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.