Carbohydrates

4.2

Carbohydrates

Introduction

Carbohydrates are important as a source of energy and the basic structure of some organisms
Carbohydrates are organic compounds consisting of the elements carbon (C), hydrogen (H) and oxygen (O) in the ratio \(1: 2: 1\) and with the chemical formula \((\text{C}\text{H}_2\text{O})_n\)
There are three main types of carbohydrates, which are
- Monosaccharides (simple sugars)
- Disaccharides
- Polysaccharides (complex sugars)

Monosaccharides

Monosaccharides are carbohydrate monomers, which are the simplest carbohydrate units
Monosaccharides can combine to form polymers through a condensation reaction
Most monosaccharides taste sweet, can form crystals and dissolve in water
Examples of monosaccharides:
- Glucose is a sugar found in plants such as rice and wheat as well as fruits such as grapes
- Glucose is the most commonly found monosaccharide and most polysaccharides are formed from this sugar
- Fructose is the sugar found in honey and sweet fruits
- Galactose is found in milk
Monosaccharide has the reducing power, which is the ability to transfer hydrogen (or electron) to other compounds
This is called the reducing process
When the monosaccharide is heated in Benedict’s solution, the monosaccharide will reduce the blue copper (II) sulphate to a brick red precipitate of copper (I) oxide which is not soluble in water
All monosaccharides give this reaction and it is known as reducing sugars

Disaccharides

Disaccharide molecules are formed when two simple sugar molecules (monosaccharides) combine through condensation to form a disaccharide unit
This process involves the removal of a water molecule
Examples:
- glucose + glucose \(\xrightarrow{condensation}\) maltose + water
- glucose + fructose \(\xrightarrow{condensation}\) sucrose + water
- glucose + galactose \(\xrightarrow{condensation}\) lactose + water
Disaccharides can also be broken down to their monosaccharide units through hydrolysis and the addition of one water molecule
Examples:
- maltose + water \(\xrightarrow{hydrolysis}\) glucose + glucose
- sucrose + water \(\xrightarrow{hydrolysis}\) glucose + fructose
- lactose + water \(\xrightarrow{hydrolysis}\) glucose + galactose
Examples of disaccharides include sucrose, maltose and lactose
Lactose and maltose are reducing sugars while sucrose is a non-reducing sugar

Polysaccharides

Polysaccharides are sugar polymers consisting of monosaccharide monomers
Similar to disaccharides, polysaccharides are formed through the condensation process and involves hundreds of monosaccharides to form long molecular chains
Polysaccharides are not soluble in water due to their large molecular size
Polysaccharides neither taste sweet nor crystallise
Polysaccharides can also disintegrate through hydrolysis with the help of dilute acids, boiling and enzyme action
Polysaccharides play various roles in organisms

Importance of Carbohydrates in Cells

As a source of energy, for example glucose
As a food reserve, for example glycogen in animal cells and starch in plant cells
- Glycogen is the main storage of polysaccharide found in muscle cells and animal liver cells
- Starch is the main storage of polysaccharide in plants
- Starch is also found in chloroplasts
- Source: grains, potatoes and legumes.
As a support structure, for example cellulose in the plant cell wall
- Cellulose forms the main structure of the plant cell wall

4.2

Carbohydrates

Introduction

Carbohydrates are important as a source of energy and the basic structure of some organisms
Carbohydrates are organic compounds consisting of the elements carbon (C), hydrogen (H) and oxygen (O) in the ratio \(1: 2: 1\) and with the chemical formula \((\text{C}\text{H}_2\text{O})_n\)
There are three main types of carbohydrates, which are
- Monosaccharides (simple sugars)
- Disaccharides
- Polysaccharides (complex sugars)

Monosaccharides

Monosaccharides are carbohydrate monomers, which are the simplest carbohydrate units
Monosaccharides can combine to form polymers through a condensation reaction
Most monosaccharides taste sweet, can form crystals and dissolve in water
Examples of monosaccharides:
- Glucose is a sugar found in plants such as rice and wheat as well as fruits such as grapes
- Glucose is the most commonly found monosaccharide and most polysaccharides are formed from this sugar
- Fructose is the sugar found in honey and sweet fruits
- Galactose is found in milk
Monosaccharide has the reducing power, which is the ability to transfer hydrogen (or electron) to other compounds
This is called the reducing process
When the monosaccharide is heated in Benedict’s solution, the monosaccharide will reduce the blue copper (II) sulphate to a brick red precipitate of copper (I) oxide which is not soluble in water
All monosaccharides give this reaction and it is known as reducing sugars

Disaccharides

Disaccharide molecules are formed when two simple sugar molecules (monosaccharides) combine through condensation to form a disaccharide unit
This process involves the removal of a water molecule
Examples:
- glucose + glucose \(\xrightarrow{condensation}\) maltose + water
- glucose + fructose \(\xrightarrow{condensation}\) sucrose + water
- glucose + galactose \(\xrightarrow{condensation}\) lactose + water
Disaccharides can also be broken down to their monosaccharide units through hydrolysis and the addition of one water molecule
Examples:
- maltose + water \(\xrightarrow{hydrolysis}\) glucose + glucose
- sucrose + water \(\xrightarrow{hydrolysis}\) glucose + fructose
- lactose + water \(\xrightarrow{hydrolysis}\) glucose + galactose
Examples of disaccharides include sucrose, maltose and lactose
Lactose and maltose are reducing sugars while sucrose is a non-reducing sugar

Polysaccharides

Polysaccharides are sugar polymers consisting of monosaccharide monomers
Similar to disaccharides, polysaccharides are formed through the condensation process and involves hundreds of monosaccharides to form long molecular chains
Polysaccharides are not soluble in water due to their large molecular size
Polysaccharides neither taste sweet nor crystallise
Polysaccharides can also disintegrate through hydrolysis with the help of dilute acids, boiling and enzyme action
Polysaccharides play various roles in organisms

Importance of Carbohydrates in Cells

As a source of energy, for example glucose
As a food reserve, for example glycogen in animal cells and starch in plant cells
- Glycogen is the main storage of polysaccharide found in muscle cells and animal liver cells
- Starch is the main storage of polysaccharide in plants
- Starch is also found in chloroplasts
- Source: grains, potatoes and legumes.
As a support structure, for example cellulose in the plant cell wall
- Cellulose forms the main structure of the plant cell wall