Glycolysis

Q1: The active form of glycogen phosphorylase is phosphorylated, while the dephosphorylation of which active form occurs?

A Glycogen synthase

B Glycogen semisynthase

C Glycogen hydrolase

D Glycogen dehydrogenase

ANS:A - Glycogen synthase

I haven't understood this. Please explain me in detail.

Q2: In glycolysis, ATP is formed by the transfer of a high-energy phosphate from 1,3-bisphosphoglycerate to ADR No such high-energy phosphate donor has ever been isolated in mitochondria because

A the techniques for isolating the phosphate donor are not refined enough

B no such phosphate donor exists

C the high-energy phosphate donor is very short-lived and difficult to isolate

D None of the above

ANS:B - no such phosphate donor exists

What's ADR? Please explain.

Q3: Glycolytic pathway regulation involves

A allosteric stimulation by ADP

B allosteric inhibition by ATP

C feedback, or product, inhibition by ATP

D all of the above

ANS:D - all of the above

Phospho kinase 1 enzyme has about 4 active sites i.e active site for ATP, Citrate, AMP & Fructose 2-6 Bisphosphate site, Increase in Fructose 2-6 Bisphosphate (a very powerful stimulant of Phospho Kinase 1).

ATP & Citrate, signals Phospho Kinase 1 to Phosphorylate more Fructose 6 phosphate into Fructose 1-6 bisphosphate. In my opinion this is the Enzymatic Allosteric Regulation.

Q4: Why does the glycolytic pathway continue in the direction of glucose catabolism?

A There are essentially three irreversible reactions that act as the driving force for the pathway

B High levels of ATP keep the pathway going in a forward direction

C The enzymes of glycolysis only function in one direction

D Glycolysis occurs in either direction

ANS:A - There are essentially three irreversible reactions that act as the driving force for the pathway

The most important and very crucial steps in Glycolysis are Phosphorylation of Glucose upto the stage when Fructose 1-6 bisphosphate is formed and the irreversible step 1 i.e Glucose Phosphorylation that helps Glucose to remain in polar state not to exit the cell (Hexokinase & Glucokinase),

And Phosphorylation of Fructose 6 phosphate into Fructose 1-6 Bisphosphate (PhosphoFructoKinase 1) which is actually under regulation very close stimulation and inhibition of (ATP, Citrate) and AMP respectively and ofcose Fructose 2-6 bisphosphate (formed by PhosphoFructokinase 2) avery powerful stimulant of PFK 1, and and inhibitor of gluconeogenesis enables the cycle in one direction.

Q5: Which of the following is not true of glycolysis?

A ADP is phosphorylated to ATP via substrate level phosphorylation

B The pathway does not require oxygen

C The pathway oxidizes two moles of NADH to NAD+ for each mole of glucose that enters

D The pathway requires two moles of ATP to get started catabo-lizing each mole of glucose

ANS:C - The pathway oxidizes two moles of NADH to NAD+ for each mole of glucose that enters

Yes @Henry.

Glucolysis can still occur without Oxygen.

Q6: Fructose-2,6-bisphosphate

A activates fructose-1,6-bisphosphatase

B activates phosphofructokinase

C inhibits fructose-1,6-bisphosphatase

D both (b) and (c)

ANS:D - both (b) and (c)

Fructose-2, 6bis phosphate inhibits phoshphofruktokinase-2(PFK-2).
PFK-2 : It catalise fructose-6-P into fructose-1,6-bis phosphate.

Thus indirectly fructose-2, 6-bis phosphate inhibits fructose-1,6-bis phosohate.

Q7: Which of the following is not a mechanism for altering the flux of metabolites through the rate-determining step of a pathway?

A Allosteric control of the enzyme activity

B Diffusional coupling between adjacent active sites

C Genetic control of the enzyme concentration

D Covalent modification of the enzyme

ANS:B - Diffusional coupling between adjacent active sites

No answer description is available.

Q8: The amount of energy received from one ATP is

A 76 kcal

B 7.3 kcal

C 760 kcal

D 1000 kcal

ANS:B - 7.3 kcal

Hydrolysis of 1 mole of ATP into ADP releases 30.5 kilo-joules or 7.5 kilo calories of energy.

Q9: Which of the following could act as an uncoupler of electron transport and ATP synthesis?

A The Fo base-piece of ATP synthase (without the Fl subunit)

B Dinitrophenol

C neither (a) nor (b)

D Both (a) and (b)

ANS:D - Both (a) and (b)

Uncouplers of oxidative phosphorylation in the mitochondria inhibit the coupling between the electron transport and phosphorylation reactions thus inhibit ATP Synthesis without affecting the respiratory chain and ATP synthase. 2, 4 DNP and so base are uncouplers.

Q10: Which of the following regulates glycolysis steps?

A Phosphofructokinase

B Hexose kinase

C Pyruvate kinase

D All of these

ANS:D - All of these

How? Explain the given answer.

Q11: Glucose from the breakdown of glycogen is obtained in

A the liver by phosphorolysis

B the muscles by phosphorolysis

C the muscles by hydrolysis

D both (a) and (b)

ANS:D - both (a) and (b)

Muscle which contains only hexokinase can use this enzyme to phosphorylate fructose producing F6P which is a direct glycolytic intermediate. In liver the glucokinase, is specific for glucose as a substrate, therefore it requires an alternative enzyme to phosphorylate fructose. Hepatic fructokinase can phosphorylate fructose on C-1 to produce fructose-1-phosphate (F1P).

Instead of F 1,6 biphosphate aldolase , the liver containing aldolase B that can use F1P as a substrate to generate dihdroxyacetone phosphate( DHAP) and glyceraldehyde. The DHAP is converted, by triose phosphate isomerase(TIM), to G3P while the glyceraldehyde is phosphorylated to G3P by triose kinase.

