Polysaccharides

• The cell wall structure adds strength and rigidity to the cell, allowing plants to stand upright and grow tall
• Polysaccharide: Many monosaccharides joined together in a chain, forming a complex carbohydrate
• Poly: In the context of biological molecules, it refers to many
• Polysaccharides are complex carbohydrates made up of long chains of monosaccharide units.
• Polysaccharides are formed by the condensation of many monosaccharides
• Cellulose is an example of a polysaccharide found in plants. It is the main structural component of plants, due to its strength
• Cellulose is a polymer consisting of long straight chains of beta-glucose joined together by 1,4 glycosidic bonds
• In order to make the chains straight in cellulose, every other glucose is inverted
• Each cellulose chain forms hydrogen bonds with surrounding chains, forming microfibrils
• Hydrogen bonds on their own are weak, but many of them together allows for cellulose to be strong
• The high tensile strength of cellulose allows it to be stretched without breaking which makes it possible for cell walls to withstand turgor pressure
• Cellulose fibres are freely permeable which allows water and solutes to leave or reach the cell surface membrane
• Starch is a polysaccharide found in plants. It is the main energy store in plants
• Due to the many monomers in starch, it takes longer to digest than pure glucose
• Starch is insoluble. This means that it has no osmotic effect on plants
• Despite glucose being faster to digest than starch, glucose would lower the water potential of a cell and cause water to move in – thus causing cell damage
• Starch is made up of two different types of polysaccharide: amylopectin and amylose
• Amylose consists of unbranched spiralling chains of alpha-glucose molecules, joined by 1,4 glycosidic bonds
• Amylose's coiled structure means that it is very compact so lots of amylose can be packed into a cell
• Amylopectin consists of branched chains of alpha-glucose molecules
• Amylopectin's branches increase its surface area which means that enzymes can quickly break it apart when glucose is needed for respiration
• Amylopectin contains 1,4 and 1,6 glycosidic bonds
• Glycogen is the main energy store for animals and fungi
• Glycogen consists of branched chains of alpha-glucose, with 1,4 and 1,6 glycosidic bonds
• Glycogen is similar to amylopectin but has more side-branches and is more compact
• In cellulose, every other glucose is inverted, forming straight chains that can wrap together to form fibrils. These are strong. Cellulose also contains lots of hydrogen bonds. Many hydrogen bonds add strength
• Animals store excess glucose as glycogen in the liver and muscle cells
• Hydrogen bonds make fibrils very strong yet still flexible, allowing them to provide support
• Animals have higher metabolic rates than plants so have more highly branched structures to allow for a faster release of glucose
• Glycogen needs to be more branched than starch so glucose can be hydrolysed and released more quickly (animals have a higher metabolic rate)