Protein

Cards (71)

  • The living matter is composed of mainly carbon, hydrogen, oxygen, nitrogen, phosphorus and sulfur. These elements together constitute about 90% of the dry weight of the human body
  • Other functionally important elements found in cells
    • Ca
    • K
    • Na
    • Cl
    • Mg
    • Fe
    • Cu
    • Co
    • I
    • Zn
    • F
    • Mo
    • Se
  • Chemical composition of the human body
    Water is the solvent of life and contributes to more than 60% of the weight, followed by protein (mostly in muscle) and lipid (mostly in adipose tissue), carbohydrate content is rather low in the form of glycogen
  • Water
    • The most abundant chemical compound in living human cells, accounting for 65 percent to 90 percent of each cell, also present between cells e.g. in blood and cerebrospinal fluid
  • Fat
    • The percentage varies from person to person, but even an obese person has more water than fat
  • Protein
    • In a lean male, the percentages of protein and water are comparable, about 16 percent by mass, found in muscles, hair, fingernails, and skin
  • Minerals
    • Account for about 6 percent of the body, include salts and metals like sodium, chlorine, calcium, potassium, and iron
  • Carbohydrates
    • Although used as an energy source, only account for about 1% of body mass
  • Carbon is the most predominant and versatile element of life, possessing the ability to form stable covalent bonds and C-C chains of unlimited length, about 90% of compounds found in living systems contain carbon
  • Most elements are found within compounds, water and minerals are inorganic compounds, organic compounds include fat, protein, carbohydrates, and nucleic acids
  • Proteins
    The most versatile macromolecules in living systems, serving crucial functions in essentially all biological processes including as catalysts, transport, structural support, immune protection, movement, nerve impulses, growth and differentiation
  • Origin of the word 'protein'
    Derived from the Greek word proteios, meaning holding the first place, suggested by Berzelius and Mulder to refer to the high molecular weight nitrogen-rich and most abundant substances present in animals and plants
  • Functions of proteins
    • Structural (e.g. collagen, elastin, keratin)
    • Dynamic (e.g. enzymes, hormones, blood clotting factors, immunoglobulins, membrane receptors, storage proteins, genetic control, muscle contraction, respiration)
  • Proteins may also contain other elements such as P, Fe, Cu, I, Mg, Mn, Zn
  • Proteins
    Polymers of amino acids, formed by the incorporation of 20 standard amino acids during synthesis, some of which undergo post-translational modifications
  • Central dogma of molecular biology
    The flow of genetic information from DNA to RNA to proteins, first proposed by Francis Crick
  • Amino acids
    Organic compounds containing amino and carboxyl functional groups, exist in ionized form in biological systems
  • Optical isomerism of amino acids
    • Amino acids (except glycine) have four distinct groups attached to the alpha carbon, resulting in left-handed (L) and right-handed (D) optical isomers, proteins are composed of L-alpha amino acids
  • The preference for L-amino acids in proteins is likely due to their slightly higher solubility compared to racemic mixtures
  • Classification of amino acids based on polarity
    • Non-polar (hydrophobic)
    • Polar with no charge
    • Polar with positive charge
    • Polar with negative charge
  • Nutritional classification of amino acids
    • Essential (indispensable)
    • Non-essential (dispensable)
    • Semi-essential
  • Physical properties of amino acids
    • Soluble in water, insoluble in organic solvents, high melting points, varying tastes (sweet, tasteless, bitter)
  • Aspartame
    An artificial sweetener 200 times sweeter than sucrose, a methyl ester of the aspartic acid/phenylalanine dipeptide, most stable at pH 4.3, deemed safe for human consumption by regulatory agencies
  • Chemical properties of amino acids
    Undergo decarboxylation to form amines, dicarboxylic amino acids react with ammonia to form amides, act as ampholytes (can donate or accept protons)
  • Aspartame
    Most stable at pH 4.3, where its half-life is nearly 300 days
  • Aspartame has been deemed safe for human consumption by over 100 regulatory agencies in their respective countries, including the FDA
  • Amino acids
    General reactions are mostly due to the presence of two functional groups: carboxyl (COOH) group and amino (NH2) group
  • Decarboxylation
    Amino acids undergo decarboxylation to produce corresponding amines
  • Reaction with ammonia
    The carboxyl group of dicarboxylic amino acids reacts with NH3 to form amide
  • Amino acids as ampholytes
    Amino acids contain both acidic (COOH) and basic (NH2) groups, they can donate a proton or accept a proton
  • Zwitterion or dipolar ion
    A hybrid molecule containing positive and negative ionic groups
  • Amino acids rarely exist in a neutral form with free carboxylic (COOH) and free amino (NH2) groups
  • Isoelectric point (pI)
    The pH at which a molecule exists as a zwitterion or dipolar ion and carries no net charge
  • Isoelectric point (pI)
    • The negatively and positively charged molecular species are present in equal concentrations
    • The molecule is electrically neutral
  • Neutral side chain amino acids
    • Characterized by two pKas: pKa1 for the carboxylic acid and pKa2 for the amine
    • The isoelectric point is the average of these two pKas
  • Acidic side chain amino acids
    The isoelectric point is at a lower pH because the acidic side chain introduces an "extra" negative charge
  • Basic side chain amino acids
    The isoelectric point is at a higher pH because the basic side chain introduces an "extra" positive charge
  • Electrophoresis
    Used to show the distribution of charged species in a sample by observing the movement of solute molecules in an electric field
  • Peptide bond
    Formed when the amino group of an amino acid combines with the carboxyl group of another amino acid
  • Peptides containing more than 10 amino acids are referred to as polypeptides