3.2.4 The variety of life is extensive and this is reflected in similarities and differences in its biochemical basis and cellular organisation.
Carbohydrates

• The structure of b-glucose and the linking of b-glucose by glycosidic bonds formed by condensation to form cellulose.
• The basic structure and functions of starch, glycogen and cellulose and the relationship of structure to function of these substances in animals and plants.

The monomers of carbohydrates are monosaccharides. 

• One example of a monosaccharide is glucose. 🍬 
• In our previous post on GCE AQA Biology’s “Carbohydrate digestion”, we were introduced to alpha-glucose, one type of glucose. 
• Another type of glucose you need to know about is beta-glucose. 
  • Note the up/down orientation of the hydroxyl groups (-OH) in clockwise order is up, down, up, down. This is important to distinguish beta-glucose from alpha-glucose.

Many carbohydrate monosaccharides can be linked up to form long polymers known as polysaccharides. 

• Beta-glucose molecules can be linked up to form cellulose. 
• The glucose molecules are linked up via a condensation reaction. 
  • Adjacent hydroxyl (-OH) groups react, forming a glycosidic bond
  • The glycosidic bond is the C-O-C holding adjacent glucose molecules together
  • The reaction is called ‘condensation’ because a byproduct of the reaction is water

There are many different types of polysaccharides found in nature. In GCE AQA Biology, you should be familiar with three: starch, cellulose, and glycogen. 

1. Starch 

2. Cellulose

3. Glycogen

Wanna Boost Up Your GCE AQA Biology? Check out our study tips here! 

Written by Justine | Biology Specialist @ Tuttee

References

Toole, G., & Toole, S. (2015). Aqa biology A level. Oxford: Oxford University Press.

Images from:

1. https://quizlet.com/196411347/biochem-exam-2-structures-flash-cards/
2. https://mybiochem.wordpress.com/tag/cellulose/
3. https://futurefoodchemist.weebly.com/amylose-or-amylopectin.html
4. https://www.philpoteducation.com/mod/book/tool/print/index.php?id=782&chapterid=1125 
5. https://ecampusontario.pressbooks.pub/humannutrition/chapter/introduction-5/
6. https://commons.wikimedia.org/wiki/File:Healthy_food.jpg