With the use of site-directed mutagenesis, hemoglobin has been prepared in which the proximal histidine residues in both alpha and the beta subunits have been replaced by glycine. The imidazole ring from the histidine residue can be replaced by adding free imidazole in solution. Would you expect this modified Hb with free imidazole to exhibit oxygen binding? Why or why not?

The modified hemoglobin with free imidazole cannot be expected to show cooperativity in oxygen binding. The movement of iron ion takes place up in the plane of heme when binding of one subunit of hemoglobin takes place with oxygen. One of the iron's and oxygen's axial ligands comprise the proximal histidine's imidazole ring.  

With the movement of iron into the hemoglobin ring, the pulling of proximal histidine takes place along with it. Therefore, when binding of oxygen takes place with one subunit, a modification also takes place in the intersubunit associations, this also comprises displacement of the alpha helix. This phenomenon plays an essential role in modifying the hemoglobin's tensed state to the relaxed state. The withdrawal or mutation of the imidazole ring from the histidine residue does not further permit the cooperative binding as it is not associated physically with the alpha-helix.  

1. dermis

2. chemical

3. urine

4. viruses

5. antibodies

an individual’s sex (i.e., whether they are a male or female) is determined by the sex chromosomes. most people have two sex chromosomes, one that is inherited from their mother and one that is inherited from their father. typically, females have two x chromosomes (xx) and males have one x chromosome and one y chromosome (xy). conditions caused by changes (“mutations”) in genes located on the x chromosome are considered x-linked.

x-linked recessive inheritance

most x-linked conditions are recessive. this means that in a person with two x chromosomes (most females), both copies of a gene (i.e., one on each x chromosome) must have a change or mutation whereas in a person with one x chromosome (most males), only one copy of a gene must have a mutation. a female with a mutation in one copy of a gene on the x chromosome is said to be a “carrier” for an x-linked condition. a male with a mutation in a gene on the x chromosome is typically affected with the condition. because females have two copies of the x chromosome and males have only one x chromosome, x-linked recessive diseases are more common among males than females. however, x-linked recessive diseases can occur in both males and females.

for x-linked recessive disorders, an unaffected carrier mother who has a mutation in a gene on the x chromosome can transmit either the x chromosome with this mutation or a “normal” x chromosome to her children. if the father is unaffected, none of her daughters will be affected and all of her daughters will be unaffected—since they will inherit at least one normal x chromosome from their father. however, each daughter will have a 50% chance of being an unaffected carrier like her mother and a 50% chance of both x chromosomes being normal.