BIOL2220 Lecture 6

How much ATps are consumed in gluconeogenesis?

6 ATPs iare consumed to turn 2 pyruvate into a glucose

Which 3 steps do gluconeogenesis and glycolysi use different types of enzymes?

Step1: turning glucose into glucose-6-phosphate by hexokinase
Step3: turning fructose-6-phosphate into fructose-1,6-biphosphate by using PFK-1 and ATP

Step10: turning PEP into pyruvate byusing pyruvate kinase and ADP

In the step of turning pyruvate back into PEP ( the reverse of step 10 in glycolysis ) which 2 enzymes are used and what did they do?

1. Pyruvate carboxylase, which add a carboxylic group COO to pyruvate by using bicarbonate as carboxylic gorpu donor, so pyruvate (3C) turns into oxaloacetate (4C)

2. phosphoenolpyruvate carboxykinase PEPCK, which adds a phosphate froup to oxaloacetate form ATP and remove a carboxylic group into Co2, so oxaloacate is turnt into PEP (3C)

What and how an enzyme is used in turning fructose-1,6-biphosphate back into fructose-6-phosphate (reverse of step 3 in glycolysis)?

fructose-1,6-biphsohate used fructose-1,6-biphosphatase, which remove a phosphate gorup and discard it into water, to turning into fructose-6-phosphate, which can unser go a reverse reaciton form fructose-6-phopsphate into glucose-6-phosphate

How glucose-6-phospahte turin into glucose ( reverse of step 1 in glycolysis )?

It made use of enzyme glucose-6-phosphatase to discard the phospahte group directly to water

Why in most of the mammalian tissue the glucose-6-phosphatase enzyme is absent?

glucose-6-phosphatase is an enzyme the convert glucose-6-phosphate into glucose. As tissue often use glucose-6-phospahte to make glycogen, so the corresponding enzyme is absent

Which mammalian tissue will have glucose-6-phosphatase and why?

Liver, kidney and small intestine
As they make glucse from glucose-6-phosphate

like liver will release free glucose into the blood

what do precoursors for gluconeogenesis mean?

a non-carbohydrate organic molecules that can be able to initiate gluconeogenesis

how lactate can be precursors of gluconeogenesis?

It used enzyme lacatate dehydrogenase and NAD+ to change itself into pyruvate

where does the reaction of turning lacate into glucsoe occur in human?

Liver

which bimolecules provide the ATP for the reaciton of turning lactate into glucose?

fatty acids, as the reaction is about generating glucose, so glucose will not undergoes glycolysis to provide ATP, which will only turns out of a net consumption of ATP

How amino acid (alanine) can act as precursors of gluconeogenesis?

alanine will donate its amino group and one proton away, while getting a oxygen atom, so it can turn into pyruvate.

how glycerol can be used as precursor of gluconeogenesis?

Glycerol from triacylglycerol will first turn into glycerol-3-phosphate with the help of glycerol kinase and ATP
Then glycerol-3-phosphate will turn into DHAP through 2 pathways:
1. Using cytosolic glycerol-3-phosphate dehydrogenase and NAD to lose a proton
2. using glycerol-3-phospahte dehydrogenase complex that is located in the inner mitochondrial membrane to lose a proton
These 2 steps come to a common product of DHAP which is a product of glycolysis step4, so it can join the process of gluconeogensis midway

why fatty acid cannot be a precursor of gluconeogenesis in humans and animals?

For animals and humans, the precursors are all at least 3-C
3C: amino acids, lacatate glycerol
4C; amino acid that directly turn into oxaloacetate

but fatty acids can only change into Acetyl-CoA which is 2C, and animals cannot undergo the reaciton of glyoxylate pathway, which is turning acetly-CoA into oxaloacetate

What does reciprocal regulation between gluconeogensis and glycolysis mean?

same molecules have different effect on enzymes in 2 different reaction

for step3 of glycolysis, which molecules have reciprocal reculation on glycolysis and gluconeogensis?

