6) * Earlier this semester (in the Class 1 Handout Practice Problems), we learned that individuals with an HIV infection...

The body's immune system is in charge of warding off infection. It accomplishes this in a variety of methods, including physical and chemical barriers as well as cells. However, HIV (human immunodeficiency virus) is a virus that affects immune cells and can be transmitted from one person to another by certain bodily fluids. As a result, the body becomes more susceptible to other infections and diseases. If HIV is not treated, it can progress to AIDS (acquired immunodeficiency syndrome).

Azidothymidine (AZT) is another name for zidovudine (ZDV). It is an antiretroviral medication for patients with HIV/AIDS. AZT is usually given twice a day in combination with other antiretroviral drugs.

As given,

The blood in an average human adult $= 5 L or 5000 mL.$
The concentration of AZT in a typical patient's bloodstream $= 90 \mu g/mL$

Therefore, the total concentration of AZT in a typical patient's bloodstream having $5 L$of blood:

$$\begin{gathered} = 90\times 5000 \mu g \\ = 4,50,000 \mu g \\ = 0.45 grams \end{gathered}$$

The molecular formula of NZT as given is $C_{10}{H}_{13}{N}_5{O}_4$.

The molecular weight of the AZT will be as follows: 

$$\begin{gathered} =(10\times 12)+(13\times 1)+(5\times 14)+(4\times 16) grams/mole \\ =267 grams/mole \end{gathered}$$

Thus, $267 g$ of NZT contains $6.022\times {10}^{23}$molecules.

(*Avogadro constant $= 6.022\times {10}^{23}$)

Hence, $0.45$grams of NZT contains

$$\begin{gathered} =\frac{0.45\times 6.022\times {10}^{23}}{267} \\ =1.0149\times {10}^{21} molecules \end{gathered}$$

As described, the person has $90 \mu g/mL$ AZT in his bloodstream and has $5 L$blood. On the basis of the molecular formula given, there are about $1.0149\times {10}^{21}$molecules of AZT in the patient's body.