MGD S1 Lecture 2 PDF

Amino Acids—>proteins Nucleotides —> nucleic acids Covalent bond: A covalent bond forms when two atoms come very close together and share one or more of their electrons. Each atom forms a fixed number of covalent bonds. MonoSach—>polySach Subunits of Macromolecules Acid Fatty acids—> fats,lipid...

Amino Acids—>proteins Nucleotides —> nucleic acids Covalent bond: A covalent bond forms when two atoms come very close together and share one or more of their electrons. Each atom forms a fixed number of covalent bonds. MonoSach—>polySach Subunits of Macromolecules Acid Fatty acids—> fats,lipids,membranes Base A chemical that can combine with a hydrogen ion (H+), i.e. it is a proton acceptor. ( or electron donor ) Ka:The tendency of an acid to lose a proton is defined by the acid dissociation constant • dec [H] & have PH >7 Amino acid: The building blocks of proteins. They are composed of a central carbon atom attached to four other chemical groups: an amino group (-NH2), a carboxyl group (COOH), a hydrogen atom and a variable group (R). • The higher Ka is, the more easily the acid dissociates, and the stronger it is •ka is directly related to [ H] -high Ka —>more acidic -low ka —>less acidic • Amino acids are most commonly classified by the chemical nature of their R group Pka (ph‫) ﻧﻔﺲ ﻣﻔﮭﻮم ال‬ The stronger the tendency of an acid to dissociate the lower the pKa value The stronger an acid, the greater the ionization, the lower the pKa, and the lower the pH the compound will produce in solution Types of bonds & interactions •Pka is directly related to PH -high pka—>less acidic -low pka —> more acidic In a titration curve Buffer: A solution of a weak acid and its conjugate base that resists a change in pH when a small amount of acid or alkali is added. pKa = -log Ka Hydrophobic Interaction: A weak electrostatic interaction between two hydrophobic groups. Since the properties of biological substances vary significantly with small changes in pH, they require environments in which the pH is insensitive to additions of acids or bases. And this is done by buffers Ka = [H+] [A-]/[HA] •or interaction involving a hydrogen atom located between a pair of other atoms having a high affinity for electrons Disulfide bond: is a covalent linkage formed from the sulfhydryl group (–SH) of each of two cysteine residues A buffer is a solution that can resist pH change upon the addition of an acidic or basic components. It is able to neutralize small amounts of added acid or base, thus maintaining the pH of the solution relatively stable. •inc [H] & have PH<7 Hydrogen bond: A weak electrostatic interaction between a hydrogen atom bound to an electronegative atom (N, O) and another electronegative atom. Ionic bond: A bond formed between two atoms where there is a complete transfer of an electron resulting in the formation of two ions (one positive and one negative) e.g. NaCl A chemical that can dissociate to release hydrogen ions (H+), i.e. it is a proton donor. ( or electron acceptor ) PH & PK MGD S1 lecture2 Buffers • It is able to neutralize small amounts of added acid or base, thus maintaining the pH of the solution relatively stable. Are mixtures of a weak acid and its conjugate base and they work by resisting changes in pH Definitions Amphipathic molecule has both a polar (hydrophilic) and non-polar (hydrophobic) end. Henderson-Hasselbalch equation pH=pKa+log[A-]/[HA] •The pH of a solution can be calculated from this equation if the molar proportion of A- to HA and the pK a of HA are known. Isoelectric point: The pH at which a protein has no overall net charge. • Conversely, the pKa of an acid can be calculated if the molar proportion of A- to HA and the pH of the solution are known. A type of covalent bond which joins amino acids in proteins. The bond forms between the carboxyl group of one amino acid and the amino group of the second. •nonpolar——nonpolar Van der Waals Interaction: A weak interaction between any two atoms in close proximity — For strong acid-weak base titration, pH < 7 Ionic Interaction: may be Attraction (between two groups with different charges), or Repulsion (between two groups with the same charges). PH A measurement of the concentration of H+ ions in solution. pH =-logio[H+] Water Helps in regulation of temperature since it is able to absorb large amounts of heat. Water is the principal fluid medium of the cell, which is present in most cells, except for fat cells which contain less, in a concentration of 70 to 85 per cent. •Water is polar molecule. •Water is highly cohesive (hydrogen bonds between water molecules). •Helps in regulation of intracellular pH since it is amphoteric solvent. Water properties &Functions Amphipathic molecule: has both a polar (hydrophilic) and nonpolar (hydrophobic) end. Ionization of water :Kw is the ion product of water. At 25°C, Kw is 1.0 × 10-14. the con. of H+ and OHare reciprocally related. If the concentration of H+ is high, then the concentration of OHmust be low, and vice versa. • Many cellular chemicals are dissolved in the water. Hydrophobic molecules: Substances that contain nonpolar bonds and insoluble in water. Water molecules are not attracted to their molecules and so have little tendency to surround them and carry them into solution. (unable to interact with water) •Used for transporting, delivering nutrients and for removing waste from cells. According to the ability of subs. To dissolve in water they are grouped to :•Hydrophilic •Hydrophobic •Amphipathic Hydrophilic molecules: substances that dissolve readily in water. They are composed of ions or polar molecules that attract water molecules through electrical charge effects. Water molecules surround each ion or polar molecule on the surface of such a solid and carry it into solution. (Able to interact with water molecules) •The pH of a solution will affect the charge on biological molecules and it is essential that biological molecules are kept in their optimal ionic state in order to function correctly Protein A polymer composed of amino acids joined by peptide bonds. The pH of the solution at equivalence point is dependent on the strength of the acid and strength of the base used in the titration. — For weak acid-strong base titration, pH > 7 PH meter The pH of a solution may be accurately and easily determined through electrochemical measurements with a device known as a pH meter. The equivalence point of an acid-base reaction (the point at which the amounts of acid and of base are just sufficient to cause complete neutralization — For strong acid-strong base titration, pH = 7 Peptide bond: • And, the molar proportion of Ato HA can be calculated if the pH and pKa values are known. pKa is a pH at which the concentration of weak acid and its conjugate base will be in equimolar concentrations. A low pH represents a high concentration of H+ and hence an acidic solution. A high pH represents a low concentration of H+ (and a high concentration of OH-) and hence a basic solution. Titration is a technique to determine the concentration of an unknown solution. As illustrated in the titration setup above, a solution of known concentration (titrant) is used to determine the concentration of an unknown solution (titrand or analyte).