Compare the structure of cellulose to the structure of starch PDF

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Comparing cellulose and starch ...

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Compare the structure of cellulose to the structure of starch Structure

Characteristics Function

Cellulose Beta glucose Straight chains of beta glucose joined by 1, 4 bonds that lie side by side, with every second beta glucose molecule inverted. Hydrogen bonding between the rotated beta glucose within each chain and between different chains gives the chain additional strength and stops it from spiralling. Cellulose chains make up microfibril, which make up macrofibril which are imbedded in pectins to form the cell wall, and criss-cross in order to support the wall. There is a space between macrofibrils for water and mineral ions to pass through on their way in and out of the cell. This makes the cell fully permeable. A tough, insoluble and fibrous substance. Cellulose helps make up the plant cell wall, and so must be very strong in order to support plants which do not have skeletons to support them. Cellulose is less soluble and very hard to digest, as the glycosidic bonds between the glucose molecules are harder to break. High tensile strength—stops the plant walls from bursting when they are turgid. Turgid cells press against each other which supports the whole cell as a whole.

Both Carbohydrates Homopolysaccharide Polysaccharides 1, 4 carbon links

Starch Alpha glucose AMYLOPECTIN: Glycosidic bonds between carbon 1 and 4, and branches formed by glycosidic bonds between carbons 1 and 6. It coils into a spiral shape, held together with hydrogen bonds, but with branches emerging from the spiral. AMYLOSE: This molecule is a long chain of alpha glucose molecules with glycosidic bonds between carbons 1 and 4. May form a double helix—presents a hydrophobic external surface which is the only part of the polysaccharide which is in contact with the surrounding solution.

big in size compact less soluble than monosaccharides, so do not affect water potential; big size, regions with free hydrogen which could bond with water are hidden inside the molecule both essential in plants

coils into a spiral shape Branched—more compact for storage, and also offer the chance for a lot of glucose molecules to be snipped off by hydrolysis at the same time, allowing for rapid respiration in times when energy is needed quickly Unbranched—storage of energy

Cellulose and starch are both large homopolysaccharides that are made up of many monosaccharides joined together. They are both essential components in plants that have very different structures which enable to fulfil their unique functions within the cell. Cellulose is a homopolysaccharide made of beta glucose that are joined by 1, 4 carbon bonds. Every second beta glucose is inverted, meaning it is rotated by 180 degrees. The inversion of every second beta glucose and the 1, 4 glycosidic link help to prevent the chain from spiralling, and keep the chains straight and lined up side by side. Hydrogen bonding between the rotated beta glucose within each chains, and also between the different chains gives the chain additional strength and also stops it from spiralling. Cellulose chains make up microfibril, which make up macrofibril, which are imbedded in pectins to from the cell wall. There is a space let between the macrofibrils for water and mineral ions to pass through their way in and out of the cell, which makes the cell fully permeable. This means that the cell wall will not dissolve in water, which is important as if this was not the case, then the cell would not be able to support itself—and so the plant cell will be a mere shell of a cell Starch consists of amylase and amylopectin, which are both homopolysaccharides made of alpha glucose. Amylose is a long chain formed by alpha glucose joined with glycosidic links between carbons 2 and 4. Amylose sometimes forms a double helix, which creates a hydrophobic external surface, which is the only part of the polysaccharide which is in contact with the surrounding solution. The structure of amylopectin is similar to that of amylose, in that it consists of alpha molecules with 1, 4 bonds. It differs, however, in that amylopectin has branches formed by glycosidic bonds between carbons 1 and 6. This causes it to coil into a spiral shape, held together with hydrogen bonds, but with branches emerging from the spiral. The structure of cellulose and starch are similar in that they are both homopolysaccharides, made from many glucose molecules with 1, 4 carbon links and are less soluble than monosaccharides. They are different in that cellulose is made from beta glucose with every second beta glucose molecule inverted, whereas amylose is made of alpha glucose, and amylopectin also branches off with 1, 6 links to create a spiral shape. The function of cellulose is to make up the cell wall in plants. This means cellulose must be strong in order to support plants, as they do not possess skeleton to help support them. Cellulose is less soluble, and very hard to digest, as the glycosidic bonds between the molecules are harder to break. Additionally, cellulose has high tensile strength which stops the plant walls from bursting when they are turgid. Turgid cells press against each other which helps to support the whole cell, and plant, as a whole. The function of starch is to be an energy store in plants. Both amylopectin and amylose are more compact, making them ideal for storage as they do not occupy a large amount of space within the cell. Amylopectin is branched, which means many glucose molecules can be snipped off by hydrolysis at the same, allowing for rapid respiration in times when energy is needed quickly. Both cellulose and starch carry out significant, essential, functions in plants. They are less soluble than monosaccharides meaning they do not affect water potential due to their large size and the fact that free hydrogens which could bond with water are hidden within the molecule. The main function of starch is to build up the cell wall in plants, which explains the need for the inverted beta glucose molecule and hydrogen

bonding both within and between chains, as cellulose needs to be strong enough to support the cell. Starch, on the other, is used as storage of energy in plants, which is amylopectin is branched as it allows for many glucose molecules to be hydrolysed all at the same time when energy is needed quickly. To conclude, cellulose and starch are both very important but have differing structures which allow them to carry out their unique functions.

Bibliography 1.

Hocking, S et al. (2015). Module 2 Foundations in Biology, Chapter 2.2 Biological Molecules. In: Goldby, P and Needham, C OCR AS/A level Biology A. 2nd ed. London: Pearson Education Limited. 56-60....