Proteins and Nucleic Acids

Proteins and Nucleic Acids

Chapter 5 Macromolecules: Proteins Proteins Most structurally & functionally diverse group of biomolecules. : o Involved in almost everything o Enzymes o Structure (keratin, collagen) o Carriers & transport (membrane channels) o Receptors & binding (defense) o Contraction (actin & myosin) o Signaling (hormones) o Storage (bean seed proteins) Structure: o Monomer = amino acids 20 different amino acids o Polymer = polypeptide Protein can be 1 or more polypeptide chains folded & bonded together. Large & complex molecules Complex 3-D shape Amino Acids o Structure: Central Carbon Amino Group Carboxyl Group (acid) R Group (side chain) Variable group Confers unique chemical properties of the amino acid. Nonpolar Amino Acids (Hydrophobic) WHY? 1

Polar Amino Acids (Hydrophilic) WHY? Building Proteins Peptide Bonds: dehydration synthesis o Linking NH 2 of 1 amino acid to COOH of another. o C N bond Polypeptide Chains o N-terminal = NH 2 end o C-terminal = COOH end o Repeated sequence (N-C-C) is the polypeptide backbone Grow in one direction 2

Protein Structure & Function depends on structure. o 3-D structure Twisted, folded, coiled into unique shape. All starts with the order of amino acids. o What determines that order of amino acids? Primary (1 ) Structure Order of amino acids in chain o Amino acid sequence determined by DNA o Slight change in amino acid sequence can affect protein s structure & it s function Even just one amino acid change can make all the difference! Secondary (2 ) Structure Folding along short sections of polypeptide o interaction between adjacent amino acids o H bonds between R groups o α-helix o β-pleated sheet Tertiary (3 ) Structure Determined by interactions between R groups o Hydrophobic interactions Effect of water in cell o Anchored by disulfide bridges (H & ionic bonds) 3

Quaternary (4 ) Structure Joins together more than 1 polypeptide chain. o Only then is it a functional protein. Protein Structure Review Denature a protein Disrupt 3 structure o ph salt temperature Unravel or denature protein. Disrupts H bonds, ionic bonds & disulfide bridges. Some proteins can return to their functional shape after denaturation, many cannot. 4

Chapter 5 Macromolecules: Nucleic Acids Nucleic Acids : o Store & transmit hereditary information Examples: o RNA (ribonucleic acid) o DNA (deoxyribonucleic acid) Structure: o Monomers = nucleotides Nucleotides 3 parts o Nitrogen Base (C-N ring) o Pentose Sugar (5C) Ribose in RNA Deoxyribose in DNA o PO 4 group 2 Types of Nucleotides o Different Nitrogen bases o Purines Double ring N base Adenine (A) Guanine (G) o Pyrimidines Single ring N base Cytosine (C) Thymine (T) Uracil (U) 1

Nucleic Polymer Backbone o Sugar to PO 4 bond o Phosphodiester bond New base added to sugar of previous base Polymer grows in one direction o N bases hang off the sugar-phosphate backbone RNA & DNA RNA o Single nucleotide chain DNA o Double nucleotide chain N bases bond in pairs across chains. o Spiraled in a double helix. Double helix 1st proposed as structure of DNA in 1953 by James Watson & Francis Crick. Pairing of Nucleotides o Nucleotides bond between DNA strands o H bonds between purine AND pyrimidine A :: T 2 H bonds G :: C 3 H bonds Information Polymer o Series of bases encodes information Like the letters of a book o Stored information is passed from parent to offspring Need to copy accurately o Stored information = genes DNA Molecule Double helix o H bonds between bases join the 2 strands A :: T C :: G Why is it important that the strands are bonded by H bonds? Copying DNA o Replication 2 strands of DNA helix are complementary Have one, can build other Have one, can rebuild the whole Why is this a good system? When in the life of a cell does replication occur? mitosis meiosis 2

Cool Beans Ratio of A-T::G-C affects stability of DNA molecule. o 2 H bonds vs. 3 H bonds More G-C = need higher T to separate strands. High T organisms have more G- C. Parasites have many A-T (don t know why). ATP Adenosine Triphosphate Modified nucleotide o Adenine ribose + Pi + Pi + Pi Macromolecule Review 1) Carbohydrates Structure / monomer o monosaccharide o Energy o Raw materials o Energy storage o Structural compounds Examples o glucose, starch, cellulose, glycogen 3

2) Lipids Structure / building block o Glycerol, fatty acid, cholesterol, H-C chains o Energy storage o Membranes o Hormones Examples o Fat, phospholipids, steroids 3) Proteins Structure / monomer o Amino Acids o Levels of structure Enzymes, Defense, Transport, Structure, Signals, Receptors Examples o Digestive enzymes, membrane channels, insulin hormone, actin 4)Nucleic Acids Structure / Monomer o Nucleotide o Information storage & Transfer Examples o DNA, RNA 4