell however the reactants have a higher concentration than products
20
Q
What is the third reaction in the preparatory phase of glycolysis?
A
- The conversion of fructose-6-phosphate to fructose-1,6-bisphosphate
- It is the addition of a phosphate group replacing the hydroxyl
- Second irreversible reaction of glycolysis and the first commited step of glycolysis (rate limiting)
21
Q
What is the enzyme that catalyses the third reaction of the preparatory phase of glycolysis?
A
Phosphofructokinase-1 (PFK-1)
22
Q
What can be said about the delta Go of the third reaction of the preparatory phase of glycolysis?
A
The delta Go is -14.2 which is small and negative understandard conditions
This reaction is favourable anyway because the [Fructose 6-phosphate] > [Fructose 1,6-bisphosphate]
23
Q
What is the 4th reaction of the preparatory phase of glycolysis?
A
It is the cleavage of fructose 1,6-bisphosphate (F-1,6-bP)
Where adolase cuts the F-1,6-bisP in the middle producing dihydroxyacetone phosphate and glyceraldehyde 3-phosphate, each with a single phosphate attached.
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Q
What enzyme catalyses the fourth reaction of the prepatory phase of glycolysis?
A
Aldolase cuts the F-1,6-bisP in the middle, producing DHAP and GA-3-P, each with a single phosphate attached. The enzyme can catalyze the reverse reaction, which is more favourable & is in fact named after the reverse reaction which is an “aldol condensation”.
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What can be said about the delta Go of the fourth reaction in the prepatory phase of glycolysis?
The delta Go is large and positive so under standard conditions not favourable.
But in the cell the concentration of F-1,6-bisP is high and the products of this reaction are removed quickly
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What is the fifth reaction in the preparatory phase of glycolysis?
It is the isomerisation of DHAP to glyceraldehyde-3-phosphate
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What enzyme is used in the fifth reaction in the prepatory phase of glycolysis?
Triose Phosphate Isomerase pulls a hydrogen atom off one carbon atom and replaces it on a neighboring carbon atom. A special glutamate amino acid in the active site (Glu165) performs the transfer.
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What can be said about the delta Go of the fifth reaction in the preparatory phase of glycolysis?
The delta Go is 7.5 kJ/mol which is small and positive but the concentration of the product G3P is low as it is used in the next step so this reaction is favourable
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How many ATP are produced during the preparatory phase of glycolysis?
There is a net loss of 2 ATP
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What is the sixth reaction in glycolysis?
The oxidation of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate.
A phosphate group is added to G3P
Oxidation state of carbon is changed as O is added so couple with a reduction of NAD+
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What enzyme catalyses the sixth reaction of glycolysis?
Glyceraldehyde 3-phosphate dehydrogenase
Its activity depends on the turnover of NAD+ in the cytosol of the cell. Rapid turnover of NAD+ is achieved only under anaerobic conditions
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What can be said about the delta Go of the sixth reaction of glycolysis?
Delta Go is small and positive but there is lots of incoming reactant and the product is used up so it is favourable
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What is the seventh reaction of glycolysis?
Conversion of 1,3-bisphosphoglycerate to 3-phosphoglycerate
The phosphate group is transferred onto ADP in order to make ATP
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What enzyme is responsible for the seventh reaction of glycolysis?
Phosphoglycerate kinase transfers the phosphate from 1,3-BPG to ADP to form ATP
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What can be said about the delta Go of the seventh reaction of glycolysis?
The Delta Go is large and negative meaning it is very favourable.
But the conversion of ADP and Pi to ATP is very unfavourable so the removal of the phosphate group must be a very favourable reaction, about -50kj/mol
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What is the eight reaction of glycolysis?
Mutase reaction converts 3-phosphoglycerate to 2-phosphoglycerate.
Moving the phosphate group to carbon 2
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What enzyme catalyses the eighth reaction of glycolysis?
Phosphoglycerate mutase begins the final capture of energy by shifting the phosphate from carbon 3 of the phosphoglycerate molecule to carbon 2 priming it for phosphate transfer to ADP
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What can be said about the delta Go of the eighth reaction of glycolysis?
It is 4.4 which is small and positive.
But the pathway favours conversion of reactants to products
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What is the ninth reaction in glycolysis?
The dehydration of phosphoglycerate to phosphoenolpyruvate
2-phosphoglycerate is not a very good P donor so we need to make it more unstable and reactive by removing H2O
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What is the enzyme that catalyses the ninth reaction of glycolysis?
