Proteins and Amino Acids

• amino acids are the building blocks of proteins
• bonding of two amino acids leads to water loss
• amino acids contain an ammonium group and carboxylate group, wherein N-C-C is the backbone
• all amino acids have the same base structure; they only differ in the R group
• there are only 20 amino acids commonly found in the proteins of living organisms (called the essential amino acids)
• nonpolar amino acids have hydrocarbon side chains and are hydrophobic
• polar amino acids have polar or charged side chains and are hydrophilic
• acidic amino acids contain a carboxylate group and are hydrophilic
• basic amino acids contain an amine group and are hydrophilic
• essential amino acids are not produced by the body and must be obtained from the diet
• Cystine & Methionine are the only amino acids with sulfur
• amino acids are all chiral except for glycerine, and only L amino acids are used in proteins
• all proteins are amino acids but not all amino acids are proteins
• zwitterions are molecules with a net neutral charge; they contain an isoelectric point (pI)
• zwitterions have NH3+ and COO- groups
• in strongly alkaline conditions (pH > pI), a negative ion forms and amino acids act as acids; NH3+ donates a proton
• in strongly acidic conditions (pH < pI), a positive ion forms and amino acids act as bases; COO- accepts a proton
• proteins are derived from the Greek word proteus which means "of first importance"
• proteins are the most prevalent and diverse biomolecules
• proteins are composed of amino acids linked by a peptide bond
• structural proteins provide structural components; example includes collagen
• contractile & motor proteins make muscles move; examples are myosin and actin
• transport proteins carry essential substances throughout the body; examples are hemoglobin and lipoproteins
• storage proteins store amino acids; example is casein
• hormone proteins regulate body metabolism and nervous system; example is insulin
• enzymatic proteins are catalysts in biochemical reactions; examples are sucrase and trypsin
• defensive proteins recognize and destroy foreign substances; examples are immunoglobulins
• receptor proteins respond to cell stimuli
• peptides are composed of carbonyl group and amino group bonded by an amide bond (called a peptide bond)
• the free amino group is called the N-terminus while the free carboxylate group is called the C-terminus
• two amino acids form a dipeptide; naming starts with the amino acid at the N-terminus and the -yl suffix is added for all except the one at the C-terminus
• Primary structure of a protein is the sequence of amino acids that make up the backbone of the peptide chain or protein.
• Insulin was the first primary structure determined, consisting of two polypeptide chains linked by disulfide bonds, with chain A consisting of 21 amino acids and chain B consisting of 30 amino acids.
• Secondary structure of a protein is a 3D spatial arrangement similar to a corkscrew, held together by hydrogen bonds.
• Secondary beta pleated structure is a side-by-side arrangement of amino acids, with hydrogen bonds present, found in fibrous proteins.
• Secondary triple helix structure consists of 3 polypeptide chains (crosslinks), found in collagen, connective tissues, skin, tendons, cartilage.
• Tertiary structure of a protein involves interactions between nonpolar group (hydrophobic), disulfide group (bridges), hydrogen bond, and ionic bond, resulting in an overall 3D shape with a pocket for oxygen, found in globular proteins.
• Quaternary structure of a protein involves two or more protein units.
• denaturation refers to an untangling of a protein that results in a primary structure
• protein denaturation can be caused by heat, acids & bases, organic compounds, heavy metal ions, and agitation