bio molecules

• general fomula of monosaccharides

  ( CH2O ) n
• what gives reducing property of sugar

  free carbonyl group (in linear form)
• aldose vs ketose


  aldose: C=O group at beginning

  ketose: C=O nested in C skeleton
• beta ring glucose

  OH same side as ch2oh
• soluble: many OH groups to form H bonds with H2O
• features of monosaccharides

  1. solubility
  2. reducing ppty
  3. stable building blocks for large molecules (exist stable rings to form glycosidic bond)
  4. diversity
• gen fomula disaccharides

  ( CH2O ) n-1
• maltose (glucose + glucose)

  sucrose (glucose + fructose)

  lactose (glucose + galactose)
• monomers of starch

  amylose: alpha 1-4 gb, helical coils (unbranched)

  amylopectin: alpha 1-4 gb within branch, alpha 1-6 gb at branch point, branched helical coils
• glycogen same structure as amylopectin but more extensive branched
• glycogen and starch both have no interchain H bonding
• starch and glycogen good storage mols as

  1. They are helical molecules. This arrangement allows many alpha-glucose monomers to be

  packed per unit volume, compact energy store

  2. They are branched with multiple branch ends which hydrolytic enzymes can work on, more

  glucose mols can be released rapidly at the same time

  and more ATP can be generated by respiration per unit

  time.

  3. Most OH grps, intra Hb within the helix, few OH

  grps avail for Hb with H2O, insoluble in water, does not affect cell wp

  4. large molecules, insol
• cellulose

  β(1-4) glycosidic bond links monomers

  in a molecule
• 1. Alternate glucose monomers are rotated 180 wrt eo, form a long, straight mol with free OH grps proj out

  in both directions, allow inter HB btwn cellulose mols parallel to eo ➔ forming microfibrils with high tensile strength

  2. large mol, insol

  3. meshwork of microfibrils that form cw have porous struct, cwis freely permeable to water

  and solutes, allows movement of subs across the cw. Are strong and rigid and distributes stress in all directions to prevent plant cells from bursting due to osmotic stress.

  4.Cellulases rarely found in nature. cannot be hydrolysed by most organisms
• The nucleotide sequence in DNA determines the amino acid sequence in the polypeptide which

  determines the types and locations of R groups which determine R group interactions which determine the specific 3D conformation and hence

  the function of the protein.
• Primary structure

  • Refers to the number and sequence of amino acids in a single polypeptide chain

  • The amino acids are linked by peptide bonds
• Secondary structure

  • Structure formed by regular coiling or folding of a single polypeptide chain.

  • Maintained by hydrogen bonds between C=O and N-H groups of the polypeptide backbone.
• Examples of secondary structures:

  alpha-helix

  Made up of a single polypeptide chain wound into a spiral structure. A hydrogen bond forms between C=O group of one amino acid residue and the N-H group of another amino acid residue 4 amino acids away along the

  backbone of a single polypeptide. There are 3.6 amino acid residues in every turn of the helix
• Examples of secondary structures:

  β-pleated sheet

  Two or more segments of a single polypeptide chain lying side by side, linked together by hydrogen bonds formed between the C=O group of an amino acid residue and a N-H group of another amino acid residue on an adjacent segment, along the backbone of a single polypeptide

  ▪ Chains may run parallel or anti-parallel

  ▪ Forms flat sheet which becomes folded
• Tertiary structure

  • Structure formed by further extensive folding and bending of a single polypeptide chain, giving rise to a spherical, globular protein with a specific 3D conformation

  • Maintained by 4 bonds, formed between R groups of amino acid residues within a polypeptide
• Refers to the association of two or more polypeptide chains into one functional

  • Maintained by all 4 types of interactions
• monomeric


  only 1 pptnunit: up to tertiary struct
• strength of interactions

  disulfide > ionic > H > HI
• Each subunit is arranged so that most of its hydrophilic amino acid side chains are on external surface while its

  hydrophobic amino acid side chains are buried in interior


  soluble in an aqueous environment, can take part in chemical reactions in red blood cells, enabling the transport of oxygen from the lungs to the tissues which -> allowing the survival of an organism.
• Haemoglobin has quaternary structure made up of 4

  polypeptide subunits: 2 alpha-globin subunits and 2 beta-globin subunits. Each subunit is made of globin + haem group. Each haem group consists of a porphyrin ring and an iron ion (Fe2+)


  Fe2+ of the haem group binds reversibly to O2, so 1 Hb

  molecule can carry up to 4 O2, at a time forming

  oxyhaemoglobin.
• The 4 subunits held together by H, I, HI (no disulfide) btwn R grps. the subunits can move with respect to each other


  binding of one oxygen molecule to one

  haemoglobin subunit induces a conformational change

  in remaining 3 subunits such that their affinity for

  oxygen increases. This is known as the cooperative

  binding of oxygen.
• tropocollagen consists of three helical

  polypeptide chains wound around

  each other like a rope. (no tertiary structure)
• Each chain contains a repeating sequence, usually a repeating tripeptide unit: glycine-X-Y, where X is usually proline, Y is usually hydroxyproline. 


  can form a tight, compact coil as almost every third amino acid in each polypeptide chain is a glycine, the smallest amino acid. allowinh the R group to fit into the restricted space in the center of the triple helix.

  Bulky and inflexible proline and

  hydroxyproline residues give rigidity to the molecule.
• Extensive hydrogen bonds form between amino acid

  residues of adjacent polypeptides


  Increases tensile strength & insoluble as interaction with water molecules are limited
• Adjacent tropocollagen molecules are arranged in a staggered manner


  minimizes points of weaknesses along fibrils
• Covalent cross-links between lysine residues at C

  and N ends of adjacent tropocollagen molecules results in the formation of fibrils. 


  Increases tensile strength
• Bundles of fibrils unite to form long collagen fibres. 


  Increases tensile strength
• fibrous vs globular

  f: structural role, long str fibres, less variety of aa used to construct sequence (repetitive regular sequences)

  g: metabolic role, spherical, length of ppt always identical btwn 2 samples of the same protein, or else may be non-functional
• denaturation

  3D shape of a protein may be changed by:

  (a) Heat (affect H, HI)

  (b)Acids/Alkalis (affect H, I)
• diff R grps, diff type & location of bonds formed