chap 3.1 biological molecules

• carbohydrates are organic molecules made up of the elements carbon, oxygen and hydrogen.
• sugars provide us with energy to do work or carry out activities
• single sugars are the basic unit of carbohydrates. It can pass through the cell membranes and be absorbed into the cells
• the common simple sugars are glucose and fructose
• glucose are found in plants and animals whereas fructose are commonly found in plants but rarely in animals
• double sugars are formed when two single sugars are joined together
• Maltose are can be produced from two glucose molecules
• sucrose is made up of one glucose molecule and one fructose molecule joined together
• a double sugar can be split into two single sugar molecules by suing an organic molecule called an enzyme
• when a solution of maltose is mixed with an enzyme maltase. glucose molecules are produced
• glucose, maltose and fructose are also known as reducing sugars.
• reducing sugars will produce a red precipitate when boiled with Benedict's solution.
• after mixing solution with Benedict's solution,

  solution remains blue, no reducing sugars

  solution turned blue to green, traces of reducing sugar

  solution turned from blue to yellow or orange, moderate amount of reducing sugars

  solution turned from blue to brick red precipitate formed, reducing sugar is present
• complex carbohydrates are made up of many similar molecules of single sugar joined together to form a large molecule
• plants store glucose in the form of starch. Animals cannot make or store starch in their bodies. We got most of our carbohydrates from plants in the form of starch
• In animals, main store of glucose is glycogen. glycogen is stored in animal liver and muscle tissue. it is used as energy source during exercise
• Glycogen and starch are suitable as storage materials in cells as:

  • they are insoluble in water, they don change water potential in cells.
  • they are large molecules that cannot diffuse through cell membrane, so they will not be lost from the cell
  • they can be easily be broken down to glucose when needed
  • their molecules have compact shape, so they occupy less space,
• breakdown of starch

  the enzyme amylase digests starch to form the sugar maltose. Amylase cannot break maltose down to glucose. Maltose is then hydrolysed to glucose by maltase.
• hydrolysed is the reaction of breaking down the bonds of starch and maltose to form glucose molecules with the help of enzymes.
• what are the functions of carbohydrates?

  carbohydrates are needed:

  • as a substrate for respiration to provide energy for cell activities
  • to form supporting structures, e.g cell walls in plants
  • to be converted into other organic compounds such as amino acids and fats
  • to synthesis lubricants, e.g mucus which consist of a carbohydrate and a protein; and to synthesis the nectar in some flowers.
• how to test for starch?

  iodine test, by adding a few drops of iodine solution to a food sample.

  if iodine solution turns from brown to blue-black, starch is present. if it remains brown there is no starch present.
• starch is found in storage organs of plants, it is a storage form of carbohydrates in plants. when needed, it can be digested to glucose to provide energy for cell activities, it is made up of several thousand glucose molecules joined together
• cellulose is present in the cell wall and it protects plant cells from bursting or damage and it prevents constipation. it is made up of many glucose molecules joined together.
• glycogen is stored in the liver and muscles of mammals, it is storage form of carbohydrates in mammal, when needed, it is digested to glucose to provide energy. it is made up of many glucose molecules joined together.