Carboidratos parte 3 POLISSACARIDEOS

Summary

This video delves into the structural diversity and versatility of carbohydrates, explaining the formation of polysaccharides like cellulose and starch. It highlights how the molecular geometry of glucose affects the properties of these compounds, such as the spiral structure of alpha-linked starch and the linear formation of beta-linked cellulose. The discussion includes the importance of these polysaccharides in biology, such as cellulose in plant cell walls and glycogen in humans for energy storage. It also touches on the culinary applications of starch and the biological processes involving glycogen breakdown during physical exertion.

Takeaways

• 😀 Carbohydrates can form complex and versatile molecular structures, including disaccharides and polysaccharides.
• 😀 A reducing disaccharide has a free reactive hydroxyl group on its hemiacetal carbon, which allows it to participate in further reactions.
• 😀 Polysaccharides can be homopolysaccharides (formed by one type of monosaccharide) or heteropolysaccharides (formed by more than one type of monosaccharide).
• 😀 Polysaccharides can also be branched or unbranched, with branching occurring due to hydroxyl groups at the vertices of the molecule.
• 😀 The position of the hydroxyl group on the glucose molecule (alpha or beta) affects the structure and properties of the polysaccharide.
• 😀 Alpha-hydroxyl groups lead to the formation of a spiral or helical structure, while beta-hydroxyl groups allow for a linear arrangement, enabling strong hydrogen bonds.
• 😀 The strong hydrogen bond interactions in beta-glucan chains form cellulose, which makes up plant cell walls and is used in paper production.
• 😀 Humans cannot break down beta-1,4 linkages in cellulose to release glucose, unlike ruminants that have microorganisms capable of breaking these bonds.
• 😀 Alpha-1,4 linkages in glucose form starch, which can be either amylose (unbranched) or amylopectin (branched).
• 😀 Starch granules in plants serve as energy reserves and are extracted in common foods like potato, corn, and wheat starch.
• 😀 Allowing dough to rest before baking enables starch granules to open, interact with water or milk, and form a network that gives dough elasticity.

Q & A

What are polysaccharides and how do they form?

Polysaccharides are long chains of sugar molecules (monosaccharides) linked together. They form when the hydroxyl group of one monosaccharide reacts with the hydroxyl of another, creating a bond. This can result in homopolysaccharides, composed of one type of monosaccharide, or heteropolysaccharides, composed of different types.

What is the difference between alpha and beta linkages in carbohydrates?

The difference between alpha and beta linkages lies in the position of the hydroxyl group. In alpha linkages, the hydroxyl is on the same side of the sugar ring, resulting in a helical structure, while in beta linkages, the hydroxyl is on the opposite side, forming a linear structure.

How does the position of the hydroxyl group affect the structure of polysaccharides?

The position of the hydroxyl group determines the geometry of the polysaccharide. For example, an alpha configuration leads to a helical structure, while a beta configuration allows the formation of a more rigid, linear structure. This structural difference significantly impacts the properties of the polysaccharide.

What is cellulose and how is it related to glucose?

Cellulose is a structural polysaccharide made up of glucose units linked by beta-1,4-glycosidic bonds. It is found in plant cell walls and provides strength and rigidity due to its strong hydrogen bonding between parallel chains of glucose molecules.

Why can humans not digest cellulose?

Humans cannot digest cellulose because they lack the enzyme necessary to break the beta-1,4 linkages between glucose molecules. Unlike ruminants, which rely on microorganisms in their stomachs to digest cellulose, humans cannot access the glucose stored in cellulose.

What is the function of starch in plants, and how does it differ from cellulose?

Starch is a polysaccharide used by plants to store energy. Unlike cellulose, which is rigid and structural, starch is made up of glucose units linked by alpha-1,4-glycosidic bonds. Starch can be either unbranched (amylose) or branched (amylopectin), and its structure allows it to be easily broken down for energy when needed.

How does the human body store glucose?

Humans store glucose in the form of glycogen, which is a highly branched polysaccharide. Glycogen is stored in the liver and muscles and can be quickly broken down when the body needs a rapid supply of glucose, especially during stressful situations or physical activity.

What role does glycogen play in the 'fight or flight' response?

During the 'fight or flight' response, the hormone adrenaline triggers the breakdown of glycogen into glucose. This provides a quick source of energy for muscles to either fight or flee from a threat. The rapid release of glucose is essential for increased energy during stress.

How does the structure of starch contribute to its use in cooking?

The structure of starch, which consists of granules containing amylose and amylopectin, allows it to absorb water and swell when heated. This process helps in thickening liquids and giving elasticity to doughs, as seen in cooking with flour or potatoes.

Why is it important to let dough rest before baking?

Letting dough rest before baking allows the starch granules to swell and absorb water, which opens up the chains of amylopectin. This process helps the dough achieve the right elasticity and texture, making it less likely to break during baking.