Polysaccharides

State general formula for disaccharides

C12H22O11

Describe polysaccharides

• Formed by condensation of many glucose units

• Polysaccharides are insoluble so have no osmotic effect

How is glycogen formed?

• Condensation of a-glucose

How is cellulose formed?

Condensation of B-glucose

Where is starch found?

• Produced by all green plants

What is starch used for?

Energy store

Describe starch

• Compact - So large quantities can be stored

• Insoluble - So will have no osmotic effect, unlike glucose which would lower the water potential of a cell

How much amylose is starch?

10-30%

Explain the shape of amylose

• Unbranched helix-shaped chain with 1,4 glycosidic bonds between a-glucose molecules

Why does amylose form into a spiral shape?

• Helix shape enables it to be more compact & thus is more resistant to digestion

What type of bond forms between the glucose monomers in amylose?

1,,4 glycosidic bond

How much amylopectin is starch?

70-90%

Explain shape of amylopectin

• Branched form of starch

What type of bonds form between glucose molecules in amylopectin?

1,4 glycosidic bonds & 1,6 glycosidic bonds

What is the importance of amylopectin being a branched structure?

• It has 1,4 glycosidic bonds between a-glucose molecules, but also 1,6 glycosidic bonds form between glucose molecules, creating the branched structure

• The branches result in many terminal glucose molecules that can be easily hydrolysed for use during cellular respiration or added to for storage

Explain the shape of glycogen

• Glycogen is the storage polysaccharide of animals & fungi - highly branched & not coiled

Which cell types have the most glycogen & why?

• Liver & muscle cells have a high concentration of. glycogen, as the cellular respiration rate is high in these cells

Explain the importance of glycogen being more branched than amylopectin

Makes it more compact, which helps animals store more

Branching enables more free ends where glucose molecules can be either added or removed, allowing for condensation & hydrolysis

What type of bonds form between glucose monomers in glycogen?

• 1,6 glycosidic bonds & 1,4 glycosidic bonds reactions to occur rapidly, thus the storage or release of glucose can suit demands of cell

Where is cellulose found?

Polysaccharide found in plant cells

What are the monomers of cellulose & what bonds form between them?

• Long chains of monomer beta glucose, joined together by 1,4 glycosidic bonds

Why do the monomers of cellulose need to be rotated 180 degrees?

• As B-glucose is an isomer of a-glucose, to form the 1,4 glycosidic bonds, consecutive B-glucose molecules must be rotated 180 degrees to each other

Why are hydrogen bonds important in cellulose?

Gives cellulose its strength

State the functions of cellulose

1. Main structural component of cell walls due to its strength as result of many hydrogen bonds found between parallel chains of microfibrils

2. High tensile strength - allows it to be stretched without breaking, which makes it possible for cell walls to withstand turgor pressure

3. Strengthened cell walls provide support to plant

4. Cellulose fibres are freely permeable which allows water to& solutes to leave/reach cell surface membrane

5. As few organisms have the enzyme (cellulose) to hydrolyse cellulose, it is a source of fibre.