Campbell Biology - Chapter 5: Protein Structure and Function PDF

Campbell Biology Third Canadian Edition Chapter 5 The Structure and Function of Large Biological Molecules Copyright © 2021 Pearson Canada, Inc. 5-1 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 m...

Campbell Biology Third Canadian Edition Chapter 5 The Structure and Function of Large Biological Molecules Copyright © 2021 Pearson Canada, Inc. 5-1 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 – Speeding up (catalyzing) chemical reactions – structural support – storage – transport – cellular communications – movement – defense against foreign substances Copyright © 2021 Pearson Canada, Inc. 5-2 Enzymes Enzymes are a type of protein that act as catalysts to speed up chemical reactions Enzymes can perform their functions repeatedly, functioning as workhorses that carry out the processes of life Copyright © 2021 Pearson Canada, Inc. 5-3 An Overview of Protein Functions (1 of 8) Enzymatic proteins Function: Selective acceleration of chemical reactions Example: Digestive enzymes catalyze the hydrolysis of bonds in food molecules. Figure 5.13 An overview of protein functions. Copyright © 2021 Pearson Canada, Inc. 5-4 An Overview of Protein Functions (2 of 8) 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. Figure 5.13 An overview of protein functions. Copyright © 2021 Pearson Canada, Inc. 5-5 An Overview of Protein Functions (3 of 8) Hormonal proteins Function: Coordination of an organism’s activities Example: Insulin, a hormone secreted by the pancreas, causes other tissues to take up glucose, thus regulating blood sugar concentration Figure 5.13 An overview of protein functions. Copyright © 2021 Pearson Canada, Inc. 5-6 An Overview of Protein Functions (4 of 8) 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. Figure 5.13 An overview of protein functions. Copyright © 2021 Pearson Canada, Inc. 5-7 An Overview of Protein Functions (5 of 8) Defensive proteins Function: Protection against disease Example: Antibodies inactivate and help destroy viruses and bacteria. Figure 5.13 An overview of protein functions. Copyright © 2021 Pearson Canada, Inc. 5-8 An Overview of Protein Functions (6 of 8) 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. Figure 5.13 An overview of protein functions. Copyright © 2021 Pearson Canada, Inc. 5-9 An Overview of Protein Functions (7 of 8) 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. Figure 5.13 An overview of protein functions. Copyright © 2021 Pearson Canada, Inc. 5 - 10 An Overview of Protein Functions (8 of 8) 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. Figure 5.13 An overview of protein functions. Copyright © 2021 Pearson Canada, Inc. 5 - 11 Animation: Contractile Proteins Copyright © 2021 Pearson Canada, Inc. 5 - 12 Animation: Defensive Proteins Copyright © 2021 Pearson Canada, Inc. 5 - 13 Animation: Enzymes Copyright © 2021 Pearson Canada, Inc. 5 - 14 Animation: Gene Regulatory Proteins Copyright © 2021 Pearson Canada, Inc. 5 - 15 Animation: Hormonal Proteins Copyright © 2021 Pearson Canada, Inc. 5 - 16 Animation: Receptor Proteins Copyright © 2021 Pearson Canada, Inc. 5 - 17 Animation: Sensory Proteins Copyright © 2021 Pearson Canada, Inc. 5 - 18 Animation: Storage Proteins Copyright © 2021 Pearson Canada, Inc. 5 - 19 Animation: Structural Proteins Copyright © 2021 Pearson Canada, Inc. 5 - 20 Animation: Transport Proteins Copyright © 2021 Pearson Canada, Inc. 5 - 21 Proteins are Polymers of Amino Acids All proteins are polymers constructed from the same set of 20 amino acids Amino acids are linked together into unbranched polymers called polypeptides (few to more than 1000 monomers) A protein is a biologically functional molecule that consists of one or more polypeptide Copyright © 2021 Pearson Canada, Inc. 5 - 22 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 UnFigure 5.1 Copyright © 2021 Pearson Canada, Inc. 5 - 23 The 20 Amino Acids of Proteins: Nonpolar Amino Acids Figure 5.14 The 20 amino acids of proteins. Copyright © 2021 Pearson Canada, Inc. 5 - 24 The 20 Amino Acids of Proteins: Polar Amino Acids Figure 5.14 The 20 amino acids of proteins. Copyright © 2021 Pearson Canada, Inc. 5 - 25 The 20 Amino Acids of Proteins: Electrically Charged Amino Acids Figure 5.14 The 20 amino acids of proteins. Copyright © 2021 Pearson Canada, Inc. 5 - 26 Polypeptides (Amino Acid Polymers) Amino acids are linked by peptide bonds A polypeptide is a polymer of amino acids Figure 5.15 Making a polypeptide chain. Copyright © 2021 Pearson Canada, Inc. 5 - 27 Amino Acid Polymers Polypeptides range in length from a few to more than a thousand amino acids Each polypeptide has unique linear sequence of amino acids, with an amino end (N-terminus) and a carboxyl end (C-terminus) Figure 5.15b Making a polypeptide chain. Copyright © 2021 Pearson Canada, Inc. 5 - 28 Protein Structure and Function (1 of 2) A functional protein consists of one or more polypeptides folded precisely into a unique shape, or conformation – Protein function relies on intricate three-dimensional architecture Figure 5.16 Visualizing Proteins Copyright © 2021 Pearson Canada, Inc. 5 - 29 