* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Proteins
Fatty acid metabolism wikipedia , lookup
Signal transduction wikipedia , lookup
Nucleic acid analogue wikipedia , lookup
Expression vector wikipedia , lookup
Gene expression wikipedia , lookup
G protein–coupled receptor wikipedia , lookup
Ancestral sequence reconstruction wikipedia , lookup
Magnesium transporter wikipedia , lookup
Ribosomally synthesized and post-translationally modified peptides wikipedia , lookup
Peptide synthesis wikipedia , lookup
Point mutation wikipedia , lookup
Metalloprotein wikipedia , lookup
Interactome wikipedia , lookup
Western blot wikipedia , lookup
Nuclear magnetic resonance spectroscopy of proteins wikipedia , lookup
Two-hybrid screening wikipedia , lookup
Protein–protein interaction wikipedia , lookup
Genetic code wikipedia , lookup
Amino acid synthesis wikipedia , lookup
Biosynthesis wikipedia , lookup
Macromolecules 3: Proteins Your Assignment Your Protein Structure Assignment 1. Define proteins and their function 2. What is an amino acid (monomers joined via dehydration synthesis) 3. How is a peptide bond formed? 4. What are the main uses of proteins in cells (plants and animals)?? Your Protein Shape Assignment 1. What are the various levels of protein ‘shape’? (primary, secondary, tertiary, quaternary) 2. How does structure relate to function with regard to proteins? 3. What does it mean to denature a protein?, Give one or more example. Additional Resources (1) • The Tree of Life, proteins and DNA module Additional Resources (2) Protein structure and conformation links • Molecular Workbench DNA and protein module • http://www.youtube.com/watch?v=iaHHgEoa 2c8&feature=related • http://www.youtube.com/watch?v=Q7dxi4ob 2O4&feature=related Protein Functions Proteins • > 50% of the dry mass of a cell is protein Proteins are used for: • Structural support • Energy storage • Transport of other substances • Signalling from one part of the organism to another • Movement • Defence against foreign substance • Enzymes • Humans have tens of thousands of different proteins • Most structurally sophisticated molecule, due to unique 3D shape or conformation Amino Acid (Monomers) Amino acid structure: NH3 - C - COOH Amino acids differ due to the R (functional) group The structure of the R-group determines the chemical properties of the amino acid Proteins Chemical composition C-H-O-N-(S) Proteins are made up of smaller monomers called AMINO ACIDS Amino Acids differ ONLY in the type of R (functional) group they carry Amino acids composed of 3 parts 1. Amino Group 2. Carboxylic group 3. Functional ®-group (Makes 20 different amino acids) 20 Amino Acids Hydrophilic Amino Acids Polar uncharged amino acids are hydrophilic & can form H-bonds Serine Threonine Glutamine Asparagine Tyrosine Cysteine Hydrophobic Amino Acids Nonpolar amino acids are hydrophobic and are usually found in the center of the protein. They also found in proteins which are associated with cell membranes. Glycine Alanine Valine Leucine Isoleucine Methionine Phenylalanine Tryptophan Proline) Electrically charged Amino Acids The electrically charged amino acids have electrical properties that can change depending on the pH. Aspartic Acid Glutamic Acid Lysine Arginine Histidine Special Amino Acids Cysteine can form covalent disulfide bonds Proline had a unique structure and causes kinks in the protein chain Amino Acids link together to form polypeptides • 2 Amino Acids form a covalent bond, called a PEPTIDE BOND,through a condensation reaction to form a dipeptide • Multiple amino acids can bond to each other one at a time, forming a long chain called a POLYPEPTIDE Peptide Bonds – link amino acids Protein shape • Each protein has a specific, and complex shape • Proteins are composed of one or more polypeptides • Different shapes allow proteins to perform different functions Protein Shape Determines Function • Proteins with only primary and secondary structures are called fibrous proteins (claws, beaks, keratin, wool, collagen, ligaments, reptile scales) • Proteins with only 1,2,3 shapes are called globular proteins • If a protein is incorrectly folded, it can’t function correctly • Not understood how proteins fold themselves, seem to have molecules called chaperone proteins or chaperonins that assist others • A