Enolase is a Mg2+ dependent enzyme that converts 2-PG (which has a relatively low phosphoryl group transfer potential of -17.6 kJ/mol) to PEP (-61.9 kJ/mol).
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What can be said about the delta Go of the ninth reaction of glycolysis?
It is 7.5 which is small and positve but reaction pathway favours conversion of reactants to products
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What is the tenth reaction in glycolysis?
The production of ATP from the conversion of PEP to pyruvate.
PEP is a phosphate donor to ADP
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What is the enzyme that catalyses the tenth reaction of glycolysis?
It is pyruvate kinase
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What can be said about the delta Go of the tenth reaction of glycolysis?
It is -31.4
Production of ATP is not very favourable so the reaction of converting PEP to pyruvate must be very favourable ~ 60kj/mol
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What is the overall stoichiometry of glycolysis?
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How can glycolysis be used to detect cancer?
* Glycolysis occurs at a rate 10x faster in cancer cells, so some drugs inhibit hexokinase
* The high glycolytic turnover in cancer cells is also used for diagnosis by injecting isotopically labelled glucose (18FdG 6-phospho-18FdG) followed by PET scanning.
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What is the warburg hypothesis?
Otto Warburg proposed that most cancer cells produce energy by anaerobic glycolysis rather than by oxidation of pyruvate in the mitochondria (which is common to healthy cells). This is known as the “Warburg Hypothesis”.
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What is gluconeogenesis?
metabolic pathway that results in the generation of glucose from certain non-carbohydrate carbon substrates.
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What three irreversible steps in glycolysis have to be catalysed by different enzymes in gluconeogenesis?
1. Conversion of pyruvate to PEP occurs via oxaloacetate by using mitochondrial pyruvate carboxylase and cytosolic PEP carboxykinase
2. Conversion of F-1,6-bisP to F-6-P is catalyzed by fructose 1,6-bisphosphatase
3. Conversion of G-6-P to glucose occurs in the ER lumen using Glucose-6-Phosphatase
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What is the first irreversible step of glycolysis that gluconeogenesis must overcome?
A bicarbonate group is added to pyruvate which becomes oxaloacetate
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What enzyme catalyses the formation of oxaloacetate in the first step of gluconeogenesis?
Pyruvate Carboxylase is a mitochondrial enzyme that adds a carboxylic acid to pyruvate to form oxaloacetate using BIOTIN (vitamin B7) as a cofactor.
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How does oxaloacetate end up being PEP in the gluconeogenesis?
PEP carboxinase reacts oxaloacetate with GTP to generate PEP and also releases the GDP and CO2 which it used before
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What is the second reaction in gluconeogenesis that is an alternative to the irreversible reaction in glycolysis?
Fructose 1,6-bisphosphate is converted to fructose 6-phosphate by FBPase-1 (fructose-1,6-bisphosphatase)
The phosphate group is snipped off and that bond is hydrolysed
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What can be said about the delta G of the reaction in gluconeogenesis converting fructose 1,6-bisphosphate to fructose 6-phosphate?
It is -16.3 kj/mol which is moderately sized and negative
Hydrolysis of phosphate groups are generally energetically favourable
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What is the third reaction in gluconeogenisis that overcomes an irreversible step of glycolysis?
* Glucose-6-phosphate is converted to glucose by **glucose-6-phosphatase** and this occurs in the lumen of ER in hepatocytes of the liver and in the cortex of the kidney
* G6P generated in cytosol is moved into lumer of the ER where enzyme snips off P to make free glucose again, this glucose exported out via same transporter that bought it in
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What are the 5 major fates of pyruvate?
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What is the reaction for fermentation starting with pyruvate?
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What happens in anaerobic glyclysis?
Pyruvate is converted to L-lactate by lactate dehydrogenas in the muscles
Pyruvate is reduced and NADH is oxidised
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Why is anaerobic glycolysis and important step for glycolysis?
Because conversion of pyruvate to l-lactate produces NaD+ and this is needed in step 6 of glycolysis
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What is acidosis?
When there are high amounts of lactic acid in the tissues
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What is the cori cycle?
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What is the percentage composition of energy stores in humans?
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What is glycogenolysis and what enzymes does it involve?
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What is glyogenesis and what enzymes does it involve?
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What is the role of glycogen phosphorylase in glycogenolysis?
* Glycogen phosphorylase chops off the terminal non reducing sugar
* Uses phosphate as a tool to chop the bond and phosphate is left on the leaving unit
* It cannot join glycolysis as it is not glucose 6 phosphate
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What is the role of the debranching enzyme in glycogenolysis?
