Biochemistry

• Polar


  A molecule is polar when it has an unequal distribution of charge. This unequal distribution creates full or partial negative and positive charges.
• Hydrophilic


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


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

  May also have distinct functions: Energy source, energy carrier (building blocks)
• Components of carbohydrates


  • Carbon
  • Hydrogen
  • Oxygen (water)
• Monosaccharides

  Simple sugars, the building blocks of carbohydrates
• Molecular formula of carbohydrates

  n x CH2O, where n = 3, 4, 5 or 6

  
• Functional groups of carbohydrates

  Carbonyl and Hydroxyl
• Properties of carbohydrates

  • 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 of monosaccharides

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

  
• Optical isomers

  Monosaccharides can occur as optical isomers or enantiomers (D- or L- isomers) - mirror image forms
• Most naturally occurring sugars are D- isomers
• α- and β- forms of glucose

  When glucose is in the ring structure, the hydroxyl attached to carbon 1 (aldehyde) has two possible positions (α- and β-), which interconvert rapidly in solution

  
• Complex carbohydrate formation

  Formed by glycosidic bond between monosaccharides. The α- or β- configuration is 'locked' when the bond is formed.

  
• Disaccharides

  Two monosaccharides linked by a glycosidic bond

  
• Polysaccharides

  Polymers of glucose acting as energy stores (starch- plants (amylose and amylopectin), glycogen- animals)

  
• Structure of glycogen


  • Glycogen has a similar chemical structure to amylopectin, but with more branches. Chains- α-1,4 glycosidic bonds, Branches- α-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, including triacylglycerols, glycerophospholipids, steroids and cholesterol
• Fatty acids


  The monomeric building blocks of triacylglycerols 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)

  
• 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) and form the cell membrane.
• Steroids and Cholesterol


  The steroid template (fused alkyl rings) is the basis for steroid hormones and the sterol lipid, cholesterol.
• Functions of 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 of RNA and DNA, consisting of a pentose sugar, nitrogenous base, and phosphate

  
• Pentose sugars

  Ribose in RNA and Deoxyribose in DNA

  
• Nitrogenous bases

  • A, C, G, T found in DNA
  • A, C, G, U found in RNA
• Formation of nucleic acids

  Nucleotides join together to form nucleic acids, joined by phosphodiester bonds. The base-pair sequence of DNA forms the genetic code.

  
• Nucleotides also have other functions: ATP, which carries chemical energy in its phosphoanhydride bonds
• Proteins


  • Carry out the mechanical, structural and transport functions of the body, and play a crucial role as enzymes (biological catalysts). Different proteins display a wide variety of shapes and sizes, determined by the information in the DNA sequence of the gene.
• Protein folding

  Proteins fold up spontaneously from linear chains of amino acids
• Amino acids

  Building blocks of proteins, 20 amino acids, water soluble and electrically charged at physiological pH, each differing in the properties of its side group (R group)

  
• Peptide bond formation

  In polypeptides, amino acids are linked by peptide bonds. Side chains (R groups) are not involving in peptide bonding. Interactions of side chains determine how proteins fold

  
• pH is the measure of free hydrogen ions (H+) in a solution, ranging from 0-14 and determining a solution's acidity or alkalinity. The higher the H+, the lower the pH (more acidic).
• Acid

  A H+ ion (proton) donor
• Base


  A H+ ion (proton) acceptor
• Strong acids and bases

  • Strong acids completely dissociate in a solution, strong bases readily accept H+ from an acid
• Weak acids and bases

  • Weak acids only dissociate partially and are a poor source of hydrogen ions, weak bases are poor H+ acceptors and only partially dissociate