Fibrous and globular proteins

• what are the different types of proteins?

  • globular proteins - conjugated and simple (non-conjugated)
  • fibrous proteins
• describe a globular protein

  • have a 3-D ball shape
  • hydrophobic amino acids on the inside
  • hydrophilic amino acids on the outside
  • have no prosthetic group
  • are soluble in water
  • have a role in metabolic reactions
  • examples include - antibodies, plasma proteins, enzymes
• describe conjugated proteins

  • have a 3-D ball shape
  • hydrophobic amino acids on the inside
  • hydrophilic amino acids on the outside
  • have a prosthetic group
  • are soluble in water
  • have a role in metabolic reactions
  • examples include - haemoglobin, catalase
• describe fibrous proteins

  • form fibres
  • have a repetitive primary structure
  • are insoluble in water
  • have a structural role
  • examples include - keratin, collagen, elastin
• what are the properties and functions of collagen?

  • a fibrous protein, a connective tissue found in skin, tendons, ligaments and the nervous system
  • is made of 3 polypeptide chains wound together in a long and strong rope-like structure
  • is flexible and strong
  • contains lots of glycine
• what are the properties and functions of elastin?

  • fibrous protein found in elastic fibres which are present in the walls of blood vessels and the alveoli of the lungs
  • gives these structures the flexibility to expand when needed, but also to return to their original size
  • is a quaternary protein made from many stretchy molecules called tropoelastin
• what are the properties and functions of keratin?

  • present in the hair, skin and nails
  • has a large proportion of the sulpher-containing amino acids, cysteine
  • this results in many strong disulphide bonds (disulphide bridges) forming strong, inflexible, and insoluble materials
  • has more cysteine than elastin
  • the degree of disulphide bonds determines the flexibility
• what is the structure of haemoglobin?

  • formed from four separate polypeptide chains
  • each polypeptide chain also has a haem group, which is an example of a prosthetic group
  • has 2 alpha chains and 2 beta chains
  • oxygen binds reversibly to the haem group
• what is a prosthetic group?

  • non-protein molecule that forms an essential part of a certain enzyme (if on a protein, makes it a conjugated protein)
• what is the difference between a conjuncted protein and a simple protein?

  • simple proteins are chemically just amino acids, however conjuncted proteins have other chemical groups attached such as carbohydrates, lipids, bound metal ions and other organic groups
• what is the structure, properties and functions insulin?

  • a hormone to regulate blood glucose levels
  • causes a release of sugar
  • 2 polypeptide
• what is the structure, properties and functions of catalase/pepsin?

  • is an enzyme that catalyses the breakdown of hydrogen peroxide into oxygen and water
  • quaternary structure - 4 polypeptide chains and 4 haem prosthetic group
  • the presence of the iron II in the prosthetic groups allow catalase to interact with hydrogen peroxide and speed up its breakdown
  • catalase makes sure that the common by product of metabolism (hydrogen peroxide) doesn’t damage cells and cell components (doesn’t let it accumulat)
• what is the structure, function and properties of haemoglobin?

  • quarternary structure - made from 4 polypeptides, 2 alpha and 2 beta subunits, each subunit contains a prosthetic haem group
  • binds and releases oxygen
  • the iron II present in haem groups are each able to combine reversibly with an oxygen molecule - this enables haemoglobin to transport oxygen around the body
• how can a computer model the 3-D shape of a protein if its primary structure is known?

  • tertiary structure cab be determined using Xray crystallography - but this is very expensive
  • computer modelling uses a reference library of known primary and tertiary structures
  • as the primary structures will affect the tertiary structure - the programme will generate how certain primary structures will fold up to form the tertiary structure
• what are the benefits of using a computer modelling?

  if a new protein is discovered - its primary sequence can be compared to the reference library and its tertiary structure predicted