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