Question

All the cells in a multicellular organism have the same genetic constitution, yet they function differently. How would you account for this?

Answer 1

This phenomenon is accounted for by differential gene expression. While every cell contains the exact same “instruction manual” (DNA), different cell types, like neurons or muscle cells, only “read” specific chapters of that manual.

The primary mechanisms that allow this include:

• Selective Transcription: Cells use regulatory proteins called transcription factors to turn specific genes on or off. A liver cell will activate genes for bile production, while a skin cell will keep those same genes tightly silenced. Epigenetic
• Modifications: Chemical tags (such as methyl groups) can be added to DNA or to the proteins that wrap around it (histones). These tags act like “locks,” making certain sections of DNA inaccessible in some cells but open for use in others, without changing the actual genetic code.
• Alternative Splicing: As we discussed with exons, a single gene can produce different versions of a protein depending on which segments the cell chooses to keep during RNA processing.
• Environmental Signalling: Cells receive chemical signals from their neighbours or the environment that trigger specific internal pathways, telling the cell which proteins to build at any given time.

Essentially, it is not the presence of genes that determines a cell’s identity, but which genes are active and being translated into proteins.