Carbohydrates Overview Flashcards

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Questions and Answers

What are the learning objectives related to carbohydrates?

To define CHO terminology & classification, discuss nutritional characterization & measurement of dietary CHO, demonstrate understanding of digestion and metabolism of CHO, review the roles of CHO, discuss the links between CHO and disease, and define mechanisms controlling plasma glucose.

What are carbohydrates?

Carbohydrates are a group of chemically defined substances that consist of sugar molecules, serve as principal substrates for energy metabolism, and influence satiety, insulin response, weight gain, and chronic health.

How are carbohydrates classified chemically?

Carbohydrates are classified according to molecular size, degree of polymerization, type of linkage, and characteristics of individual monomers.

Describe mono and di saccharides.

Monosaccharides are single unit sugars like glucose, fructose, mannose, and galactose. Disaccharides are two sugar units, such as maltose (glucose-glucose), lactose (glucose-galactose), and sucrose (glucose-fructose). Signup and view all the answers

What are polyols and their characteristics?

Polyols are alcohols of glucose and other sugars, such as sorbitol, mannitol, xylitol, and maltitol. They are found naturally in some fruits and are used as sucrose replacements. Signup and view all the answers

Describe oligosaccharides.

Oligosaccharides are short-chain carbohydrates made of monosaccharide units joined by glycosidic linkages, averaging a degree of polymerization of 10 units. Examples include malto-oligosaccharides and fructo-oligosaccharides. Signup and view all the answers

Describe the characteristics of polysaccharides.

Polysaccharides are carbohydrate polymers consisting of tens to several thousand monosaccharide units, primarily containing glucose. They are synthesized by plants and animals for storage, structural support, or metabolism for energy. Signup and view all the answers

What is starch and its characteristics?

Starch is the main form of energy storage in plants, found in cereal grains and tubers. It is a mixture of amylose and amylopectin and has a crystalline structure that retards digestion. Signup and view all the answers

Describe the effects of cooking on starch.

Cooking breaks down the crystalline structure of starch, allowing it to swell and become gelatinised, which enhances digestibility. Signup and view all the answers

What factors influence the digestion of starch?

Factors include physiological differences among individuals, extent of chewing, concentration of pancreatic amylase, and transit time from the stomach to the small intestine. Signup and view all the answers

Describe the characteristics of glycogen.

Glycogen is the reserve carbohydrate of animals, more branched than amylopectin, and consists of glucose units joined by specific glycosidic bonds. A well-nourished person has about 350 g of glycogen stored equally in the liver and muscles. Signup and view all the answers

Describe the characteristics of NSP cellulose.

Cellulose is a major component of rigid plant cell walls, a linear polysaccharide polymer of glucose units linked by β glycosidic bonds, making it indigestible by humans. Signup and view all the answers

Study Notes

Learning Objectives

Define carbohydrate terminology and classification.
Discuss nutritional characterization and measurement of dietary carbohydrates (CHO).
Understand the digestion and metabolism of carbohydrates.
Review the roles of carbohydrates in health.
Explore links between carbohydrates and diseases.
Define mechanisms that control plasma glucose and their roles in disease.

What are Carbohydrates?

Carbohydrates consist of sugar molecules with diverse physical and physiological properties.
Serve as the principal substrates for energy metabolism.
Influence satiety, insulin response, weight gain, and chronic health conditions.

Chemical Classification of Carbohydrates

Classified based on molecular size, degree of polymerization, type of linkage, and characteristics of monomers.

Monosaccharides and Disaccharides

Monosaccharides: Single unit sugars, e.g., glucose, fructose, mannose, galactose.
Disaccharides: Two sugar units; examples include:
- Maltose: glucose-glucose
- Lactose: glucose-galactose
- Sucrose: glucose-fructose

Polyols

Alcohols derived from glucose and other sugars (e.g., sorbitol, mannitol).
Naturally found in fruits such as apples and pears; can be commercially produced.
Used as sucrose replacements for diabetic diets; vary in absorption and metabolism.

Oligosaccharides

Comprise monosaccharide units joined by glycosidic linkages, averaging about 10 units in degree of polymerization.
Types include:
- Alpha-glucans (e.g., malto-oligosaccharides) used as sweeteners and fat substitutes.
- Non-alpha-glucans (e.g., raffinose, stachyose) found in legumes.
- Fructo-oligosaccharides found in wheat and onions; resist enzymatic breakdown.
- Milk oligosaccharides promote beneficial gut bacteria.

Characteristics of Polysaccharides

Polysaccharides are carbohydrate polymers consisting of tens to thousands of monosaccharide units.
Predominantly contain glucose as the monosaccharide unit.
Synthesized by plants and animals for energy storage, structural support, or direct metabolism for energy.

Starch Characteristics

Main energy storage form in plants; found in cereal grains and tubers (e.g., potatoes).
Composed of amylose (10-20%) and amylopectin (80-90%).
Granules are water-soluble, but crystalline structures hinder digestion by pancreatic amylase.

Cooking Effects on Starch

Cooking breaks down semi-crystalline structures of starch, enhancing digestibility.
Heating swell starch granules and disrupts crystalline structure.
Cooling leads to retrogradation, where amylose recrystallizes quickly and amylopectin slowly.

Factors Influencing Starch Digestion

Influenced by individual physiological factors:
- Extent of chewing and concentration of pancreatic amylase.
- Transit time from stomach to small intestine.

Glycogen Characteristics

Reserve carbohydrate in animals, closely resembling amylopectin.
Composed of glucose units linked by a-(1-4) bonds in chains and a-(1-6) bonds at branch points.
More branched than amylopectin, with a well-nourished individual having about 350 g stored mainly in liver and muscle.

NSP Cellulose Characteristics

Major component of rigid plant cell walls; linear polysaccharide polymer of glucose.
Contains β-glycosidic linkages, making it indigestible to humans, contrasting with α-linkages in starch.

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Description

This quiz aims to enhance your understanding of carbohydrates by defining key terminology, discussing their nutritional characterization, and reviewing their digestion and metabolism. You'll also explore the roles of carbohydrates, their links to diseases, and mechanisms controlling plasma glucose. Perfect for students seeking to master carbohydrate concepts.