proteins and nucleic acid

• Proteins


  The most versatile cell components made up of amino acids

  
• Amino acids


  The subunits of proteins

  
• Amino acids


  • Have an amino group (-NH2) and a carboxyl group (-COOH) bonded to the same asymmetrical carbon atom, known as the alpha carbon
  • 20 amino acids are commonly found in proteins, each identified by the variable side chain (R group) bonded to the 𝝰 carbon

  
• Amino acids in neutral pH solutions

  The carboxyl group (-COOH) donates a proton and becomes ionized (-COO-), whereas the amino group (-NH2) accepts a proton and becomes -NH3+
• Properties of amino acid side chains

  • Nonpolar side chains tend to have hydrophobic properties
  • Polar side chains are more hydrophilic
  • Acidic amino acid has a side chain that contains a carboxylic group
  • Basic amino acid becomes positively charged when the amino group in its side chain accepts a hydrogen ion
• Peptide bonds


  Join amino acids

  
• An almost infinite variety of protein molecules is possible differing from one another in the number, types, and sequence of amino acids

  
• Levels of protein organization

  • Primary structure
  • Secondary structure
  • Tertiary structure
  • Quaternary structure

  
• Primary structure


  • The sequence of amino acids joined by peptide bonds
  • The sequence is specified by the instructions in a gene
  • Represented in a simple, linear, "beads-on-a-string" form

  
• Secondary structure


  • Hydrogen bonding of the peptide backbone causes the amino acid to fold in a repeating unit

  
• Tertiary structure


  • The overall shape assumed by each individual polypeptide chain
  • The 3D structure is determined by the interactions among R groups

  
• Interactions that determine tertiary structure

  • Hydrogen bonds between R groups
  • Ionic bonds between R groups with positive and negative charges
  • Hydrophobic interactions of nonpolar R groups
  • Disulfide bonds or bridges between cysteine subunits

  
• Quaternary structure


  • Composed of two or more polypeptide chains interacting in specific ways

  
• Nucleic acids


  Polymers made of monomers called nucleotides
• Genes


  Consist of DNA which belongs to the class of compounds called nucleic acids
• Nucleotide


  Composed of a five-carbon sugar (pentose), a nitrogen-containing base, and one to three phosphate groups
• Nucleoside


  The portion of a nucleotide without any phosphate group