1. AMP (allosteric activator of PFK-1, allosteric inhibitorof fructose-1,6-biphsphatase)

2. Fructose-2,6-biphsophate (allosteric activator of PFK-1, allosteric inhibitor for frutcose-1,6-phosphatase)

how fructose-2,6-biphsophate is produced?

fructose-6-phsphate and fructose-2,6-phsophate are interconvertable by a bifunciton enzyme that has both phosphofructosekinase-2 activites (adding phosphate group to fructose-6-phosphate using a ATP) and activity og fructose-2,6-biphosphatase (removing phosphate gorup from frucotse-2,6-phosphate into water)

How glucagon works when glucose level is low?

It fosters the formation of cAMP, which is an activator of a protein kinase PKA.

Activated PKA further phosphorlyated the byfunctional enzyme that convert fructose-6-phospahte and fructose-2,6-phosphate.

The phosphorylated bifunctional enzyme will activate the fructose-2,6-phosphatase activity, while inactivate the phosphofructose kinase-2.

Therefore the concentration of fructose-2,6-biphosphate diecreases

As frucotse-2,6-biphsphate is an allosteric activator for glycolysis (PFK-1), while an allosteric inhibitor for gluconeogenesis (fructose-1,6-biphosphatase)

therefore glycolysis is low down, while gluconeogenesis speeds up to produce more glucose

What is the function of Pentose Phosphate Pathway PPP?

It generate:
1. ribose-5-phopshate for nucleotide biosynthesis

2. NADPH for biosynthesis reactions or protection against oxidative damages

Why PPP is more activei n rapidly dividing cells and tissue with active biosynthesis?

As diving cells need nucleotids to replicate the DNA, while PPP generate ribulose-6-phopshate which helps nucleotids biosynthesis

At the same time anthoer product of PPP, NADPH helps biosynthesis

What is the pathway in PPP that glucose-6-phosphate and NADP turn into ribose-5-phosphate and NADPH?

Oxidative phase

What is the process in PPP of turning ribulose-5-phosphat back glucose-6-phosphate?

nonoxidative phase

How oxidative phase of PPP works?

glucose-6-phsopahte turn 6-phosphogluconolactone using enzyme Gluose-6-phophate dehehydrogenase and NADP+

6-phosphogluconolactone turn into 6-phosphogluconate using gluconolactonase

6-[hosphogluconate turn into ribulose-5-phosphate by using 6-phosphogluconate dehydrogenase to lose a carboxylic gorup into CO2 and losing a proton and form C=O

How ribulose-5-phospahte turn into ribose-5-phosphate?

use if ribose-5-phospahte isomerase, to change funcitona group from ketone to aldehyde

How ribulose-5-phospahte turn into xylulose-5-phosphate?

use of enzyme ribulose-5 -phosphate-3-epimerases to change the position og -OH in C3

how does non-oxidative phase inPPP work?

1. Xylulose-5-phsoate (3C) and ribose-5-phospahte (3C) are generated from ribulose-5-phosphate and isomerase

2. use of transketolase to directly trasnsfer the first 2 Carbon chain gropu form xyulose-5-phosphate to ribose-5-phosphate, so that a G3P (3C) and sedoheptulose-7-phosphate (7C)

3. Use of transaldolase to transfer between first 3 carbon chain group from sedoheptulose-7-phosphate and the aldehyde group of G3P to form a Eryhrose-4-phosphate (4C),and a tructose-6-phsoaphate (6C), which can undergoes isomerization to return to glucose-6-phosphate

4. The erythrose-4-phosphate will react with another xyulose-5-phosphate and under go transketolase to form G3P and fructose-6-phosphate

5. G3P can undergo gluconeogenesis to return back to glucose-6-phosphate

why in the rarrangement of carbon skeltons in nonoxidative phase 6 ribulose-5-phosphate are need?

becuase the product of nonoxidative phase is ia 6C glucose-6-phsophate
in order to not adding or eliminating any carbon atoms

the L.C.M of 6 and 5 are needed which is 30

so we need 6 5C ribulose-5-phoshate and 5 6C glucose-6-phosphate

How is the PPP regulated?

in oxidative pathway, the glocuose-6-phosphate-dehydrogenase is inhibited by NADPH, so it is a feedback mechanism.

what is the relationship between glycogen and glucose?

glycogen is a polymer of glucose under alpha-1,4 linkage in linear and alpha-1,6-linkage for branch point

what is the function of glycogen in liver and muscles?

in liver, glycogen serve as a buffer to maintain blood glucose levels

in muscles: glycogen use to meet energy needs

what does glycogen degradation mean?

glycogen broke down into a large amount of glucose

how glycogen degrades?

