Trace a molecule of CHO (carbohydrate) from Hot Fudge Cake from your fork to a c

Question

Trace a molecule of CHO (carbohydrate) from Hot Fudge Cake from your fork to a cell of the right quadraceps. This should include all parts the Hot Fudge Cake touches, passes through, or travels in, including digestive breakdown beginning in the mouth, stomach, and intestines (what chemicals are responsible for it) and then diffusion into the cell (refer back to Krebs Cycle). This should read like a road map of where the food goes and what it travels through. List the chemicals that break it down in parenthesis next to where it would take place in the road map.

Explanation / Answer

1. Digestion of carbohydraes starts from mouth only. The salivary amylase present in saliva converts Starch into alpha-dextrin which is then converted into maltose by the action of gluco-amylase. Only upto 5% of starch gets digested in mouth.

2. In stomach, there is no digestion of carbohydrate. Digestion of carbohydrates resume only once food reaches duodenum of small intestine. In duodenum, the pancreatic amylase present in pancreatic juice hydrolyses polysaccharides into corresponding disaccharides. The secretions of the brush border cells of the intestinal mucosa alongwith the secretions of the goblet cells constitute the intestinal juice or succus entericus. This juice contains a variety of disaccharidases (e.g., lactase, maltase) that hydrolyse disaccharides into corresponding monosaccharides (simple molecules).

3. The simple molecules are now absorbed in the jejunum and ileum regions of the small intestine. The undigested and unabsorbed substances are passed on to the large intestine. No significant digestive activity occurs in the large intestine.

4. The undigested, unabsorbed substances called faeces enters into the caecum of the large intestine. It is temporarily stored in the rectum till defaecation.

5. Absorption of simple sugars occur mostly in small intestine, where numerous fi nger-shaped villi and microvilli provide an enormous surface area through which materials can pass from the intestinal lumen into the circulation; although, some absorption occurs in stomach also. The absorbed substances finally reach the tissues which utilise them for their activities. This process is called assimilation.

6. In tissues, glucose is metabolized as a fuel to provide energy in the form of ATP. First of all, in cytoplasm, the glucose (6 carbon molecule) is converted into 2 molecules of pyruvate (3-carbon molecule) via several intermediate conversions. Puruvate is then transported into mitochondria for further metabolism. First, pyruvate is then converted into Acetyl conzyme A by enzyme pyruvate dehydrogenase, releasing one CO2 molecule.

7. Acetyl Co-A thus produced reacts with Oxalo acetate to form Citrate which enters into Kreb's cycle. Citrate is furtehr converted into isocitrate. This isocitrate with the help of isocitrate dehydrogenase gets converted into alpha-ketoglutarate, releasing another CO2 molecule. Alpha-ketoglutarate reacts with coenzyme-A in the presence of alpha-ketoglutarate dehydrogenase to produce succinyl coenzyme-A, releasing another CO2 molecule.

Thus all the 3 carbons of pyruvate are released as CO2 molecule. NADH and FADH2 thus produced in glycolysis and Kreb's cycle enter electron transport system to produce ATPs.

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