Biological Molecules

• most carbohydrates are polymers
• most carbohydrates and proteins and nucleic acids are polymers
• polymers are large, complex molecules composed of long chains of monomers joined together
• monomers are small basic molecular units
• examples of monomers include monosaccharides, amino acids and nucleotides
• Carbohydrates are made from monosaccharides
• all carbohydrates contain the elements C,H and O
• The monomers that they're made from are monosaccharides: glucose, fructose, galactose.
• Glucose is a hexose sugar - a monosaccharide with six carbon atoms in each molecule.
• There are two types of glucose, alpha and beta - they are isomers which are molecules with the same molecular as each other but with the atoms connected in a different way
• Alpha glucose vs Beta glucose structure difference

  
• condensation reactions join monosaccharides together
• a condensation reaction is when two molecules join together with the formation of a new chemical bond and a water molecule is released when the bond is formed.
• a glycosidic bond forms between the two monosaccharides as a molecule of water is released
• a disaccharide is formed when two monosaccharides join together
• Two alpha glucose molecules are joined together via a glycosidic bond to form maltose
• sucrose is a disaccharide formed from a condensation reaction between a glucose molecule and a fructose molecule
• lactose is a disaccharide formed from a glucose molecule and a galactose molecule
• Hydrolysis reactions break polymers apart
• polymers can be broken down into monomers via hydrolysis
• a hydrolysis reaction breaks the chemical bond between monomers using a water molecule
• carbohydrates can be broken down into their constituent monosaccharides by hydrolysis reactions
• Benedicts test for sugars
• sugar is a general term for monosaccharides and disaccharides - all sugars can be classified as reducing or non-reducing
• reducing sugars test, add benedict's reagent which is blue to the sample and heat it in a water bath that's been brought to a boil. If the tests positive it will form a coloured precipitate which are solid particles suspended in the solution. Blue - green - yellow - orange - brick red. The higher the concentration of reducing sugars test, the further the colour change goes - you can use this to compare amount of reducing sugar in solutions or filter solution and weigh the precipitate
• non-reducing sugars test- if result of reducing sugars is negative, first break them down to monosaccharides, get a new sample of test solution, adding dilute hydrochloric acid and carefully heat it in a water bath that's been brought to a boil. Then neutralise it with sodium Hydrogen-carbonate. Then carry out Benedict's test as usual like for a reducing sugar. If test is positive it will form a colour precipitate and if its negative it will stay blue.
• A polysaccharide is formed when two or more monosaccharides join together by a condensation reaction
• Lots of alpha glucose molecules are joined together by glycosidic bonds to form amylose
• Starch is main energy storage material in plants
• Cells can get energy from glucose and plants store excess glucose as starch and when more energy is needed it breaks down starch to release the glucose
• Starch is a mixture of two polysaccharides of alpha glucose - amylose and amylopectin
• Amylose- a long, unbranched chain of alpha glucose. Angles of the glycosidic bonds give it a coiled structure like a cylinder. Making it compact, really Good for storage as you can fit more in a small space
• Amylopectin- a long, branched chain of alpha glucose. Its side branches allow the enzymes that break down the molecule to get at the glycosidic bonda easily. Thus glucose can be released quickly.
• Starch is insoluble in water and doesn't affect water potential so it doesn't cause water to enter cells by osmosis which would make them swell. Makes it good for storage.
• Use iodine test for starch
• Add iodine dissolved in potassium iodide solution to the test sample. If any starch is present, the sample changes from browny, orange to a dark blue, black colour.
• Glycogen is the main energy storage material in animals
• Animal cells get energy from glucose too but store excess glucose as glycogen which is a polysaccharide of alpha glucose.
• Its structure of glycogen is very similar to amylopectin, has loads more side branches coming off it. Loads of branches mean that stored glucose can be released quickly which is important for energy release in animals. It is also a very compact molecule so its good for storage.
• Cellulose is the major component of cell walls in plants