Question

Describe intrinsic and extrinsic noise in gene expression.

Answer 1

Cellular noise is a measure of expression level variability between individual cells. It can be intrinsic or extrinsic noise.

Intrinsic noise is caused by internal differences in stochastic collisions and expression does not covary. It refers to variation in identically-regulated quantities within a single cell: for example, the intra-cell variation in expression levels of two identically-controlled genes.

Extrinsic noise is caused by external differences and causes expression of two identical genes to covary. It refers to variation in identically-regulated quantities between different cells: for example, the cell-to-cell variation in expression of a given gene.

Example: a bacterial culture where cells at the top are more oxygenated than those near the bottom and may respond differently (extrinsic noise), but when all cells are getting the same amount of oxygen, the same genes might respond differently in different cells (intrinsic noise).