AQA AS Biology Unit 1: Proteins

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  • Created on: 22-08-13 17:04
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Proteins are very large molecules and each organism contains them however, they differ from
species to species.
The shape of any one type of protein molecule differs from that of all other types of proteins.
Proteins are the most important molecules to life.
One group of proteins, enzymes, is involved in almost every living process.
There is a vast range of different enzymes that between them perform a very diverse number of
Functions of proteins:
Usually roughly spherical in shape due to the tight folding of the polypeptide chains.
They're soluble and often have roles in metabolism e.g. some enzymes break down large
food molecules and other enzymes help to synthesise large molecules
Involved in the immune response
They're made up of two light polypeptide chains and two heavy polypeptide chains bonded
Antibodies have variable regions ­ the amino acid sequences in these regions vary greatly
Transport proteins
Present in cell membranes.
They contain hydrophobic and hydrophilic amino acids which cause the protein to fold up
and form a channel.
These proteins transport molecules and ions across membranes
Structural proteins
They are physically strong.
They consist of long polypeptide chains lying parallel to each other with cross-links between
them. Structural proteins include keratin (found in hair and nails) and collagen (found in
connective tissue)

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The Structure of an Amino Acid
Amino acids are the basic monomer units which combine to make up a polymer called a
polypeptide. Polypeptides can be combined to form proteins. About 100 amino acids have been
identified, of which 20 occur naturally in proteins.
Every amino acid has a central carbon atoms to which are attached four different chemical groups:
1. Amino group ­ a basic group which the amino part of the name amino acid is derived
2.…read more

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The formation of a peptide bond
Amino acid monomers can combine to form a diapeptide.
The process is called a condensation reaction because it is the removal of a water
The water is made by combining an ­OH from the carboxyl group of one amino acid, with
an ­H from the amino group of another amino acid.
The two amino acids then become linked by a new peptide bond between the carbon atom
of one amino acid and the nitrogen atom of the other.…read more

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The Primary Structure of Proteins
Through a series of condensation reactions, many amino acid monomers can be joined
together in a process called polymerisation.
The resulting chain of many hundreds of amino acids is called a polypeptide.
The sequence of amino acids in a polypeptide chain forms the primary structure of any
protein.…read more

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Tertiary Structure of Proteins
The -helices of the secondary protein structure can be twisted and folded even more
to give the complex 3-D structure of each protein. This is known as the tertiary structure.
This structure is maintained by a number of different bonds, including:
Disulfide bonds: fairly strong and therefore not easily broken down
Ionic bonds: formed between any carboxyl and amino groups that are not involved in
forming peptide bonds.…read more

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Protein Shape and Function
Proteins perform many different roles in living organisms.
Their roles depend on their molecular shape, which can be of two basic types:
- Fibrous proteins such as collagen have structural functions
- Globular proteins such as enzymes and haemoglobin, carry out metabolic functions
It is the very different structure and shape of each of these types of proteins that enables
them to carry out their functions.
Fibrous Proteins
Fibrous proteins form long chains which run parallel to one another.…read more


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