Proteins
• Are the enzymes that catalyse all
biochemical reactions in the body.
• Are the structure of the body
• Carry oxygen
• Fight disease
• Make up cell membranes
• Are chemical messengers
Structure of proteins
• Are polymers
• (note: often confusion over peptides,
proteins and polypeptides = all are amino
acid chains, difference is length.)
• Units are amino acids (made up from 64
nucleotide combinations)
• 20 different amino acids therefore some
amino acids are specified by more than
one codon. This is called degeneracy.
This buffers against mutations as a single
base change may not result in an affect
• Are joined together by condensation
• Some hydrophilic and some hydrophobic
allowing proteins fold into specific shapes.
• Fibrous proteins and globular proteins
(long and stringy or round and ball like).
• AUG is always the start signal
• Stop signals always come at the end –
UAA,UGA,UAG
• Read amino acid tables for mRNA code:
read left hand side, top and then right side.
•
•
•
•
•
So remember:
DNA: ATG CTG AGG GGT TAT TAA
TAC GAC TCC CCA ATA ATT
mRNA: AUG CUG AGG GGU UAU UAA
Don’t forget – U not T in RNA, read amino
acid code from mRNA.
Protein structure and Function
• There are four
levels of protein
structure.
• The final shape of
the protein
determines its
function.
• For enzymes, the
shape is crucial for
correct function.
• Primary structure = order of amino acids
• Secondary structure = how tight the coil or
chain is
• Tertiary structure = how the chains loop
back on themselves again and again.
• Quaternary structure = how separate
protein molecules join to each other.