AQA AS Level Biology: Carbohydrates

Functions of Carbohydrates

• Serve as a primary energy source for living organisms.
• Play a crucial role in metabolic processes and structural components.

Disaccharide Examples

• Sucrose, lactose, and maltose are common examples of disaccharides, which are formed by two monosaccharide units.

Bonds in Polysaccharides

• Glycosidic bonds form between monosaccharides, linking them to create polysaccharides such as starch and glycogen.

Energy Storage in Animals

• Glycogen is the main carbohydrate involved in energy storage in animals, primarily found in the liver and muscle tissues.

Cellulose vs. Starch

• Cellulose consists of linear chains of glucose units with beta-glycosidic bonds, making it structurally distinct from starch, which has alpha-glycosidic bonds and is branched.

Carbohydrates Overview

• Carbohydrates are organic compounds consisting of carbon, hydrogen, and oxygen, commonly known as sugars and starches.
• They are categorized into three main types: monosaccharides, disaccharides, and polysaccharides.

Monosaccharides

• Monosaccharides are the simplest form of carbohydrates and function as the building blocks for more complex sugars.
• Examples include glucose (important energy source), fructose (found in fruits), and galactose.
• They typically have the general formula (CH2O)n where n is the number of carbon atoms.

Disaccharides

• Formed by the condensation reaction of two monosaccharides joined by glycosidic bonds.
• Common disaccharides include sucrose (glucose + fructose), lactose (glucose + galactose), and maltose (glucose + glucose).
• Hydrolysis of disaccharides produces their constituent monosaccharides.

Polysaccharides

• Composed of long chains of monosaccharide units linked together by glycosidic bonds.
• Key examples include starch (energy storage in plants), glycogen (energy storage in animals), and cellulose (structural component in plant cell walls).
• Polysaccharides can be branched or unbranched, affecting their solubility and digestibility.

Functions of Carbohydrates

• Serve as a primary energy source for living organisms.
• Play a vital role in cellular recognition and signaling through glycoproteins and glycolipids.
• Contribute to the structure of cells, particularly in plants with cellulose.

Dietary Sources

• Rich sources include fruits, vegetables, grains, and legumes.
• Simple carbohydrates (sugars) are quickly absorbed, while complex carbohydrates (starches) provide a slower, sustained release of energy.

Glycogen Storage and Utilization

• Glycogen is stored primarily in the liver and muscles and is broken down into glucose when energy is needed.
• Enzymes such as glycogen phosphorylase regulate the breakdown process, pivotal for energy management during physical activity.

Impact on Health

• Excessive consumption of carbohydrates, particularly simple sugars, can lead to health issues such as obesity and diabetes.
• A balanced intake of carbohydrates, focusing on complex carbohydrates, is essential for maintaining overall health and energy levels.