Proteins, which are vital to the functionality of all living organisms, are made up of multiple amino acid monomers linked together via peptide bonds. Peptide bonds are chemical covalent bonds linking one amino acid to the other, and they form between a carbon atom of one amino acid and a nitrogen atom of the other amino acid. The end of a protein with a free nitrogen atom is referred to as the N-terminus, while the other end of a protein with a free carbon atom is referred to as the C-terminus.
Amino acids are composed of a central carbon atom bonded to a hydrogen atom and a functional R group, which determines the amino acid identity, and a carboxyl group on one side and an amino group on the other. Upon peptide bond formation, the carbonyl group of the first amino acid loses a hydroxyl (OH) and the amino group of the second amino acid loses a hydrogen (H). This process is known as dehydration, and forms a covalent bond between the two amino acids involved, known as the peptide bond, and generates a water molecule in the process.
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A protein molecule is generally composed of a multitude of amino acids, or peptides, linked together via peptide bonds. The human body makes use of 20 naturally occurring amino acids. Proteins differ in the number and type of amino acids they possess.
Protein nomenclature can be dependent on the number of peptides they encompass. For example:
As explained earlier, a protein is made of a sequence of amino acids linked together via peptide bonds in a process titled polymerization. The order and sequence of amino acids are specific to each protein, which gives rise to the protein's primary structure.
A protein is said to be a polymer of amino acid monomers. The specific order in which amino acids are bonded is crucial to assemble the protein in a particular manner which is necessary for protein function. Upon protein assembly in the cytoplasm, multiple cellular checkpoints occur to ensure the sequence of amino acids is correct. Mutations in the genetic code or DNA, which provides instructions on the assembly of every protein, could cause a change in the protein's primary structure and hence its shape and function. For example, sickle cell disease is brought upon by a change in the DNA sequence which gives rise to coding the valine amino acid instead of glutamine. This results in impairment in beta-globin structure, which is detrimental to red blood cell functions.
As mentioned earlier, the formation of a peptide bond between two amino acids brings about the formation of a molecule of water. As a carboxyl group loses its hydroxyl (OH) and an amine group loses its hydrogen (H) atom, they combine to form one molecule of water for each peptide bond. This process is reversible; peptide bonds can be broken by the addition of a water molecule. The water molecule restores the hydroxyl (OH) to the carboxyl group and a hydrogen atom to the amine group, thus giving rise to two separate individual amino acids per peptide bond and releasing energy. This process is referred to as a hydrolysis reaction.
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Deoxyribonucleic acid (DNA) serves as the code that dictates protein expression in both eukaryotic and prokaryotic cells. DNA is made of a sugar (deoxyribose), a phosphate group, and a nitrogenous base. The sugar and phosphate molecules together form what is called the sugar-phosphate backbone of DNA, which anchors to the nitrogenous base and gives it the ability to form hydrogen bonds with nitrogenous bases of the complementary DNA strand. Recent scientific breakthroughs allowed the development of peptide nucleic acids (PNAs). PNAs are man-made DNA look-alike substances, in which the sugar-phosphate backbone is replaced with a peptide polymer. Because of their flexible and uncharged nature, they bind to complementary DNA strands in a very efficient manner. Therefore, PNAs are used in research and diagnostic settings, in which they are employed in hybridization assays.
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A peptide bond is occurs between the carboxyl group of one amino acid and an amine group with the other amino acid.
Two amino acids bind via a peptide bond. The formation of a peptide bond occurs between a carboxyl group of one amino acid and an amine group of the other.
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