Protein Structure and Function (2 of 2) The sequence of amino acids determines a protein’s three-dimensional structure Protein structure determines its function – Function usually depends on ability to recognize and bind other molecule(s) Figure 5.17 Complementarity of shape between two protein surfaces. Copyright © 2021 Pearson Canada, Inc. 5 - 30 Four Levels of Protein Structure (1 of 2) Primary structure of a protein is its unique amino acids sequence Secondary structure are coils and folds within the polypeptide chain Tertiary structure is determined by interactions among various side chains (R groups) Quaternary structure is when a protein consists of multiple polypeptide chains Copyright © 2021 Pearson Canada, Inc. 5 - 31 Four Levels of Protein Structure (2 of 2) Animation: Protein Structure Introduction Right-click slide / select “Play” Copyright © 2021 Pearson Canada, Inc. 5 - 32 Protein Structure and Function (1 of 6) Figure 5.18a Exploring Primary structure, the Levels of Protein Structure. sequence of amino acids, is like the order of letters in a long word Primary structure is determined by inherited genetic information Copyright © 2021 Pearson Canada, Inc. 5 - 33 Protein Structure and Function (2 of 6) Animation: Primary Protein Structure Right-click slide / select “Play” Copyright © 2021 Pearson Canada, Inc. 5 - 34 Protein Structure and Function (3 of 6) Secondary structure results from hydrogen bonds between repeating constituents Figure 5.18b Exploring Levels of Protein Structure. Typical secondary structures include: – coil called an α-helix, and – folded structure called a β-pleated sheet Copyright © 2021 Pearson Canada, Inc. 5 - 35 Protein Structure and Function (4 of 6) Animation: Secondary Protein Structure Right-click slide / select “Play” Copyright © 2021 Pearson Canada, Inc. 5 - 36 Protein Structure and Function (5 of 6) Tertiary structure is the overall shape of a polypeptide, and is determined by interactions between R groups, not by interactions between backbone constituents Figure 5.18 Exploring Levels of Protein Structure. Copyright © 2021 Pearson Canada, Inc. 5 - 37 Protein Structure and Function (6 of 6) Animation: Tertiary Protein Structure Right-click slide / select “Play” Copyright © 2021 Pearson Canada, Inc. 5 - 38 Protein Structure and Function: Tertiary Structure Interactions between R groups include hydrogen bonds, ionic bonds, hydrophobic interactions, and van der Waals interactions Strong covalent bonds called disulfide bridges reinforce the protein’s structure Figure 5.18 Exploring Levels of Protein Structure. Copyright © 2021 Pearson Canada, Inc. 5 - 39 Quaternary Structure (1 of 2) Quaternary structure results when two or more polypeptide chains form one macromolecule Figure 5.18 Exploring Levels of Protein Structure. Copyright © 2021 Pearson Canada, Inc. 5 - 40 Quaternary Structure (2 of 2) Animation: Quaternary Protein Structure Right-click slide / select “Play” Copyright © 2021 Pearson Canada, Inc. 5 - 41 Example of Quaternary Structure (1 of 2) Collagen is a fibrous protein consisting of three polypeptides coiled like a rope Figure 5.18 Exploring Levels of Protein Structure. Copyright © 2021 Pearson Canada, Inc. 5 - 42 Example of Quaternary Structure (2 of 2) Hemoglobin is a globular protein consisting of four polypeptides: two alpha and two beta chains Figure 5.18 Exploring Levels of Protein Structure. Copyright © 2021 Pearson Canada, Inc. 5 - 43 Sickle-Cell Disease: A Change in Primary Structure A change in primary structure can affect a protein’s structure and function Sickle-cell disease results from an amino acid substitution in hemoglobin Figure 5.19 A single amino acid substitution in a protein causes sicklecell disease. Mike Agliolo/Science Source Copyright © 2021 Pearson Canada, Inc. 5 - 44 What Determines Protein Structure? In addition to primary structure, physical and chemical conditions can affect structure Alterations in pH, salt concentration, temperature, or other environmental factors can cause a protein to denature, or unravel – Denatured proteins are biologically inactive Figure 5.20 Denaturation and renaturation of a protein. Copyright © 2021 Pearson Canada, Inc. 5 - 45 Protein Folding in the Cell It is hard to predict a protein’s structure from its primary structure Most proteins probably go through several stages on their way to a stable structure Diseases such as Alzheimer’s, Parkinson’s, and mad cow disease are associated with misfolded proteins Copyright © 2021 Pearson Canada, Inc. 5 - 46 Protein structure X-ray crystallography can be used to determine a protein’s 3-D structure Another method is nuclear magnetic resonance (NMR) spectroscopy – does not require protein crystallization Bioinformatics uses computer programs to predict protein structure from amino acid sequences Copyright © 2021 Pearson Canada, Inc. 5 - 47 Inquiry: What can 3-D Shape of RNA Polymerase II Tell Us About Its Function? In 2006, Roger Kornberg received Nobel Prize for solving 3-D conformation of RNA Polymerase II Determined function of different regions Figure 5.21 Research Method X-Ray Crystallography Copyright © 2021 Pearson Canada, Inc. 5 - 48