Published on November 22, 2008
Slide 1: Chapter 03 Amino Acids Slide 2: Amino Acids: Building Blocks of Proteins Slide 3: General Structure of Amino Acids An amino acid has a carboxylate group (whose carbon atom is designated C-1), an amino group, a hydrogen atom, and a side chain (or R group), all attached to C-2 (the -carbon). Slide 4: Ball-and-stick model of serine (whose R group is —CH2OH) Slide 5: It is chiral since four different groups are attached to the α-carbon. Slide 6: Mirror Images of L-serine and D-serine. Note that the two molecules are not identical; they cannot be superimposed Slide 7: The zwitterionic structure carries both + and – charges but the net charge is zero. Zwitterions are amphoteric in nature because they can donate or accept a proton. The identity of the R group gives rise to variation in AAs. Slide 8: There are some substances that rotate plane polarized light to the right and some to the left Levorotary and Dextrorotary Amino Acids Slide 12: FALSE Slide 13: Aliphatic Amino Acids The R group is made of alkyl chains They are non-polar & neutral in nature Consists of six amino acids (GAVLIP) Glycine Alanine Valine Leucine Isoleucine Proline Slide 14: Glycine (G or Gly) Achiral Small Flexible Slide 15: Alanine (A or Ala) Has a methyl group Forms pyruvate when oxidatively deaminated Pyruvate serves as important intermediate in many metabolic reactions (e.g. glycolysis) Serve as ammonia repository & substrate for glucose synthesis (gluconeogenesis) Slide 16: Valine (V or Val) One of the branched-chain amino acid (BCAA) An essential amino acid Named after Valerian Sickle-Cell Connection Slide 17: Leucine (L or Leu) One of the branched-chain amino acid (BCAA) An essential amino acid Slide 18: Isoleucine (I or Iso) One of the branched-chain amino acid (BCAA) An essential amino acid Slide 19: Proline (P or Pro) Cylic and rigid amino acid Slide 20: Aromatic Amino Acids The R group has benzene (aromatic) ring They are non-polar & neutral in nature Consists of three amino acids (FYW) F - Phenyalanine Y - Tyrosine W - Tryptophan Slide 21: Phenylalanine (F or Phe) Has a phenyl ring , serve as precursor of dopamine Dopamine is an important neurotransmitter at the reward center of the brain and the basal motor ganglia Parkinson’s disease results from dopamine deficiency, it is characterized by progressive loss of muscular control Slide 22: Tyrosine (Y or Tyr) Hydroxylated phenylalanine (phenol) An intermediate in dopamine synthesis Slide 23: Tryptophan (W or Trp) Has an indole ring, precursor of serotonin Serotonin is an important neurotransmitter that affects our mood, temperature, and sleep cycle. Clinical depression results from serotonin deficiency, which increases suicidal tendencies Slide 25: Alcoholic Amino Acids Contains hydroxyl (-OH) group Polar & neutral in nature Consists of two amino acids (ST) Serine Threonine Slide 26: Serine (S or Ser) R group is a primary alcohol The hydroxyl group can form ester or ether bond Slide 27: Threonine (T or Thr) R group is a secondary alcohol The hydroxyl group can form ester or ether bond Slide 28: Sulfur-containing Amino Acids Has sulfur atom Slightly polar & neutral in nature Consists of two amino acids (CM) Cysteine Methionine Slide 29: Cysteine (C or Cys) Has a thiol or sulfhydryl group(-SH) Two cysteine residues can form a disulfide bridge which stabilizes the structure of peptides & proteins Slide 30: Formation of Cystine. When oxidation links the sulfhydryl groups of two cysteine molecules, the resulting compound is a disulfide called cystine. Slide 32: Methionine (M or Met) Has a thioether group(C-S-C) The dangling methyl group can be transferred by methyltransferase enzyme Slide 33: Acidic Amino Acids Has extra carboxylic acid in the side chain Polar & negatively charged in nature Consists of two amino acids (DE) D - Aspartic acid (Aspartate) E - Glutamic acid (Glutamate) Slide 34: Aspartic Acid (D or Asp) An α,β dicarboxylic acid Forms oxaloacetate (OAA) when decarboxylated OAA is important intermediate in many metabolic reactions (e.g. In Kreb’s cycle) Slide 35: Glutamic Acid (E or Glu) An α,γ dicarboxylic acid Serves as an excitatory neurotransmitter Monosodium glutamate (MSG) is a popular seasoning that is used as meat flavor enhancer Excessive intake of MSG results to Chinese Food Syndrome (CFS) which is characterized by dizziness, headache, and even fainting Slide 36: Amide Amino Acids Amide derivative of aspartic & glutamic acid Polar & neutral in nature Consists of two amino acids (NQ) N - Asparagine Q - Glutamine Slide 37: Asparagine ( N or Asn) Amide derivative of aspartic acid First isolated from asparagus which is rich in this amino acid Slide 38: Glutamine ( Q or Gln) Amide derivative of glutamic acid One of the substrate s in the biosynthesis of nucleotides Slide 40: Basic Amino Acids Contains a basic nitrogenous group Polar & positively charged in nature Consists of three amino acids (KHR) K - Lysine H - Histidine R - Arginine Slide 41: Lysine ( K or Lys) Has an ε-amino group in the side chain Popular ingredients in nutritional supplement for kids as it helps in increasing appetite Slide 42: The (epsilon) ε-amino group in the side chain of Lysine Slide 43: Histidine (H or His) Contains an imidazole ring Precursor of histamine, the chemical mediator of allergic responses Slide 44: Arginine ( R or Arg) Contains a guanidino group in its side chain Source of urea which is the main waste product of nitrogen metabolism Precursor of nitric oxide, an important vasodilator Slide 45: The 21st and 22nd Amino Acid Slide 46: Compounds derived from common amino acids. -Aminobutyrate a derivative of glutamate Slide 47: Histamine is a derivative of histidine. Slide 48: Epinephrine is a derivative of tyrosine Slide 49: Thyroxine and triiodothyronine are derivatives of tyrosine. Thyroxine contains one more atom of iodine (in parentheses) than does triiodothyronine Slide 50: Titration Curve for Alanine The first pKa value is 2.4 the second is 9.9 pIAla represents the isoelectric point of alanine. Slide 51: Ionization of Histidine Titration curve for histidine. The three pKa values are 1.8, 6.0, and 9.3. pIHis represents the isoelectric point of histidine. Slide 52: Deprotonation of the imidazolium ring of the side chain of histidine Slide 53: Ionization of the protonated -carboxyl group of glutamate The negative charge of the carboxylate anion is delocalized. Slide 54: Deprotonation of the guanidinium group of the side chain of arginine The positive charge is delocalized. Slide 61: TRUE Slide 62: Essential Amino Acids They cannot be synthesized by our body or when synthesized it is in inadequate amounts Should be obtained from dietary sources or from supplementation There are ten essentials amino acids Isoleucine Methionine Tryptophan Arginine Leucine Threonine Phenylalanine Histidine Lysine Valine In Adults + in Infants Slide 63: FALSE Slide 64: FALSE Slide 65: Food Sources of Amino Acids Animal Sources are considered as complete sources of essential amino acids Plant Sources are often incomplete sources of essential acids Cereals are poor in lysine Legumes are poor in methionine Slide 66: Kwashiorkor is a disease that results from severe deficiency in essential amino acids. Failure of growth, the weight and height of the child are too low for the age Many parts of the body are swollen because of excessive fluid accumulation in tissues. The hair changes its color, becoming brown to almost white. It loses its curl and is thin and sparse. The skin turns paler than normal. Misery: the child shows no interest in anything and looks unhappy, and has no energy even to cry. Usually has diarrhea.