Q12: During catabolism, only about 40% of the energy available from oxidizing glucose is used to synthesize ATP. Remaining 60%

A is lost as heat

B is used to reduce NADP

C remains in the products of metabolism

D is stored as fat.

ANS:A - is lost as heat

60% of energy lost in order to maintain homeostasis and internal body Osmolarity.

Q13: During glycolysis, the major energy generating step involves

A pyruvate kinase

B phosphoglycerate kinase

C glyceraldehyde-3 -dehydrogenase

D Phosphofructokinase

ANS:C - glyceraldehyde-3 -dehydrogenase

Because these step gives 6ATP.
From step 5 all energy produced is times 2.

In electron transport chain,
1ATP = 1ATP.
1NADH = 3ATP.

Therefore, 2 NADH produced = 3 times 2 = 6.
6ATP.

Q14: A kinase is an enzyme that

A removes phosphate groups of substrates

B uses ATP to add a phosphate group to the substrate

C uses NADH to change the oxidation state of the substrate

D removes water from a double bond

ANS:B - uses ATP to add a phosphate group to the substrate

In fact kinases EXCHANGES (rather than adding) phosphate group from one high energy phosphate substrate to another low energy substrate.
It is true Kinases (hexokinase) "adds" (rather EXCHANGES) phosphate groups from one high-energy substrate (ATP) to low energy substrate (glucose).

In the case of pyruvate kinase, the same thing is true too. One substrate is ADP (low energy) and the other substrate is phospho-enol-pyruvate (high energy). Now the high energy molecule is phosphoenolpyruvate and the low energy molecule is ADP exchanges phosphate group. The phosphate exchange is carried out by a kinase.

Why do we say it adds instead of exchanges? That is what confuses everybody.

Let us see what phosphatase does?

I think phosphatase hydrolyses phosphate (Glucose-6-phosphate ) to Glucose and a FREE PHOSPHATE molecule. It DOES NOT exchange phosphate groups between substrates!

It is possible, those free phosphates combine with ADP to form ATP by the enzyme ATP synthase. I don't think phosphatase is capable of making ATP by itself. When we read glucogenesis, we assume that ATP is made by phosphatases from ADP. I suspect very much that is what really happening.

Disclaimer: This is just my speculation and open for debate! I need to read more to confirm that! You are welcome to criticise my explanation.

Thank you!

Q15: The enzymes of glycolysis in a eukaryotic cell are located in the

A intermembrane space

B plasma membrane

C cytosol

D mitochondrial matrix

ANS:C - cytosol

Cytosol in prokayotic cell.

Q16: When concentration of the reactants is higher than the equilibrium concentration then

A the gibbs free energy will be positive

B the gibbs free energy will be negative

C more products will be formed

D both (b) and (c)

ANS:D - both (b) and (c)

When there is high concentration of reactant means will favors forward reaction and more product will be formed and the process of product formation involve breaking of bond so there energy which is given out (negative).

Q17: For every one molecule of sugar glucose which is oxidized __________ molecule of pyruvic acid are produced.

A 1

B 2

C 3

D 4

ANS:B - 2

In the reaction fructose 1, 6 phosphate is broken down in to two components which are glyceraldhyde phosphate and di hydroxyphosphate acetone, then this is isomerased to glyceadehyde 3 phosphate resulting in two molecules that produce the end products.

Q18: Glycogen has

A α-1,4 linkage

B α-1,6 linkages

C α-1,4 and α-1,6 linkages

D α-1,4 and β-1,6 linkage

ANS:C - α-1,4 and α-1,6 linkages

Starch and glycogen are homopolysaccharides of glucose 1-4 alpha linkage forms during linear polymer and 1-6 alpha linkage during formation of branching.

Q19: ATP is from which general category of molecules?

A Polysaccharides

B Proteins

C Nucleotides

D Amino acids

ANS:C - Nucleotides

The nucleotides is the much related formation of ATP.

Q20: In the glycogen synthase reaction, the precursor to glycogen is

A glucose-6-P

B UTP-glucose

C UDP-glucose

D glucose-1-P

ANS:C - UDP-glucose

@Alvin Morales.

The UDP-glucose synthesized from glucose 1-phosphate and UTP in which glucose 1-phosphate obtained from glucose 6-phosphate by enzyme (phosphoglucomutase).

Q21: The released energy obtained by oxidation of glucose is stored as

A a concentration gradient across a membrane

B ADP

C ATP

D NAD+

ANS:C - ATP

NADH, H+b& ATP are both storage form of energy in glycolysis.

In the first payoff phase, NAD+ is converted to NADH, H+ and Glyceraldehyde-3P is phoshorylated to 1, 3-Bisphosphoglycerate. (Glyceraldehyde-3P dehydrogenase is responsible for this rxn).

Q22: Phosphofructokinase, the major flux-controlling enzyme of glycolysis is allosterically inhibited and activated respectively by

A ATP and PEP

B AMP and Pi

C ATP and ADP

D Citrate and ATP

ANS:C - ATP and ADP

Here, it is about inhiation and activation inhibited by ATP and activated by ADP when the substrate concentration increases the AT inhibit the enzyme and the concentration of substrate decreases the ADP activate the enzyme that's true citrate inhibits the enzyme but question is regarding activation and inhiation.

Q23: The glycolytic pathway (glucose → 2 pyruvate) is found

A in all living organisms

B primarily in animals excluding particles

C only in eukaryotes

D only in yeast

ANS:A - in all living organisms

Glycolysis is the catabolism of glucose to pyruvate and this is very significant in all living organism to survive. Base on research no organism could exist without glycolysis



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