3 - Biological Molecules

• The nutrients in food:

  • provide energy (ATP)
  • supply raw materials to make new cells
  • help us stay healthy (fibre, vitamins, minerals)
• The 4 main types of nutrients are:

  • carbohydrates
  • fats
  • proteins
  • nucleic acids
• Water is an essential component of all body tissues.

  70% of our body weight is water

  • water is a solvent in which chemical reactions take place
  • it is essential for photosynthesis
  • it keeps cells turgid/firm
  • it helps in the transport of mineral salts in plants
  • it regulates body temperature
  • it helps to transport dissolved substances around the body
• organic compounds are carbon containing compounds that are found in living organisms

  these compounds contain carbon and hydrogen
• macromolecule are large molecules composed of covalently connected atoms
• all organic compounds are macromolecules.

  some macromolecules are polymers. polymers are macromolecules build from monomers
• carbohydrates are organic molecules made up of carbon, hydrogen and oxygen.
• [carbohydrates]

  • the hydrogen and oxygen atoms are present in the ration 2 to 1
  • the general formula for carbs is CnH2mOm
• Carbohydrates - simple sugars

  • readily soluble in water, therefore exerts osmotic pressure
  • sweet to taste

  Monosaccharides

  • glucose
  • fructose
  • galactose
  • ribose

  Disaccharides

  • maltose
  • sucrose
  • lactose
• Carbohydrates - complex carbohydrates

  • insoluble in water, therefore does not exert osmotic pressure
  • does not taste sweet

  Polysaccharides

  • starch
  • glycogen
  • cellulose
• monosaccharides: a single unit of sugar

  • ribose
  • fructose
  • glucose
  • galactose

  
  

  • glucose, fructose and galactose have the same chemical formula - C6H12O6
  • fructose and glucose are isomers as they both have the same chemical formula, but different structures
• disaccharides: 2 units of monosaccharides

  • sucrose (glucose fructose)
  • maltose (glucose glucose)
  • lactose (galactose glucose)
• DISACCHARIDES

  • disaccharides are produced through the condensation reaction between two monosaccharides
  • a disaccharide molecule can be broken down into its monosaccharide units by hydrolysis in the presence of an enzyme
• condensation reaction:

  a chemical reaction where two monosaccharides join together to form a larger molecule with the removal of one molecule of water

  • a glycosidic bond is formed, and one water molecule is produced as a by-product
• Hydrolysis:

  a reaction in which a water molecule is needed to break up a complex molecule into simple molecules
• reducing sugars include:

  • glucose (monosaccharide)
  • fructose (monosaccharide)
  • maltose (disaccharide)
• testing for reducing sugars: benedicts test

  1. add an equal amount of benedicts solution to the sample in a test tube
  2. shake the mixture
  3. heat the contents in a boiling water bath for 2-3 minutes

  • solution remained blue - no reducing sugar
  • solution turned green - traces of reducing sugar
  • solution turned yellow/orange - moderate amounts of reducing sugar
  • solution turned red - large amounts of reducing sugar
• a complex carbohydrate is made up of many molecule of monosaccharides joined together to form a large molecule.

  e.g.

  • starch
  • glycogen
  • cellulose
• starch has a structure of several thousand glucose molecules joined together. It is a storage form of carbohydrates in plants. it can be digested to glucose to provide energy for cell activities when needed. starch occurs in storage organs of plants, such as potato tubers
• cellulose has a structure of many glucose molecules joined together, but bonded differently from starch. the cellulose cell wall protects plant cells from damage/ bursting. cellulose cannot be digested in our intestines, but serves as a dietary fibre that prevents constipation. cellulose is present in cell walls of plants.
• glycogen has a structure of branched molecules of many glucose molecules. it is a storage form of carbohydrates in animals, and is stored in the liver and muscles of mammals.
• starch and glycogen are stores of glucose. they are suitable as storage materials because:

