3.7 Types of Proteins - Quaternary Proteins Flashcards
What type of protein is Haemoglobin?
Globular
What type of protein is Catalase?
Globular
What type of protein is Insulin?
Globular
What type of protein is Collagen?
Fibrous
What type of protein is Keratin?
Fibrous
What type of protein is Elastin?
Fibrous
Describe the structure of Haemoglobin.
• 4 polypeptide subunits (2 alpha, 2 beta) each wrapped around a prosthetic haem group, protecting it from being oxidised.
• When oxygen touches it, the quaternary structure changes to accommodate it.
What are the properties of Haemoglobin?
- Fe2+ ions in haem groups can combine reversible with oxygen molecules.
- Therefore one Haemoglobin molecule binds to 4 oxygen molecules.
What is the function of Haemoglobin?
Transports oxygen in the lungs to the cells that need it (via RBC) where it is released.
Describe the structure of catalase.
• Tetrameric enzyme containing 4 haem prosthetic groups
• Has Fe2+ ions present in prosthetic groups
What are the properties of Catalase?
- Has Fe2+ ions which interact with hydrogen peroxide to speed up breakdown in the liver.
- Roughly spherical shape
What is the function of Catalase?
Breaks down hydrogen peroxide in the liver. Hydrogen peroxide is a product of metabolism and is toxic to cells and cellular components when accumulated.
Describe the structure of insulin.
• 2 polypeptide chains - alpha and beta - held together by disulfide bonds
• ^ precise shape required to fit into receptors on cell-surface membrane to take effect
What are the properties of insulin?
Water soluble (as it has to be transported in the blood stream)
What is the function of insulin?
Regulation of blood glucose concentration (initiates conversion of glucose to glycogen)
Describe the structure of collagen.
• 3 polypeptides wound together in a triple helix structure due to high proportion of glycine
• Staggered ends with cross-linking between molecules to increase strength of microfibril structure
What are the properties of collagen?
Strong and flexible, insoluble in water
What is the function of collagen?
Plays a structural role in the tendons, ligaments and skin.
Describe the structure of keratin.
• Long stranded molecules
• 2 polypeptide chains
• High proportion of sulfur-containing amino acid cysteine
• Results in the formation of many strong disulfide bonds/bridges
• Degree of disulfide bonds determines flexibility (e.g. hair has fewer, nails have more)
What are the properties of keratin?
Strong, insoluble in water, inflexible
What is the function of keratin?
Plays a structural role in the hair, fingernails, skin (+horns and feathers)
Describe the structure of elastin.
• Made from stretchy molecules of tropoelastin
• Long cross-linked strands containing hydrophobic regions
• These regions of different strands associate, causing molecules to group together
• When stretched, strands move apart but remain attached at cross links
What are the properties of elastin?
Supple and elastic
What is the function of elastin?
Plays a structural/supportive role in the skin, walls of arteries, alveoli of lungs.
What are some common properties of globular proteins?
Water-soluble, spherical shape, compact, physiological function (involved in reactions)
What are some common properties of fibrous proteins?
Insoluble (high concentration of hydrophobic R-groups), large number of repetitive sequences of amino acids, structural/supportive function
What is a conjugated protein?
A polypeptide chain with a prosthetic group
