AQA AS Level Biology: Carbohydrates

Study Notes

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.

Description

Assess your knowledge of carbohydrates in living organisms, including their primary function, types of bonds, and their role in energy storage. Questions cover disaccharides, polysaccharides, and the characteristics of cellulose and starch.