chapter 3

• peptide bond


  covalent bond between 2 adjacent amino acids in a chain of amino acids
• hydrolysis to break down peptide bonds

  by adding water, a peptide bond it broken and is the reverse of the dehydration synthesis that forms peptide bonds
• carbohydrates


  carbon, hydrogen, oxygen, in the ratio Cx(H2O)x
• lipids


  carbon, hydrogen, oxygen
• proteins


  carbon, hydrogen, oxygen, nitrogen, sulfur
• nucleic acids


  carbon, hydrogen, oxygen, nitrogen, phosphorous
• polymers


  long chain molecules made up by the linking of multiple individual monomers in a repeat pattern
• monomers of carbohydrates


  sugars (saccharides)
• monomers of proteins


  amino acids
• polar molecules


  have regions of negativity and regions of positivity, such as O-H, oxygen has a negative dipole and hydrogen has a positive dipole
• polar molecules such as water interact with each other as the positive and negative regions attract each other to form hydrogen bonds, which are weak interactions which break and reform during constantly moving water molecules
• characteristics of water - high boiling point


  small molecule, but requires lots of energy to increase the because of the hydrogen bonds
• characteristics of water - ice


  ice is less dense than water because as the water is frozen, the hydrogen bonds fix the position of the polar molecules slightly further apart than in liquid state, which produces a giant and open structure with every oxygen with a tetrahedral arrangement, so ice floats
• characteristics of water - cohesion


  moves as one mass because the molecules are attracted to each other (how water travels up a straw), more cohesive to each other than they are to air, so water has a skin of surface tension
• characteristics of water - adhesion

  water molecules are attracted to other materials, so when you wash your hands the water doesn't run straight off
• water can act as a solvent because solutes in an organism can be dissolved in it, and it also acts as a medium for chemical reactions and helps transport dissolved compounds in and out of cells
• capillary action


  process by which water can rise up a narrow tube against the force of gravity
• water acts as a coolant to help buffer temperature changes because of large amounts of energy required to overcome hydrogen bonding
• water is stable and does not change temperature or become a gas easily, so it is a good habitat
• monosaccharide


  single sugar unit
• glucose


  C6H12O6, monosaccharide composed of 6 carbons so it is a hexose monosaccharide

  
• glucose molecules are polar and soluble in water because of the hydrogen bonds that form between the hydroxyl groups and water molecules, solubility is important because glucose is dissolved in cytosol of a cell
• alpha glucose


  hydroxyl (OH) group is below the carbon
• beta glucose


  hydroxyl (OH) group is above the carbon
• condensation reactions in glucose

  when 2 alpha glucose are side by side, the 2 OH groups interact, 2 hydrogen atoms and an oxygen atom is removed to form a water molecule, a glycosidic bond forms between carbons 1 and 4 on the glucose molecule
• glycosidic bond


  covalent bond between 2 monosaccharides
• disaccharide


  molecule made up of 2 monosaccharides
• fructose and galactose are hexose monosaccharides, fructose naturally occurs in fruits in combination with glucose to form sucrose
• galactose and glucose form the disaccharise lactose, which is found in milk and milk products
• fructose is sweeter than glucose and glucose is sweeter than galactose
• pentose monosaccharides


  sugars that contain 5 carbon atoms, 2 pentose sugars are important for biological processes in the body:

  1. ribose - sugar present in RNA nucleotides
  2. deoxyribose - sugar present in DNA nucleotides
• starch


  polysaccharide formed from alpha glucose molecules either joined to form amylose or amylopectin
• glucose made by photosynthesis in plant cells is stored as starch, it is a chemical energy store
• one of the polysaccharides in starch is called amylose, which is formed by alpha glucose molecules joined together only by 1-4 glycosidic bonds
• amylose 1-4 glycosidic bond angle means that the long chain twists to form a helix which is stabilised by hydrogen bonding within the molecule, making the polysaccharide more compact and much less soluble than glucose
• amylopectin


  made by 1-4 glycosidic bonds between alpha glucose molecules, but also has glycosidic bonds that are formed by condensation reactions between carbon 1 sand carbon 6, so it has a branched structure where the 1-6 bonds occur every 25 sub units
• equivalent to starch in plants is glycogen in animals, forms more branches than amylopectin which means it is more compact and less space is needed for it to be stored.
• branches on glycogen mean there are lots of free ends where glucose molecules can be added or removed, which speeds up the process of storing or releasing glucose molecules
• key properties of amylopectin and glycogen

  insoluble, branched, and compact, so they are suited for the storage roles
• to release glucose for respiration, starch or glycogen undergo hydrolysis reactions, which require the addition of water, and these reactions are catalysed by enzymes, reverse of condensation that form the glycosidic bonds