Carbohydrates: Starch and Glycogen | A-level Biology | OCR, AQA, Edexcel

Carbohydrates: Starch and Glycogen in a Snap! Unlock the full A-level Biology course at http://bit.ly/2BD2spR created by Adam Tildesley, Biology expert at SnapRevise and graduate of Cambridge University.

SnapRevise is the UK’s leading A-level and GCSE revision & exam preparation resource offering comprehensive video courses created by A* Oxbridge tutors. Our courses are designed around the OCR, AQA, SNAB, Edexcel B, WJEC, CIE and IAL exam boards, concisely covering all the important concepts required by each specification. In addition to all the content videos, our courses include hundreds of exam question videos, where we show you how to tackle questions and walk you through step by step how to score full marks.

Sign up today and together, let’s make A-level Biology a walk in the park!

The key points covered in this video include:

1. Starch
2. Structure of Starch - Amylose
3. Structure of Starch - Amylopectin
4. Glycogen

Starch

In plants, the polysaccharide energy store is called starch. Starch is most commonly found in photosynthesising cells in leaves and storage cells in seeds and storage organs. It is compacted into dense, insoluble grains stored in a special organelles called amyloplasts. Storage organs contain cells with numerous amyloplasts to ensure the plant always has a sufficient supply of energy.

Structure of Starch - Amylose

Starch consists of two different polysaccharides - amylose and amylopectin. Amylose is a long chain of α-glucose molecules joined together by 1,4 glycosidic bonds. Amylose coils into a helix shape that makes it more compact. Each amylose molecule only has two accessible ends where the enzyme amylase can bind. This means that amylose can only be broken down slowly.

Structure of Starch - Amylopectin

The other polysaccharide found in starch is amylopectin. Amylopectin is also a long chain of α-glucose molecules joined together with 1,4 glycosidic bonds. However, amylopectin also has occasional 1,6 glycosidic bonds. The additional 1,6 glycosidic bonds causes amylopectin to have side branches with more accessible ends. This makes amylopectin more easily broken down by enzymes when glucose is needed.

Glycogen

In animals, the polysaccharide energy store is called glycogen. Glycogen is found in cells with a high metabolic rate - e.g. liver cells and muscle cells. Glycogen has a similar structure to amylopectin, with many α-glucose molecules joined together by 1,4 and 1,6 glycosidic bonds. However, in glycogen, the 1,6 glycosidic bonds are very frequent resulting in a highly branched structure. Glycogen therefore has a very high number of accessible ends. This allows glycogen to be rapidly hydrolysed to α-glucose by enzymes. This is important as animals have higher metabolic requirements than plants.

Summary

Polysaccharides are formed by joining together many monosaccharides in a series of condensation reactions
Polysaccharides are broken down into monosaccharides in a series of hydrolysis reactions
Polysaccharides have many properties that make them good energy stores as they are:
· compact
· large
· insoluble
· easily hydrolysed
In plants, the polysaccharide energy store is called starch
Starch is made up of amylose and amylopectin molecules
In animals, the polysaccharide energy store is called glycogen
The more branched the polysaccharide, the faster it can be broken down into glucose for energy

Видео Carbohydrates: Starch and Glycogen | A-level Biology | OCR, AQA, Edexcel канала SnapRevise