* Transfers a block of 3 glucose residues to a nearby non reducing end
* Hydrolyses the alpha 1,6 linkage to release free glucose
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What is the role of phosphoglucomutase?
Transfers a phosphoryl group on glucose-1-phosphate from C1 to C6 to form glucose-6-phosphate which is freely reversible
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What does hitting the wall refer to in a marathon?
When runners become disoriented, unbalanced and collapse.
They have used up their glycogen storage completely and the brain takes priority
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What is the role of the enzyme UDP glucose pyrophosphorylase in glycogenesis?
* It synthesises UDP glucose from UTP and glucose-1-phosphate and also produces pyrophosphate (ppi)
* G1P reacts with Nucleotide triphosphate to generate UDP linked glucose and 2 phosphates from UTP come off as pyrophospahtes which break down to 2 simple Pis
* UDP glucose used as sugar donor to form new glycosidic bond in glycogen
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What is the role of glycogen synthase in glycogenesis?
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What is the role of the glycogen branching enzyme in glycogenesis?
* Catalyses the transfer of a block of 6 or 7 glucose residues from the non reducing end of a glycogen branch that has 11 residues
* transfers to the C6 hydroxyl group of a glucose residue in a more inner position within the same or different glycogen chain
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What is the role of glycogenin in glycogenesis?
* Glycogen synthase cannot initiate the synthesis of a new glycogen chain since it requires a primer which is usually a preformed 1→4 polyglucose chain
* Glycogenin is both the primer on which new chains are synthesised and the enzyme that catalyses their assembly
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What is the role of pyruvate dehydrogenase complex in glycolysis/krebs cycle?
* Takes pyruvate from the end of glycolysis and converts into Acetyl CoA
* This is an oxidation and NAD+ is reduced
* Allosterically regulated at separate sites by ATP, acetyl CoA, NADH and ADP, pyruvate
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What are some B group vitamins?
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What is the first reaction of the Kreb's cycle?
* The formation of citrate from oxaloacetate and the acetyl-Coa catalysed by citrate synthase
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What enzyme catalyses the first reaction of Kreb's cycle?
* Citrate synthase
* Oxaloacetate induces a large conformational change in the enzyme allowing acetyl-CoA to then bind
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What is the delta Go like for the first reaction of the Kreb's cycle?
* Delta Go is -32.2 kj/mol
* Large and negative which is favourable under standard conditions even though the availability of oxaloacetate is low
* Reaction is highly exergonic because it involves the hydrolysis of a thioester (S-CoA)
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What is the second reaction of the Kreb's cycle?
* Citrate is converted to isocitrate in two steps (via a cis-aconitate intermediate) catalysed by aconitase.
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What is the Delta Go like for the second reaction of the Kreb's cycle?
* Delta Go is small and positive
* Although the reaction favours citrate formation it is driven to the right by the rapid consumption of isocitrate in the cycle
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What is the third reaction in Kreb's cycle?
* Isocitrate is then converted to alpha-ketoglutarate by isocitrate dehydrogenase producing CO2 and also redox energy in the form of NADH that is equivalent to 2.5 ATP.
* Together with PDH and alpha-KG DH complex, isocitrate DH serves as the 2nd of 3 control points in the cycle
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What is the fourth reaction of the Kreb's cycle?
* Alpha-ketoglutarate is converted to succinyl-CoA by the **alpha-ketoglutarate dehydrogenase** complex
* 3rd and last control point in the cycle
* Essentialy CoA is added, redox energy stored to make ATP later
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What can be said about the delta G of the fourth reaction of Kreb's cycle?
* It is large and negative and helps drive the cycle in the desired direciton
* -33.5 kj/mol
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What is the fifth reaction of Kreb's cycle?
* Succinyl-CoA is then converted to succinate by succinyl-Co-A synthetase
* Energy released in the form of hydrolysis of a thioester bond used to drive synthesis of GTP
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What additional effect does the production of GTP in reaction 5 of the Kreb's cycle have?
* GTP can be converted to ATP by the nucleoside diphosphate kinase
* High GTP concentration inhibits oxidative metbaolism of amino acids, suppressing protein metabolism as a source of energy
* Tells the cell it has energy via Kreb's cycle so amino acids don't need to be broken down
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What can be said about the delta Go of the 5th reaction of Kreb's cycle?
