1.1 Proteins

Question 1

Describe the structure of an amino acid.

Answer 1

Question 2

what are the bonds present in the primary structure of a protein

Answer 2

Peptide bonds

Question 3

what are the bonds present in the secondary structer of a protein

Answer 3

The polypeptide chain is held together by peptide bonds and the chain is held in the alpha helix and beta pleated sheet with hydrogen bonds

Question 4

what are the bonds present in the tertiary structure of a protein

Answer 4

• Hydrogen (these are between R groups)
• Disulphide (only occurs between cysteine amino acids)
• Ionic (occurs between charged R groups)
• Weak hydrophobic interactions (between non-polar R groups)

Question 5

what are the bonds present in the quaternary structer of a protein

Answer 5

• Hydrogen (these are between R groups)
• Disulphide (only occurs between cysteine amino acids)
• Ionic (occurs between charged R groups)
• Weak hydrophobic interactions (between non-polar R groups)

Question 6

what are the characteristics of a globular protein

Answer 6

• Globular proteins are compact, roughly spherical (circular) in shape and soluble in water
• Globular proteins form a spherical shape when folding into their tertiary structure because:
  
  • their non-polar hydrophobic R groups are orientated towards the centre of the protein away from the aqueous surroundings and
  • their polar hydrophilic R groups orientate themselves on the outside of the protein
• This orientation enables globular proteins to be (generally) soluble in water as the water molecules can surround the polar hydrophilic R groups
• The solubility of globular proteins in water means they play important physiological roles as they can be easily transported around organisms and be involved in metabolic reactions
• The folding of the protein due to the interactions between the R groups results in globular proteins having specific shapes. This also enables globular proteins to play physiological roles, for example, enzymes can catalyse specific reactions and immunoglobulins can respond to specific antigens
• Some globular proteins are conjugated proteins that contain a prosthetic group eg. haemoglobin which contains the prosthetic group called haem

Question 7

Describe the structer of Hemoglobin.

Answer 7

2x Alpha Globin

2x Beta Globin

Question 8

Describe the structer of collegen

Answer 8

• Collagen is formed from three polypeptide chains closely held together by hydrogen bonds to form a triple helix (known as tropocollagen)
• Each polypeptide chain is a helix shape (but not α-helix as the chain is not as tightly wound) and contains about 1000 amino acids with glycine, proline and hydroxyproline being the most common
• In the primary structure of collagen almost every third amino acid is glycine
  
  • This is the smallest amino acid with a R group that contains a single hydrogen atom
  • Glycine tends to be found on the inside of the polypeptide chains allowing the three chains to be arranged closely together forming a tight triple helix structure
• Along with hydrogen bonds forming between the three chains there are also covalent bonds present
• Covalent bonds also form cross-links between R groups of amino acids in interacting triple helices when they are arranged parallel to each other. The cross-links hold the collagen molecules together to form fibrils
• The collagen molecules are positioned in the fibrils so that there are staggered ends (this gives the striated effect seen in electron micrographs)
• When many fibrils are arranged together they form collagen fibres
• Collagen fibres are positioned so that they are lined up with the forces they are withstanding composed of three chains

tight triple helix

The chains are staggered