PROTEINS Flashcards
Proteins
proteins are large molecules. all enzymes are proteins. protein is a polymer made up of large number of smaller sub units called amino acids.
major component elements in protein
CHONS - carbon, hydrogen, oxygen, nitrogen and sulphur
examples of protein
hormone - insulin and glucagon
- oxygen carrying pigments - myoglobin and haemoglobin
- structural protein - collagen found in connective tissues and keratin found in hair and nails.
- actin and myosin.
feature of amino acids
amphoteric
can act as an acid or a base.
what is the bond that joins amino acids?
peptide bonds
peptide bonds
peptide bond is a chemical bond formed when two amino acids are joined together in a condensation reaction.
it is formed when oh group on acidic end of one amino acid reacts with h group on amino end of the next amino acid.
structures of protein
primary, secondary, tertiary and quaternery
primary structure of protein
it is the sequence of amino acids in a polypeptide chain.
why is primary structure important?
because it is determined by the genetic code - determines the order and position of the R group - controls the shape - determines the function.
secondary structure of protein
secondary structure of protein is the molecule which is resulted from the regular coiling or folding of chain of amino acids.
what causes the chain to fold ? what shapes are formed?
the hydrogen bonds
as a result two shapes can be formed that is either alpha helix or beta pleats.
what can break the hydrogen bonds
high temperature and pH.
tertiary structure of protein
the way in which a protein coils to form a precise three dimensional shape. it is a result of much stronger bonds when there is attraction between alpha helices and beta pleats.
bonds present in tertiary structure
- hydrogen bonds
- disulfide bridges
3 ionic bond - hydrophobic interaction or weak vander waals force
hydrogen bonds
not strong when isolated but really strong when together
disulfide bridge
covalent bond between two cysteine molecules. ionic and disulfide bonds forms between different r groups of amino acids.
ionic bond
formed between ionised amino group and ionised carboxylic group
hydrophobic interactions
occurs between non polar r groups.
These strong covalent bonds holds the protein in its specific 3d shape. the 3d shape creates pockets or holes in protein surface which is very important for protein functioning.
Quaternery structure of protein
it is when two or more tertiary structures stick together to form a large molecule. not all proteins have it. eg haemoglobin.
Haemoglobin
haemoglobin carries oxygen and is found in red blood cells. it consists of 4 polypeptide chains. 2 of which are 141 amino acids long and other two are 146 amino acids long.
structure of haemoglobin
- haemoglobin is nearly spherical in shape.
- the hydrophobic group are pointed inwards towards the centre wheras the hydrophilic groups are on the outside.
- the hydrophobic interactions on the inside are important for maintaining a precise 3d shape
- the hydrophilic gropups help to maintain solubility.
what happens if a protein is denatured
if a protein is denatured then the bonds which hold the secondary and tertiary structure in shape breaks and therefore the unique 3d shape is lost. enzymes lose their unique active site.
imp of primary structure
if even one amino acid sequence changes it will cause the ionic,hydrogen or disulphide bonds to form in a different location which results in a different 3d shape.
test for protein
biuret test.
biuret reagent is added to the sample of protein that is to be tested.
lilac color indicates positive results.