protein is denatured when it loses its shape and therefore its ability to function correctly 21 20 Four Levels of Protein Structure/ Conformation 1. Primary - unique linear sequence in which amino acids are joined, can have dire circumstances if changed (insulin) 2. Secondary - refers to three dimensional shapes that are the result of H bonding at regular intervals, due to interactions between the amino acid backbones • alpha helix is a coiled shape • beta pleated sheet is an accordion shape 19 3. Tertiary Complex 3-D globular shape due to interactions between R groups of amino acids in it • Globular proteins such as enzymes are held in position by these interactions 4. Quaternary Consist of more than one polypeptide chain subunits, associated with interactions between these chains 22 Protein Conformation Primary Structure – sequence of amino acids Secondary structure – Folding and coiling due to H bond formation between carboxyl and amino groups of non-adjacent amino acid. R groups are NOT involved. Tertiary structure – disulfide bridges, ionic bonding, or H-bonding of R-groups Quaternary structure – 2+ amino acid chains R- group interactions, H bonds, ionic interactions Primary Structure • A unique sequence of amino acids in a long polypeptide chain • Any changes in primary structure can affect a protein’s conformation and its ability to function • Example: Sickle cell anemia Primary structure • The sequence of amino acids • Involves peptide bonds between the carboxyl and amine groups LYS VAL PHE GLY ARG CYS Sickle cell anaemia • Sickling occurs due to a mutation of the Hb gene, associated with replacement of glutamic acid by valine Secondary Structure • Segments of the polypeptide strand repeatedly coil or fold in a pattern which contributes to the overall conformation • Made by hydrogen bonds between the backbone of the amino acids (amino group and carboxyl groups) Structures formed include: • α-helices: area with a helical or spiral shape. Held together by H bonds between every 4th amino acid • β-pleated sheets: area where 2 or more regions of the polypeptide chain lie in parallel Secondary Structure Secondary structure • The amino acids in the primary structure can bond together to form : • a) An alpha helix b) a beta pleat • The bonds involved are hydrogen bonds • Large proteins will have regions containing both structures Tertiary Structure Made of irregular contortions from interactions between side chains (R groups) 1. Hydrogen Bonds: between polar side groups 2. Ionic Bonds: between positively and negatively charged side chains 3. Hydrophobic Interactions: non-polar side chains end up on the inside of a protein, away from water—caused by water excluding these side chains from H bond interactions. Once together, held in place by dipole-dipole interactions 4. Disulfide Bridges: strong covalent bonds between cytosine’s sulfhydryl (-SH) groups TERTIaRY STRUCTURE • The protein molecule undergoes further twisting and folding to form a 3 dimensional shape • The structure is held in place by interactions between R-groups of the different amino acids Tertiary Structure Quaternary Structure The overall protein structure that results from the aggregation of 2 or more polypeptide subunits QUATERNARY STRUCTURE • Proteins can contain more than one protein chain • E.g. immunoglobulins (form antibodies) Chain 3 Chain 2 Chain 1 • The bonds involved are the same as those for tertiary structure Review: The Four Levels of Protein Folding Denaturing of Protein Proteins can be denatured by: • Transfer from aqueous solution to an organic solvent (e.g. chloroform) • Any chemical that disrupts H-bonds, ionic bonds, & disulfide bridges • Excessive heat • Changes in pH Denaturation • Protein conformation depends on the physical and chemical conditions of the protein’s environment • pH, salt concentration, temperature, and other aspects of the environment (aqueous or organic solvent) can unravel or change the conformation of the protein. • Change in protein shape causes it to lose its function • Some proteins can renature and reform their conformation, other cannot. TESTING FOR PROTEINS • Measure out 2cm3 of test solution into a test tube • Add 2 cm3 of Biuret solution • Shake and record colour change for each sample • Positive result = colour change from blue to lilac