BIO - S1 - Biological Molecules

1.1 Biological Molecules

Evidence for Evolution --> All organisms share the same biochemistry. They all contain the same groups of carbon-based compounds that interact in similar ways - e.g they use the same nucleic acids (DNA and RNA) as genetic material and the same amino acids to built proteins. This provides indirect evidence for evolution.Monomers and Polymers Polymers are large, complex molecules composed of long chains of monomers joined together.

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Making Polymers

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Biological polymers are formed from their monomers by condensation reactions. A condensation reaction forms a chmical bond between monomers, releasing a molecule of water.

Breaking Down Polymers

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Biologycal polymers can be broken down into monomers by hydrolysis reactions A hydrolysis reaction breaks the chemical bond between monomers using a water molecule

1.2 Sugars

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All carbohydrates contain the elements C, H and O The monomers that carbohydrates are made from are monosaccharides - glucose, fructose and galactose Glucose is a hexose sugar - a monosaccharide with six carbon atoms in each molecules Types of glucose --> alpha glucose and beta glucose They are isomers --> molecules with the same molecular formula as each other, but with the atoms connected in a different way

Caption: : Monosaccharides

1.3 Disaccharides

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A disaccharide is formed when two monosaccharides join together They join together by a condensation reactions A glycosidic bond forms between the two monosaccharides as a molecules of water is released. Glucose joined to fructose forms sucrose Glucose joined to galactose forms lactose

Polysaccharides

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A polysaccharide is formed when more than two monosaccharides are joined together by condensation reactions Polysaccharides can be broken down into monosaccharides by hydrolysis reactions.

1.4 Functions of Polysaccharides

Starch Cells get energy from glucose Plants store excess glucose as starch   starch is a mixture of two polysaccharides of alpha-glucose Is insoluble in water and does not affect the water potential, so it does not cause water to enter by osmosis --> this makes it good for storage Amylose Long, unbranched chain of alpha-glucose The angles of glycosidic bonds give it a coiled structure This makes it compact, so a lot of it can be stored

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Caption: : Starch - Amylose

Starch - Amylopectin

Long, branched chain of alpha-glucose Its side branches allow the enzymes that break down the molecule to get at the glycosidic bonds easily This means that the glucose can be released quickly

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Glycogen

Animals store excess glucose as glycogen A polysaccharide of alpha-glucose Its strcture is very similar to amylopectin, except that it has loads more side branches coming off it Loads of branches means that stored glucose can be released quickly, which is important for energy release in animals It is a very compact molecule, so it is good for storage

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Cellulose

Cellulose is made of long, unbranched chains of beta-glucose.  When beta-glucose molecules bond, they form straight cellulose chains  The cellulose chains are linked together by hydrogen bonds to form strong fibres called microfibrils The strong fibres mean cellulose provides structural support for cells

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1.5 Lipids