1. using enzyme glycogen phosphorylase (adding an inorganic phosphate group to an acceptor molecule without using ATP) and phosphoric acid to remove a terminal glucose from the glycogen, which has a free non-reducing end (C4)
   
   glycogen phosphorylase cannot cleave beyonf a point 4 glucse upstream of an alpha-1,6-branch. Therefore on each branch point, there are 4 residues remain

2. use enzyme 4-alpha-glucotransferase transfer 3 of the 4 remaining terminal glucose to the end of the parent chain

3. use of amylo-1,6-glucosidase activity to cleaves the remaining alipha-1,6-linked glucose

4. glycogen phosphorylase will cleave the parent chain one by one

how glucose released fomr glycogen breakdown can be used?

the glucose-1-phsophate release form glycogen degradation using glycogen phosphorylase will turn into glucose-6-phosphate using enzyme phosphoglucomutase, then glucose-6-phosphate can undergoes PPP for nucleotide synthesis; glycolysis in brain and muscle for release of ATP; turning into glucose in liver, which is then sent to otehr body part

how glycogen synthesis is initiated?

a glycogenin bind to C1 of UDP-glucose causing the UDP to be removed. The glucose binded to glycogenin will be the centre of glycogen, allowing further UDP-glucose to add on by joing glucose to the OH group in the non-reducing end (terminal end) 6 times. Then UDP-glucose joins the terminal end,with the help of glycogen synthase,

how glucose synthesis continue?

1. glucose-6-phosphate turn into glucose-1-phosphate by using phosphoglucomutase

2. Glucose-1-phospahte add UTP and turn into UDP-glucose and a pyrophosphate (PPi) by using enzyme UDP-glucose pyrophosphorylase

3. Using glycogen synthase, UDP-glucose will leavea UDP and using its glucose C1 to join the C4 (terminal end and non-reducing end) of glycogen+

4. Enzyme Amylo-(1,4 → 1,6)-transglycosylase will cut glucose sections further than 4 glucose from glycogen core glycogenin, then joining that section to the first glucose from the core by alpha-1,6-linkage to make branches

What are the properties and function of branches?

more brances will increase the solubility of glycogen

increases of branches will increase the rate of both glycogen synthesis and degradation, as both of them start from the terminal residues (non-reducing ends)

How is glycogen metabolism regulated?

glycogen synthase for glycogen synthesis is active when depohsohorylatedm while inactive when phosphorylated

Glycogen phosphorylase for glycogen degradation is active when phosphorylated while inactive when dephosphorylated

When blood level is low, how will the glycogen mechaism change?

cAMP production will be promoted to attach to PKA, making it active. active pKA can also increase nucleogensis rate by lowering the concentration of fructose-2,6-biphosphate.

At the same time, active PKA will make use of ATP to add phosphate group to glycogen syntahse, to make it inactive, so less Glycogen is being synthesized. while active PKA adding phosphate group to glycogen phosphorylase to make it active, so glycogen degradation will speed up. therefore in overall, glycogen will be broken down into glucose

When blood level is high, how will the glycogen mechaism change?

Insulin which can affect the glucose intake by bring glucose transporter GLUT4 into cell membrane can also activate phosphoprotein phosphatase-1 which remove phospahte gorup into water from phosphorylated protein. therefore glycogen synthase will lose phosphate gorup and be active, increase the rate of glycogen synthesis. While glocogen phosphorylase will also lsoe a phospahte gorup and be inactive, decrease the rate of glycogen degradation. therefore overall, there will be a increase in glycogen sythesis