Topic 2

• How does hydrogen bonding occur between water molecules?

  Water is polar because oxygen is more electronegative than hydrogen so there are partial positive and negative parts, positive and negative parts of different molecules attract each other, forming hydrogen bonds
• Properties of water


  High boiling point, less dense when solid than when liquid, cohesive, adhesive, high surface tension
• Cohesion


  The attraction of molecules to each other.
• Roles of water


  Solvent, transport medium, coolant, stable habitat
• Which properties of water make it a good solvent?

  It is polar so it can dissolve polar substances, such as most solutes
• Which properties of water make it a good transport medium?

  Cohesion, adhesion
• What allows water to do capillary action?


  Adhesion, cohesion
• Capillary action


  Water can move up a tube against the force of gravity
• What makes water a good habitat to live in?

  Doesn't change temperature easily, less dense as a solid so will float when it freezes
• What makes water a good coolant?

  It takes a lot of energy to overcome the hydrogen bonds
• Monomer


  Molecule that consists of a single unit and can join with others to form a polymer
• Polymer


  Large molecules composed of many similar smaller molecules called monomers
• Chemical elements in carbohydrates

  Carbon, hydrogen, oxygen
• Chemical elements in lipids

  Carbon, hydrogen, oxygen
• Chemical elements in proteins

  Carbon, hydrogen, oxygen, nitrogen, sulfur
• Chemical elements in nucleic acids

  Carbon, hydrogen, oxygen, nitrogen, phosphorus
• What is glucose an example of?

  Hexose monosaccharide
• Example of a hexose monosaccharide

  Glucose
• What is ribose an example of?

  Pentose monosaccharide
• Example of a pentose monosaccharide

  Ribose
• Difference between alpha and beta glucose

  In alpha glucose, the OH group on carbon 1 is down. In beta glucose, it is up.
• Difference between a hexose and pentose monosaccharide

  A hexose sugar has 6 carbons. A pentose sugar has 5 carbons.
• How is a disaccharide synthesised?

  OH group removed from one monosaccharide, H removed from the other in a condensation reaction, glycosidic bond forms between carbons 1 and 4
• How are disaccharides broken down?

  Hydrolysis reactions occur, catalysed by enzymes, which adds a water molecule which breaks the glycosidic bond
• Monosaccharides in sucrose


  Glucose, fructose
• What do glucose and fructose make?

  Sucrose
• Monosaccharides in lactose


  Galactose, glucose
• What do galactose and glucose make?

  Lactose
• Monosaccharides in maltose


  Two glucoses
• What do two glucoses make?

  Maltose
• Structure of starch


  Two polysaccharides in amylose and amylopectin,
• Structure of amylose


  Made of alpha glucose molecules joined together by 1-4 glycosidic bonds, the angle of the bond makes it twist to form a helix, stabilised by hydrogen bonding
• Structure of amylopectin


  Made of alpha glucose molecules joined together by 1-4 and 1-6 glycosidic bonds, 1-6 bonds give a branched structure, 1-6 bonds occur every 25 glucose subunits
• Structure of glycogen


  More branched than amylopectin, made of alpha glucose molecules
• Structure of cellulose


  Made of beta glucose molecules, unable to bond like alpha glucose molecules because the OH groups are too far from each other, alternate beta glucose molecules rotate by 180 degrees, straight chain molecule forms, cellulose molecules make hydrogen bonds thus forming microfibrils, the microfibrils join together to form macrofibrils, macrofibrils combine together to form fibres
• Properties of glucose


  Polar, soluble
• Why it is important that glucose is soluble

  Glucose is dissolved in the cytosol of the cell
• Function of glucose


  To be used in aerobic respiration to produce ATP which can provide energy.
• Why is glucose soluble?


  Hydrogen bonds can form between hydroxyl groups and water molecules.
• Properties of amylose


  Compact, insoluble