Lecture-5B-Proteins-_42855

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

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

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 ...
View Full Document

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.

Ask a homework question - tutors are online