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Proteins are made from long chain of amino acids;
The monomers of proteins are amino acids
A dipeptide is formed when two amino acids join together
A polypeptide is formed when more than two amino acids join together
Proteins are made up of one or more polypeptides
Different amino acids have different variable groups;
All amino acids have the same general structure a carboxyl group (-COOH) and a amino group (-NH2)
attached to a carbon atom. The different between different amino acids is the variable group;
For example in this picture this shows the general structure
of the amino acids. The `R-group' can vary for example in
Glycine it simply `H' which is the smallest amino acids
Proteins have four structural levels;
Proteins are big complicated molecules they are much
easier if broken down into there four levels for example
1. Primary This is the basic sequence of amino acids
in the polypeptide chain
2. Secondary Structure The polypeptide doesn't
keep its flat shape. Hydrogen bonds form between the
amino acids which makes it coil into a alpha helix or fold
into a beta pleated sheet
3. Tertiary Structure The amino acids id further coiled or folded further. More bonds are present. And
proteins made from a single polypeptide chain, the tertiary structure forms their final 3D structure.
4. Quaternary Structure When proteins have several different polypeptide chains held together by
bonds. From proteins made from more than one polypeptide chain the quaternary structure is the
proteins final 3D Shape.
A proteins shape determines its function for example haemoglobin is a compact soluble protein which
makes it easy to transport. This makes it great for carrying oxygen around the body. Collagen has three
polypeptide chains tightly coiled together which makes it strong. This makes it great supportive tissues in
Polypeptides are formed by condensation reactions;
Amino acids are linked together to form polypeptides by a condensation
reaction. A molecule of water is released during the reaction. The bonds
formed between amino acids are called peptide bonds the reverse reaction
happens during digestion.
Proteins have a variety of functions;
There are loads of different proteins found in living organisms. They've all
got different structures and shapes which makes them specialised to carry
out particular jobs.
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Enzymes; usually spherical in shape die to the tight folding of the polypeptide chains they are also soluble
and have role sin metabolism. Some enzymes break down large food molecules will other enzymes help to
make large molecules.
Antibodies; which are involved in the immune response. They are made up of two light polypeptide chains
and two heavy/long poly peptide bonded together. Antibodies have variable regions the amino acids
sequences ion these regions vary greatly.
Transport Proteins; they are present in cell membranes.…read more