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)
 
This image is an infographic titled types of carbohydrates. It is divided into three sections: 1. Monosaccharides - Simplest sugar. 2. Disaccharides - consists of two monosaccharides 3. Polysaccharides - long chain of 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

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)
 
This image is an infographic titled types of carbohydrates. It is divided into three sections: 1. Monosaccharides - Simplest sugar. 2. Disaccharides - consists of two monosaccharides 3. Polysaccharides - long chain of 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