PROTEINS

• Protein - Most abundant macromolecule
• The word protein comes from the Greek word πρώτα ("prota"), meaning "of primary importance" or "first."
• Polymer of amino acids linked by peptide bonds.
• POLYMER a natural or synthetic giant molecule formed from smaller molecule.
• How proteins were discovered?

  Proteins were first described and named by the Swedish chemist Jöns Jakob Berzelius in 1838.
• Linus Pauling did some of the earliest work in the study of proteins. He won the Nobel Prize in Chemistry in 1954 "for his research into the nature of the chemical bond and its application to the elucidation of the structure of complex substances."
• The first protein to be sequenced was insulin. Frederick Sanger won the Nobel Prize in Chemistry in 1958 "for his work on the structure of proteins, especially that of insulin.”
• Two of the first protein structures to be described were hemoglobin by Max Peruts and myoglobin Sir John Cowdery Kendrew, both in 1958. Perutz and Kendrew were awarded the 1962 Nobel Prize in Chemistry "for their studies of the structures of globular proteins."
• ???

  A) hormones

  B) protective/defense

  C) structural

  D) catalyst

  E) regulatory

  F) transport

  
• Structural component. These proteins provide structure and support for cells. On a larger scale, they also allow the body to move. An example is actin.
• The main structural material for plants is cellulose
• For animals, two important structural proteins are collagen and keratin.
• Catalysis. All the reactions that take place in living organisms are catalyzed by proteins called enzymes.
• Enzymes carry out almost all of the thousands of chemical reactions that take place in cells. They also assist with the formation of new molecules by reading the genetic information stored in DNA. An example is phenylalanine.
• Enzymes increase the rates of biological reactions. Example: lysozymes.
• Regulatory. Some proteins not only control the expression of genes, thereby regulating the kind of proteins synthesized in a particular cell, but also dictate when such manufacture takes place.
• Hormones. Many hormones are proteins including insulin, erythropoietin and human growth hormone.
• Protective/Defense. Antibodies bind to specific foreign particles, such as viruses and bacteria, to help protect the body. An example is immunoglobulin (IgG).
• Transport/Storage. These proteins bind and carry atoms and small molecules within cells and throughout the body. An example is ferritin.
• Fibrous proteins are only found in animals.
• Fibrous proteins form “rod' or ‘wire' -like shapes and are usually inert structural or storage proteins. They are generally water-insoluble. Fibrous proteins are usually used to construct connective tissue, tendons, bone matrix and muscle fiber.
• Examples of fibrous proteins include keratins, collagens and elastins.
• 2 major types of proteins:

  • Fibrous proteins, also called scleroproteins
  • Globular proteins, or spheroproteins
• Globular proteins, or spheroproteins are one of the two main protein classes, comprising “globe”-like proteins that are more or less soluble in aqueous solutions (where they form colloidal solutions). This characteristic distinguishes them from fibrous proteins (the other class), which are practically insoluble.
• Types of proteins:

  • constitutive
  • non-constitutive
• Constitutive - always present in the body (e.g. structural proteins, lipoproteins, hemoglobin)
• Non-constitutive - present only when needed (e.g. digestive enzymes)
• Non-polar amino acid – is an amino acid that contains one amino group, one carboxyl group, and a non-polar side chain.
• Classification of Amino Acid Based on Polarity

  • Non-polar (Hydrophobic)
  • Polar Uncharged
  • Acidic
  • Basic
• Polar neutral amino acid – is an amino acid that contains one amino group, one carboxyl group, and a side chain that is polar but neutral.
• Polar acidic amino group – is an amino acid that contains one amino group and two carboxyl groups, the second carboxyl group being part of the side chain.
• Polar basic amino acid – is an amino acid that contains two amino groups and one carboxyl group, the second amino group being part of the side chain.
• Essential amino acid is an amino acid needed in the human body that must be obtained from dietary sources because it cannot be synthesized within the body from other substances in adequate amounts.
• The Essential Amino Acids for Humans

  • Arginine
  • Methionine
  • Histidine
  • Phenylalanine
  • Isoleucine
  • Threonine
  • Leucine
  • Tryptophan
  • Lysine
  • Valine
• Arginine is required for growth in children but is not required by adults.
• LYSINE, METHIONINE, TRYPTOPHAN – used to enrich human blood and livestock feeds as a way to extend the world’s limited supply of high quality food protein.
• Amino Acids are Zwitterions- not only in water solution but also in the solid state
• A complete dietary protein is a protein that contains all the essential amino acids in approximately the same relative amounts in which the human body needs them.
• Zwitterions – are compounds that have a positive charge in one atom and a negative charge on another
• Zwitterion from the German word Zwitter meaning “hybrid”