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Molecules of Life II CHAPTER 3 Proteins • Amino Acid Monomers • Polypeptide (protein) Polymers • Levels of Protein Structure • Importance of Structure to Function Nucleic Acids • Nucleotides • Polymers • DNA vs.. RNA Proteins • A protein is a polymer constructed from amino acid monomers. • Proteins perform most of the tasks the body needs to function: • Structural Support • Docking and Reception • Storage • Catalysis (Enzymes) • Movement • Transport • Chemical messaging (hormones) • Sensing • Body or Cellular Defense • Regulation and Control Examples of Some Types of Proteins and Their Functions Figure 3.19 The Monomers: Amino Acids • • All proteins are constructed from a common set of 20 kinds of monomers known as amino acids or peptides Each amino acid consists of: 1. A central carbon atom bonded to four covalent partners 2. An amino (NH2) group, which is basic and polar 3. A carboxyl ( ) group, which is acidic and polar 4. A side group that can be either hydrophobic or hydrophylic Example of An Amino Acid Which Allegedly Makes One Sleepy Figure 3.1 Proteins as Polymers • Cells link amino acids together by dehydration reactions, forming peptide bonds between them Protein Polymers (Polypeptides) are Highly Variable • Your body has tens of thousands of different kinds of protein. – The kind and arrangement of amino acids makes each one different. – Once an amino acid chain is built inside a cell, the chain folds up into a unique shape – Because structure gives rise to function, two proteins with even slightly different structure fold differently and behave differently – Any chemical or type of stress that changes the folded structure of a protein ruins its functionality Protein Structure Introduction Molecules of Life II CHAPTER 3 Proteins • Amino Acid Monomers • Polypeptide (protein) Polymers • Levels of Protein Structure • Importance of Structure to Function Nucleic Acids • Nucleotides • Polymers • DNA vs.. RNA Four Levels or Degrees of Protein Folding 1. Primary (1o) structure • The specific kinds of amino acids and their sequence in a polypeptide (protein chain) • A slight change in the primary structure of a protein affects its ability to function. Primary Protein Structure Four Levels or Degrees of Protein Folding 2. Secondary (2o) structure • The polypeptide chain folds into an alpha helix, sustained by Hbonds. • The polypeptide chain folds into a pleated sheet, sustained by Hbonds (b) Secondary Structure Four Levels or Degrees of Protein Folding 3. Tertiary (3o) structure • The alpha helices and pleated sheets then fold among each other • New level of structure is supported by hydrogen, ionic, disulfide, and nonpolar bonds Tertiary Structure Four Levels or Degrees of Protein Folding 3. Quaternary (4o) structure • Several polypeptide chains join together to form a protein complex with subunits (d) Quaternary structure Unfavorable temperature and pH changes can cause a protein to unravel and lose its shape (denature) and thereby lose functionality Molecular Reconstruction of a Quaternary Structured Protein The Strength of Spider and Silkworm Protein • Especially strong because of multiple pleated sheet structures •These proteins are five times as strong as steel, twice as elastic as nylon, waterproof, and stretchable Hydrogen bonds Molecules of Life II CHAPTER 3 Proteins • Amino Acid Monomers • Polypeptide (protein) Polymers • Levels of Protein Structure • Importance of Structure to Function Nucleic Acids • Nucleotides • Polymers • DNA vs. RNA Nucleic Acids • Nucleic acids are information storage molecules. – They provide the directions for building proteins. • Nucleic acids are build of monomers called nucleotides – Ribonucleotides are used in making the polymer called ribonucleic acid (RNA) – Deoxyribonucleotides are used in making the polymer called deoxyribonucleic acids (DNA) Nucleotides are Composed of a Phosphate, Sugar, and Nitrogenous Base Nitrogenous Bases Contain Either One or Two Rings • Nucleotide monomers are linked into long chains. – These chains are called polynucleotides, or DNA strands. – A sugar-phosphate backbone joins them together. DNA and RNA Structure Nucleic Acids Are Polymers of Nucleotides RNA is a simple chain of ribonucleotides DNA is a Double Stranded Molecule Held Together By Hydrogen Bonds DNA Molecule as a Ladder: The DNA Molecule is twisted into a Two Rails Held Together By Rungs spiral in 3-dimensional space Evolution Connection: DNA and Proteins as Evolutionary Tape Measures • Evolutionary relationships between organisms can be assessed. – Molecular genealogy extends to relationships between species. Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings Genetic and Evolutionary Relatedness Can Be Determined From DNA and Protein Similarities Figure 3.30 Molecules of Life II CHAPTER 3 Proteins • Amino Acid Monomers • Polypeptide (protein) Polymers • Levels of Protein Structure • Importance of Structure to Function Nucleic Acids • Nucleotides • Polymers • DNA vs.. RNA