3.1.4 Proteins Flashcards
What are proteins?
+ diverse group of large and complex polymer molecules
+ made up of long chains of amino acids
Biological roles of proteins?
structural: proteins are the main component of body tissues, such as muscle, skin, ligaments and hair
catalyctic: all enzymes are proteins, catalysing many biochemical reactions
signalling: many hormones and receptors are proteins
immunological: all antibodies are proteins
What are amino acids?
+ basic monomer units which combine to form a polymer called polymerisation
+ combined to form proteins
+ every amino acid has a central carbon atom to which are attached four different chemical groups
How are peptide bonds formed?
+ amino acid monomer combines to form a dipeptide, containing a peptide bond, by a condensation reaction
What is the primary structure?
+ through a series of condensation reactions, many amino acid monomers can be joined together in a process called polymerisation
+ results in a chain of 100s of amino acids in a particular order called a peptide
+ determines shape and hence the function of a protein
What is the secondary structure?
+ the hydrogen on the NH has a positive charge, while the O in C-O has a negative charge
+ these 2 groups form weak bonds, called hydrogen bonds
+ causes the chain to be twisted into an alpha-helix, creating a 3D shape
What bonds are in the tertiary structure?
- disulphide bonds - fairly strong, only occur if the protein has aa containing sulfur
- ionic bonds- formed between carboxyl and aa groups, easily broken
- hydrogen bonds - numerous
How to test for proteins? (detailed)
- equal volume of NaOH at room temp added to the sample
- few drops of dilute (0.05%) copper (II) sulfate and mixed gently with he sample
What is the quaternary structure?
+ large and complex molecule
+ contains a number of individual polypeptide chains that are linked in various ways
+ may also be a non- protein group associated with the molecule which helps with its function
+ e.g the iron-containing haem group in haemoglobin
How to identify amino acids?
+ use paper chromatography
+ different aa move at different rates on the paper because of differences in their R groups
+ rate of movement of biomolecule is reported as its relative mobility (Rf)
Rf = distance moved by biomolecule / distance moved by solvent
What is the tertiary structure?
+ alpha-helix can be twisted and folded even further to give the complex 3D structure of each protein
How to test for proteins? (simple)
- Add Biuret reagent
- Purple colour = protein is present
Blue = protein is absent