Just like ADP phosphorylation, formation of GTP is quite unfavourbale. So the hydrolysis of succinyl CoA thiol ester bond must be really favourable to counter that.
delta Go is -2.9 kj/mol
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What is the sixth reaction of Kreb's cycle?
* Succinate is converted to fumerate by succinate dehydrogenase
* Utilizes FAD as a cofactor and thus produces a FADH2 during the reaction which is equivalent to 1.5 ATP
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What can be said about the delta Go of the sixth reaction of succinate dehydrogenase?
* The Delta Go is 0 kj/mol
* Under standard conditions succinate and fumerate are in equal concentrations
* Since kreb's cycle produces lots of succinate the reaction is to the right
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What is seventh reaction of the Kreb's cycle?
Fumerate is converted to L-malate via a carbanion intermediate
* Via enzyme **fumerase**/fumerate hydratase
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What is the enzyme that catalysed the seventh reaction of the Kreb's cycle and its specificity?
The enzyme is fumerase and is highly stereospecific and thus cannot bind or react with the cis isomer of fumerate (maleate) or the D malate isomer
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What is the delta Go like for the seventh reaction in Kreb's cycle?
Detla Go small and negative which is favoured weakly but lots of fumerate produced in the step before will push the reaction in the desired direction
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What is the eighth reaction in Kreb's cycle?
The final reaction is the conversion of malate to oxaloacetate by **malate dehydrogenase** produces another NADH and thus 2.5 ATP
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What can be said about the delta Go of the eighth reaction of Kreb's cycle?
* It is large and positve, 29.7kj/mol which is highly unfavourable under standard conditions
* But since oxaloacetate is used up rapidly it will keep its concentration low, driving it in the desired direction as the cycle produces lots of malate
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What is the site of oxidative phosphorylation in eukaryotes?
Mitochondria
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What is oxidative phosphorylation?
* The process of transforming redox energy formed under aerobic conditions during glycolysis and the citric acid cycle into chemcial energy in the form of ATP
* Redox energy converted to an electrochemical gradient which drives unfavourable formation of ATP
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What is the first major step of oxidative phosphorylation?
Transfer of electrons from NADH to complex 1 and/or from FADH2 to Complex II
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What is the second major step of oxidative phosphorylation?
Flow of electrons through large multi component inner mitochondrial membrane complexes and mobile electron transporters of the electron transport chain
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What is the third major step of oxidative phosphorylation?
Pumping of protons (H+) from the matrix to the intermembrane space using the proton pumps of Complex 1, III, and IV as electrons flow through these complexes
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What is the fourth major step of oxidative phosphorylation?
* The flow of protons from the intermembrane space through the Fo component of ATP synthase (FoF1 ATPase) back into the matrix
* resulting in the rotation of the Fo component and gamma subunit of F1 and the synthesis of ATP from ADP and Pi by the F1 component
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How is a proton gradient created in the electron transport chain?
* The flow of electrons through complexes in the inner mitochondrial membrane
* subsequent pumping of protons from the matrix into the intermembrane space creates the proton gradient
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What complex is this from the electron transport chain?
Complex 1
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What is the role of complex I in the electron transport chain?
* It is where NADH is received and e- are traken from the reduced form of NADH and oxidised to NAD+
* Passed through a series of redox Fe-S centres onto coenzyme Q
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What electron movement does Complex 1 cause in the electron transport chain?
Highly exergonic movement of electrons and powers the pumping of 4H+ across the membrane into IMS
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What molecule is this?
Coenzyme Q
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What is coenzyme Q and what does it do?
Coenzyme Q is a lipophillic inner mitochondrial membrane dwelling mobile electron carrier that transfers electrons from Complex I and Complex II to Complex III.
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What are the different forms of coenzyme Q?
* The oxidised form (Q) is known as ubiquinone and the reduced form (QH2) is referred to as ubiquinol.
* Coenzyme Q can also exist as a partly reduced form referred to as a semiquinone (QH).
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What molecule is this?
COmplex II from the electron transport chain
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What is the role of Complex II in the electron transport chain?
* It is the site where e- is received from FADH2
* e- are taken from the reduced form FADH2 and passed through Fe-S centres until they reach ubiquinone at the binding site
* Ubiquinone reduced to ubiquinol and leaves complex
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At what stage does Kreb's cycle intersect with electron transport chain?
* Complex 2 is wehre e- are received from FADH2 which is generated here from FAD
* Does not leave complex 2 because it is the same enzyme from Kreb's
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What is the role of complex III in the electron transport chain?
