Bioquímica - Aula 07 - Carboidratos

Summary

In this biochemistry lecture, Professor Ângelo Cortel explores the critical role of carbohydrates in cellular processes. The lecture covers the various types of carbohydrates, including monosaccharides, oligosaccharides, and polysaccharides, highlighting their structures, properties, and functions in organisms. Key topics include aldoses, ketoses, and their optical isomerism, as well as important biochemical derivatives such as carboxylates and phosphorylated sugars. The lecture also explains how carbohydrates contribute to energy storage and structural integrity, with a focus on their role in plant and animal biology, including polysaccharides like cellulose, chitin, and glycogen.

Takeaways

• 😀 Carbohydrates are essential molecules in living organisms, involved in carbon capture and incorporation.
• 😀 Carbohydrates can be classified as polyhydroxy aldehydes (aldoses) or polyhydroxy ketones (ketoses), forming monomers called monosaccharides.
• 😀 Monosaccharides can form oligosaccharides (2-30 monosaccharides) or polysaccharides (more than 30 monomers).
• 😀 Aldoses and ketoses can have various structures depending on the number of carbon atoms (e.g., triose, pentose, hexose).
• 😀 Aldoses, such as glucose, galactose, and manose, exhibit optical isomerism due to the presence of asymmetric carbon atoms.
• 😀 Ketoses, like fructose, are important sugars and can form various isomers depending on the carbon configuration.
• 😀 Monosaccharides can undergo derivation to form products like carboxylates (e.g., glucuronic acid) and phosphates (e.g., glucose-6-phosphate).
• 😀 Some monosaccharides also form derivatives with amino groups, such as glucosamine and N-acetylglucosamine.
• 😀 Disaccharides, such as maltose, lactose, and sucrose, are formed by the condensation of two monosaccharides, which can be in alpha or beta configurations.
• 😀 Polysaccharides like cellulose (structural) and starch (energy reserve) have different structures, with beta-linked sugars being linear and alpha-linked sugars being more globular and coiled.

Q & A

What are carbohydrates and why are they important in biochemistry?

Carbohydrates are a group of molecules that are vital for living organisms. They play an important role in the uptake, fixation, and incorporation of carbon in biological systems. Carbohydrates are essential for energy storage, structural support, and other biochemical processes.

What are the main classifications of carbohydrates?

Carbohydrates are classified into monosaccharides, oligosaccharides, and polysaccharides. Monosaccharides are simple sugars like glucose, oligosaccharides contain 2 to 20 monosaccharides, and polysaccharides contain more than 20 monosaccharide units.

What are aldoses and ketoses?

Aldoses are sugars with an aldehyde group, while ketoses are sugars with a ketone group. Aldoses, like glucose, can have one or more asymmetric carbon atoms, which contribute to their optical properties. Ketoses, like fructose, have different structural characteristics.

What is the significance of optical isomerism in sugars?

Sugars exhibit optical isomerism due to the presence of asymmetric carbon atoms. This results in two possible forms: D-isomers and L-isomers, which differ in how they rotate polarized light. D-isomers are the most commonly encountered form in biological systems.

How do monosaccharides cyclize in solution?

Monosaccharides, such as glucose, cyclize when the hydroxyl group on the penultimate carbon atom reacts with the aldehyde or ketone group. This forms a ring structure, which is more stable than the open-chain form. The result is two possible isomers: alpha and beta forms.

What are some common sugar derivatives, and what are their functions?

Common sugar derivatives include carboxylates, phosphorylated sugars, and amino sugars. Carboxylates (like glucuronic acid) are involved in detoxification processes, while phosphorylated sugars (like glucose-6-phosphate) are crucial for metabolic pathways. Amino sugars, such as glucosamine, are components of structures like cartilage.

What is the difference between alpha and beta glycosidic bonds?

Alpha glycosidic bonds result in a more angular structure, while beta glycosidic bonds form linear chains. The type of glycosidic bond determines the physical properties and biological functions of the polysaccharide. For example, alpha-linked polysaccharides like starch are used for energy storage, while beta-linked polysaccharides like cellulose are structural.

How do polysaccharides like starch and cellulose differ in structure?

Starch is composed of two components: amylose (a non-branched chain of glucose) and amylopectin (a branched structure). Cellulose, on the other hand, consists of long, linear chains of glucose linked by beta-glycosidic bonds, making it a structural polysaccharide found in plant cell walls.

Why is the structure of cellulose important for its function?

Cellulose's linear, beta-linked structure allows it to form strong hydrogen bonds between chains, resulting in a rigid and durable material. This structural integrity is crucial for the support and protection of plant cells.

What role do carbohydrates play in biological membranes and cartilage?

Carbohydrates, in the form of sugar derivatives like sialic acid and hyaluronic acid, are integral to biological membranes, influencing cell signaling and interactions. In cartilage, glycosaminoglycans like hyaluronic acid provide resilience and flexibility by attracting water, which helps protect joints from shock.