* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Proteins
Paracrine signalling wikipedia , lookup
Ribosomally synthesized and post-translationally modified peptides wikipedia , lookup
Peptide synthesis wikipedia , lookup
Signal transduction wikipedia , lookup
Gene expression wikipedia , lookup
Expression vector wikipedia , lookup
G protein–coupled receptor wikipedia , lookup
Ancestral sequence reconstruction wikipedia , lookup
Magnesium transporter wikipedia , lookup
Amino acid synthesis wikipedia , lookup
Point mutation wikipedia , lookup
Genetic code wikipedia , lookup
Homology modeling wikipedia , lookup
Biosynthesis wikipedia , lookup
Interactome wikipedia , lookup
Protein purification wikipedia , lookup
Metalloprotein wikipedia , lookup
Western blot wikipedia , lookup
Two-hybrid screening wikipedia , lookup
Protein–protein interaction wikipedia , lookup
Proteins Concept 5.4: Proteins have many structures, resulting in a wide range of functions • Proteins account for more than 50% of the dry mass of most cells • Protein functions include structural support, storage, transport, cellular communications, movement, and defense against foreign substances [Animations are listed on slides that follow the figure] Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Animation: Structural Proteins Animation: Storage Proteins Animation: Transport Proteins Animation: Receptor Proteins Animation: Contractile Proteins Animation: Defensive Proteins Animation: Enzymes Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Animation: Hormonal Proteins Animation: Sensory Proteins Animation: Gene Regulatory Proteins Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Enzymes are a type of protein that acts as a catalyst, speeding up chemical reactions • Enzymes can perform their functions repeatedly, functioning as workhorses that carry out the processes of life Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 5-16 Substrate (sucrose) Glucose Enzyme (sucrose) Fructose Polypeptides • Polypeptides are polymers of amino acids • A protein consists of one or more polypeptides Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Amino Acid Monomers • Amino acids are organic molecules with carboxyl and amino groups • Amino acids differ in their properties due to differing side chains, called R groups • Cells use 20 amino acids to make thousands of proteins Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 5-UN78 a carbon Amino group Carboxyl group LE 5-17a Glycine (Gly) Alanine (Ala) Valine (Val) Leucine (Leu) Isoleucine (Ile) Nonpolar Methionine (Met) Phenylalanine (Phe) Tryptophan (Trp) Proline (Pro) LE 5-17b Polar Serine (Ser) Threonine (Thr) Cysteine (Cys) Tyrosine (Tyr) Asparagine (Asn) Glutamine (Gln) LE 5-17c Acidic Basic Electrically charged Aspartic acid (Asp) Glutamic acid (Glu) Lysine (Lys) Arginine (Arg) Histidine (His) Amino Acid Polymers • Amino acids are linked by peptide bonds • A polypeptide is a polymer of amino acids • Polypeptides range in length from a few monomers to more than a thousand • Each polypeptide has a unique linear sequence of amino acids Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Determining the Amino Acid Sequence of a Polypeptide • The amino acid sequences of polypeptides were first determined by chemical methods • Most of the steps involved in sequencing a polypeptide are now automated Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Protein Conformation and Function • A functional protein consists of one or more polypeptides twisted, folded, and coiled into a unique shape • The sequence of amino acids determines a protein’s three-dimensional conformation • A protein’s conformation determines its function • Ribbon models and space-filling models can depict a protein’s conformation Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 5-19 Groove A ribbon model Groove A space-filling model Four Levels of Protein Structure • The primary structure of a protein is its unique sequence of amino acids • Secondary structure, found in most proteins, consists of coils and folds in the polypeptide chain • Tertiary structure is determined by interactions among various side chains (R groups) • Quaternary structure results when a protein consists of multiple polypeptide chains Animation: Protein Structure Introduction Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 5-20 b pleated sheet +H 3N Amino end Amino acid subunits a helix • Primary structure, the sequence of amino acids in a protein, is like the order of letters in a long word • Primary structure is determined by inherited genetic information Animation: Primary Protein Structure Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 5-20a Amino end Amino acid subunits Carboxyl end • The coils and folds of secondary structure result from hydrogen bonds between repeating constituents of the polypeptide backbone • Typical secondary structures are a coil called an alpha helix and a folded structure called a beta pleated sheet Animation: Secondary Protein Structure Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 5-20b b pleated sheet Amino acid subunits a helix • Tertiary structure is determined by interactions between R groups, rather than interactions between backbone constituents • These interactions between R groups include hydrogen bonds, ionic bonds, hydrophobic interactions, and van der Waals interactions • Strong covalent bonds called disulfide bridges may reinforce the protein’s conformation Animation: Tertiary Protein Structure Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 5-20d Hydrophobic interactions and van der Waals interactions Polypeptide backbone Hydrogen bond Disulfide bridge Ionic bond • Quaternary structure results when two or more polypeptide chains form one macromolecule • Collagen is a fibrous protein consisting of three polypeptides coiled like a rope • Hemoglobin is a globular protein consisting of four polypeptides: two alpha and two beta chains Animation: Quaternary Protein Structure Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 5-20e Polypeptide chain b Chains Iron Heme Polypeptide chain Collagen a Chains Hemoglobin Sickle-Cell Disease: A Simple Change in Primary Structure • A slight change in primary structure can affect a protein’s conformation and ability to function • Sickle-cell disease, an inherited blood disorder, results from a single amino acid substitution in the protein hemoglobin Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 5-21a 10 µm Red blood Normal cells are cell shape full of individual hemoglobin molecules, each carrying oxygen. 10 µm Red blood cell shape Fibers of abnormal hemoglobin deform cell into sickle shape. LE 5-21b Sickle-cell hemoglobin Normal hemoglobin Primary structure Val His 1 2 Leu Thr 3 4 Pro Glu 5 6 Secondary and tertiary structures 7 b subunit Quaternary Normal hemoglobin structure (top view) Primary structure Secondary and tertiary structures Molecules do not associate with one another; each carries oxygen. His Leu Thr Pro Val Glu 1 2 3 4 5 6 7 Exposed hydrophobic region b subunit a Quaternary structure b Val b a Function Glu Sickle-cell hemoglobin b a Function Molecules interact with one another to crystallize into a fiber; capacity to carry oxygen is greatly reduced. b a What Determines Protein Conformation? • In addition to primary structure, physical and chemical conditions can affect conformation • Alternations in pH, salt concentration, temperature, or other environmental factors can cause a protein to unravel • This loss of a protein’s native conformation is called denaturation • A denatured protein is biologically inactive Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 5-22 Denaturation Normal protein Denatured protein Renaturation The Protein-Folding Problem • It is hard to predict a protein’s conformation from its primary structure • Most proteins probably go through several states on their way to a stable conformation • Chaperonins are protein molecules that assist the proper folding of other proteins Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 5-23a Cap Hollow cylinder Chaperonin (fully assembled) LE 5-23b Polypeptide Steps of Chaperonin Action: An unfolded polypeptide enters the cylinder from one end. Correctly folded protein The cap attaches, causing the cylinder to change shape in such a way that it creates a hydrophilic environment for the folding of the polypeptide. The cap comes off, and the properly folded protein is released. • Scientists use X-ray crystallography to determine a protein’s conformation • Another method is nuclear magnetic resonance (NMR) spectroscopy, which does not require protein crystallization Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 5-24a X-ray diffraction pattern Photographic film Diffracted X-rays X-ray source X-ray beam Crystal LE 5-24b Nucleic acid X-ray diffraction pattern 3D computer model Protein