Gene Control
- The nucleus of every cell in the human body contains the same genes
- However not every gene is expressed in every cell
- Not all of these genes are expressed all the time
- There are several mechanisms that exist within cells to make sure the correct genes are expressed in the correct cell at the right time
- They involve regulatory genes
Structural & regulatory genes
- A structural gene codes for a protein that has a function within a cell
- For example, the F8 gene codes for the protein Factor VIII involved in blood clotting
- A regulatory gene codes for a protein that helps to control the expression of another gene
- Structural and regulatory genes that work together are usually found close together
Inducible & repressible enzymes
- Some genes code for proteins that form enzymes
- Some enzymes are required all the time and some are required only at specific times
- The expression of enzyme-producing genes can be controlled
- Inducible enzymes are only synthesised when their substrate is present
- The presence of the substrate induces the synthesis of of the enzyme by causing the transcription of the gene for the enzyme to start
- Repressible enzymes are synthesised as normal until a repressor protein binds to an operator
- The presence of the repressor protein represses the synthesis of the enzyme by causing the transcription of the gene for the enzyme to stop
- Controlling when enzymes are synthesized can be beneficial for cells as it stops materials and energy being wasted
- For example, using materials and energy to synthesize an enzyme when its substrate is not present and it can’t carry out its function would be highly wasteful
