·Describe the biological functions of hemoglobin, myoglobin · Describe the gener

Question

·Describe the biological functions of hemoglobin, myoglobin

· Describe the general structural characteristics of hemoglobin in terms of the number of

polypeptide chains, number of O2 binding sites, the general location of the heme, the general

chemical and structural characteristics of the heme.

· Describe the bonding of the ferrous iron in the heme.

· Describe the role that the proximal His plays in hemoglobin.

· Describe the role that the distal His plays in hemoglobin.

· Explain the term “cooperative binding” for hemoglobin.

· Describe the definition and meaning of the term P50 as it relates to Hb and Mb O2 binding and

its relationship with oxygen affinity.

· Describe the relationship between the shape of the binding curve and whether binding is

cooperative or not.

· Describe the benefit of cooperative O2 binding by hemoglobin and be able to show it using

oxygen binding curves (sigmoidal versus hyperbolic!).

· Describe what “T” and “R” states refer to in general and for Hb.

· Describe and explain the role of the polypeptide chain in reducing carbon monoxide toxicity to

humans, specifically, in minimizing the affinity difference between oxygen and carbon

monoxide.

· Explain the reason that the polypeptide chain in hemoglobin helps increase oxygen affinity

but not carbon monoxide affinity thereby reducing their affinity difference.

· Explain why the distal histidine interacts with the heme-bound oxygen but not the hemebound

carbon monoxide.

· Describe the fact that the R state binds the ligand (such as oxygen for Hb) with higher affinity

than the T state.

· Explain why R state binds the ligand with a higher affinity.

· Describe the major structural differences between deoxy- and oxy-Hb.

· Describe how O2 binding induces the conformational change in Hb.

· State the Bohr Effect and its physiological significance.

· Show the Bohr Effect using oxygen binding curves.

· Explain the underlying mechanism of the Bohr Effect (hint: think acidity/CO

concentration)

· Describe the fact that the oxygen affinity difference between Mb and Hb is due to BPG

binding to Hb.

· Describe the number of BPG bound to Hb and its location in Hb.

· Describe that BPG binds to deoxyHb, not the oxyHb.

· Describe that BPG lowers Hb oxygen affinity.

· Explain how BPG lowers Hb oxygen affinity.

· Explain in words and in graphs that the presence of [BPG] makes it possible for Hb to

deliver enough oxygen to the tissue. (Consider transition from T ‡ R state)

Explanation / Answer

Answer 1) The biological functions of hemoglobin and myoglobin.

A) The biological functions of hemoglobin :.

i) Heamoglobin is Fe-containing oxygen-transport metalloprotein in the RBC's of all vertebrates

ii) Hemoglobin in the blood carries oxygen from the respiratory organs i.e. lungs to the rest of the body (to tissues) where it is required for an Aerobic respiration.

iii) In some tissues Heamoglobin has the anathor unusual role i.e. as an Antioxidant and regulation of Fe metabolism.

iv) Hemoglobin and hemoglobin-like molecules found in many invertebrates like fungi, and plants wherein hemoglobins may carry oxygen, or they may act to transport and regulate other small molecules and ions such as carbon dioxide, nitric oxide, sulfide etc.

v) A simmilar molecule called leghemoglobin, is used to scavenge oxygen away from anaerobic systems, such as the nitrogen-fixing nodules of leguminous plants, before the oxygen deactivate the system.

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B) The biological functions of myoglobin :

i) Like Heamoglobin, Myoglobin is also a cytoplasmic protein which binds a heam group. In Heamoglobin there are 4 heam groups and in Myoglobin there is one heam group only. Myoglobin is astorage protein unlike Heamoglobin which is a transport protein.

ii) Myoglobin is an iron- and oxygen-binding protein found in the muscle tissue of vertebrates.In humans, myoglobin is only found in the bloodstream after muscle injury

iii) Myoglobin is the primary oxygen-carrying pigment of muscle tissues high concentrations of which in muscle cells allow organisms to hold their breath for a longer period of time.

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