Understanding Beta Pleated Sheet Structure in Proteins
Beta pleated sheet structure is a secondary structure found in proteins where peptide chains lie side by side to form a flat sheet held together by hydrogen bonds. Proteins like keratin and fibroin exhibit this structure, while denaturation can alter the secondary and tertiary structures of proteins, leading to changes in their properties. Heat, mineral acids, and alkalis can denature proteins, affecting their biological activities.
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B.Sc 3rd (6th Sem) Organic chemistry Topic: Beta pleated structure Proteins I.B. (PG) College, Panipat Era Garg Asstt. Professor (Chemistry)
Secondary structureb- pleated sheet structure of protein A protein may or may not have the same secondary structure throughout its length . Some part may have helix structure ,while others may have pleated sheet structure.
Peptides chain lies side by side to form FLAT SHEET. Each chain is held by H-bonds to the two neighbouring chains may be either parallel or antiparallel.
KERATIN : The protein present in hair has parallel FIBROIN : The silk protein has antiparallel pleated sheet structure SYNTHETIC POLYGLYCINE : Because of the presence of no side chains is expected to have flat sheet structure.
Denaturation/Renaturation of proteins Action of heat, mineral acids , alkalis etc. brings about coagulation of proteins. For example: 1.On heating an egg (boiling hard) the soluble globular protein (albumin) present in it,is denatured resulting in the formation of insoluble fibrous protein.
2.When milk is heated with an acid (lemon juice/tartaric acid)cheese is formed. During the denaturation,the globular milk protein (lactalbumin) becomes fibrous. This coagulation also results in loss of biological activities of protein. The coagulated protein so formed are called denatured protein.
Chemically, denaturation has no effect on primary structures but secondary and tertiary structures are changed. Denaturation involves breaking of many of the weak linkages , or bonds(example: H bonds)within a protein molecule that are responsible for highly ordered structure of protein in its natural state. Denatured protein has a looser ,more random structure.
RENATURATION The original structure of some proteins can be regenerated upon removal of the denaturing agent and restoration of favourable conditions. Proteins subject to renaturation includes serum albumin from blood,haemoglobin,ribonuclease(enzymes). The denaturation of many proteins,like egg white is irreversible.
