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3.1- General properties of proteins - Coggle Diagram
3.1- General properties of proteins
polymer of amino acids also known as polypeptides
the amino acid sequence in the primary structure is what determines the proteins shape and function . changing a single amino acid could change the shape and function
The secondary structure of a polypeptide, the shape that the polypeptide chain folds into, resulting from the arrangement of hydrogen bonds formed . either forms a coiled a-helix structure or b-pleated sheet because the H in the peptide bond is positive and O is negative
tertiary structure; further folding of the polypeptide into a complex 3D structure. The position of amino acids in sequence determine the tertiary structure and the tertiary structure is very closely related to the function of the protein (the complementary structure of an active site or receptor for example)
tertiary structure is the result of interaction between amino acid R groups
Hydrogen bonds form between R groups of amino acids. many of these bonds but they are easily overcome
Ionic bonds form between positively and negatively charged amino acid R groups. stronger than H bonds but weaker than disulphide bridges
disulphide bridges form between S atoms in the R groups of amino acids. Fairly strong covalent bonds that are harder to overcome than ionic and H bonds
main categories of tertiary structure are fibrous and globular
globular proteins are more compact and spherical and have biochemical functions. they are soluble. e.g. haemoglobin and enzymes
Fibrous proteins are typically long and thin and insoluble, having a structural role. e,g, keratin/collagen. in collagens tertiary structure, polypeptide chains are tightly wound. in its quaternery structure cross links tightly wind three individual polypeptide chains together
some proteins (containing more than one polypeptide chain) have a quaternary structure which is the way in which two or more polypeptide chains are combined. The polypeptides are held by the same bonds contributing to tertiary structure .
Haemoglobin has a quaternary structure and non protein component (prosthetic group)
amino acids are the monomer units that make up polypeptides, joined in sequence by peptide bonds have different chemical properties and biological functions
Properties of amino acids:
colourless crystalline solids that are soluble in water
base is a proton acceptor and acid is a proton donor so amino acids act as buffers in solutions; when pH decreases they act as proton acceptors , when pH increases they act as proton donors
amino acids are amphoteric- they have basic and acidic properties due to COOH acidic group and NH2 basic group
therefore they exist as dipolar ions called zwitterions in neutral aqueous solutions
one central carbon atom bonded to 4 chemical groups: NH2, COOH , H , R group that is different for every amino acid
amino acid is positively charged and basic when: second amino group
amino acid is negatively charged and acidic when: second carboxyl group
R group determines the properties and chemical function of each amino acid
amino acid is non polar and hydrophobic when : simple hydrocarbon chain
amino acid is polar and hydrophilic when: polar hydrocarbon chain
formation of polypeptides by peptide bonds (condensation of amino acids leads to bond between one carbon atom and N atom due to removal of -OH and -H)
amino group and carboxylic acid group react in a condensation reaction to form a peptide bond
amino acids in sequence are oriented in the same direction so there is always a carboxylic acid group at one end of the polypeptide chain and an amino group at the other which can react
Biuret reagent test detects peptide bonds; sodium hydroxide solution added to sample and then a few drops of copper sulfate solution. the solution turns blue to purple in the presence of proteins. NaOH and CuSO4
Protein structures relate to their function
antibodies are made up of two light short polypeptide chains and two long heavy polypeptide chains bonded together.
In the highly specific variable region of antibodies, amino acid sequences vary greatly as they are specific to the function of the particular antibody
Channel proteins are made of both hydrophilic and hydrophobic amino acids in order to be able to transport water-soluble molecules and ions across membranes
Globular:
Haemoglobin is compact and soluble so it is easy to transport ; therefore can help transport oxygen around the body
Enzymes are spherical due to tight folding of polypeptide chains. they are soluble (can be stored in the cytoplasm) and have roles in metabolism; breaking down
Structural proteins consist of long polypeptide chains parallel to each other with cross-links between them. E.g. collagen which has three polypeptide chains tightly coiled together. makes it useful for its role as supportive tissue