PRELIMS 4

• Protein


  A naturally-occurring, unbranched polymer in which the monomer units are amino acids
• Proteins


  • Compounds of high molecular weight
  • Consist of chains or series of amino acids
• Amino acids


  Monomers that make up proteins, united by peptide bonds
• Proteins are composed of approximately 50% of Carbon, 7% of Hydrogen, 16% of Nitrogen, and 23% of Oxygen, and around 0-3% of Sulfur
• The average nitrogen content of proteins is 15.4% by mass
• Proteins also contain Iron (Fe), phosphorus (P) and some other metals in some specialized proteins
• Polypeptide


  A protein in which at least 40 amino acid residues are present
• Proteins


  • Sometimes, proteins and polypeptide are used interchangeably
  • Proteins contain 400–500 amino acid residues
  • Small proteins contain 40–100 amino acid residues
• Monomeric protein


  A protein containing one peptide chain
• Multimeric protein


  A protein containing more than one peptide chain
• Protein classification based on chemical composition

  • Simple proteins
  • Conjugated proteins
• Simple proteins


  Proteins in which only amino acid residues are present
• Conjugated proteins


  Proteins that have one or more non-amino acid entities (prosthetic groups) present in their structure
• Types of conjugated proteins

  • Lipoproteins
  • Glycoproteins
  • Metalloproteins
• Four types of protein structures

  • Primary structure
  • Secondary structure
  • Tertiary structure
  • Quaternary structure
• Primary structure of proteins


  The order in which amino acids are linked together in a protein by the peptide bonds
• Frederick Sanger sequenced and determined the primary structure for the first protein - Insulin
• Secondary structure of proteins


  The arrangement of atoms of the backbone in space
• Types of secondary structures

  • Alpha-helix
  • Beta-pleated sheet
  • Random pattern
• Alpha-helix


  • A single protein chain adopts a shape that resembles a coiled spring
  • H-bonding between same amino acid chains
  • R-group outside of the helix
• Beta-pleated sheet


  • Completely extended amino acid chains
  • H-bonding between two different chains
  • Side chains below or above the axis
• Tertiary structure of proteins


  The overall three-dimensional shape of a protein
• Interactions in tertiary structure

  • Disulfide bonds
  • Electrostatic interactions
  • H-bonding
  • Hydrophobic interactions
• Quaternary structure


  The highest level of protein organization, when two or more chains or subunits attract to form a protein
• Most multimeric proteins contain an even number of subunits
• Hemoglobin


  • A protein with quaternary structure, containing two identical alpha chains and two identical beta chains
• Denaturation


  The process where the bonds of the four types of protein structure can be destroyed, causing inactivation of protein function
• Factors that can cause denaturation

  • Heat
  • pH changes
  • Adding of chemicals
• Protein classification based on shape

  • Fibrous proteins: Collagen
  • Globular proteins: Myoglobin
  • Globular proteins: Hemoglobin
• Collagen


  • Most abundant protein in humans, major structural material in tendons, ligaments, blood vessels, bones, teeth, and skin
  • Predominant structure is a triple helix
  • Rich in proline
• Myoglobin


  • Spherical in shape, participates in tissue oxygenation, an oxygen storage molecule in muscles, binds one O2 molecule, has a higher affinity for oxygen than hemoglobin
• Hemoglobin


  • An oxygen carrier molecule in blood, transports oxygen from lungs to tissues, can transport up to 4 oxygen molecules at a time, iron atom in heme interacts with oxygen
• Proteins are the most versatile macromolecule in our system
• Myoglobin


  Oxygen-storage protein present in muscle
• Myoglobin has a higher affinity than hemoglobin


  The good thing
• Hemoglobin


  Oxygen carrier molecule in blood, important in oxygen transportation, can carry more than one oxygen atom
• Oxygen stored in myoglobin molecules


  Serves as a reserve oxygen source for working muscles
• Hemoglobin


  • Tetramer (four peptide chains), each subunit has a heme group, can transport up to 4 oxygen molecules at time, iron atom in heme interacts with oxygen
• Functional versatility of proteins stems from

  • Ability to bind small molecules specifically and strongly
  • Ability to bind other proteins and form fiber-like structures
  • Ability integrated into cell membranes to become a plasma membrane components
• Major categories of proteins based on function

  • Catalytic proteins (enzymes)
  • Defense proteins (immunoglobulins/antibodies)
  • Transport proteins
  • Messenger proteins
  • Contractile proteins
  • Structural proteins
  • Transmembrane proteins
  • Storage proteins
  • Regulatory proteins
  • Nutrient proteins