UNIT 4: PROTEINS LESSON 1 AMINO ACIDS

• Proteins


  Molecular tools that perform an astonishing variety of functions in addition to serving as structural materials in all living organisms
• Proteins


  • Involved in catalysis, metabolic regulation, transport, and defense
  • Composed of one or more polypeptides, unbranched polymers of 20 different amino acids
  • The genomes of most organisms specify the amino acid sequences of thousands or tens of thousands of proteins

  
• This unit begins with an introductory discussion on the structures and chemical properties of amino acids, the building blocks of proteins

  
• This is followed by descriptions of the structural and functional features of peptides and proteins and the protein folding process

  
• The emphasis of presentation is on the intimate relationship between the structure and function of polypeptides
• This unit deals with the classification, physical and chemical properties, color reactions that help in the identification of an amino acid which is the repeating unit of proteins

  
• It also discusses separation methods and determination of amino acid sequence, the four levels of protein structure, and interactions that stabilize these structures as well as the denaturation process of proteins

  
• Amino acids


  The building blocks of proteins

  
• Amino acids


  • They are -amino acids, so named because the amino group is bonded to the carbon atom, next to the carbonyl group
  • The physical and chemical properties of a protein are determined by its constituent amino acids
  • The individual amino acid subunits are joined by amide linkages called peptide bonds

  
• Isoelectric pH (pI)


  The pH at which the net charge an amino acid is zero
• Amino acids with acidic side chain contain an extra carboxylic group, because of this they tend to become polar and ionizable
• Proline


  The only cyclic amino acid, also known as imino acid
• Polar neutral amino acid


  An amino acid with a polar but uncharged side chain
• Ketogenic amino acids


  Amino acids that break down to form ketone bodies
• Non-essential amino acid


  An amino acid that can be synthesized by the body and does not need to be obtained from the diet
• Standard amino acid


  An amino acid composed of C, H, O, N, and sometimes S

  
• Disulfide bond


  A covalent bond formed between the sulfur atoms of two cysteine residues
• Amino acids as fuel source

  The carbon skeletons of amino acids are used in the citric acid cycle to produce energy
• Tyrosine


  Amino acid that contains a phenol group
• Arginine


  Amino acid containing guanidine group
• pK2


  The ionization value assigned to the carboxyl group of an amino acid
• Ninhydrin


  Reagent used to detect the presence of arginine in a qualitative test
• Ninhydrin


  A chemical used to detect ammonia or primary and secondary amines which can also be used to visualize fingerprints
• Tryptophan


  The amino acid that contains a 2-ring system known as indole group

  
• Isoelectric point (pI)


  The pH at which the net charge an amino acid is zero
• Biuret test


  A test used for the detection of aromatic amino acids tyrosine, tryptophan, and phenylalanine in a protein solution

  
• The magic words are: PROLINE, TYROSINE, ARGININE, CARBOXYL, NINHYDRIN, TRYPTOPHAN, ISOELECTRIC POINT, BIURET
• Protein


  A biomolecule or macromolecule that contains the building blocks called amino acids whose primary structure is a linear sequence of -amino acids and whose final structure results from folding of the chain into a specific three-dimensional structure

  
• Proteins are the most versatile macromolecules in living systems and serve crucial functions in essentially all biological processes
• Proteins


  • They function as catalysts, they transport and store other molecules such as oxygen, they provide mechanical support and immune protection, they generate movement, they transmit nerve impulses, and they control growth and differentiation
• Protein function depends on the linear sequence of amino acids
• Proteins spontaneously fold up into three-dimensional structures that are determined by the sequence of amino acids in the protein polymer
• Proteins


  • They contain a wide range of functional groups including alcohols, thiols, thioethers, carboxylic acids, carboxamides, and a variety of basic groups
  • They can interact with one another and with other biological macromolecules to form complex assemblies
  • Some are quite rigid, whereas others display limited flexibility

  
• Amino acids


  Organic compounds that contain amine (-NH2) and carboxyl (-COOH) functional groups, along with a side chain (R group) specific to each amino acid

  
• About 500 naturally occurring amino acids are known (though only 20 appear in the genetic code)
• 1. amino acids


  Amino acids where the stereogenic carbon alpha to the amino group has the D-configuration

  
• Only L-amino acids are manufactured in cells and incorporated into proteins

  
• All naturally occurring proteins from all living organisms consist of L-amino acids
• Classification of amino acids based on nutrition and metabolic fate

  • Essential amino acids
  • Non-essential amino acids
• All amino acids except glycine are chiral because they all contain at least one chiral center