Proteins

Proteins

1. PROTEINS are 1 or more polypeptide bonds bonded together

2. Amino acids

   • 1) All amino acids have the same structure except the R group which varies
   • 2) Amino acids are monomers of proteins
   • 3) There are 20 different amino acids, 9 which are essential for life and can be obtained from what we eat
   • 4) Amino acids have an amino group, a carboxylic group and an R group
   • SYNTHESIS OF PEPTIDES
     • 1) PEPTIDE BOND- bond formed between 2 amino acids
     • 1) Amino acids join when the amine and carboxylic groups connected to the central carbon atoms react
     • 3) DIPEPTIDE BOND- when 2 amino acids are joined by a peptide bond
     • 4) POLYPEPTIDE- many amino acids joined by peptide bonds
     • 5) The presence of different sequences of amino acids leads to different structures with different shapes being produced
     • 6) From amino acid to water it's CONDENSATION ( forms a peptide bond) from water to amino acid HYDROLYSIS ( breaks down a peptide bond)

3. Protein structures

   • PRIMARY STRUCTURE
     • 1) This is the sequence in which amino acids are joined
     • 2) The sequence of the amino acid is determined by the genetic code
     • 3) The structure of protein is determined by the amino acid sequence
     • 4) Each amino acid has a different R group. The R group determines the folding, bonding, shape and function of the protein
     • 5) The only bonds in primary are PEPTIDE bonds.
   • The protein function is determined by the structure of that protein
   • SECONDARY STRUCTURE
     • 1) Forms when a chain of amino acids folds and coils
     • 2) The chain of amino acids can fold and coil into BETA PLEATED SHEETS and ALPHA HELICES
     • 3) The amino acid folds into a repeating pattern because of the hydrogen bonding of the polypeptide backbone
     • 4) The hydrogen bonds are the weakest bonds so they can easily be broken
   • TERTIARY STRUCTURE
     • 1) It's formed when secondary structures ( beta pleated sheets and alpha helices) fold back on themselves
     • 2) Creates a 3D structure
     • 2) The following interactions can occur between R groups:
     • HYDROPHILIC AND HYDROPHOBIC interactions- weak interactions between polar and non polar R groups
     • HYDROGEN BONDS- weakest bonds formed
     • IONIC BONDS- stronger than hydrogen bonds form between oppositely charged R groups
     • DISULFIDE BONDS ( disulfide bridges)- they are covalent and are the strongest of the bonds but only form between R groups that contain sulfur atoms
   • QUATERNARY STRUCTURE
     • 1) They are made up from more than one polypeptide subunit joined together
     • 2) The interactions are the same as the tertiary structure
     • 3) The protein subunits can be identical or different. in enzymes they are normally 2 identical subunits . Haemoglobin has 4 sub units of made up of 2 indentical pairs.
   • HYDROPHILIC AND HYDROPHOBIC INTERACTIONS
     • 1) Proteins are made in aqueous environments of the cytoplasm
     • 2) The way in which a protein folds depends on whether the R group are hydrophilic or hydrophobic
     • 3) Hydrophillic groups are on the outside of the protein and hydrophobic are on the inside where they are shielded from water in the cytoplasm

4. Types of proteins

   • GLOBULAR PROTEINS
     • I Hate Coughs ( Insulin, Haemoglobin, Catalase)
     • 1) Globular proteins are compact, water soluble and are usually spherical. Have 3D shape
     • 2) They form when proteins fold into their tertiary structure such that the hydrophobic R groups are kept away from aqueous environments
     • 3) The hydrophillic R groups are on the outside of the protein meaning the proteins are soluble in water
     • 4) The solubility is important is important for many different functions of globular proteins. They are essential in regulating many of the processes necessary to life e.g immunity and muscle contractions
     • INSULIN
       • 1) It's the hormone involved in the regulation of blood glucose concentration
       • 2) Hormones are transported in the blood stream so need to be soluble-insulin is soluble
       • 3) Hormones also have to fit into specific receptor sites on the cell surface membrane
     • CONJUGATED PROTEINS
       • 1) This are globular proteins that have a PROSTHETIC GROUP ( non protein component)
       • 2) SIMPLE PROTEINS don't have a prosthetic group
       • 3) Catalase and haemoglobin both have haem groups and haem groups are examples of prosthetic groups
       • HAEMOGLOBIN
         • 1) It's found in red blood cells and it's a pigment that carries oxygen
         • 2) It has a quarternary structure made from 4 polypeptides, 2 alpha and 2 beta subunits
         • 3) Each subunit has a prosthetic haem group
         • 4) The haem groups are able to combine with oxygen molecules and this enables haemoglobin to transport oxygen around the body
       • CATALASE
         • 1) It's an enzyme an d enzyme catalyse reactions meaning they increase reaction rates
         • 2) Each enzyme is specific to a particular reaction
         • 3) Has a quarternary structure which has 4 haem prosthetic groups.
         • 4) The iron (II) ions in the prosthetic groups allow catalase to interact with hydrogen peroxide and speed up it's breakdown
   • FIBROUS PROTEINS
     • 1) They are formed from long insoluble molecules. This because of the many amino acids with hydrophobic R groups in their primary structures
     • 2) They have limited range of amino acids usually with small R groups
     • 4) The amino acid sequence is usually repetitive, this leads to organised structures reflected in the roles of fibrous proteins often have
     • King Edward Come ( Keratin, Elastin, Collagen)
     • KERATIN
       • 1) Found in hair,skin and nails
       • 2) Has large amounts of cysteine ( has sulfur amino acids) meaning it has many disulfide bonds forming strong, inflexible and insoluble materials
       • 3) The degree of the disulfide bond determines the flexibility- hair has fewer bonds making it more flexible than nails which have more bonds
       • 4) The unpleasant smell when hair and skin is burnt is due to large amounts of sulfur being present
     • ELASTIN
       • 1) It's found in elastic fibres which are found in the walls of blood vessels and in the alveoli in the lungs
       • 2) They give these structures flexibility to expand when needed but also return to their normal size
       • 3) It's a quarternary protein made from tropoelastin which are soluble which link together to make a large insoluble cross linked structure
       • 3) Elastin gives strength and elasticity to the skin and other tissue organs in the body
     • COLLAGEN
       • 1) It's a connective tissue found in skin, tendons, ligaments and the nervous system. It's function is to give mechanical strength
       • 2) All are made up of 3 polypeptides wound together in a triple helix structure which are held together by hydrogen bonds
       • 3) It's flexible
       • 4) water soluble
       • 5) Has quarternary structure
       • 6) Each collagen molecule is covalently bonded to 2 others adding strength
       • 35% of amino acids are the amino acid glycine