Fundamental Structures In Proteins Flashcards
What is the primary structure of a protein ?
Covalent bonds forming polypeptide chains ie order of amino acid residues in the polymer
What is the secondary structure of a protein?
Regular folded form stabilised by intra-chain hydrogen bonding eg: alpha helices, beta sheets and beta turns
Describe the structure of beta sheets and strands
Beta sheets are formed from hydrogen bonding between adjacent beta strands either in anti parallel or parallel arrangement
Beta strands are connected by loops or short turns either in anti parallel or parallel arrangement
Describe the structure of alpha helices
Right handed helix stabilised by hydrogen bonds which are 4 residues apart between residue 1 and 5.
3.6 residues per turn or 0.54nm per turn
What is the tertiary structure of a protein ?
Overall 3D structure ,stabilised by non-covalent bonds and forces and sometimes by infra-chain covalent bonds .
Formed from folding alpha helices ,beta sheets or beta turns into densely packed generally globular structures
What factors affect formation?
Interaction between outward facing side chains and many weak chemical bonds but may sometimes be stabilised by covalent bonds
What is the quaternary structure of a protein ?
Organisation of polypeptides into assemblies , stabilised by non-covalent bonds and foxes (as for tertiary )and sometimes by inter-chain covalent bonds
Formed from 2 or more polypeptide chains
The same bond stabilise the structure as for tertiary structure
What gives proteins their properties ?
The arrangement of the variable side chains give the proteins their properties and are important for structure and function .
The side chains in both the alpha helix and beta sheet protrude outwards from the structures
What is another name for cofactors?
Coenzyme
Examples of proteins that require cofactors
Heme of haemoglobin
Nicotinamide adenine diphosphate (NAD)
Flavin adenine dinicleotide(FAD) = redox cofactor
Other proteins might include : Zn2+,Mg2+,Ca2+ or other ions
What is the most common shape for water soluble proteins ?
Give examples of some that a least common
Globular
Some may assemble into filaments eg : actin or tubes eg tubulin or coiled coils eg cortexillin
Describe the organisation of residues in membrane proteins
Membrane spanning regions have externally located hydrophobic residues that interact with the membrane lipids which also may have hydrophilic channels
