1.1 and 1.2

• Carbohydrates are molecules which consist only of carbon, hydrogen and oxygen. they are long chains of sugar units called saccharides. There are three types of saccharides- monosaccharides, disaccharides and polysaccharides
• • Monosaccharides are single sugar monomers
  • Disaccharides are two monosaccharides
  • Polysaccharides of many monosaccharides
• Monosaccharides can join together to form disaccharides and polysaccharides by glycosidic bonds which are formed in condensation reactions
• Glucose is a monosaccharide containing 6 carbon atoms in each molecule and is the main substrate for respiration
• Glucose has two isomers, alpha and beta glucose
• The structure of alpha and beta glucose

  
• A monosaccharide is an organic monomer hat cannot be hydrolysed to a simpler sugar
• The 3 hexose monosaccharides are glucose, fructose and galactose
• The molecular formula for hexose monosaccharides is C6H12O6
• A pentose sugar is a monosaccharide with five carbon atoms. Ribose is a pentose sugar and a component of RNA. DNA contains an ismoer of ribose called deoxyribos, which lacks the OH group on the second carbon of the sugar ring.
• Relate the structure of glucose to its functions (alpha):

  • small and water soluble = easily transported in bloodstream
  • complementary shape to anti port for co = transport for absorption in gut
  • complementary shape to enzymes for glycolysis = respiratory substrate
• In a condensation reaction, a chemical bond forms between two molecules and a molecule of water is produced
• In a hydrolysis reaction a water molecule is used to break a chemical bond between two molecules
• List the disaccharides:

  • Maltose is a disaccharide formed by condensation of two glucose molecules
  • Sucrose is a disaccharide formed by condensation of glucose and fructose
  • Lactose is a disaccharide formed by condensation of glucose and galactose
• Polysaccharides are formed from many glucose units join to get together and include:

  • Glycogen and starch which are both formed by the condensation of alpha glucose
  • Cellulose formed by the condensation of beta glucose
• Glycogen is the main energy storage molecule in animals and is formed from many molecules of alpha glucose join together by 1,4 and 1,6 glycosidic bond. It has a large number of sidebranches meaning that the molecule can be hydrolysed an energy can be released quickly. It’s also a relatively large but compact molecule therefore maximising the amount of energy it can store.
• Starch stores energy in plants and it is a mixture of two polysaccharides called amylose and amylopectin:

  • Amylose is unbranched chain of glucose molecules joined by 1,4 glycosidic bond. As a result, amylose is coiled and thus it is a very compact molecule meaning it can store a lot of energy
  • Amylopectin is made up of glucose molecules joined by 1,4 and 1,6 glycosidic bonds, making it a branched molecule. Due to the presence of many side branches it is rapidly digested by enzymes, therefore, energy is released quickly
• The functions of starch are:

  • insoluble = no osmotic effect on cells
  • large = does not diffuse out of cell
• The structure of cellulose is a polymer of beta glucose which gives rigidity to plant cell walls, which prevents bursting under turgor pressure and therefore holds stem up
• Functions of cellulose:

  • H-bond crosslinks between parallel strands form microfibrils and microfibres which are strong threads made of long cellulose chains joined together by hydrogen bonds = provide structural support in plant cells (high tensile strength)
• Lipids are biological molecules which are only soluble in organic solvents such as alcohols
• There are two types of lipids:

  • saturated lipids such a state is found in animal fats- saturated lipids only contain carbon-carbon single bonds
  • unsaturated lipids which can be found in plants- unsaturated lipids contain carbon-carbon double bonds and melt at lower temperatures than saturated fats
• Intermolecular forces are weaker in unsaturated lipids and therefore they have a lower melting point. As a result, saturated lipids are solid at room temperature and unsaturated lipids are liquid at room temperature. Saturated lipids are more compact as the molecules can pack closer together because there are no kinks in the carbon chain.
• Properties of lipids:

  • lipids are waterproof because the fatty tail is hydrophobic.
  • very compact and better gram-for-gram energy release than in carbohydrates or proteins because more C-O bonds are hydrolysed.
  • lipids are no—polar and insoluble in water therefore they are good for storage, they don’t interfere with the water-based reactions in the cytoplasm.
  • lipids conduct heat slowly therefore they provide a thermal insulation
• Triglycerides are lipids made of one molecule of glycerol and three fatty acids joined by ester bonds formed in condensation reactions. Triglycerides are used as energy reserves in plant and animal cells.
• Relate the structure of triglycerides to their functions:

  • high energy:mass ratio = high calorific value from oxidation (energy storage)
  • insoluble hydrocarbon chain = no effect on water potential of cells and used for waterproofing
  • slow conductor of heat = thermal insulation
• The structure of phospholipids is a glycerol backbone with two hydrophobic fatty acid tails and a negatively charged polar phosphate head which is hydrophilic
• Phospholipids form the phospholipid bilayer in the cell membrane, with the phosphate heads pointing towards the aqueous environment and fatty acid tails pointing away
• What is the structure of alpha glucose?


  Alpha glucose is an isomer of glucose with has the hydroxy group (OH) on carbo-1 above the plane of the ring
• What is the structure of beta glucose?

  Beta is an isomer of glucose which has the hydroxy group (OH) on carbon-1 below the plane of the ring
• What does OH stand for?

  Hydroxy group
• What is cellulose? 


  A structural polysaccharid found in plants that composes the cell wall
• What is cellulose made up of?

  Beta glucose monomers joined by 1,4 glycosidic bonds
• What is a glycosidic bond?

  A type of covalent bond formed between two sugars during a condensation reaction in the form C-O-C
• When are glycosidic bonds formed?

  During a condensation reaction
• What is an ester bond?


  A type of bond formed in a condensation reaction which joins each of the fatty acid tails to the glycerol molecule in a triglyceride.