BCHM 3050 1st Edition Lecture 4 Outline of Last Lecture I Molecular structure of water II Bonds III Non Polar Covalent bonds IV Polar Covalent bonds V Hydrogen Bonding VI Ionic Bonds VII Van der Waals Forces VIII Water is an ideal biological solvent IX Hydrophobic Effect X Solvent Properties of Water Outline of Current Lecture I Weak Acids II Ionization of Water III Buffers IV Henderson Hasselbalch Equation V Types of Buffers VI Amino Acids Current Lecture I II Weak Acids a Weak acids dissociate but not completely b Lose proton gain negative charge c Water gains the proton d Conjugate base has one less proton than its weak acid e Conjugate base of H2PO4 is HPO42Ionization of Water a Strong acid all protons are dissociated all hydrogen ions is on the right side of the reaction b With strong acid only need to worry about pH These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute III IV V VI c Strength of weak acid is expressed by pKa d Reactions with weak acids are reversible e Ka how much of the weak acid is dissociated f Weak acids HF HCN Buffers a Need a weak acid to make a buffer b Cannot have a strong acid and a strong base living in the same test tube c HCl NaOH H2O NaCl both of the original reacts completely dissociated d CH3COOH NaOH CH3COO Na H2O some of the reactants are still left e Perfect buffer have equal concentrations of both ideal balance f pH pKa Henderson Hasselbalch Equation a Establishes the relationship between pH and pKa for selecting a buffer b Buffers are most effective when they are composed of equal parts of weak acid and conjugate base c pH pKa log A HA d Practice Calculate the pH of a mixture of 0 25 M acetic acid CH 3COOH and 0 1 M sodium acetate NaC2H3O2 The pKa of acetic acid is 4 76 i pH 4 76 log 0 1 0 25 4 36 ii If a base is added to the buffer the balance shifted to A iii Ex add 0 05M NaOH 0 05M added to A and 0 05M lost from HA Types of Buffers a Bicarbonate is a very common physiological buffer in our body b Protein buffer hemoglobin c Phosphate buffer Amino Acids a Amino acids are the building blocks of proteins and polypeptides b Central Dogma explains the relationship between macromolecules i explains the storage retrieval expression of genetic information ii Replication Duplication of DNA to make an identical copy iii Transcription Reading of a gene and its transcription into RNA iv Translation Translation of RNA sequence into the corresponding sequence of amino acids to form a protein c Proteins are the first biological step towards the outward display of phenotypic traits i Collagen is present in hair and skin d General Structure of Amino Acids i 20 standard amino acids ii Basic structure iii Amino group NH2 basic b c has the ability to accept a proton iv Carboxyl group COOH acidic will donate H v R group what is different between the amino acids vi Isoelectric point the pH at which an amino acid has a net charge of zero vii Zwitterion can have positive and negative charge in the same molecule e Classification of Amino Acids i R group is what lends uniqueness to the amino acid ii R groups can be polar or nonpolar iii Neutral polar no charge but still hydrophilic due to side groups iv Memorize them in polar nonpolar acidic basic groups v Nonpolar only carbons and hydrogens in R groups sometimes sulfurs but not terminal sulfur anything that cannot interact with water vi Polar terminal OH SH CONH2 most are neutral polar form hydrogen bonds and do not contribute to a full positive or negative charge vii Acidic amino acids have COO negatively charged viii Basic amino acids have terminal amino group positively charged
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