MCAT Biochemistry
Amino acids, the building blocks of protein, consist of a carboxylic acid group, an amino group, and a unique side chain, all attached to the central alpha carbon. Amino acids in humans exist in the L-stereoisomer form and are joined together by peptide bonds to form polypeptides. The major classes of amino acids include nonpolar, polar, acidic, and basic.
Nonpolar amino acids are hydrophobic and include glycine, alanine, leucine, isoleucine, valine, methionine, proline, tryptophan, and phenylalanine. Polar amino acids have side chains with polar groups that are either partially charged or capable of forming hydrogen bonds, and include tyrosine, threonine, asparagine, serine, cysteine, and glutamine. Branched-chain amino acids consist of leucine, isoleucine, and valine, while aromatic amino acids include phenylalanine, tryptophan, and tyrosine. The acidic amino acids aspartate and glutamate have a negative charge at body pH, while the basic amino acids arginine, lysine, and histidine have unique charges and are essential for growth. Threonine, methionine, tryptophan, phenylalanine, leucine, isoleucine, valine, histidine, and lysine are essential amino acids that the body cannot synthesize. Amino acids can be classified as glucogenic, ketogenic, or both depending on their ability to be metabolized for various functions such as glucose conversion or acetyl-CoA production.
Lesson Outline
<ul> <li>Introduction</li> <ul> <li>Amino acids are the building blocks of proteins.</li> <li>All amino acids have a carboxyl group, an amino group, a unique side chain, and a central alpha carbon.</li> </ul> <li>Nonpolar Amino Acids</li> <ul> <li>Glycine</li> <li>Alanine</li> <li>Leucine</li> <li>Isoleucine</li> <li>Valine</li> <li>Methionine</li> <li>Proline</li> <li>Tryptophan</li> <li>Phenylalanine</li> </ul> <li>Polar Amino Acids</li> <ul> <li>Tyrosine</li> <li>Threonine</li> <li>Asparagine</li> <li>Serine</li> <li>Cysteine</li> <li>Glutamine</li> </ul> <li>Acidic Amino Acids</li> <ul> <li>Aspartate</li> <li>Glutamate</li> </ul> <li>Basic Amino Acids</li> <ul> <li>Arginine</li> <li>Lysine</li> <li>Histidine</li> </ul> <li>Essential Amino Acids</li> <ul> <li>Threonine</li> <li>Methionine</li> <li>Tryptophan</li> <li>Phenylalanine</li> <li>Leucine</li> <li>Isoleucine</li> <li>Valine</li> <li>Histidine</li> <li>Lysine</li> </ul> <li>Glucogenic, Ketogenic, and Both</li> <ul> <li>Glucogenic amino acids can be converted into glucose through gluconeogenesis</li> <li>Ketogenic amino acids can be converted into ketone bodies</li> <li>Strictly ketogenic: Leucine, Lysine</li> <li>Both glucogenic and ketogenic: Isoleucine, Phenylalanine, Threonine, Tryptophan, Tyrosine</li> <li>Glucogenic: the remaining 13 amino acids</li> </ul> </ul>
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FAQs
Nonpolar amino acids have hydrophobic side chains, meaning they are not attracted to water and prefer to stay away from aqueous environments. These amino acids typically have side chains made up of hydrocarbons. Examples include alanine, valine, leucine, and isoleucine. On the other hand, polar amino acids have hydrophilic side chains that readily interact with water. They have side chains containing functional groups that can participate in hydrogen bonding, such as hydroxyl, carboxyl, or amino groups. Examples include serine, threonine, asparagine, and glutamine.
Essential amino acids are the amino acids that our body cannot synthesize on its own, so they must be obtained from our diet. There are nine essential amino acids: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. These amino acids play a crucial role in protein synthesis. They are the building blocks of proteins and must be supplied in the correct proportions to allow the body to create the many different proteins necessary for proper growth, development, and maintenance of tissues and organs.
Glucogenic amino acids are those that can be converted into glucose through gluconeogenesis, a metabolic process in which glucose is generated from non-carbohydrate precursors. These amino acids are broken down into substrates like pyruvate, alpha-ketoglutarate, and oxaloacetate, which can eventually be converted to glucose in the liver. On the contrary, ketogenic amino acids are those that can be converted into ketone bodies or fatty acids. They are catabolized into acetoacetate or acetyl-CoA, which can be utilized as an energy source, especially by the brain, during periods of low glucose availability, such as during fasting or prolonged exercise.
Branched-chain amino acids (BCAAs) are a group of amino acids that have a branched aliphatic side chain. They include leucine, isoleucine, and valine. BCAAs play essential roles in muscle protein synthesis, energy production, and reducing muscle fatigue. They also serve as nitrogen donors in the synthesis of other amino acids. Aromatic amino acids, on the other hand, contain an aromatic ring in their side chain. Examples include phenylalanine, tyrosine, and tryptophan. They serve as precursors for a variety of important molecules, such as neurotransmitters, hormones, and vitamins. Phenylalanine, for instance, is the precursor of tyrosine, which is further converted into dopamine, norepinephrine, epinephrine, and thyroid hormones.
