Lecture-5B-Proteins-_42855 - Protein Biomolecules •...

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Unformatted text preview: Protein Biomolecules • Proteins perform most all functions in an organism: – – – – Enzymes: catalyze chemical reactions Structural & movement functions Transport & Regulatory functions Extracellular: hormones, antibodies, digestive functions • Proteins are polymers Central, of amino acids: all α=carbon amino acids have the same structural plan (dotted line) in common; but each possess 1 of 20 unique side chains, Amino group or R‐groups. Carboxyl group R • Differences in the amino acid side groups give them their individual properties: – Polar, charged: negative charge (acidic) or positive charge (basic) – Polar, uncharged; and Nonpolar – Adjacent cystiene sulfhydryl groups (‐SH) form a disulfide bridge: ‐S‐S‐ α‐carbon – Proline: has a unique ring structure • Dehydration reactions link amino acids monomers together; result in formation of a peptide bond: H 2O • Proteins are comprised of one or more polypeptide chains. – Polypeptide = few to a 1000 amino acids in length – Each protein: possesses a unique sequence of amino acids … *Important, because most proteins depend on the ability to recognize & bind other molecules. …that precisely forms into a unique 3‐D shape the structure determines how it functions • Protein structure of lysozyme (an enzyme) Coiling & folding of polypeptide chain. Groove: binding occurs here Globular shape: Proteins have Four Levels of Structure: Primary, Secondary, Tertiary, & Quarternary 1. Primary Structure: the sequence & types of amino acids comprising a polypeptide chain • This underlies and determines the higher levels of structure Ala Lys Polypeptide chain Peptide linkages *The information dictating the primary structure of all proteins is stored in DNA (in the form of genes). Secondary Structure H‐bond formation between amino groups & carbonyl groups of the polypeptide backbone produced by twists & turns of the amino acid chain. α Helix: coils; provides elasticity H‐bonds β‐sheets: folds; more rigid, some flexibility. Tertiary structure: R Group Interactions The content of α‐, β‐ helices and R‐group interactions folds each protein into its tertiary structure. • Referred to as it’s overall 3‐D shape, or conformation. • Primary structure ultimately dictates what helices & interactions will form. • The particular shape formed varies, and is critical to its’ function. 2 cystiene amino acids Quarternary structure • Quarternary structure results from the aggregation of multiple polypeptide chains to form a functional protein. • Collagen is a fibrous protein of 3 coiled polypeptide chain; this structure provides strength & some flexibility. – Collagen comprises tendons & ligaments • Hemoglobin is a globular protein (4 polypeptide chains); each contain heme (iron) Polypeptide that binds chains oxygen. Found in red blood cells. Hemoglobin Collagen Protein solubility and structure: • Water soluble proteins possess amino acids with polar R‐groups exposed on the surface, while nonpolar types occupy the interior core. • Proteins in membranes have nonpolar regions contacting the inner hydrophobic membrane, & polar segments interacting with the exterior membrane & surrounding aqueous phase. Importance of the Primary Structure of a Protein: Sickle Cell Disease Sickle cell disease is due to a single mutation in the gene for the β‐hemoglobin subunit , leading to an amino acid substitution: Glu = Glutamic Acid R group ‐ CH2‐CH2 ‐C‐O CH Val = Valine O _ = / CH3 R group ‐CH CH3 • Normal Hb Normal function; bind oxygen β β α • Sickle Cell Hb – Structural change causes Hb molecules to bind together – Oxygen binding capacity low Exposed hydrophobic region β α Sickle cells α β α α ββ α α β ββ β α α Normal cells • The structure of most proteins is flexible, allowing for conformational changes; such changes influence protein activity. • Extreme physical conditions can cause a protein to unfold from its original conformation resulting in loss of function. – Denaturation is this process; causes: High temperature, pH, salt concentration, organic solvents – Can be reversible in some cases Denaturation • In a cell, chaperone proteins guide the proper folding of newly synthesized proteins. Renaturation Summary of Protein Structure Hydrogen bonding within polypeptide backbone R‐ group interactions 2 or more polypeptide chains Single polypeptide chain Nucleic Acids are Polymers of Nucleotides • Monomer Unit: deoxyribonucleotide (polymer = DNA); ribonucleotide (polymer = RNA) • Functions DNA: carrier of genetic information inherited from parents – Indirectly controls & programs all of the cell’s functions – Is replicated during cell division – DNA information organized into genes; most genes specify the primary structure of proteins RNA: different RNA molecules execute the retrieval & conversion of information in DNA into proteins. – Nucleotides • Energy transfer (ATP, GTP); critical to metabolism • Cell Signaling (cAMP) The Cellular Flow of Information • DNA RNA protein • Flow of information common to all life. • Eukaryotic cell shown to the right. • DNA stores information; “working copies” of this information formed as messenger RNAs, which are then deciphered to form proteins. • A nitrogen‐containing base (pyrimidine/purine). • A pentose sugar (ribose or deoxyribose) • A phosphate group. DNA & RNA are nucleic O5’ acid polymers comprised Phosphate O=P-OCH2 of monomers called nucleotides that contain: O4’ O Pentose sugar: 3’ 2’ Adenine, Guanine, Base Cytosine, Thymine, 1’ Uracil Nucleotide Nitrogenous bases DNA: A, G, C, T RNA: A, G, C, U Linking nucleotides (via condensation) forms a phosphodiester linkage. This forms the basis for the sugar‐phosphate backbone of DNA/RNA. Features of nucleotide polymer: Ends of polymer: indicated by arrows. Sugar‐phosphate backbone (circled) 5’ end has phosphate, 3’ end has hydroxyl group; DNA strands arranged as a double helix DNA strands are antiparallel; strands run in opposite directions: 5’ ‐‐‐‐‐‐ 3’ 3’ ‐‐‐‐‐‐ 5’ Hydrogen bonding DNA strands are complimentary to each other; bases pair together A:T, G:C DNA is a charged molecule (acidic) DNA DOUBLE HELIX Information stored in the sequence of bases; unique for each gene. “Ends” of DNA; 3’ –OH, 5’ ‐ P CH2 3’ OH 5’ Replication of DNA Double Helix • Each strand serves as a template for synthesis. • Replication yields two identical copies of the DNA double helix. transfer transfer RNA molecule (involved in protein synthesis) • RNA: single stranded, but can form elaborate shapes due to regions of complimentarity within the single strand Summary of Macromolecule Types Macro‐ molecule Proteins (polar & non‐polar regions) Carbo‐ hydrates (polar) Lipids (hydro‐ phobic) Nucleic Acids (polar) Monomer → Polymer Amino acids Polypeptide Monosaccharide Polysaccharide N/A Bonds & Functional Features & Groups Types Peptide bond 4 levels of structure Amino‐,Carboxyl‐ ends, R groups Hb, Collagen Glycosidic linkage ‐OH and C=O Triglyceride= Glycerol + 3 Fatty Acids (‐C‐H) Phosphodiester H‐bonding Sugar‐phosphate backbone Starch Cellulose Glycogen Phospholipid Steroids Fats/Oils RNA; DNA double helix; Base pairing antiparallel Nucleotides Nucleic Nucleic acid ...
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This note was uploaded on 10/16/2010 for the course HE 012928 taught by Professor Storrs,london during the Spring '10 term at École Normale Supérieure.

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