Chemistry of life

Secondary structure

The secondary structures of proteins - α-helices and β pleated sheets – are held together by hydrogen bondhydrogen bond
An intermolecular attractive force between hydrogen, when it is covalently bonded to a highly electronegative atom (fluorine, oxygen or nitrogen), and an oxygen, nitrogen or fluorine atom on another molecule. s between polar moleculespolar molecules
Covalent molecules which contain dipoles. in the backbone of the polypeptidepolypeptide
A long chain of hundreds or even thousands of amino acids joined by peptide bonds. chain. Hydrogen bonds are relatively weak but there are many of them.

Tertiary structuretertiary structure
The final 3D structure of a protein chain. This structure is produced when the secondary structure of the polypeptide chain is folded.

The tertiary structure of a protein is produced when the secondary structure of the polypeptidepolypeptide
A long chain of hundreds or even thousands of amino acids joined by peptide bonds. chain is folded up - for example to form a globular protein such as an enzyme. The folds are held in place by

• Hydrogen bondhydrogen bond
  An intermolecular attractive force between hydrogen, when it is covalently bonded to a highly electronegative atom (fluorine, oxygen or nitrogen), and an oxygen, nitrogen or fluorine atom on another molecule. s – there are huge numbers of these relatively weak bonds.
• Ionic bondsionic bonds
  Bonds formed by the complete transfer of one or more electron from one atom to another, so both achieve a stable outer shell. The positive and negative ions formed are held together by strong electrostatic forces - these are ionic bonds.  – strong bonds form between acid and basic (i.e. has the properties of a base, can accept a proton H⁺ ion) amine groups of some amino acidamino acid
  The basic building blocks of proteins. There are twenty amino acids used, in different combinations, to make every protein required by the human body. s in the polypeptide chains.
• Disulfide bonds - bonds formed between amino acids containing sulfur groups e.g. cysteine or methionine, when they occur close together in polypeptide structures. A covalent bondcovalent bond
  Formed when atoms share electrons to achieve a stable outer shell; a covalent bond is a shared pair of electrons.  is formed between the sulfur-containing groups to form a sulfur bridge (also known as a disulfide bridgedisulfide bridge
  A covalent S-S bond that joins two cysteine amino acids together, also called an SS-bond or disulfide bond. ).

Quaternary structurequaternary structure
In some proteins several polypeptide chains fit together to form a larger molecule. The quaternary structure refers to the way the different polypeptide chains fit together.

In some proteins several polypeptidepolypeptide
A long chain of hundreds or even thousands of amino acids joined by peptide bonds. chains fit together to form a large biologically active molecule e.g., haemoglobinhaemoglobin
The protein that carries oxygen within red blood cells. . The quaternary structure refers to the way the different polypeptide chains fit together and are held in place by hydrogen bondhydrogen bond
An intermolecular attractive force between hydrogen, when it is covalently bonded to a highly electronegative atom (fluorine, oxygen or nitrogen), and an oxygen, nitrogen or fluorine atom on another molecule. s along with some ionic bondsionic bonds
Bonds formed by the complete transfer of one or more electron from one atom to another, so both achieve a stable outer shell. The positive and negative ions formed are held together by strong electrostatic forces - these are ionic bonds. and disulphide bonds.