Carbohydrates 3: Structural units
- Created by: Lois
- Created on: 19-04-13 14:15
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- Carbohydrates 3: Structural units
- Carbohydrate polymers - structural units
- Beta-glucose can be boned together to form polymers through numerous condensation reactions
- Alpha-glucose molecules can also be condensed to form coiled, spring-like chains
- Beta-glucose molecules have a slightly different shape so when condensed form a long straight chain
- These straight chain molecules can contain 10000 beta-glucose molecules, they are stronger tham the chains found in amylose
- these beta-glucose polymer chains are called cellulose chains
- cellulose is only found in plants, it is the most abundant structural polysaccharide in nature
- these beta-glucose polymer chains are called cellulose chains
- Cellulose
- Cellulose fibres are arranged in a specific way to form plant cell walls
- because the glucose monomers contain so may OH groups, many hydrogen bonds can form between them
- about 60-70 cellulose molecules become cross-linked by hydrogen bonds to form bundles called microfibrils
- these in turn are held together by more hydrogen bonds forming macrofibrils
- The macrofibrils have great mechanical strength, they are embedded in a polysaccharide glue of substances called pectins, to form cell walls
- Structure & function of plant cell walls
- The cell walls around plant cell give great strength to each cell, supporting the whole plant
- The arrangement of macrofibrils allows water to move through & along cells walls & can pass in/out of the cell easily
- Water moving into plant cells does not cause them to burst - the wall prevents this and in turgid cells it helps to support the whole plant
- The arrangement of macrofibrils in cell walls determines how cells can grow or change shape
- e.g. guard cell walls have arrangement of macrofibrils that result in the opening/closing of stomata
- Cell walls can be reinforced with other substances to provide extra support, or to make the walls waterproof
- Other structural carbohydrates
- A number of organisms use structural carbohydrate polymers
- the polysaccharide chitin forms the exoskeleton of insects
- the polysaccharide peptidoglycan is the basis of the cell walls found around most bacterial cells
- Carbohydrate polymers - structural units
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