Question 1

What happens during the cell harvesting stage of downstream processing?

Accepted Answer

Cell harvesting separates cells from the liquid medium using centrifugation or filtration. For extracellular products, the supernatant is collected directly. For intracellular products, harvested cells proceed to disruption. This initial separation is critical for recovering target molecules from fermentation broths.

Question 2

Why is cell disruption necessary for intracellular products?

Accepted Answer

Intracellular products are trapped inside cells and must be released before purification. Common disruption methods include homogenization, sonication, and chemical lysis. These techniques break open cells, releasing intracellular components into the liquid phase for subsequent clarification and purification steps.

Question 3

How does clarification remove impurities from the crude product?

Accepted Answer

Clarification uses centrifugation or depth filtration to remove solid debris and particulate matter, producing a clear solution containing the crude product. This step prepares the liquid for primary purification by eliminating unwanted solids while retaining dissolved target molecules and impurities.

Question 4

What role does ammonium sulfate precipitation play in primary purification?

Accepted Answer

Ammonium sulfate precipitation concentrates the target product and reduces impurities by altering protein solubility. This technique selectively precipitates proteins while leaving many contaminants in solution. The precipitated product is then collected and concentrated using ultrafiltration for further purification.

Question 5

How does ultrafiltration concentrate and purify the product?

Accepted Answer

Ultrafiltration applies transmembrane pressure to separate molecules by size, retaining larger target proteins while smaller molecules and impurities pass through. This concentrates the product and removes low-molecular-weight contaminants. The process reduces volume while increasing product concentration for subsequent chromatographic purification.

Question 6

What chromatographic techniques achieve high purity in downstream processing?

Accepted Answer

Ion exchange chromatography and affinity chromatography isolate target proteins based on their chemical properties. Affinity chromatography specifically binds target molecules while impurities pass through. Diafiltration may also exchange buffer systems and remove remaining low-molecular-weight impurities for final product purity.

Question 7

How does formulation and stabilization preserve the final purified product?

Accepted Answer

Formulation adjusts pH, adds stabilizing agents, or applies lyophilization to preserve product activity and extend shelf life. These final steps protect the purified product from degradation during storage and distribution. Proper formulation ensures the pharmaceutical or industrial product maintains efficacy until use.

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