biological molecules

• several monomers join together to form a polymer
• monomers in biological molecules form polymers by condensation reactions and break by hydrolysis.
• glucose, fructose and galactose are monosaccharides
• sucrose maltose and lactose are disaccharides
• carbohydrates (starch) are polysaccharides
• alpha glucose - on carbon 1 the hydroxy group is on the bottom and the hydrogen is on the top
• beta glucose - on carbon 1 the hydroxy group is on the top and the hydrogen is on the bottom
• both isomers of glucose - on carbon 3, the hydroxy group is on the top and the hydrogen is on the bottom
• a glycosidic bond forms when two monosaccharide units join together by condensation reaction to form a disaccharide
• chitin is found in insect exoskeletons and fungi cell walls
• two alpha glucose molecules are joined by a glycosidic bond to form a maltose molecule
• alpha glucose + galactose -> lactose
• alpha glucose + fructose -> sucrose
• glucose, fructose, maltose and galactose are reducing sugars
• Benedicts test is used to identify the presence of reducing sugar
• when benedict’s reagent is reduced it forms an orange precipitate
• amylose is a long chain of alpha glucose molecules linked by 1,4- glycosidic bonds
• amylopectin is a polymer of alpha glucose joined by 1,4-glycosidic bonds but it is branched due to 1,6-glycosidic bonds
• starch consists of amylose and amylopectin
• sucrose is a non-reducing sugar - no orange precipitate formed with Benedict’s solution, but does form orange precipitate after sucrose is boiled with dilute acid as sucrose is hydrolysed into alpha glucose and fructose
• starch is a storage molecule, and is insoluble, meaning it will not affect osmotic potential of the cell
• glycogen is made in the smooth endoplasmic reticulum and is found in lover and muscle cells as a storage molecule
• glycogen is a storage molecule in animals, bacteria and fungi
• glycogen has more branches and shorter chains, more compact than starch
• cellulose consists of beta glucose. it forms only straight very long chains which allows it to pack together better. every other beta glucose is upside down. each chain in cellulose is held to other chains by hydrogen bonds to make microfibrils
• cellulose cannot be digested by humans or any other animal as they do not have the enzyme to digest it
• chitin is similar to cellulose but with N-acetylglucosamine instead of glucose. chitin makes exoskeletons of insects and crustaceans
• lipids are non-polar substances so they aren’t soluble in water
• lipids are soluble in organic solvents such as alcohol and acetone
• triglycerides consist of glycerol + three fatty acid tails (hydrocarbon tail)
• when oxidised lipids provide twice the energy as the same mass of carbohydrate
• saturated fats lead to fatty deposits in the arteries
• roles of lipids are: biosynthetic precursors (steroid hormone from cholesterol), protection (kidneys are protected by fat), insulation (in adipose tissue)
• emulsion test for lipids

  crush sample and mix thoroughly with ethanol

  pour resulting solution into a test tube of distilled water

  white emulsion indicated presence of lipid
• phospholipids have a glycerol, two fatty acid tails and a phosphate head
• the phosphate head is hydrophilic as it is attracted to water
• the fatty acid tails are hydrophobic as they are repelled by water
• metabolism is the sum of all the chemical reactions in a cell or organism
• benedict’s test

  add 2 cm^3 of food sample to be tested to a test tube

  grind sample if needed

  add equal volume benedict’s reagent

  heat gently in boiling water bath for 5 minutes
• polysaccharides are insoluble as they are very large molecules