  • they are insoluble in water (they do not change the water potential/ solute concentration in the cells)
  • they are large molecules (they cannot diffuse through plasma membranes and be lost from the cell)
  • they can be easily hydrolysed to glucose when needed (e.g. in cellular/ tissue respiration)
  • their molecules have compact shapes (they occupy less space than all the individual glucose molecules that make up glycogen/ starch molecules)
• starch in the food we eat may be digested in our alimentary canal. when starch is digested, the bonds within the polysaccharide are broken and the glucose molecules are released. complex carbohydrates are also known as polysaccharides

  • they are composed of many monosaccharides linked together through condensation reaction
  • they may occur as long, straight, or branched chains
  • polysaccharides are polymers of monosaccharides
• • starch is broken down into maltose molecules by amylase
  • maltose molecules are broken down into glucose by maltose
• to test for starch, we can conduct the iodine test.

  • if starch is present, the iodine solution will turn blue-black
• carbohydrates are needed:

  • as a substrate for respiration, to provide energy for cell activities
  • to form supporting structures (e.g. cell wall)
  • for conversion into other organic compounds (e.g. amino acids/ fats)
  • to form nucleic acids (e.g. DNA)
  • to synthesise lubricants (e.g. mucus: carbohydrates + protein)
  • to synthesise nectar in flowers
• fats are a type of lipid.

  • lipids are organic molecules made of up carbon, hydrogen and oxygen
  • lipids contain much less oxygen in proportion to hydrogen (there are no fixed proportions)
  • lipids may contain small amounts of other elements such as fatty acids, steroids, phospholipids and triglycerides
• triglycerides are a major group of lipids that are commonly referred to as fats. fats occur as solids at room temperature, while oils occur as liquids at room temperature.

  • triglycerides are made up of 2 components, namely fatty acids and glycerol
  • triglycerides are macromolecules, but not polymers
• • fatty acids is an organic molecule that has a carboxyl group (COOH)
  • fatty acids may be saturated or unsaturated
  • saturated: fatty acid chain is straight
  • unsaturated: fatty acid chain has kinks where double bond occurs
• • glycerol is the alcohol that usually makes up triglycerides
  • glycerol has 3 carbon atoms, each bearing a hydroxyl group (-OH)
• • fats are a source and long term storage of energy. they are suitable for long-term storage as fats have a higher energy value compared to carbohydrates.
  • fats also acts as an insulating material that prevents excessive heat loss. (e.g. seals, polar bears)
  • fats are solvents for fat soluble vitamins and many other vital substances, such as hormones
  • fats are an essential part of the cell, forming the main part of cell membranes
• • fats serve as a way to reduce water loss from the skin surface
  • glands in the skin secrete an oily substance
  • this oily substance forms a thin layer over the skin surface, reducing the rate of evaporation of water
  • this oily substance also reduces the rate of heat loss from the skin
• to test for fats, the ethanol emulsion test can be conducted.

  1. add an equal amount of ethanol to the sample in a test tube
  2. shake the contents of the tube vigorously
  3. add an equal amount of water into the tube and shake the mixture

  • if fats are present, a cloudy white emulsion will form
• proteins are organic molecules made up of carbon, hydrogen, oxygen and nitrogen. (sometimes, sulfur)

  • protein molecules are made up of smaller basic units called amino acids (monomer)
  • amino acids are made up of:
  • an amino group (-NH2)
  • an acidic group (-COOH)
  • a side chain (R)
• • amino acids are the building blocks of proteins
  • peptide bonds link up amino acids to form a polypeptide
  • two or more polypeptide chains fold to form a 3D molecule, called protein
• proteins are used in the:

  • synthesis of new cytoplasm, for growth and repair of worn-out cells
  • synthesis of new enzymes and some hormones
  • formation of antibodies to combat diseases
• to test for proteins, the biuret test can be conducted.

  1. add an equal amount of biuret solution to the sample
  2. shake well and allow the mixture to stand for 5 minutes

  • a violet solution will be formed if proteins are present
• Carbohydrates - simple sugars

  • readily soluble in water, therefore exerts osmotic pressure
  • sweet to taste

  Monosaccharides

  • glucose
  • fructose
  • galactose
  • ribose

  Disaccharides

  • maltose
  • sucrose
  • lactose