Proteins

• Proteins have a wide range of functions such as hormones, antibodies, and enzymes
• Amino acids are the monomers of proteins
• There are twenty naturally occurring amino acids with different R groups
• In forming a dipeptide:

  • Amino acid 1 and 2 line up
  • Amine group reacts with the carboxylic acid group
  • Water is eliminated in a condensation reaction
  • A dipeptide is formed
• In forming a polypeptide:

  • Thousands of amino acids link up in condensation reactions
  • The number, type, and sequence of amino acids in a chain is known as its primary structure
• Secondary protein structure involves the folding of a polypeptide chain into alpha (α) helix or beta (β) pleated sheets

  • Alpha helix:
  • H bonds form between the NH group and the CO group
  • Vulnerable to fluctuations in pH & temperature
  • Beta pleated sheets:
  • Hydrogen bonds hold adjacent primary chains together
• Tertiary protein structure involves the folding of the polypeptide into a precise 3D shape maintained by various bonds:

  • H bonds
  • Disulphide bonds between 2 adjacent cysteine amino acids
  • Ionic bonds between ionised amine & carboxylic acid groups
  • Hydrophobic interactions between non-polar R-groups
• Quaternary protein structure involves two or more polypeptide chains in tertiary form fitting together

  • Classic example: Haemoglobin
  • Haemoglobin is made of 4 polypeptide chains: two alpha chains and two beta chains
  • Each chain has a haem group containing an ion of iron (Fe2+)
  • Each haem binds with one molecule of oxygen (O2)
• Globular proteins are involved in chemical reactions and are soluble molecules (e.g. Enzymes)

  • Tertiary structure is important for their function and 3D shape
  • Fibrous proteins have a structural role in biology (e.g. Collagen)
  • Secondary structure is important
• Globular and fibrous proteins have different roles in biology
• Proteins have a wide range of functions such as hormones, antibodies, and enzymes
• Amino acids are the monomers of proteins
• There are twenty naturally occurring amino acids with different R groups
• In forming a dipeptide:

  • Amino acid 1 and 2 line up
  • Amine group reacts with the carboxylic acid group
  • Water is eliminated in a condensation reaction
  • A dipeptide is formed
• In forming a polypeptide:

  • Thousands of amino acids link up in condensation reactions
  • The number, type, and sequence of amino acids in a chain is known as its primary structure
• Secondary protein structure involves the folding of a polypeptide chain into alpha (α) helix or beta (β) pleated sheets
• Alpha (α) helix:

  • Amino acids interact with each other
  • Hydrogen bonds form between the H on the NH group and the O on the CO group
• Beta (β) pleated sheets:

  • Hydrogen bonds hold adjacent primary chains together
• Tertiary protein structure involves the precise 3D folding of a polypeptide chain, maintained by various bonds such as H bonds, disulphide bonds, ionic bonds, and hydrophobic interactions
• Quaternary protein structure:

  • Involves two or more polypeptide chains fitting together
  • Classic example is haemoglobin
• Haemoglobin:

  • Made of 4 polypeptide chains (two alpha and two beta chains)
  • Hydrophobic R groups point into the molecule while hydrophilic R groups point out
  • Each chain has a haem group with an ion of iron (Fe2+) that binds with one molecule of oxygen (O2)
• Globular proteins are involved in chemical reactions and are soluble molecules like enzymes, with tertiary structure being important for their function and 3D shape
• Fibrous proteins have a structural role in biology like collagen, with secondary structure being important
• Globular and fibrous proteins have distinct roles in biology