Estrutura e Função dos Carboidratos | Curso Bioquímica Ens. Superior (AULA 7)

Introduction to Carbohydrates

Overview of Carbohydrates

• Professor Raphael Barbosa introduces the topic of carbohydrates, discussing their structure, classification, and functions in the body.

• Carbohydrates are organic substances primarily composed of carbon atoms that form various covalent bonds with hydrogen, oxygen, and nitrogen.

• They play numerous roles in metabolism, including energy storage (e.g., glycogen), structural components (e.g., nucleotides in DNA), and cellular signaling through structures like glycoalyx.

Classification of Carbohydrates

• Carbohydrates can be classified into three main types: monosaccharides, disaccharides, and polysaccharides.

• Monosaccharides have up to seven carbon atoms; examples include trioses (3 carbons), tetroses (4), pentoses (5), hexoses (6), and heptoses (7).

• Pentoses and hexoses are particularly significant in physiological processes; ribose is a key pentose found in RNA.

Functions of Key Monosaccharides

Importance of Glucose

• Glucose is highlighted as a primary energy source for cells; it is the end product of photosynthesis and its breakdown produces ATP.

• The majority of carbohydrates exist in a cyclic form which is more stable for transport within organisms.

Other Hexoses

• Fructose is an isomer of glucose that contributes to the sweetness of fruits; it can be converted into glucose by the liver.

• Galactose, found in milk, also converts to glucose within the body.

Disaccharides: Formation and Types

Formation Process

• Disaccharides result from the combination of two monosaccharides via a glycosidic bond; this process releases water.

Common Disaccharides

• Maltose consists of two glucose units and is commonly found in plants.

• Sucrose combines glucose with fructose; lactose consists of glucose plus galactose.

• Lactose intolerance affects about 75% of people due to insufficient lactase enzyme needed for digestion.

Polysaccharides: Structure and Function

Formation and Importance of Polysaccharides

• Polysaccharides are formed from the union of hundreds of monosaccharides, with their structure being crucial to their function. The first polysaccharide discussed is starch, which serves as an energy reserve in plants and algae.

• Starch is primarily composed of linked glucose molecules and is a significant carbohydrate source for humans, found in foods like corn, soybeans, rice, beans, and potatoes.

Digestive Processes Involving Starch

• Humans possess salivary amylase, an enzyme that initiates the digestion of starch in the mouth. This marks the beginning of its breakdown during the digestive process.

• Glycogen acts as an energy reserve for animals, stored mainly in the liver and muscles. It is also formed through connections between numerous glucose units.

Structural Polysaccharides

• Chitin is identified as a structural polysaccharide that constitutes the exoskeleton of arthropods and forms part of fungal cell walls.

• Cellulose serves as another structural polysaccharide present in plant cells; although indigestible by humans, it plays a vital role in preventing constipation by promoting healthy intestinal transit.

Health Implications of Cellulose Intake