6. Notes on Membrane protein, Protein formation, Enzyme
6. Notes on Membrane protein, Protein formation, Enzyme LSM1401
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This 0 page Class Notes was uploaded by HAN ZIXUAN on Thursday November 5, 2015. The Class Notes belongs to LSM1401 at National University of Singapore taught by Jayaraman Sivaraman in Fall 2015. Since its upload, it has received 17 views. For similar materials see Fundamental of biochemistry in Biology at National University of Singapore.
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Date Created: 11/05/15
Brief Notes Lecture 6 Protein Proteins are responsible for various functions in our body Proteins carry out the functions of cell such as signalling transport catalysis movement and regulation 1 Membrane protein Transporters facilitate the movement of ions or molecules across the membrane Receptors bind with ligands and sense the changes and transmit or relay the signals between cells internal and external environments Enzymes that catalyze the chemical reactions at the extracellular or intercellular surface Anchorattachmentrecognition attachment point at the intracellular matrix cytoskeleton or at the extracellular Matrix ECM component for cellcell interaction or crosslink between one cell membrane to other cell membrane Q Q Enzyme Traneperter 7 I Receptar Membrane proteins are very important proteins involved in various key functions There are two major types of membrane proteins and The integral membrane proteins are embedded in the lipid bilayer membrane whereas the peripheral proteins are located outside the cell membrane both out of the cell or in the cell or slightly into the membrane llntegralllmembranepreteilns utsidethecell Peripher mmemm nepmtem ii Lipidquot Peripheral H f chm Ed extracellular Tranarnernhrane v lit helix 39 Transvmemlorahe i harrel l39 lipidl i39 bilayer Jquot I 39 f I gt J x I gquotg i 39 i quot ti Lillitli Peripheral Inside the cell 39 an hmEd C ift t iic Helix anchored inter hail1 disullfide fllld 5 cooli Most of the membrane proteins consist of transmembrane cxhelices or Bsheet reoions 3 common regions of a membrane protein often glycosylated ie attached with sugar molecules which are necessary for the function of the protein and have 55 bond disulphide bond to stabilize the structure This region is oxidised environment which favours the formation the 55 bond h embedded in the lipid bilayer region the limitquot protein in this region is highly hydrophobic in nature As we know that lipid bilayer is also hydrophobic the protein interacts with the quot transmembrane 1 1 ii helix membrane through hvdr0phobic interactions The transmembrane 1 region of a membrane protein can be predicted by sequence analysis i3 region inside the cell This region is the reducing environment which does not favour the formation the 55 bond mom gummy NH The protein functions are associated with its three dimensional structure or shape Or proteins adopt a particular structureshape because it has to do certainspeci c function e the structure and function of any protein is highlv related 5H 2 Protein formation Protein folding is an important process in protein synthesis It has to be noted that only Drooerlv or wellfolded protein will have its function ie active Hydrogen bonds hydrophobic interactions and 55 bond contribute to the three dimensional structure of the protein There are various stages in the protein folding 1 Unfolded random polypeptide chain 2 Form local secondary structure eg cxhelices and Bsheets 3 These secondary structures condense and pack into compact globular shape which may represent the minimum energy conformation ie tertiary structure Interactions in protein formation The hvdr0phobic amino acids in any globular protein structure will cluster together and My inside the molecule to avoid interacting with the water molecules Whereas the hydrophilic amino acids protrude outside the molecules to freely engage with the water molecules 3 types of hydrogen bond Backbone vs Backbone Backbone vs Side chain Side chain vs Side chain SS Disul de bond formed in the oxidizing environment break in the reducing environment i it i h 39 id39 ll h39cl by n it am mp 39 e D The diagram here IS quot ifff T a n l 7 linearized in 3D structure GlylleValGlu6ln CysCysAla SerJJal CysSerLeuTyrGlnLeu GluvAsnTyrCysAsn 5 y lo 15 i 21 the amino aCIds are close lnterchaindisulphide bond enough to form the intra 3 Eii i39iijp 39 Phe ValeAsnG neH i5LeuCy SaG ly SerH lsLeuValGluaAlaleeuTyr LeuValCys G lyGluArgG lyaF hePheTyraThrPro LysAla 5 IO 15 20 25 30 chain SS bond 3 Enzymes Enzymes are typically the globular proteins that carry out precise chemistries A protein that catalyzes a chemical reaction is called enzyme An enzyme can reduce the energy of activation EA that is required to begin a reaction Without enzymes the reactants need more energy to begin the reaction The reaction catalyzed by the enzyme produce the products and nally the products leave the enzyme The function of an enzyme is very speci c it is not random For example the peptide bond cleavage by an acid is random it cleaves hydrolysis all the peptide bonds whereas the peptide bond cleavage hydrolysis by an enzyme is very speci c eg Trypsin cleaves the bond after a Lys or Arg basic positive charge amino acid oliigosacclhiairid es Chymotrypsin cleaves the bond after Tyr or Trp or Phe hydrophobic aa A is any enzyme that performs proteolysis that is hydrolysis of the peptide bonds that link amino acids together in a polypeptide chain The reaction is Nucleoohilic attack which is the bond formation between active site amino acid nucleophiledonate electron pair and substrate electron de cient prior to the cleavage
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