Proteins

Biruet test:

Detects peptide bonds

• Place a sample of the solution to be tested in a test tube and add an equal volume of sodium hydroxide solution at room temperature
• Add a few drops of very dilute (0.05%) of copper (II) sulfate solution and mix gently
• A purple colouration indicates the presence of peptide bonds amd hence a protein.
• If no protein is present, the solution remains blue

Protein:

Consists of one or more polypeptide arranged as complex macromolecules, they have specific biological functions

Amino acid:

• There are 20 amino acids
• Every amino acids has a central carbon atom to which are attached four different chemical groups

Amino group -

• -NH2
• A basic group from which the amino acid part of the name amino acid is derived

Carboxyl group -

• -COOH
• An acidic group which gives the amino acid the acid part of its name

Hydrogen atom

• -H

R (side) group -

• A variety of different chemical groups
• Each amino acid has a different R group
• These 20 naturally occuring amino acids differ only in their R group

Formation of a peptide bond:

• Amino acid monomers combine to form a dipeptide
• Made by condensation
• The water is made by combining an -OH from the carboxyl group from one amino acid with an -H from the amino group on another amino acid
• Two amino acids then become linked by a new peptide bond between the carbon atom on one amino acid and the nitrogen atom on the other
• Can be broken down by hydrolsysis

Primary structure:

• Many amino acid monomers joined together in polmeisation and make a chain of amino acids called a polypeptide
• This sequence is determined by DNA.
• As polypeptides have many of the 20 naturally occuring amino acids joined in different sequences, it follows that there is almost limitless number of combinations, and therefore types of primary protein structure.
• Determines its ultimate shape and therefore its structure
• A change in just one amino acid in the primary sequece can lead to a change in the shape of the protein and may stop it carrying out its function.
• Protein's shape is very specific to its function
• is 2D

Seconadary structure:

• Is the shape which the polyptide chain forms as a result of hydrogen bonding.
• The linked amino acids that make up the poplypeptide posses both -NH and -C=0 groups on either side of every peptide bond
• The hydrogen of the -NH group has an overall positive charge while the O of the -C=O group has an overall negative charge
• These two groups therefore readily form weak bonds, called hydrogen bonds
• This causes the long polypeptide chain to be twisted into a 3-D shape, such as the coil known as the alpha helix

Tertiary structure:

• Alpha-helices of the seconadry structure can be twisted and folded even further to give the complex, and often specific 3-D structure of each protein
• This structure is maintained by a number of different bonds
• Where the bonds occur depends on the primary structure of the protein
• All three…