Q.Before genetic engineering, human insulin used for treating diabetes was extracted from the pancreas of slaughtered cattle and pigs. What were the two major problems associated with this animal-derived insulin?

[!TLDR] Animal-derived insulin differed slightly from human insulin (causing allergic/immune reactions in some patients) and was limited in supply because it depended on slaughtered-animal pancreases.

[!ANSWER] The two major problems with animal-extracted insulin were: (1) it differed slightly in amino-acid structure from human insulin, which caused allergic reactions or an immune response in some patients over time, and (2) it was produced in limited quantity and at relatively high cost because it depended entirely on the supply of pancreases from slaughtered cattle and pigs, which could not easily scale with rising global demand.

Before recombinant DNA technology made human insulin production possible, diabetic patients requiring insulin treatment were given insulin extracted and purified directly from the pancreases of slaughtered cattle and pigs, since animal insulin is structurally similar enough to human insulin to have a therapeutic blood-glucose-lowering effect.

However, animal insulin is not chemically identical to human insulin -- it differs by a small number of amino acids in its structure. In some patients, the body's immune system gradually recognised this slightly foreign protein and mounted an immune or allergic response against it over repeated, lifelong use, which could reduce the treatment's effectiveness over time or cause troublesome side effects for the patient.

Separately, because this insulin depended entirely on obtaining pancreases from the meat industry as a by-product, the total available supply and its cost were both constrained by the scale of that industry, rather than by the actual medical demand for insulin. As the number of people worldwide requiring lifelong insulin treatment for diabetes grew, this supply constraint became an increasingly serious practical concern.

[!ANSWER] Animal-derived insulin therefore had two distinct problems: a structural/immunological problem (slight difference from human insulin causing allergic/immune reactions in some patients) and a supply/economic problem (limited, animal-industry-dependent production capacity) -- both of which recombinant human insulin production was specifically designed to solve.

Separate the answer clearly into the biological/immunological problem and the supply/economic problem -- they are two distinct issues.

Do not say animal insulin 'did not work' at all -- it was effective at lowering blood glucose; its problems were the structural difference (causing some immune reactions) and limited supply, not a lack of basic efficacy.