Biological Molecules

Card Set Information

Author:
Anonymous
ID:
158163
Filename:
Biological Molecules
Updated:
2012-06-11 06:21:00
Tags:
Proteins
Folders:

Description:
Biological Molecules - Proteins
Show Answers:

Home > Flashcards > Print Preview

The flashcards below were created by user Anonymous on FreezingBlue Flashcards. What would you like to do?


  1. PROTEINS
    • consist of 1 or more polypeptides folded into globular/fibrous form
    • A polypeptide is a linear polymer chain of amino acids bonded together by peptide bonds
  2. FORMATION OF PEPTIDE BOND
    • One amino acid loses a hydroxyl (-OH) group from (-COOH) group while the other loses a H atom from (-NH2) group
    • C atom of the first amino acid can thus bond with the N atom of the second, forming a peptide bond
  3. STRUCTURE OF PROTEINS

    PRIMARY STRUCTURE
    • Simple linear strand of amino acids held together by peptide bonds in the polypeptide
    • Based on the different arrangements of the 20 fundamental amino acids.
    • Amino acid sequence det the biological function, furthest levels of organisation and hence different properties of proteins.
    • Thus, a change in 1 amino acid may completely alter shape and properties of the polypeptide
  4. SECONDARY STRUCTURE
    1. alpha-helix


    • Polypeptide chain that is coiled up and held together by many intra-molecular H bonds
    • H atom of NH group of 1 amino acid H-bonded to O atom of C=O group of another amino acid 4 places ahead
    • H bond if the result of e- sharing in the NH group, leaving H atom slightly +ve and the C=O group, leaving O atom slightly -ve, so they attract each other.
  5. 2. beta-pleated sheet
    • 1 polypeptide chain consisting of parallel adj chains running in either opp or same direction
    • Chains joined by H bonds between H atom of NH group of 1 amino acid and O atom of C=O group of another amino acid in adj chain
    • Structure gives protein stability, high tensile strength & flexibility
  6. TERTIARY STRUCTURE
    • One polypeptide chain further coiled and extensively folded to form compact 3D globular structure.
    • Bonds: disulfide bridges, ionic bonds, H bonds, hydrophilic/hydrophobic interactions between R groups
    • Tertiary structure gives proteins their specific 3D configuration
  7. QUATERNARY STRUCTURE
    • Aggregation of 2 or more extensively coiled polypeptide chains
    • Bonds: disulfide linkages, ionic bonds, H bonds, hydrophobic/hydrophilic interactions between R groups
  8. TYPES OF BONDING & INTERACTIONS

    1. Peptide bonds

    • Strong covalent bonds formed between adj amino acids
    • Strongest bonds in polypeptide chains
  9. 2. Disulfide bonds
    • Strong covalent bond from from oxidation of sulphydryl (-SH) groups of 2 neighbouring cysteines' R groupds
    • Broken by reducing agents (e.g. urea)
  10. 3. Ionic bonds
    • Strong bonds formed between ionised/charged (-NH2) & (-COOH) groups.
    • R groups containing COO- attracted to R groups with NH3+
    • Formed at suitable pH but can be broken if pH changes
  11. 4. Hydrophobic/hydrophilic interactions
    Weak bonds formed when hydrophilic R groups project out and interact with water while hydrophobic R groups shielded inside protein interact with non-polar R groups of amino acids
  12. 5. H bonds
    • H atoms in NH groups or OH group form bond with O atoms in OH groups
    • H bonds formed between R groups in tertiary structure
    • Numerous; stabilise the structure
  13. GLOBULAR VS FIBROUS


  14. HAEMOGLOBIN


    - 2 alpha chains
    - 2 beta chains
    • Polypeptide chain first coiled into alpha-helices, then folded into spherical globular protein held by H bonds and ionic bonds
    • Hydrophobic side-chains point inwards to maintain 3D shape. Hydrophilic side-chains point outwards to maintain solubility
    • Each chain carries prosthetic haem group containing Fe2+ which binds to a molecule of oxygen.
    • Thus each haemoglobin molecule can bind 4 O2 molecules
  15. COLLAGEN



    - Fibrous protein with quaternary but no tertiary structure.
    - Found in skin, tendons, cartilage, bones, teeth etc.
    • Tropocollagen consists of 3 polypeptide chains wound around each other to give triple helix
    • Each polypeptide chain is a loosely wound left-handed helix that wind around 2 others and twist into a triple helix, linked by H bonds
    • Glycine at every 3rd amino acid allows close packing to form tight coil for compact structure
  16. TROPOCOLLAGEN

    • Covalent bonds formed between the lysines in adj chains. Cross-links hold tropocollagen molecules side by side, forming fibrils.
    • In fibrils, tropocollagens lie parallel with staggered ends, overlapping aids in forming strong fibres.
  17. FORMATION & ASSEMBLY OF COLLAGEN FIBRE

    • Synthesis of collagen polypeptide occus on the ribosome on RER
    • Collagen threaded into RER lumen where loose winding of polypeptide and hydroxylation of selected prolines & lysines occur
    • ER vesicles carrying polypeptide bud off ER, travel to GA where glycosylation of selected hydroxylysines occur
    • Further assembly of 3 collgen polypeptides forms tropocollagen. Glycine molecule at every 3rd AA allows close packing of collagen molecule, which buds off GA, forming secretory vesicle
    • Secretory vesicle moves towards and fuses with CSM
    • Secreted into extracellular matrix
    • Polypeptides cleaved to remove N & C terminals
    • Self assembly of tropocollagen into fibrils via cross-linking between lysine residues and overlaps of staggered ends
    • Aggregation of collagen fibrils form fibres.

What would you like to do?

Home > Flashcards > Print Preview