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Chemical and physical features of proteins 2 + 3 Important terms ISOELECTRIC POINT (pI) • ISOIONIC point • Protein classification according to the size Classification of protein according to the size Fewer than 50 aa called peptide More than 50 is called protein Insulin is 53 aa long Is it a peptide or protein hormone? Protein sequence and structure The protein seq can be directly retrieved from the corresponding gene sequence? True False Protein primary structure Amino acids are attached by ………………………. These bonds are both planner and rigid Can they rotate about their axis? Protein secondary structure Stabilized by hydrogen bonding and depends on the sequence of aa in the chain Protein secondary structure Some amino acids disrupt the secondary alpha helix structure : Proline, isoleucin, tryptophan, asparagine Do all proteins have secondary structures? Yes No Tertiary structure Stabilized by many types of bonds -electrostatic bonds (-ve & +ve) -Van der waals forces -hydrophobic or hydrophillic attractions Hbonds Disulfide bridges Quaternary structure All proteins do posses quaternary structure? True False Quaternary structure More than one polypeptide chains come together to form quaternary structure ( we call the protein oligomeric) Quaternary structure Stabilized by the same types of bonds found in the tertiary structure Disulfide bridges can be of two types: Intrachain Interchains The one polypeptide chain in oligomeric protein is called : ……….. Oligomeric protiens All subunits should be different True False Oligomeric protiens 4 chains Heamoglobin 2 alpha and 2 beta chians Oligomeric protiens On the otherhand, some proteins such as LDH enzyme is composed of 4 identical subunits. The final folded protein shape Determines the final function of this protien Protein folding There are 2 main final shapes of folded proteins: Globular proteins fibrous proteins Globular proteins Spherical in their final shape Water soluble Contains mixture of α β and other random structures Enzymes, transport proteins, hormones and antibodies fibrous proteins Are structural protiens Water insoluble Built of either α or β Include cellulose fiber in the cell wall of plant cells Collagen and elastin in human Keratin in the hair and nails Chitin in the cuticle of some organisms What you need to know to investigate the protein structure I- Molecular mass determination : 1- SDS-PAGE 2- Exclusion chromatography Size exclusion chromatography
