Carbohydrates

What is a monosaccharide? Give two examples and state the main function of monosaccharides in the cell.

Glucose and fructose have the same molecular formula, $\text{C}_6\text{H}_{12}\text{O}_6$, but different structures. Explain what type of isomerism relates them based on their linear forms and describe what happens to them when they dissolve in water: what forms do their molecules then adopt, what are α and β anomers, and how is this cyclisation related to the formation of the glycosidic bond?

Classify the following carbohydrates as monosaccharides, disaccharides or polysaccharides: glucose, sucrose, starch, fructose, lactose and cellulose.

Sucrose is formed by the joining of a glucose and a fructose molecule. What type of bond is formed between both monosaccharides, what is the reaction that forms it called, and what molecule is released during it?

State the biological function of glycogen in animals and in which organs it is mainly stored.

The diagram shows how the chains of two polysaccharides made exclusively of glucose are arranged. State which corresponds to starch and which to cellulose, explain what difference exists in the bonding of their monomers (α or β bond), and reason how the shape of their chains justifies why one serves as an energy reserve and the other has a structural function.

Two insoluble structural polysaccharides are isolated: polymer A comes from the cell wall of a plant cell (oak) and polymer B from the exoskeleton of a crustacean (crab). Both present linear chains linked by beta-(1->4) glycosidic bonds, but elemental analysis reveals the presence of nitrogen only in polymer B.

1. a) Identify polymers A and B and state the name of the constituent monomer of each one.
2. b) Explain why the spatial conformation of the beta-(1->4) bond is ideal for the mechanical support function compared to the alpha-(1->4) bond of glycogen or starch, detailing the role of intra- and interchain hydrogen bonds in the formation of insoluble microfibrils.
3. c) If a solution of purified cellulase enzyme is added to a suspension of polymer B, reasonably predict whether hydrolysis will occur and justify it based on enzyme specificity.

A sports nutrition laboratory designs two energy recovery drinks with identical polysaccharide concentration and total mass: drink A contains highly branched amylopectin, while drink B contains linear amylose of similar molecular mass.

1. a) Reasonably predict which of the two drinks will induce a faster blood glucose spike after ingestion, based on the specificity of digestive enzymes (alpha-amylases) and the molecular structure of both polymers (type of glycosidic bonds and availability of non-reducing ends).
2. b) In myocytes, absorbed glucose is stored as glycogen and not in the form of free glucose or starch. Justify this biological adaptation taking into account cellular osmotic pressure and the speed with which the cell must mobilise energy in response to an urgent metabolic demand.

An infant dairy product advertised as "no added sugars" contains in its nutritional table 4,8 g of lactose and 12 g of cornstarch per 100 g of product.

1. a) Refute the claim that this food is free of carbohydrate or sugar intake for the body. Chemically classify lactose and starch (type of carbohydrate, monomers, and type of bond) and describe the monosaccharides that will pass into the blood after their complete digestion.
2. b) In the laboratory, a sample of the product is subjected to Fehling's test before and after incubating it with alpha-amylase. Predict and justify the result of the test on the initial sample (indicating to which component it is due) and explain with reasoning how the intensity of the reaction will vary after enzymatic action on the starch, based on the concept of anomeric carbon and reducing end.