* It is the receiver of the ubiquinol molecules which pass through the iron sulphur centre and the heme ring
* Electrons are removed from ubiquinol and it becomes ubiquinone to pick up more electrons
* pumps 4 protons from matrix to intermembrane space
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What molecule is this?
Cytochrome C
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What is the role of cytochrome C?
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What molecule is this?
Complex IV from electron transport chain
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What is the role of complex IV in the electron transport chain?
* Electrons from Cytochrome C arrive from intermembrane space
* 2 electrons need to be accepted from 2 copies of cytchrome C to power the next reaction
* Oxygen combines these electrons with protons and becomes reduced to water
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What are the three phases/conformations of the F1 component of ATP synthase?
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How do phosphates enter the matrix of the mitochondria in the electron transport chain?
* Phosphate translocase
* Each time we bring a phosphate into the matrix it brings in a proton as it needs to neutralise the negative charge of phosphate to get through the transporter
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What does allosteric mean?
involving a change in the shape and activity of an enzyme that results from the binding of a regulatory molecule at a site other than the active site
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What are the three irreversible steps/control points of glycolysis?
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What are the allosteric regulators for the third reaction of glycolysis?
* ATP is the final product so if there is high enough ATP the cell has enough energy therefore its an inhibitor to slow down glycolysis
* Lots of citrate means enough glycolysis is occuring therefore its an inhibitor
* ADP and AMP means ATP stores are low so we need to activate glycolysis therefore its an activator
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What is the quaternary structure like of phosphofructokinase-1 which is the third step in glycolysis?
* Homotetramer of 4 copies of the same subunit all with the same fold
* Each subunit contains an active and regulatory site
* Yellow and orange AS to the front and vice versa
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What is the allosteric regulator for hexokinase in glycolysis?
* Hexokinase is regulated by Glucose-6-phosphate, the product of the reaction it catalyses
* Lots og G6P slows down glycolysis
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What do these Km values show?
* Hexokinase will be operating close to Vmax anyway because normal [blood glucose] is around 5mM
* For hexokinase Km 0.1 mM this enzyme is operating close to Vmax at all times so its activity needs to be regulated in another way, through using G6P as an allosteric regulator and binding at separate site to slow activity
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How is pyruvate kinase allosterically regulated?
* Liver and muscle pyruvate kinase both allosterically inhibited by ATP4- and alanine and positively regulated by fructose-1,6-bisP
* If there's lots of ATP we don't need glycolysis working so hard
* Lots of Alanine also slows down glycolysis as alanine is one of the products generated from pyruvate
* F-1,6-bisP senses high concentration of earlier substates so increasing activity of pyruvate kinase further down increases flow throught the pathway
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What's the difference between liver and muscle pyruvate kinase?
There is covalent modification in the liver vs the muscle
Phosphorylation occurs to inhibit its activity
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In the fasting state what does glucagon activate?
* Drop in blood glucose below 4.5 mM triggers glucagon release from the pancreas: resting [glucose]blood = 5.0 mM
* Glucagon causes an increase in blood glucose levels
* Glucagon activates gluconeogenesis (GNG) & glycogenolysis (GGL) in the liver
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In the fasting state what does glucagon inhibit?
Inhibits glycolysis (GL) and glycogenesis (GG)
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In the fasting state what tissues are given priority?
Priority to supply glucose to brain and erythrocytes
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What are the five components of glucagon signalling in the alpha cells of the pancreas?
1. Glucagon the first messenger
2. GLucagon receptor
3. Guanyl nucleotide G protein
4. cAMP second messenger
5. cAMP-dependent protein kinase or protein kinase A
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How does the Guanyl Nucleotide G protein change its conformations?
* It has three subunits alpha beta and gamma
* Alpha unit contains the binding site where GDP exchanged for GTP activiting the G protein
* Then intrinsic GTPase activity of the alpha subunit will eventually hydroluse GTP back to GDP
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What is the role of cAMP in glucagon signalling?
* Its the second messenger in the pathway and the G proteins go on to activate enzyme called Adenylate cyclase
* This activation causes it to produce cAMP from ATP
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What is the role of protein kinase A (PKA) in glucagon signalling?
