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Amino acids, the building blocks of proteins, possess several fundamental properties that are critical to their role in biological molecules and processes: Structural Components: Every amino acid has a basic structure consisting of a central carbon atom (alpha carbon) bonded to an amino group (NH2), a carboxyl group (COOH), a hydrogen atom, and a distinctive side chain or R group that varies among different amino acids. Classification Based on Side Chains: The properties of amino acids are largely determined by their side chains, which can be nonpolar (hydrophobic), polar but uncharged, positively charged (basic), or negatively charged (acidic). This classification influences their solubility in water and their role in protein structures. Zwitterionic Nature: In solution at physiological pH, amino acids exist as zwitterions, meaning they contain both a positively charged amino group and a negatively charged carboxyl group. This dual charge facilitates their solubility and participation in a variety of biochemical reactions. Optical Activity: Except for glycine, all amino acids are chiral, possessing a central carbon atom with four different groups attached. This chirality gives rise to two enantiomers (L- and D- forms) for each amino acid. In proteins, only the L-forms are incorporated. Peptide Bond Formation: Amino acids can link together through peptide bonds, formed in a dehydration synthesis reaction between the carboxyl group of one amino acid and the amino group of another. This bond formation leads to the creation of peptides and proteins, defining the primary structure of proteins. Acid-Base Behavior: Amino acids can act as both acids and bases, a property known as amphoteric. They can donate a proton from the carboxyl group and accept a proton with the amino group, allowing them to buffer changes in pH within organisms. Isoelectric Point (pI): Each amino acid has a specific isoelectric point, which is the pH at which the amino acid has no net charge. The pI value depends on the nature of the side chain and influences amino acid behavior in electric fields and in solubility at various pH levels. Functional Versatility: Beyond their role in proteins, amino acids participate in numerous metabolic pathways, serving as precursors to neurotransmitters, hormones, and other biologically active molecules. They can also be converted into glucose or ketone bodies, highlighting their versatility in metabolism. These properties enable amino acids to play diverse and crucial roles in the structure and function of all living organisms, from serving as the fundamental components of proteins to participating in critical metabolic processes. Problem: Amino acids that have a net positive charge under physiological pH are known as: A) Acidic amino acids B) Basic amino acids C) Polar amino acids D) Nonpolar amino acids What is the bond called that forms between the carboxyl group of one amino acid and the amino group of another, releasing a molecule of water? A) Ionic bond B) Hydrogen bond C) Peptide bond D) Covalent bond
