Building models of Protein Structure
Genes on strands of mRNA code for 20 different amino acids which are built into polypeptides on ribosomes. Using just three mRNA bases for each amino acid the code details the exact order of amino acids in a protein. Amino acids can be linked together in any sequence giving a huge range of possible polypeptides.
Modelling ribosomes making polypeptides
1.
Take one pipe cleaner and about 30 small craftbeads.
2.Add the beads one at a time to the pipe cleaner. Each bead represents one aminoacid.
The sequence of amino acids is called a polypeptide after the bonds holding them together.
The sequence is also called the primary structure of a protein. To prevent the beads falling off the chain, fold each end of the pipe cleaner back on itself.
3.Coil the chain of beads around a pencil to make a spiral. This shape is common in proteins and is like the shape of the polypeptides in the protein collagen. This coil of polypeptide is called an alpha-helix, one example of a secondary structure ofprotein.
4.Stretch out the coil into a line again and then fold the beads in a zigzag shape. This is another secondary structure of protein, called a beta pleated sheet. A common structure found in spider’ssilk.
5.Now try to build a protein made from your chain of beads which has both of these secondary structures. The mix of different secondary structures makes the tertiarystructure
6.Lastly get together with three other students and make a super-structure of four polypeptides each with the same tertiary structure. This is known a quaternary structure.
IBDP Biology HL/SL / Activity /Questions
A. Name the bonds which hold the amino acids together in the primary structure of a protein.
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The three-dimensional shape of a protein is determined by the sequence of amino acids.
IBDP Biology HL/SL / Activity /Sometimes a protein is made of a number of polypeptide chains, each with their own tertiary structures. They are often held together by something which is not a protein. Haemoglobin is a good example of this type of protein.
Whatever the structure of the protein the shape of the molecule is important.
Research
Look up the functions of these protein molecules and record the functions in the table below.
Protein example / Function of the proteinrubisco
insulin
immunoglobulins
rhodopsin
collagen
spider silk