Proteins Flashcards
Functions of protein
Protein
Polypeptides & protein are chains of amino acids linked to each other by peptide bonds.
Proteins that are needed by humans
all the proteins that are needed by humans can be made by the sequential arrangement of 20 amino acids
Condensation reaction
Many amino acids linked together by peptide bonds form polypeptide
Heirarachies of protein structure
- Primary structure
- Secondary structure
- Tertiary structure
- Quaternary structure
Primary structure of protein
It is the sequence of amino acids in a polypeptide chain held together by peptide bonds
Primary structure example if polypeptides are different
Polypeptide A & polypeptide B differ in the type, number & sequence of amino acids
The eventual shape, properties & function of both polypeptide chains is going to be different as the primary structure is different
Primary structure example if polypeptides are different
If two polypeptide have the same primary structure then their secondary & tertiary structures will be similar because they will form similar bonds between the amino acids
Secondary structure of protein
The secondary structure refers to the folding of the polypeptide chain (primary structure) into helices & pleated sheets. It is held together by H-bonds in the polypeptide backbone
Alpha helix
The polypeptide chain is wound to form a helix.
It is held together by hydrogen bonds running parallel with the long helical axis.
There are many H-bonds making this a very stable & strong structure.
Beta pleated sheet
The polypeptide chain zig-zags back & forwards forming a sheet. It is also held together by H-bonds
Tertiary structure of protein
The tertiary structure of a protein is the complex 3D globular shape the polypeptide chain takes when the polypeptide chain twists & folds around itself
The tertiary structure is maintained by:
- Hydrophobic interactions
- Hydrogen bond
- Disulphide bridge
- Ionic bond
Hydrogen bond
The bond forms between some H-atoms [S+] & O atoms [S-]
When these charged groups are close to each other, opposite charges attract, forming H-bond
Bonds are weak the large number of bonds provide a considerable force to maintain the 3D shape
Ionic bond
Formed between some of the strongly positive & negative amino acid chains which are sometimes found deep inside the protein molecule. They are stronger than H-bonds but can be broken by changes in pH & high temperatures
Quaternary structure of protein
Quaternary structure is the linking together of two or more polypeptide chains.
It describes the way these polypeptide chains fit together in three dimensions
Hydrophilic & hydrophobic interactions
The hydrophobic regions of the polypeptide chain face away from water by folding inwards. The hydrophilic regions of the chain remain on the surface of the globular structure
Quaternary structure examples:
Collagen
Haemoglobin
Denaturation
Changes in conditions such as temperature or pH affects the bonds that keep the 3D shapes of protein in place.
Even small changes can cause the bonds to break resulting in the loss of 3D shape of the protein. This is called denaturation
Quaternary structure of proteins
Quaternary structure is the linking together of two or more polypeptide chains.
It describes the way these polypeptide chains first together in three dimensions
Types of proteins
Proteins can be divided into two groups according to their structure:
Fibrous - fiber - like with a uniform secondary structure
Globular - like with 3D compact structures
Fibrous proteins
Fibrous proteins are structural proteins & have little or no tertiary structure
