2.2.e Describe the molecular structure of polysaccharides including starch (amylose and amylopectin), glycogen and cellulose and relate these structures to their functions in living organisms.
STARCH
- Starch is a macromolecule made up of amylose and amylopectin.
- Amylose and amylopectin are polysaccharides made from glucose.
The table above shows the similarities and differences between amylose and amylopectin
✍️Note: ‘1,4 linked’ means there is a link between carbon atoms 1 and 4 of successive glucose units.
The above image shows the branched and helical structures of amylopectin and amylose.
⚡💯If a GCE CIE Biology exam question on the similarities between amylose and amylopectin arises, make sure to use the following key terms to get full marks:
- Macromolecules/polymers
- Polysaccharides
- Made from α-glucose
- Glucose units held together by 1,4 links
- Branches formed by 1,6 links
GLYCOGEN
- Glycogen is a macromolecule made from α-glucose molecules.
- Structurally similar to amylopectin (above), but more branched.
- Glycogen forms granules that are found in liver cells and muscle cells.
- Glycogen stores energy for animal cells.
The above image shows the branched structure of glycogen.
CELLULOSE
- Cellulose is a macromolecule made from β-glucose molecules and comprises 1, 4 glycosidic bonds.
- Tightly cross-linked to form microfibrils.
- Microfibrils are held together in bundles with hydrogen bonds holding the structure together.
- Cellulose increases strength by making the cell rigid.
- Found in cell wall of plant cells.
The above image shows the structure of cellulose.
Alrighty! Completed! 😋
References:
- Illustrations from Anatomy & Physiology, Connexions Web site. https://openstax.org/books/anatomy-and-physiology/pages/2-5-organic-compounds-essential-to-human-functioning, Jun 19, 2013.
- Jones, M., & Parkin, M. (2018). Cambridge International AS and A Level Biology. Cambridge: Cambridge University Press.