Molecules of life

• Polar

  A molecule is polar when it has an unequal distribution of charge
• Hydrophilic


  Polar molecules are hydrophilic, attract water (water loving)
• Hydrophobic


  Non-polar molecules are hydrophobic, repel water (water hating)
• Monomers


  May have distinct functions: Energy source, energy carrier (building blocks)
• Carbohydrates


  • Consists of carbon, hydrogen and oxygen (water)
  • Monosaccharides (simple sugars) are the building blocks
  • Molecular formula: n x CH2O, N + 3, 4, 5 or 6
  • Functional group: Carbonyl and Hydroxyl
  • Properties: Hydrophilic, polar, water soluble

  
• Aldoses and Ketoses

  Monosaccharides are classed as aldoses or ketoses depending on whether they contain an aldehyde or a ketone group

  
• Ring formation

  In aqueous solution, 5 and 6 carbon sugars spontaneously form ring structures, the carbonyl (aldehyde or keto) group reacts with a hydroxyl group

  
• Isomers

  • Monosaccharides can occur as optical isomers or enantiomers (D- or L- isomers) - mirror image forms
  • Most naturally occurring sugars are D- isomers
  • D-glucose, but not L-glucose can be metabolized by cells in glycolysis pathway
  • When glucose is in the ring structure, the hydroxyl attached to carbon 1 (aldehyde) has two possible positions (a- and b-)
  • The a- and b- forms interconvert rapidly in solution

  
• Complex carbohydrates


  • Formed by glycosidic bond between monosaccharides
  • The a- or b- configuration is 'locked' when the bond is formed

  
• Complex carbohydrates

  • Disaccharides: Two monosaccharides linked by a glycosidic bond
  • Polysaccharides: Polymers of glucose act as energy stores (starch- plants (amylose and amylopectin), glycogen- animals)
  • Glycogen has a similar chemical structure to amylopectin, but with more branches
  • Chains- a-1,4 glycosidic bonds
  • Branches- a-1.6 glycosidic bonds

  
• • Sugars can be modifying and linked to lipids or proteins
  • Complex oligosaccharides (a few saccharides) can form recognition molecules on cell surfaces e.g., blood group determinants
• Lipids

  • Molecules in cells that are water-insoluble (hydrophobic) but soluble in organic solvents
  • Triacylglycerols
  • Glycerophospholipids
  • Steroids and Cholesterol
• Fatty acids

  • The monomeric building blocks of triacylglycerol's and glycerophospholipids
  • The length and structural formula (saturated/ unsaturated) of the fatty acid carbon chain determines its physical properties (shape, melting point- longer + saturated = higher melting point)
  • Saturated: No double carbon bonds
  • Unsaturated: Double carbon bond

  
• Triacylglycerols

  • Formed by ester linkages between fatty acids and glycerol
  • Important energy storage molecules
  • Hydrophobic (insoluble) so stored as fat droplets within cells

  
• Glycerophospholipids

  • Also based on glycerol, but one fatty acid is replaced by a phosphate group
  • The phosphate group is also linked to a hydrophilic 'head group'
  • They are amphipathic (hydrophilic head and hydrophobic tails)
  • This causes them to aggregate in an aqueous environment
  • The phospholipids bilayer forms the cell membrane

  
• Steroids and Cholesterol

  The steroid template (fused alkyl rings) is the basis for steroid hormones and the sterol lipid, cholesterol
• Cholesterol

  • Necessary component of animal cell membrane
  • Rigid structure inserts between glycerophospholipids – modulates membrane fluidity at both ends of the temperature scale
• Nucleic Acids

  Ribonucleic acid and deoxyribonucleic acid (RNA / DNA), act as information molecules for the cell

  
• Nucleotides

  • Building blocks or RNA + DNA
  • Consists of: Pentose sugar, nitrogenous base, phosphate

  
• Pentose sugar

  Can be ribose in RNA and Deoxyribose in DNA

  
• Nitrogenous bases

  • A, C, G, T found in DNA
  • A, C, G, U found in RNA
• DNA/ RNA

  1. Nucleotides join together to form nucleic acids

  2. Joined by phosphodiester bonds

  3. The base-pair sequence of DNA forms the genetic code
• Nucleotides also have other functions: ATP, which carries chemical energy in it's phosphoanhydride bonds
• Proteins

  • Carry out the mechanical, structural and transport functions of the body
  • They also play a crucial role as enzymes (biological catalysts)
  • Different proteins display a wide variety of shapes and sizes
  • Each protein structure is unique and is determined by the information in the DNA sequence of the gene
  • Proteins fold up spontaneously from linear chains of amino acids
• Amino acids

  • Building blocks of proteins
  • 20 amino acids
  • Amino acids are water soluble and electrically charged at physiological pH
  • Each amino acid differs in the properties of its side group (R group)
  • Amino acids can be grouped according to the characteristic of their side chains

  
• Peptide bond formation


  1. In polypeptides, amino acids are linked by peptide bonds

  2. Side chains (R groups) are not involving in peptide bonding

  3. Interactions of side chains determine how proteins fold