Explain what causes molecules of a particular protein always to fold into the same shape?

Answer 1

Bonds and interactions between R groups. They will be the in the same place/between the same R groups in all polypeptide chains of the same type, meaning the always form the right shape. The four types are...
Hydrogen bonds, between strongly polar groups.
Di-sulphide bonds between cysteine molecules.
Ionic bonds between ionised amine and carboxylic acid groups.
Hydrophobic interactions between non-polar side chains.

Answer 2

Although enzymes can help proteins to fold correctly, in most cases the proteins fold the same was as a result of intermolecular forces. Hydrophobic residues will usually "hide" in the core to get away from water. Residues that are acidic will be attracted to basic residues and repelled by other acidic residues. The bottom line is protein folding is done in the most energetically favorable manor, that's why you only get one maybe two conformations of the protein.

Answer 3

There are 4 levels of structure. Consider the primary structure
which is the amino acid sequence e.g.
[gly]-[ala]-[cys]- etc. etc. The individual amino acids are held together by peptide bonds which are planar. In the secondary structure, cross-linkage occurs e.g. [cys] at amino acid position 20 attaches to a [cys] at position 40 on the same polypeptide chain forming a closed loop stabilised by a Sulphur-Sulphur bond called a thiol bond since [cys] contains Sulphur; and Sulphur reacts with Sulphur.

Answer 4

enzymes do it...