Lecture 5Outline of Last Lecture I. Structures of Nonpolar Amino AcidsA. PhenylalanineB. TryptophanII. Structures of Polar Uncharged Amino AcidsA. SerineB. ThreonineC. TyrosineD. CysteineE. AsparagineF. GlutamineIII. Structures of Polar Charged Amino AcidsA. AspartateB. GlutamateC. LysineD. ArginineE. Histidine Outline of Current Lecture I. Synthesis of Amino AcidsII. Essential Amino AcidsA. Definition of Essential Amino AcidsB. Definition of Nonessential Amino AcidsIII. Amino Acids and HerbicidesA. Definition of ESPS SynthaseIV. Phosphorylation of Amino Acids V. Acid and Base ReviewVI. Amino Acid pKa ValuesCurrent Lecture All 20 known amino acids can be made by some organisms. These organisms include plants, yeast, and bacteria. Humans can make some amino acids directly from materials in the various metabolic pathways used. One example is the common metabolic intermediate pyruvate, which can be used to make the amino acid alanine. Bacteria, yeast, and plants can use the shikimic acid pathway. This is a very long, complex metabolic pathway that humans can’t perform. Due to what humans consume, this pathway cannot be completed. Thoseorganisms who can use this pathway can make various aromatic amino acids.Essential amino acids are those that humans and other organisms cannot make themselves. Nonessential amino acids are those that can be synthesized. The essential amino acids are: arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Though tyrosine is an BCHM 309 1st Editionaromatic compound, is often classified as a nonessential amino acid. This is due to the fact that the human body can synthesize tyrosine from phenylalanine. Herbicides often target essential amino acid metabolic pathways. Glyphosate is a common herbicide used to kill weeds. All plants have EPSP synthase. EPSP synthase is an enzyme found in the shikimic acid pathway. Glyphosate blocks this enzyme, which in turn blocks aromatic amino acids from being produced. This will eventually lead to the death of the targeted plant. Glyphosate will not normally harm humans, because wedo not make the aromatic amino acids. Some plants have been genetically modified to prevent glyphosate from inhibiting the enzyme. Soybeans are one target of this altered gene. They have one native gene and one recombinant gene. The soybeans are thus able to still generate the aromatic amino acids. Therefore, weeds arekilled when sprayed with the herbicide but the soybean crop is not. A constant use of the same herbicide can lead to strains of resistant weeds, though.Some amino acids can be phosphorylated or hydroxylated to take part in protein regulation. Hydroxyproline and hydroxylysine are hydroxylated amino acids that are found in connective tissues. Vitamin C, ascorbic acid, is needed in order to produce these forms of the amino acids. Vitamin C deficiency can lead toa condition called scurvy. Biological molecules, such as amino acids, are either bases or acids. Acids can donate protons and bases can accept them. Biological molecules can influence how many protons are in a cell, based on their acid or base properties. This will cause a shift in the cell’s pH, which can affect protein interactions. The pKa of a molecule gives the pH at the time when 50% of the solution’s molecules are deprotenated.Biochemical molecules have wide pKa ranges. The carboxyl group of an amino acid is considered acidic and theamino group is basic. Even though amino acids have charges within them, their net overall charge is neutral (when their R group is uncharged). These amino acids are known as zwitterions, when in a neutral pH. An amino acid is charged if its R group has a charge. This in turn, leads to charged proteins. Amino acids can also have separate pKa values for their amino, carboxyl, and R
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