1.2- Proteins (after prelim)
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4 structures of protein
primary, secondary, tertiary, quaternary
amino acids link by ….. bonds to form …..
peptide, polypeptides
Primary structure of protein
the sequence in which the amino acids are synthesised into the polypeptide
Due to the make up of AAs, the primary sequence has an ……… at one end and a ……. at the other
N-terminus, C-terminus (amino & carboxyl)
Secondary structure of protein
Hydrogen bonding along the backbone of the protein strand results in regions of secondary structure
3 types of secondary structure
alpha helix beta sheets turns
Alpha helix (secondary structure)
formed by twisting the polypeptide chain into a spiral and then stabilising with hydrogen bonding The R groups stick out
Beta sheet (secondary structure)
have parts of the chain running alongside each other, forming a sheet The R groups sit above and below the sheet
Anti-parallel beta sheets
the chains run in opposite directions from each other
Tertiary structure
the final folded shape of the polypeptide is stabilised by many different interactions between the R groups of AAs
Possible R group interactions for tertiary structure
hydrophobic interactions ionic bonds LDFs hydrogen bonds disulphide bridges
What do turns (secondary structure)
They reverse the direction of the polypeptide chain and the chain folds back on itself.
hydrophobic interactions (tertiary)
hydrophobic amino acids tend to cluster together on the interior of a protein, away from the surface (and away from water)
Ionic bonds (tertiary)
when atoms that are oppositely charged are held by an electrostatic attraction COOH and NH2 become COO- and NH3+, they are strongly charged and attracted to each other
LDFs (tertiary)
weak interactions between the electron cloud of atoms may result in an attraction/repulsion between atoms
Hydrogen bonds (tertiary)
weak electrostatic attractive interaction between a H atom and an electronegative atom (oxygen, nitrogen)
Disulphide bridges (tertiary)
covalent bond between R groups containing sulphur
Quaternary structure
exists in proteins with two or more connected polypeptide subunits which are linked by bonds between the R groups
Quaternary structure describes the ……… arrangement of the subunits
spacial arrangement
prosthetic group
a non-protein unit tightly bound to a protein and necessary for its function e.g., haem in haemoglobin. The ability of haemoglobin to bind oxygen is dependent upon the non-protein haem group.
interactions of the R groups can be influenced by
pH and temperature This is why pH and temperature will affect the structure (and function) of a protein.
Increasing temperature disrupts the interactions that hold the protein in…
shape The protein begins to unfold, eventually becoming denatured.
As pH increases/decreases from the optimum, the normal ……………….. between charged groups are lost
ionic interactions which gradually changes the conformation of the protein until it becomes denatured
ligand
a substance that can bind to a protein