Carbohydrates pt 2

What do plants store carbohydrates as

Starch, stored as starch grains in chloroplasts

Note:

• Does not dissolve meaning it does not affect water potential

• Hold glucose molecules in chains that can be easily broken to be used in respiration

What does starch consist of

Two polysaccharides amylose and amylopectin

Amylose

• Made up of a straight chain of alpha glucose molecules

• Joined by 1-4 glycosidic bond

• Forms a helix shape, this shape helps to make amylose compact for storage

Amylopectin

• Made up of a branched chain of alpha molecules

• Branches occur due to having 1-6 glycosidic bonds alongside 1-4 bonds.

How come starch is insoluble

• Starch is insoluble, this is because there hundreds of thousands of glucose units, and water molecules cannot easily surround such a huge molecule

• Both amylose and amylopectin have many OH, the OH groups form hydrogen bonds between the chains, not with water

What are the advantages of branches in starches structure

• By having branches this means there are more chain ends exposed this means enzymes can hydrolyse glucose faster, allowing release glucose quickly when needed

• Allows the molecule to be stored compactly

What do animals store carbohydrates as

Glycogen, stored in the liver and muscle

Note:

• Glycogen is less dense and more soluble than starch, this indicates a higher metabolic rate of animals

• Glycogen forms due to high glucose blood levels and insulin is released

• Do not dissolve so does not affect water potential

• Hold glucose molecules in chains that can be easily broken to be used in respiration

What is the structure of glycogen

• It is made up of many glucose units

• Has 1-4 glycosidic bonds as well 1-6 glycosidic bonds, have more branches than amylopectin

What are the advantages of branches

As glycogen has more branches it makes it more compact for storage, branches also means there are more chains meaning there is quicker access to retrieve glucose through hydrolysis

What are the cell walls of a plant made of

Cellulose

Describe the structure of cellulose

• It is a polysaccharide which consists of long chains of beta glucose joined together by 1-4 beta glycosidic bonds.

• The chains form rope-like microfibrils which are layered, as hydrogen bonds form between individual cellulose fibres

• Microfibrils are held together by more hydrogen bonds to form microfibrils these are embedded in a polysaccharide glue called pectin