1.2(i) Know the difference between monosaccharides, disaccharides and polysaccharides, including glycogen and starch (amylose and amylopectin)
1.2(ii) Be able to relate the structures of monosaccharides, disaccharides and polysaccharides to their roles in providing and storing energy
1.4 Know how monosaccharides (glucose, fructose and galactose) join together to form disaccharides (maltose, sucrose and lactose) and polysaccharides (glycogen, amylose and amylopectin) through condensation reactions forming glycosidic bonds, and how these can be split through hydrolysis reactions
![broken image](http://custom-images.strikinglycdn.com/res/hrscywv4p/image/upload/c_limit,fl_lossy,h_9000,w_1200,f_auto,q_60/2455675/883377_397167.gif)
- Carbohydrates are made up of carbon, hydrogen and oxygen
- The chemical formula is (CH2O)n
- The smallest unit is called a monosaccharide
- When two or more monosaccharide join together, they can form a disaccharide (di- means two) or polysaccharide (poly- means many)
Monosaccharides
- Single saccharides
- Soluble with osmotic effect (i.e. can cause change in water potential)
- Examples:
- Glucose – main substrate for respiration
- Gelactose
- Fructose – “fruit sugar”
Disaccharides
- Two saccharides joined together
- Soluble
- Examples:
- Sucrose (glucose + fructose) – main transport sugar in plants
- Lactose (glucose + gelactose) – ‘milk’ sugar
- Maltose (glucose + glucose)
![Monosaccharides and disaccharides Monosaccharides and disaccharides](http://custom-images.strikinglycdn.com/res/hrscywv4p/image/upload/c_limit,fl_lossy,h_9000,w_1200,f_auto,q_auto/2455675/50098_814653.jpeg)
Polysaccharides
- Many saccharides joined together
- Generally insoluble
👇Two important polysaccharides to remember for IAL Edexcel Biology 👇
Starch
- Energy store in plants
- Made up of:
- Amylose
- α -glucose molecules joined by 1,4-glycosidic bonds only
- The unbranched chain forms a spiral and makes it more compact for storage
- Amylopectin
- α-Glucose molecules joined by 1,4- and 1,6- glycosidic bonds
- The branched chain has more terminal glucose units that can be used to release energy more rapidly
- Amylose
![Note the presence of 1,6-glycosidic bonds in amylopectic, which gives the molecule a branched structure. Note the presence of 1,6-glycosidic bonds in amylopectic, which gives the molecule a branched structure.](http://custom-images.strikinglycdn.com/res/hrscywv4p/image/upload/c_limit,fl_lossy,h_9000,w_1200,f_auto,q_auto/2455675/869210_615580.png)
Be sure you understand the structure of a molecule to its function
Glycogen
- Energy store in animals
- Branched chains of glucose molecules
- Similar structure with amylopectin but with more 1,6-glycosidic bonds, allowing it to be broken down very rapidly
![Structure of amylose, amylopectin and glycogen Structure of amylose, amylopectin and glycogen](http://custom-images.strikinglycdn.com/res/hrscywv4p/image/upload/c_limit,fl_lossy,h_9000,w_1200,f_auto,q_auto/2455675/835151_634156.png)
Condensation and hydrolysis reactions
- In a condensation reaction, glycosidic bonds form between saccharides and a water molecule is released
- In a hydrolysis reaction, glycosidic bonds are broken and a water molecule is required for the reaction
![In a condensation reaction, glycosidic bonds form between saccharides and water molecule is released. Conversely, in a hydrolysis reaction, glycosidic bonds are broken and a water molecule is required for the reaction. In a condensation reaction, glycosidic bonds form between saccharides and water molecule is released. Conversely, in a hydrolysis reaction, glycosidic bonds are broken and a water molecule is required for the reaction.](http://custom-images.strikinglycdn.com/res/hrscywv4p/image/upload/c_limit,fl_lossy,h_9000,w_1200,f_auto,q_auto/2455675/347304_860607.png)
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That's a wrap!
![broken image](http://custom-images.strikinglycdn.com/res/hrscywv4p/image/upload/c_limit,fl_lossy,h_9000,w_1200,f_auto,q_60/2455675/414208_89036.gif)
References:
1. Edexcel AS Biology Revision Guide. Edexcel.
2. https://www.nutritionaldoublethink.com/carbohydrates.html
3. https://futurefoodchemist.weebly.com/amylose-or-amylopectin.html