Globular Proteins Flashcards
Why are some proteins referred to as ‘globular’?
Due to their spherical shape, which is induced by their tertiary structures
Where would a globular protein’s non-polar, or hydrophobic, amino acids be found?
Buried deep into the hydrophobic interior areas
Why are hydrophilic, or polar, amino acids located on the surface?
To allow for dipole-dipole interactions, and to increase solubility
What are enzymes?
Biological catalysts
True or false: globular proteins serve as messengers.
True
What is the oxygen carrier of the blood?
Haemoglobin
What is the term given to the red pigment of striated muscle, and what is its function?
Myoglobin; oxygen store, for use during intense muscular activity
What type of structure does haemoglobin have?
Tetramer
Haemoglobin is an _____-______ protein.
Iron-binding
How many polypeptide chains does haemoglobin have?
Four
How many alpha chains does haemoglobin have, and how many amino acids are in each alpha chain?
Two alpha chains, and 141 amino acids
How many beta chains does haemoglobin have, and how many amino acids are in each alpha chain?
Two beta chains, and 146 amino acids
How many molecules of oxygen can haemoglobin bind to?
Four
How many amino acids are on the single polypeptide chain of myoglobin, and what type of helical structures do they form?
153 amino acids, and 8-heliced alpha structures
What are haem prosthetic groups comprised of?
Non-polypeptides
Where are haem prosthetic groups found?
Hydrophobic crevices
Myoglobin is concentrated in which types of muscle?
Cardiac and skeletal
Describe haem’s physiological properties.
Haem is a ferrous iron-tetrapyrrole with hydrophobic side chains on three sides, and hydrophilic carboxyl group on a fourth side. It has an intense red colour, due to its conjugate bonds; four bonds are to the pyrrole nitrogen atoms, the fifth to the histidine, and the sixth is available for the reversible attachment of oxygen
The myoglobin curve is:
Hyperbolic
What does the myoglobin curve indicate about myoglobin?
Myoglobin is almost fully saturated at low O2 pressure; therefore, it has a high affinity for O2, and does not release its O2 at the O2 pressure found in capillaries. It only releases its O2 when muscular activity further lowers the tissue O2 pressure. It acts as a reserve store for this purpose. As it becomes saturated at a lower O2 pressure than haemoglobin, it has a higher affinity for O2 than haemoglobin, and so can extract O2 from the blood to replenish its stores
The haemoglobin curve is:
Sigmoidal
What does the haemoglobin curve indicate about haemoglobin?
Higher O2 concentrations are required to half-saturate haemoglobin than is the case for myoglobin, again demonstrating myoglobin’s stronger affinity for O2. The sigmoidal curve releases most O2 at O2 pressures encountered in the capillaries, but it also means that haemoglobin is still capable of becoming saturated at the oxygen pressure of the lungs
Haemoglobin is an __________ protein.
Allosteric
True or false: oxygen binding with haemoglobin is cooperative.
True
True or false: oxygen binding with myoglobin is cooperative.
False
What type of chains are found in foetal haemoglobin (HbF)?
Alpha and gamma
True or false: HbF and HbA have vastly different oxygen affinities under similar conditions.
False
To which disease does ‘HbS’ refer to?
Sickle-cell anaemia
Which shape does the RBC take in HbS?
Crescent
Outline the pathophysiology of HbS.
The disease is as a result of exchange of a glutamic acid residue for a valine residue in the beta chain, as a polar residue is being substituted for a hydrophobic residue
Where is the sticky, hydrophobic area located in the haemoglobin of a HbS patient?
Exterior of the beta chains. In the corner between helices E and F of the beta chain of the deoxy-HbS, there is a complementary hydrophobic site.
In oxy-HbS, the complementary site is masked, so the formation of the long crescent fibres only occurs in other conditions.
True or false: genetics have no bearing on HbS.
False
Name two medical complications observed in HbS.
Cardiac failure and thrombosis
