Statement-I: Glycolysis is the first step of respiration in which glucose completely breaks into ${CO}_{2}$ and $H_{2} O$
Statement-II: In this process, there is a net gain of twenty-four molecules of $ATP.$

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Statement-I: Glycolysis is the first step of respiration in which glucose completely breaks into CO 2 and H 2 O Statement-II: In this process, there is a net gain of twenty-four molecules of ATP.

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Glycolysis / EMP pathway: Discovery: It is given by Embden, Meyerhoff, and Parnas in 1930. It is the first stage of the breakdown of glucose in the cell. Definition: Glycolysis (Gr. glykys= sweet, sugar; lysis= breaking) is a stepped process by which one molecule of glucose (6C) breaks into two molecules of pyruvic acid (3C). Site of occurrence: Glycolysis takes place in the cytosol and does not utilize oxygen. Thus, it is an anaerobic pathway. In fact, it occurs in both aerobic and anaerobic respiration. Steps of glycolysis: Glycolysis consists of 10 steps divided into 2 phases preparatory phase and pay off phase. Each step is catalyzed by a specific enzyme. Most of the reactions are reversible. Preparatory phase: In this phase, 2 molecules of ATP are utilized. Pay-off phase: In this phase, energy is released in the form of ATP and NADH 2 is formed. Energetics of Glycolysis Reaction Type Reaction Products of reaction In terms of ATP ATP Forming Reactions Substrate-level phosphorylation 2 x 1 , 3 B i p h o s p h o g l y c e r a t e + 2 A D P → B i p h o s p h o g l y c e r o k i n a s e 2 x 3 - P h o s p h o g l y c e r a t e + 2 A T P 2 ATP 2 ATP Substrate-level phosphorylation 2 x P E P + 2 A D P → K + , M g 2 + P y r u v a t e K i n a s e 2 x P y r u v a t e + 2 A T P 2 ATP 2 ATP Dehydrogenation 2 x 3 P h o s p h o g l y c e r a l d e h y d e + 2 P i + 2 N A D + → D e h y d r o g e n a s e 2 x 1 , 3 B i p h o s p h o g l y c e r a t e + 2 N A D H 2 2 NADH 2 6 ATP ATP Consuming Reactions Phosphorylation-I G l u cos e + A T P → M g 2 + H e x o k i n a s e G l u cos e 6 - P h o s p h a t e + A D P -1 ATP -1 ATP Phosphorylation-II F r u c t o s e 6 - P h o s p h a t e + A T P → M g 2 + P h o s p h o f r u c t o k i n a s e F r u c t o s e 1 , 6 - B i p h o s p h a t e -1 ATP -1 ATP Net Gain 8 ATP

Energetics of Glycolysis
Reaction Type	Reaction	Products of reaction	In terms of ATP
ATP Forming Reactions
Substrate-level phosphorylation	$2 x 1, 3 B i p h o s p h o g l y c e r a t e + 2 A D P \overset{B i p h o s p h o g l y c e r o k i n a s e}{\to} 2 x 3 - P h o s p h o g l y c e r a t e + 2 A T P$	2 ATP	2 ATP
Substrate-level phosphorylation	$2 x P E P + 2 A D P \to_{K^{+}, M g^{2 +}}^{P y r u v a t e K i n a s e} 2 x P y r u v a t e + 2 A T P$	2 ATP	2 ATP
Dehydrogenation	$2 x 3 P h o s p h o g l y c e r a l d e h y d e + 2 P i + 2 N A D^{+} \overset{D e h y d r o g e n a s e}{\to} 2 x 1, 3 B i p h o s p h o g l y c e r a t e + 2 N A D H_{2}$	2 NADH₂	6 ATP
ATP Consuming Reactions
Phosphorylation-I	$G l u \cos e + A T P \to_{M g^{2 +}}^{H e x o k i n a s e} G l u \cos e 6 - P h o s p h a t e + A D P$	-1 ATP	-1 ATP
Phosphorylation-II	$F r u c t o s e 6 - P h o s p h a t e + A T P \to_{M g^{2 +}}^{P h o s p h o f r u c t o k i n a s e} F r u c t o s e 1, 6 - B i p h o s p h a t e$	-1 ATP	-1 ATP
	Net Gain		8 ATP

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