Cellulose could provide an abundant and cheap form of glucose for humans. Why is cellulose not a source of nutrients for humans? Animals use starch and glycogen as an energy source, whereas plants use cellulose for energy. Humans cannot absorb the hydrolyzed form of cellulose. Vertebrate enzymes hydrolyze (α 1-4) glucose linkages, but not glucose in the ẞ configuration. Cellulose digestion must occur in a basic environment, but the human gut is acidic. Humans, and most vertebrates, lack the enzyme cellulase.

The cells that line the mammalian intestine produce glycoproteins with O-linked oligosaccharides. Some of the glycoproteins remain anchored to the cell surface and some are released into the intestinal space. In a healthy animal, numerous microbial species (the microbiome) live in the intestine. These organisms produce fucosidase, an enzyme that hydrolyzes glycosidic bonds involving fucose. (a) Why is this enzyme useful to the micro organisms? (b) Pathogenic (disease-causing) bacteria typically lack fucosidase. How does this help prevent the growth of pathogens in the intestine, particularly during an illness when the human host stops eating?

The fructose in honey is mainly in the β-D-pyranose form. This is oneof the sweetest carbohydrates known, about twice as sweet as glucose; the β-D-furanose form of fructose is much less sweet. The sweetness of honey gradually decreases at a high temperature. Also, high-fructose corn syrup (a commercial product in which much of the glucose in corn syrup is converted to fructose) is used for sweetening cold but not hot drinks. What chemical property of fructose could account for both these observations?

All of the following statements about glucose are true except: Glucose is metabolized in the cytoplasm of prokaryotic organisms. On a low-carb diet, keto acids from glucogenic amino acids will be used to synthesize glucose. Glucose is metabolized in the mitochondria of mature red blood cells. Under non-starvation conditions, the brain relies exclusively on glucose as its fuel source.

Some amino acids are both glucogenic and ketogenic. Explain the difference between the two types and why some amino acids can be both.

We have stated that fatty acids cannot yield a net gain in carbohydrates in organisms that lack a glyoxalate pathway. Why can odd-chain fatty acids be thought to break this rule to a small extent?

Which of the following substances derived from lipid catabolism serves as a precursor for glucose synthesis: acetoacetyl CoA acetone palmitate acetate O glycerol

If metabolites from fats, amino acids and lactate are to be converted to glucose, which of the following is a common metabolic precursor? oxaloacetate acetyl CoA alpha-ketoglutarate pyruvate succinyl CoA

NH, This compound is directly involved in: он O=P-0-CH, H но OmP-0- O oxidizing an alcohol in the conversion of sucrose to fructose. O the synthesis of malonyl coenzyme A. reducing a ketone in gluconeogenesis. reducing a C=C double bond in fatty-acid synthesis.

One example of a stage 2 reaction in the heterotrophic breakdown of food molecules is: the extracellular digestion of amylopectin into glucose monomers the intramitochondrial digestion of fatty acids into carbon dioxide and water the intracellular digestion of glucose monomers into pyruvate the extracellular digestion of triglycerides into fatty acids and glycerol the extracellular digestion of polypeptides into amino acids   Identify the three-carbon glycolysis intermediate which can be formed, in the cytoplasm, in one enzymatic step (during deamination of the amino acid alanine)? pyruvate fructose-1,6-bisphosphate fructose glucose-6-phosphate glucose