Chapter 3 - Biological Molecules

• carbohydrates are organic molecules made up of the elements carbon, hydrogen and oxygen. The hydrogen and oxygen atoms are present in the ratio of 2:1.
• carbohydrates can be classified as simple sugars(glucose, fructose), double sugars(maltose, sucrose) or complex carbohydrates(starch, cellulose, glycogen)
• food rich in carbs : rice, bread, wheat
• found in plants and animals: glucose

  common in plants but rare in animals: fructose
• carbohydrates are needed: to provide energy for cellular activities, form supporting structures (e.g. cell wall), for conversion into other organic compounds (e.g. amino acids and fats), form nucleic acids, synthesize lubricants, synthesize nectar in flowers
• fats are organic molecules made up of carbon, hydrogen and oxygen
• fats contains less oxygen in proportion to hydrogen though the proportion of the elements in fats are not fixed
• a fat molecule is made up of glycerol and fatty acid chains
• sources of fats: butter, corn oil, olives, nuts
• The function of fats are: for source and storage of energy, to act as an insulation material to prevent heat loss, a solvent for fat soluble vitamins and some hormones, form the main part of cell membrane, help reduce water loss from skin surfaces
• proteins are organic molecules made up of carbon, hydrogen, oxygen and nitrogen
• protein molecules are made of amino acids. the building blocks of proteins are made of: and amino acid group, an acid group, and a side chain
• amino acids are the building blocks of proteins. peptide bonds link up amino acids to form a polypeptide. two or more polypeptides chains fold to form a 3D molecule called protein
• sources of proteins: meat, egg, milk, cheese,fish
• Proteins are needed for the synthesis of new protoplasm for growth and repair of worn-out cells, enzymes and some hormones and antibodies.
• cellulose, glycogen and starch are synthesized from glucose
• polypeptides and proteins are synthesized from amino acids
• lipids such as fats are synthesized from glycerol and fatty acids
• Formula of Glucose is C6H12O6 with a ratio of H:O being 2:1
• Formula of maltose is C12H24O11 with its H:O being 2:1
• Types of carbohydrates: single sugar, double sugar and complex sugar
• Sugars are sweet and dissolves in water. they lower the water potential of solutions.
• Examples of single sugars: glucose and fructose(fruit sugar)
• single sugar is the basic unit of carbohydrates
• All simple sugars have the same formula of C6H12O6 but differ in the arrangement of various atoms in the molecule, giving rise to different chemical and biological properties.
• Single sugars can pass through partially permeable membranes such as cell membrane
• Glucose is found in animals and plants but fructose (fruit sugar) is commonly found in plants only
• Double sugars are the result of the combinations of 2 single sugars
• Glucose + glucose -> maltose
• maltose (malt sugar) is found in germinating grains. It is also formed when starch is partially digested
• glucose + fructose -> sucrose
• Enzymes can split double sugars into single sugars. For example, Enzyme maltase splits maltose into glucose molecules. maltose -enzyme maltase-> glucose + glucose
• All double sugars have the same formula of C12H22O11 but differ in the arrangement of various atoms in the molecules, giving rise to different chemical and biological properties
• Sucrose is commonly found in sugarcane sterns, sweet fruits and certain storage roots like carrot. It is not found in mammals
• Complex carbohydrates, also known as polysaccharides, are formed by many similar molecules of single sugars joining together.
• Starch, cellulose and glycogen are examples of complex carbohydrates that are formed by joining many units of glucose molecules in different ways. As a result they have different chemical and biological properties
• Starch is a large molecule formed by many units of glucose molecules. It can be digested to glucose to provide energy when needed. It is not formed or stored by animals but found in storage organs of plants such as potato tubers
• starch is relatively insoluble and thus, ideal for storage
• Cellulose consists of numerous units of glucose molecules linked together but the bonds between glucose units are different from that in starch
• Cellulose in cell walls protect plant cells from bursting or damaging