Question

Which of the following reactions are catalyzed by kinases:

		Glycolysis 1,2,7,9; Pyruvate processing 1, citric acid cycle 3,4,6,8
		Glycolysis 1,2,7,8; Pyruvate processing 1, citric acid cycle 5
		Glycolysis 6; citric acid cycle 5
		Glycolysis 1,2,7,10; citric acid cycle 5

Answer 1

The reactions are catalyzed by kinases- Correct option is

Glycolysis 6; citric acid cycle 5

Glycolysis is a metabolic pathway in which glucose a 6- carbon compound, is converted into pyruvate a 3- carbon compound.

In glycolysis 1,3,6,7 and 10 reactions are catalyzed by kinases. Kinases are enzymes belongs to transferases group of enzymes, They transfers phosphate groups from one molecule to other and leads to phosphorylation.

Step 1- D-glucose into glucose-6-phosphate. Catalyzed by enzyme hexokinase. Hexokinase leads to phosphorylation of glucose by adding a phosphate group to glucose ring. here, phosphate group is derived from ATP. glucose-6-phosphate (G6P) is formed due to phasphorylation of glucose.

Step 2- glucose 6-phosphate (G6P) into fructose 6-phosphate (F6P). Catalyzed by enzyme Phosphoglucose Isomerase. reaction involves an isomerization reaction not phasphorylation. So, this is not a Kinase catalyzrd reaction.

Step 3- fructose 6-phosphate into fructose 1,6-bisphosphate. Catalyzed by enzyme phosphofructokinase (PFK). phosphofructokinase leads to phosphorylation of fructose 6-phosphate using ATP, as in 1st step.

Step 6- glyceraldehyde 3-phosphate into 1,3-bisphosphoglycerate. Catalyzed by enzyme Glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Here, firstly coenzyme nicotinamide adenine dinucleotide (NAD) leads to oxidization of glyceraldehyde-3-phosphate. After that  with the help of enzyme glyceraldehyde-3-phosphate dehydrogenase a free phosphate group is added to it and it is phosphorylated.

Step 7- 1,3-bisphosphoglycerate into 3-phosphoglycerate. Catalyzed by enzyme Phosphoglycerate kinase. Phosphoglycerate kinase transfers a phosphate group from 1,3-bisphosphoglycerate to ADP. Thus ADP is conveted to ATP in this step.

Step 10- phosphoenolpyruvate (PEP) into pyruvic acid. Catalyzed by enzyme pyruvate kinase. Pyruvate kinase transfers a phosphate group from phosphoenolpyruvate to ADP. here again ADP is conveted to ATP.

So, from the options given 3rd option is correct because step 2 is not catalayzed by kinases.

Pyruvate processing 1- In this step removal of a caroboxyl group from pyruate takes place. thus CO2 is released in this process. In this step no phasphorylation takes place so, it is not catalyzed by a kinase.

citric acid cycle- oxidative metabolism of acetyl co-A leads to the production of two CO2 molecules, one GTP/ATP, three NADH and one FADH2 per turn.

Step 5- succinyl-CoA into succinate. Catalyzed by enzyme succinyl-CoA synthase. CoA is removed from succinyl-CoA and a phosphate group is added to produce succinate. energy is released which is used in substrate-level phosphorylation to form either guanine triphosphate (GTP) or adinosine triphosphate (ATP). Here, phosphorylation takes place so, the reaction is catalyzed by kinase.