LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION

LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson Chapter 5 (continued) The Structure and Function of Proteins Lectures modified by Garrett Dancik Lectures by Erin Barley Kathleen Fitzpatrick © 2011 Pearson Education, Inc. Concept 5.4: Proteins include a diversity of 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 2 © 2011 Pearson Education, Inc. Figure 5.15a Enzymatic proteins Function: Selective acceleration of chemical reactions Example: Digestive enzymes catalyze the hydrolysis of bonds in food molecules. Enzyme • Enzymes are a type of protein that acts as a catalyst to speed up chemical reactions • Enzymes can perform their functions repeatedly, functioning as workhorses that carry out the processes of life • http://www.biotopics.co.uk/other/morinf.html 3 Figure 5.15b Storage proteins Function: Storage of amino acids Examples: Casein, the protein of milk, is the major source of amino acids for baby mammals. Plants have storage proteins in their seeds. Ovalbumin is the protein of egg white, used as an amino acid source for the developing embryo. Ovalbumin Amino acids for embryo 4 Figure 5.15c Hormonal proteins Function: Coordination of an organismʼs activities Example: Insulin, a hormone secreted by the pancreas, causes other tissues to take up glucose, thus regulating blood sugar concentration High blood sugar Insulin secreted Normal blood sugar Insulin protein entry: https://www.ncbi.nlm.nih.gov/protein/AAA59172.1 5 Insulin and Glucose transport 6 Figure 5.15d Contractile and motor proteins Function: Movement Examples: Motor proteins are responsible for the undulations of cilia and flagella. Actin and myosin proteins are responsible for the contraction of muscles. Actin Muscle tissue Myosin 100 µm 7 Figure 5.15e Defensive proteins Function: Protection against disease Example: Antibodies inactivate and help destroy viruses and bacteria. Antibodies Virus Bacterium COVID example: https://www.ncbi.nlm.nih.gov/Structure/pdb/7R7N 8 Figure 5.15f Transport proteins Function: Transport of substances Examples: Hemoglobin, the iron-containing protein of vertebrate blood, transports oxygen from the lungs to other parts of the body. Other proteins transport molecules across cell membranes. Transport protein Cell membrane 9 Figure 5.15g Receptor proteins Function: Response of cell to chemical stimuli Example: Receptors built into the membrane of a nerve cell detect signaling molecules released by other nerve cells. Signaling molecules Receptor protein 10 Figure 5.15h Structural proteins Function: Support Examples: Keratin is the protein of hair, horns, feathers, and other skin appendages. Insects and spiders use silk fibers to make their cocoons and webs, respectively. Collagen and elastin proteins provide a fibrous framework in animal connective tissues. Collagen Connective tissue 60 µm 11 p53 stress response pathway Stress signals such as DNA damage activation of p53 The activated p53 protein binds to a specific DNA sequence… composed of RRRCWWGYYY (spacer of 0–21 nucleotides) RRRCWWGYYY, where R is a purine, W is A or T, and Y is a pyrimidine. https://www.nature.com/articles/1208615 12 Harris, S. L., & Levine, A. J. (2005). The p53 pathway: positive and negative feedback loops. Oncogene, 24(17), 2899–2908. Proteins • Amino acids are the building blocks (monomers) of proteins – Amino acids are organic molecules with carboxyl and amino groups – Amino acids differ in their properties due to differing side chains, called R groups (see next slide) • Polypeptides are unbranched polymers built from the same set of 20 amino acids • A protein is a biologically functional molecule that consists of one or more polypeptides 13 © 2011 Pearson Education, Inc. Figure 5.UN01 Side chain (R group) a carbon Amino group Carboxyl group 14 Figure 5.16 Nonpolar side chains; hydrophobic Side chain (R group) Glycine (Gly or G) Alanine (Ala or A) Methionine (Met or M) Isoleucine (Ile or I) Leucine (Leu or L) Valine (Val or V) Phenylalanine (Phe or F) Tryptophan (Trp or W) Proline (Pro or P) Polar side chains; hydrophilic Serine (Ser or S) Threonine (Thr or T) Cysteine (Cys or C) Electrically charged side chains; hydrophilic Tyrosine (Tyr or Y) Asparagine (Asn or N) Glutamine (Gln or Q) Basic (positively charged) Acidic (negatively charged) Aspartic acid (Asp or D) Glutamic acid (Glu or E) Lysine (Lys or K) Arginine (Arg or R) Histidine (His or H) 15 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 to more than a thousand monomers (amino acids) • Each polypeptide has a unique linear sequence of amino acids, with a carboxyl end (C-terminus) and an amino end (N-terminus) 16 © 2011 Pearson Education, Inc. Figure 5.17 Methionine (M) Tyrosine (Y) Cysteine (C) How are peptide bonds formed? Peptide bond Methionine (M) Tyrosine (Y) New peptide bond forming Cysteine (C) Side chains Backbone Amino end (N-terminus) Peptide bond Carboxyl end (C-terminus) 17 • A functional protein consists of one or more polypeptides precisely twisted, folded, and coiled into a unique shape • The sequence of amino acids determines a proteinʼs three-dimensional structure • A proteinʼs structure determines its function • Bioinformatics uses computer programs to predict protein sequence, structure and function from amino acid sequences Groove Groove (a) A ribbon model (b) A space-filling model 18 Figure 5.19 Antibody protein Protein from flu virus 19 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 20 © 2011 Pearson Education, Inc. Figure 5.20a Primary structure Amino acids • Transthyretin polypeptide Amino end • Transports thyroid hormones • Transports retinol (Vitamin A) • Primary structure Primary structure of transthyretin – The sequence of amino acids in a protein – Determined by inherited genetic information Carboxyl end 21 Figure 5.20c • • Secondary structure results from hydrogen bonds between parts of the polypeptide backbone Secondary structure a helix Includes the a helix and b pleated sheet Hydrogen bond b pleated sheet b strand, shown as a flat arrow pointing toward the carboxyl end Hydrogen bond 22 • Tertiary structure is the shape of a polypeptide in three dimensions • Quaternary structure results when two or more polypeptide chains form one macromolecule (not all proteins have a quaternary structure) – Transthyretin is composed of 4 identical polypeptides 23 Figure 5.20b Putting it all together… (but primary structure is not shown) Tertiary structure Secondary structure Quaternary structure a helix Hydrogen bond b pleated sheet b strand Hydrogen bond Transthyretin polypeptide Transthyretin protein (composed of 4 identical polypeptides) 24 Sickle-Cell Disease: A Change in Primary Structure • A slight change in primary structure can affect a proteinʼs structure and ability to function – How does the primary structure change? • Sickle-cell disease, an inherited blood disorder, results from a single amino acid substitution in the protein hemoglobin • Genpept: – https://www.ncbi.nlm.nih.gov/protein/4504349 25 © 2011 Pearson Education, Inc. Heme Iron b subunit a subunit a subunit b subunit Hemoglobin is a protein made up of 4 polypeptide chains: two a and two b subunits 26 Figure 5.21 Sickle-cell hemoglobin Normal hemoglobin Primary Structure 1 2 3 4 5 6 7 V H L T P E E Secondary and Tertiary Structures Quaternary Structure Function Molecules do not associate with one another; each carries oxygen. Normal hemoglobin b subunit a Red Blood Cell Shape 10 µm b a b 1 2 3 4 5 6 7 V H L T P V E Exposed hydrophobic region Sickle-cell hemoglobin Molecules crystallize into a fiber; capacity to carry oxygen is reduced. a b b subunit 10 µm a b 27