BCHM 3050 1st Edition Lecture 4Outline of Last Lecture I. Molecular structure of waterII. Bonds III. Non-Polar Covalent bondsIV. Polar Covalent bondsV. Hydrogen BondingVI. Ionic BondsVII. Van der Waals ForcesVIII. Water is an ideal biological solventIX. Hydrophobic EffectX. Solvent Properties of WaterOutline of Current Lecture I. Weak AcidsII. Ionization of WaterIII. Buffers IV. Henderson-Hasselbalch EquationV. Types of Buffers VI. Amino AcidsCurrent LectureI. Weak Acidsa. Weak acids dissociate but not completelyb. Lose proton & gain negative chargec. Water gains the protond. Conjugate base has one less proton than its weak acide. Conjugate base of H2PO4- is HPO42-II. Ionization of Watera. 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.c. Strength of weak acid is expressed by pKad. Reactions with weak acids are reversiblee. Ka = how much of the weak acid is dissociatedf. Weak acids – HF, HCNIII. Buffersa. Need a weak acid to make a bufferb. Cannot have a strong acid and a strong base living in the same test tubec. HCl + NaOHà H2O + NaCl (both of the original reacts completely dissociated)d. CH3COOH + NaOHßà CH3COO-Na+ + H2O (some of the reactants are still left)e. Perfect buffer have equal concentrations of both; ideal balancef. pH = pKaIV. Henderson-Hasselbalch Equationa. Establishes the relationship between pH and pKa for selecting a bufferb. Buffers are most effective when they are composed of equal parts of weak acid and conjugate basec. pH = pKa + log [A-/HA]d. Practice: Calculate the pH of a mixture of 0.25 M acetic acid (CH3COOH) and 0.1 M sodium acetate (NaC2H3O2). The pKa of acetic acid is 4.76i. pH = 4.76 + log [0.1/0.25] = 4.36ii. 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-]V. Types of Buffersa. Bicarbonate is a very common physiological buffer in our bodyb. Protein buffer = hemoglobinc. Phosphate bufferVI. Amino Acidsa. Amino acids are the building blocks of proteins and polypeptidesb. Central Dogma explains the relationship between macromoleculesi. 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 sequenceof amino acids to form a proteinc. Proteins are the first biological step towards the outward display of phenotypic traitsi. Collagen is present in hair and skind. General Structure of Amino Acids i. 20 standard amino acids ii. Basic structure: iii. Amino group (NH2 à basic b/c has the ability to accept a proton) iv. Carboxyl group (COOH à 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 zerovii. Zwitterion – can have positive and negative charge in the same moleculee. Classification of Amino Acidsi. “R” group is what lends “uniqueness” to the amino acidii. R groups can be polar or nonpolariii. Neutral polar – no charge, but still hydrophilic due to side groupsiv. Memorize them in polar, nonpolar, acidic, basic groupsv. Nonpolar – only carbons and hydrogens in R groups (sometimes sulfurs, but not terminal sulfur); anything that cannot interact with watervi. Polar – terminal OH, SH, CONH2; most are neutral polar, form hydrogen bonds and do not contribute to a full positive or negative chargevii. Acidic amino acids – have COO-; negatively chargedviii. Basic amino acids – have terminal amino group; positively
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