protein structure and function Flashcards
describe the functions of proteins
They are functional products of the genome providing
→ CARRIER FUNCTIONS: trafficking oxygen
→METABOLIC FUNCTIONS: enzymes producing and utilising energy
→FORM PARTS OF THE CELLULAR MACHINERY: spliceosomes, ribosomes
→ MAKE UP STRUCTURAL SCAFFOLD: microtubules, nucleosomes
→SENSING MOLECULES: receptors and their ligands
How do we differentiate between L (levo) and D (dextro) forms of amino acids?
An L isomer reads Co-R-N CLOCKWISE, while a D isomer reads Co-R-N ANTICLOCKWISE.
why do all amino acids have D and L isomers and what is the exception?
All amino acids except for Glycine have the two isomers due to them being tetrahedral in arrangement and due to the α carbon being chiral.
in what form are amino acids incorporated into proteins and what is the other form used for?
→All amino acids incorporated into proteins by living organisms are in the L-form.
→D-amino acid residues comprise cell walls in bacteria and are often used in therapeutics.
what is a residue?
A residue is each repeating unit in a polypeptide chain.
describe the four levels of structure in a protein
→PRIMARY STRUCTURE: covalent bonds forming a polypeptide chain - ie. the order of amino acids residue
→SECONDARY STRUCTURE: regular folded form, eg. α helices, β sheets and β turns
→TERTIARY STRUCTURE: overall 3D structure, stabilised by non-covalent bonds and forces, and sometimes by intra-chain covalent bonds
→QUATERNARY STRUCTURE: organisation of polypeptide chains into assemblies, stabilised by non-covalent bonds and forces (like tertiary), and sometimes by intra-chain covalent bonds
describe secondary structure in detail including the arrangement of the variable side chains
→ β sheets and β turns:
→They are formed by H bonds between the β strands.
→ In sheets, the H bonds are between the strands.
→In turns, there are loops or turns linking the β sheets.
α helix:
→right-handed helix
→ stablilized by H bonds between two amino acids four residues apart.
The arrangement of the variable side chains is important for structure and function. The side chains of both the α and β (sheets) protrude outwards from the structures.
describe the tertiary structure
→The secondary structure is then folded into more densely packed, generally globular structures.
→The formation of these structures depends on weak chemical bonds between the side chains.
describe quaternary structure
→2 or more folded polypeptides may be combined to form a mature protein.
→The same bonds used in the tertiary structure are used to hold the subunits together.
what are examples of two co-factors that proteins might need to work?
→FAD and NAD
→ Mg2+ and Zn2+
→haem in haemoglobin
Describe water-soluble proteins
→Water-soluble proteins are often globular in shape.
→Some water-soluble proteins may arrange into: - filaments (actin) - tubes (tubulin) - coiled coils (cortexillin)
→The hydrophilic residues are mostly on the external surface while the hydrophobic residues are mostly buried inside.
→The membrane spanning region will have externally located hydrophobic residues that interact with membrane lipids.