* cAMP activates PKA allosterically and when activated PKA phosphorylates several protein targets on Ser/Thr residues
* It is a multi subunit complex
* In the inactive state the active site is blocked by the regulatory subunits to form a pseudosubunit
* Loop withrdrawn when cAMP activates it
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Explain glucagon signalling in the liver
* Glucagon binds to the receptor causing a conformational change
* Activated G protein, heterotrimeric complex which activates adenylate cyclase producing cAMP
* Second messenger amplifies the signal
* Activates protein kinase A which starts phosphorylation of multiple target
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What are some of the targets of cAMP dependent protein kinase?
1. Bifunctional PFK-2/FBPase-2 enzyme
2. L-Pyruvate Kinase
3. A Glycogen synthase and 3B glycogen phosphorylase
4. Phosphoenolpyruvate carboxykinase (PEPCK)
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What is the role of bifunctional PFK-2/FBPase-2 enzyme?
* Controls the concentration of F-2,6-bisP, the key allosteric activator of PFK2 in glycolysis
* It is bifunctional as protein contains kinase and phosphate activity
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Why is bifunctional activity of bifunctional PFK-2/FBPase-2 enzyme useful?
* In the liver glucagon signalling causes kinase domain to become phosphorylated, reducing its activity
* So the enzyme stops producing F-2,6-bisP
* It still has active phosphatase activity and dephosphorylates F-2,6-bisP to F-6-P
* Low F-2,6-bisP stops activating PFK-1 which stops the flow of glycolysis
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How does targeting L-pyruvate kinase by glucagon signalling do anything?
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What does targetting glycogen synthase and glycogen phosphorylase do? (3A and 3B)
* PKA phosphorylates glycogen synthase (Red cross) inhibiting it and blocking movement of glucose into glycogen granule in the liver, increasing blood glucose
* Simulataneously PKA is activating phosphorylase kinase which activates glycogen phosphorylase
* Thus slowing down storage of glucose in glycogen and speeding up breakdown of glycogen into G-1-P which goes on to become glucose and exported into bloodstream
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What does phosphoenolpyrulate carboxykinase (PEPCK) do?
* Back in gluconeogenesis PKA phosphorylates the CREB protein which moves to the nucleus and causes expression of the PEPCK gene
* mRNA produced is taken into cytoplasm where PEPCK enczme is made
* It converts oxaloacteate to PEP and increases gluconeogenesis and makes more glucose for export into bloodstream
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What molecule is this?
Adrenaline
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What is the pathway for adrenaline signalling?
* Adrenaline is produced by adrenal gland and enters the bloodstream, then transported to extracellular receptors
* The receptor is beta adrenergic receptor, with 7 transmembrane helical proteins
* Adrenaline binding causes a conformational change that activates G protein in the cytoplasm
* G proteins activate adenylate cylcase to make cAMP from ATP which activates PKA
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What differs between glucagon and adrenaline signalling?
Everything except the receptor and the ligand is the same
Hepatocytes (liver cells) are more responsive to glucagon than adrenaline
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How does adrenaline signalling differ in the liver vs the muscle?
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How does concentration of F-2,6-bisP change in the liver vs the muscles due to adrenaline signalling?
1. Different isoforms of F-2,6-bisP controlling enzyme in liver and muscle cells
2. PKA phosphorylation has opposite effect on these enzyme
3. Adrenaline signalling decrease [F-2,6-bisP] in liver but increase [F-2,6-bisP] in muscle
4. Glycolysis supressed in liver but increase in muscles
5. Muscle PK not inhibited by adrenaline so pyruvate can feed into krebs cycle etc for prolonged muscle usage
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How does liver and muscle PK differ due to adrenaline signalling?
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How does Ca2+ act as a second messenger for neural signalling in the muscles after adrenaline activity?
* It activates neurons to get muscle contractions by releasing Ca2+ from sarcoplasmic reticulum
* Also calcium binding means more phosphorylase activity which is the enzyme that activates glycogen phosphorylase to release glycogen
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What is the post prandial state?
The state after a meal, insulin brings glucose back down again
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How does the structure of preproinsulin compare to proinsulin and mature insulin?
* Preproinsulin single polypeptide so under reducing conditions unpaired cysteine
* reaches oxidising environment in the ER
* Protease cleaves out purple sequence
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What is the insulin binding pathway?
Must edit later
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WHat are the pathways regulated by insulin (3 main important ones)?
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How does the regulation of GLUT4 and glycogen synthase occur due to insulin?
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How does insulin inhibit glycogen phosphorylase?
* Insulin signalling activates protein phosphatase which acts on glycogen phosphorylase so it doesn't liberate more glucose from glycogen
* Protein phosphorylase is activated and it snips off P from glycogen phosphorylase and deactivates it
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