Biological molecules

• How do hydrogen bonds form between water molecules?


  water is polar

  • O more electronegative than H, so attracts electron density in covalent bond more strongly
  • there are intermolecular forces of attraction between a lone pair on O of one molecule and H on an adjacent
• state 7 biologically important properties of water?

  • reaches maximum density at 4 degrees
  • high surface tension
  • metabolite (solvent for chemical reactions in the body)
  • high specific heat capacity
  • high latent heat of vaporisation
  • cohesion between molecules
  • incompressible (means it can not be squashes to make space for air)
• why is the incompressible nature of water important for organisms?

  • provides turgidity to plant cells
  • provides hydrostatic skeleton for some small animals e.g earthworms
• Explain why ice floats on water. Why is this important for organisms?

  • Ice is less dense than water because H-bonds hold molecules in fixed positions further away from each other.
  • insulates water in arctic climates so aquatic organisms can survive, water acts as a habitat
• why is the high surface tension of water important for organisms?

  • slows water loss due to transpiration in plants
  • water rises unusually high in narrow tubes, lowering demand on root pressure
  • some insects can skim across the surface of water
• Why is water an important solvent for organisms?


  Polar universal solvent dissolves and transport charged particles involved in intra and extracellular reactions e.g PO4 3- for DNA synthesis
• Why are the high specific heat capacity and latent of vaporisation of water important for organism?


  Acts as a temperature buffer which enables endotherms to resist fluctuations to maintain optimum enzyme activity
• define monomer 


  smaller units that join together to form larger molecules

  • monosaccharides (glucose, fructose, galactose, ribose)
  • amino acids
  • nucleotides
• define polymer 


  molecules formed when many monomers join together

  • polysaccharides
  • proteins
  • DNA/RNA
• What happens in condensation reactions?


  chemical bond forms between 2 molecules and a molecules of water is produced
• what happens in hydrolysis reactions?

  a water molecules is used to break a chemical bond between 2 molecules e.g peptide bonds in proteins
• name the elements found in carbohydrates and lipids?

  C,H,O
• name the elements found in proteins?

  C, H, O, N, S
• name the elements found in nucleic acids?

  C, H, O, N, P
• Describe the properties of alpha glucose?

  • small & water soluble = easily transported in bloodstream
  • complementary shape to antiport for co-transport for absorption in gut
  • complementary chape to enzymes for glycolysis = respiratory substrate
• describe a beta isomer 


  the OH is at the top instead of the bottom on carbon 6

  
• describe a alpha glucose 


  the OH is on the bottom instead of the top

  
• describe the properties of alpha glucose?

  • small and water soluble = easily transported in bloodstream
  • complementary shape to antiport for co-transport for absorption in gut
  • complementary shape to enzyme for glycolysis = respiratory substrate
• describe the structure of a ribose 


  pentose monosaccharide

  ring structure

  
• what type of bond forms when monosaccharides react?


  (1,4 or 1,6) glycosidic bond

  • 2 monomers = 1 chemical bond = disaccharide
  • multiple monomers = many chemical bonds = polysaccharide
• name 3 disaccharides ?


  maltose = glucose + glucose

  sucrose = glucose + fructose

  lactose = glucose + galactose

  all have molecular formula C12H22O11
• describe the structure and functions of starch

  storage polymer of alpha glucose in plant cell

  • insoluble = no osmotic effect on cells
  • large = does not diffuse out of cells
• describe the structure and functions of amylose

  • 1-4 glycosidic bonds
  • helix with intermolecular H-bonds = compact
• Describe the structure and functions of amylopectin?

  • 1-4 & 1-6 glycosidic bonds
  • branched = many terminal ends for hydrolysis into glucose
• Describe the structure and functions of glycogen?


  main storage polymer of alpha glucose in animal cells

  • 1-4 & 1-6 glycosidic bonds
  • branched = many terminal ends for hydrolysis
  • insoluble = no osmotic effect and does not diffuse out of cells
  • compact
• describe the structure and functions of cellulose?


  polymer of beta glucose gives rigidity to plant cell walls

  • 1-4 glycosidic bonds
  • straight chain, unbranched molecules
  • alternate glucose molecules are rotated 180 degrees
  • H-Bonds crosslinks between parallel strands from microfibrils = high tensile strength
• How do triglycerides form?

  condensation reaction between 1 molecule of glycerol & 3 fatty acids which forms ester bonds

  
• features of a saturated fatty acid?

  • contains only single bonds
  • straight chain molecules have many contact points
  • higher melting point = solid at room temperature
  • found in animal fats
• features of unsaturated fatty acids?

  • contains C=C double bonds
  • kinked molecules have fewer contact points
  • lower melting point = liquid at room temperature
  • found in plant oils
• how does the structure of triglyceride relate to their function?

  • high energy: mass ratio = high energy storage
  • insoluble hydrocarbon chain = no effect on water potential of cells and used for waterproofing
  • slow conductor of heat = thermal insulation e.g. adipose tissue
  • less dense then water = buoyancy of aquatic animals
  • metabolic water source
• Describe the structure and function of phospholipids?


  Structure: Phospholipids consist of a hydrophilic head (containing a phosphate group) and two hydrophobic tails (composed of fatty acids). They have a polar and nonpolar region. Function: Phospholipids are a major component of cell membranes. They form a lipid bilayer, with the hydrophilic heads facing outward and the hydrophobic tails facing inward, providing a barrier that controls the movement of substances in and out of the cell.
• are phospholipids and triglycerides polymers?


  No

  they are not made from small repeating unit. They are macromolecules
• Describe the structure and function of cholesterol?


  steroid structure of 4 hydrocarbon rings

  • hydrocarbon tail on one side, hydroxyl group on the other side
  • adds stability to cell surface phospholipid bilayer by connecting molecules and reducing fluidity
  • reduces fluidity of membrane at high temp + increase fluidity at low temp
• what is the general structure of an amino acid?


  Amino group, carboxyl group, side chain

  -COOH carboxyl/carboxylic acid group

  -R variable side group consists of carbon chain

  -NH2 amine/amino group

  
• how do polypeptides form?


  Condensation reactions between amino acids form pepride bonds (-CONH-)

  
• Define primary structure 


  a sequence of amino acids that create a polypeptide chain
• define secondary structure 


  Alpha sequence

  • spiral shape
  • hydrogen bonds parallel to the helix
• define tertiary structure of a protein?

  • they are further folded
  • disulphide bridges - strong covalent S-S bonds between molecules of the amino acid cysteine
  • ionic bonds - relatively strong bonds between charged R groups (pH changes = the bonds breaking)
  • hydrogen bonds - numerous and easily broken
  • hydrophobic and hydrophilic interactions
• define quaternary structure of a protein?

  • functional proteins may consist of more than one polypeptide
  • precise 3D structure held together by the same types of bond as tertiary structure
  • may involve addition of prosthetic groups e.g. metal ions or phosphate groups
• describe the structure and function of globular proteins?

  • spherical & compact
  • hydrophilic R groups face outwards & hydrophobic R groups face inwards = usually water soluble
  • involved in metabolic processes e.g enzymes such as amylase, insulin
  • relatively unstable structure
  • metabolic functions