PROTEINS

PROTEINS

There are millions of protiens in the body. They're the most abundant molecule in cells making up about 50% or more of a cells dry mass.
AMINO ACIDS
1. Protiens are made from long chains of AMINO ACIDS. These are called MONOMERS, the smaller molecules which linked together create a protein. Two AMINO ACIDS join together and form a DIPEPTIDE. More than two aminoacids form a polypeptide. One or more polypeptide form proteins.
  1. Different amino acids have different VARIABLE GROUPS, all amino acids have the same general structure, a CARBOXYL GROUP (-COOH) and an AMINO GROUP (-NH2) attached to a CARBON. The difference is the VARIABLE GROUP, represented by an R in a diagram.
    1. Amino acids link together through PEPTIDE BONDS and form dipeptides and polypeptides. Like CARBOHYDRATES and TRIGLYCERIDES, dipeptides and polypeptides are formed by CONDENSATION REACTIONS.
STRUCTURAL LEVELS
1. Proteins have four STRUCTURAL LEVELS.
  1. PRIMARY STRUCTURE: This is the sequence of AMINO ACIDS in the POLYPEPTIDE CHAIN.
  2. SECONDARY STRUCTURE: The polypeptide chain does not remain flats. This is because HYDROGEN BONDS for between the AMINO ACIDS in the chain. This makes it automatically coil into an ALPHA HELIX, or fold into a BETA PLEATED SHEET.
  3. TERTIARY STRUCTURE: The coiled or folded chain of amino acids is often coiled and folded further. This causes more bonds to form between different parts of the POLYPEPTIDE CHAIN. However proteins formed from only one polypeptide chain develop their final 3D STRUCTURE in the TERTIARY STRUCTURE.
  4. QUATERNARY STRUCTURE: For the proteins which are made of many POLYPEPTIDE CHAINS, this is the way that they are assembled together. Proteins made from MORE THAN ONE POLYPEPTIDE CHAIN form their final 3D STRUCTURE in the quaternary structure.
2. STRUCTURAL LEVELS AND THEIR BONDS
  1. PRIMARY STRUCTURES are held together by PEPTIDE BONDS
  2. SECONDARY STRUCTURES are held together by HYDROGEN BONDS that form nearby amino acids. These bonds create ALPHA HELIX CHAINS, or BETA PLEATED SHEETS
  3. TERTIARY STRUCTURE. These are affected by numerous types of bonds. IONIC INTERATIONS. These are weak attractions between the negative and positive charges on different parts of the molecule. DISULFIDE BONDS. Whenever molecules of CYSTEINE come together, the SULFUR ATOM in one cysteine bonds to the sulfur of the other cysteine forming a DISULFIDE BOND
  4. HYDROPHOBIC AND HYRDOPHILLIC INTERACTIONS. This is when the HYDROPHOBIC groups clump together in the protein, the means that the HYDROPHILLIC groups are pushed to the outside this affects how the protein folds up into its final structure
  5. QUATERNERY STRUCTURE. This can be influenced by all the forms of bonds mentioned above. This is often determined by the TERTIARY STRUCTURE of the individual polypeptide chains being bonded together
3. 3D STRUCTURE AND PROPERTIES
  1. The amino acid sequence of a protein determines what bonds will form and how the protein will fold up. In turn the 3D structure of a protein will determine its properties.
  2. Protein 3D Structures can be Globular or Fibrous
  3. GLOBULAR: Globular proteins are round, compact proteins made of many polypeptide chains, these chains are coiled up so that the hydrophillic parts are on the outside, where as the hydrophobic parts are on the inside. This means that the protein in SOLUBLE, and can be transported easily. E.G Haemoglobin is a globular protein madeof 4 polypeptide chains, it carries oxygen and is carried in the blood. It contains HAEM groups which bind to oxygen
  4. FIBROUS: Fibrous proteins are made of long, insoluble polypeptide chains, that are tightly coiled to form a rope shape. These are held together by lots of bonds, these fibrous proteins are strong and the means they are often found in supportive tissue. For example, collagen, which is a strong protein that forms supportive tissue in animals.
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