Exam 4 Outline CH 105 Spring 2012

Transcription

1 Exam 4 Outline CH 105 Spring 2012 You need to bring a pencil and your ACT card. Chapter 24: Lipids 1. Describe the properties and types of lipids a. All are hydrophobic b. Fatty acid-based typically contain carbons with COOH group i. Fatty acids 1. Saturated a. only alkyl b. can pack closely tend to be solids at RT 2. Unsaturated contain alkenes a. Cis i. kink in chain disrupts packing ii. liquids at RT b. Trans i. Straighter chains pack like saturated FA ii. Solids at RT 3. Polyunsaturated contain 2 or more alkenes ii. Triacylglycerols ester of glycerol (HOCH 2 CH(OH)CH 2 OH) and three FA 1. Solid at RT = fat 2. Liquid at RT = oil 3. Reactions of triacylglycerols a. Hydrogenation of unsaturated triacylglycerols i. Add H 2 to alkene groups in presence of metal catalyst (Pd, Ni, Pt, etc.) ii. Increases mp (liquid oil solid fat) Side reaction is major source of trans-fatty acids b. Saponification i. Strong base (for example: NaOH/H 2 O or KOH/H 2 O) ii. Makes glycerol + 3 RCOO M + (soap) Soap forms micelles in water 1. Spherical structure with hydrophobic interior and hydrophilic exterior 2. Single layer of fatty acid salts composes shell Glycerolphospholipids glycerol + 2 FA and 1 polar head group linked through phosphate group 1. Cell membranes a. Composed of double layer (bilayer) of lipids (glycerolphospholipids, cholesterol), and proteins b. Hydrophilic head groups pointed inward and outward (into water) c. Hydrophobic lipids point toward middle of bilayer d. Proteins flow in sea of lipids (fluid mosaic model)

2 2. Transport a. Diffusion passive transport of particles from high low concentration i. Must cross hydrophobic part of lipid bilayer ii. Often slow b. Facilitated transport diffusion from high low concentration through protein channels i. Bypasses hydrophobic barrier ii. Much faster for charged compounds Can be selective c. Active transport transport from low high concentration i. mediated by proteins ii. requires input of energy iv. Waxes esters of FA and long-chain alcohols c. Steroids all contain nucleus of 3 cyclohexane and 1 cyclopentane rings i. Cholesterol ii. Lipoproteins and the transport of cholesterol 1. Ball of triacylglycerols and cholesterol surrounded by single layer of glycerophospholipids, proteins, and cholesterol a. Polar groups on glycerophospholipids and cholesterol point outward into water, making hydrophobic particle soluble b. Used to transport cholesterol and triacylglycerols in body 2. LDL=low-density lipoprotein ( bad cholesterol ) carries cholesterol to cells and can deposit cholesterol in arteries 3. HDL=high-density lipoprotein ( good cholesterol ) carries cholesterol to liver for conversion to bile salts or elimination Chapter 18: Amino Acids and Proteins 1. Chirality (handedness) Identify the chiral atoms in organic molecules. a. Carbons with bonds to four different groups are chiral and can form two stereoisomers that are nonsuperimposible mirror images. b. You need to know this definition and should be able to recognize chiral carbons in a given structure. 2. Amino acids a. Building blocks of proteins b. Contain carboxylic acid and amino groups( COOH and NH 2 ) on same carbon (alpha carbon) c. You should know structures of six of the 20 amino acids i. Glycine ii. Alanine Methionine iv. Cysteine v. Glutamic acid/glutamate vi. Lysine

3 3. Typically, in solution, amino acids form zwitterions ( + H 3 N CHR COO ) a. Isoelectric point (pi) is ph where charges exactly balance (net charge = zero) b. At phs below pi i. COO COOH ii. Amino acid has a net positive charge c. At phs above pi... i. NH + 3 NH 2 ii. Amino acid has a net negative charge d. Be able to predict structure of amino acid at given ph if provided value of pi 4. Formation of amide bonds between COOH and NH 2 groups of two amino acids makes peptide bonds a. A peptide bond between 2 aa forms dipeptides b. Peptide bonds linking 3 aa in chain makes tripeptides, etc c. Polypeptides form by linking several aa in linear chain d. Proteins are large polypeptides 5. The polypeptide chains of proteins fold into complex structures a. Correct folding is necessary for function b. Can describe 4 levels of structure i. Primary 1. sequence of amino acids in peptide chain 2. for example, Ala Leu Cys Met ii. Secondary 1. 3-dimensional arrangements of polypeptide chains 2. Generally maintained by hydrogen bonds between backbone groups 3. Alpha helix 4. Beta pleated sheet iv. Tertiary 1. Folding of secondary structural elements 2. Generally maintained by interactions between side chains a. Hydrogen bonds b. Salt bridges c. Hydrophobic interactions d. Disulfide bonds (covalent) Quaternary 1. Combination of two or more tertiary subunits 2. Each tertiary subunit is individual polypeptide 3. Maintained by same interactions as tertiary 6. Disruption of protein structures a. No structure = no function b. Hydrolysis of peptide bonds (amides) i. Gives small peptides and eventually amino acids ii. Destroys protein structure at primary level c. Denaturation

4 i. Involves disruption of interactions that support secondary, tertiary, and quaternary structures of proteins ii. Reduction of disulfide bonds Disruption of weak interactions 1. Heat 2. Acids & bases (disrupt hydrogen bonds) 3. Organic compounds (disrupt hydrophobic interactions) 4. Mechanical agitation 7. Common Proteins a. Insoluble (fibrous) i. Keratin (skin, wool, feathers, fingernails, silk) ii. Collagen (animal hide, cornea, tendons, bone, etc) Elastin (blood vessels, ligaments) b. Soluble (globular) i. Hemoglobin (carries oxygen) ii. Albumin (transport in blood, egg white) Chapter 19: Enzymes and Vitamins 1. Enzymes are proteins that catalyze chemical reactions in biological systems reduce the activation energies of the reactions 2. Classes of enzymes a. Oxidoreductases catalyze oxidations or reductions b. Hydrolases catalyze hydrolysis reactions c. Isomerases catalyze change in 3D-arrangement of atoms in molecule d. Lyases catalyze additions to double bonds/eliminations to form double bonds e. (also transferases and ligases) 3. Enzyme action a. Active site is area of protein where reaction occurs b. Steps i. Substrate binds to active site to form enzyme-substrate complex ii. Reaction occurs Products are released iv. Repeat c. Lock-and-key model: Active site has rigid shape (lock) matching that of the substrate (key) d. Induced-fit model: Active site is flexible, adapting to shape of substrate 4. Effect of changes in temperature, ph, etc, on enzyme action a. Enzymes have optimal conditions for functioning b. High temperatures, high/low phs can disrupt protein structures 5. Inhibition of enzymes reduction in enzyme activity in presence of a compound a. Competitive i. Inhibitor reversibly binds to active site ii. Inhibitor blocks approach of substrate

5 b. Noncompetitive i. Inhibitor reversibly binds to area remote from active site (for example, protein surface) ii. Inhibitor changes shape of protein, altering active site c. Irreversible i. Inhibitor irreversibly binds to active site ii. Inhibitor permanently blocks approach of substrate dead enzyme 6. Vitamins and cofactors/coenzymes a. Enzymes often need accessory groups for proper function b. Cofactors/coenzymes i. Metal ions ii. Vitamins organic cofactors 1. Water-soluble (see table 19.3) excess excreted in urine 2. Fat-soluble (A, D, E, K) excess accumulates in fat tissue and is potentially toxic