1) What makes an operon?
- an operator (controls the access of RNA polymerase to the genes)
- the promoter (where RNA polymerase attaches here)
- genes of the operon (the entire strech of DNA required for all the enzymes produced by the operon)
2) The zygote undergoes transformation through three interrelated processes. What are these?
- cell division
- cell differentiation
- morphogenesis
- cytoplasmic determinants
- cell-cell signals
- Cells control metabolism by regulating enzyme activity or the expression of genes coding for enzymes.
- An operon site on the DNA switches the operon on or off; resulting in coordinate regulation of genes.
- Cells differ in structure and function not because they contain different portions of a common genome, but because they express different portions of a common genome.
- Differentiation is heralded by the appearance of tissue-specific proteins, which enable differentiated cells to carry out their specialized roles.
[Drosophila - gradients of morphogens encoded by maternal effect genes determine the body axes]
- A hyperactive version of a protein in an stimulatory pathway, such as Ras (a G protein), functions as an oncogene protein.
Summary:
The controls that act on gene expression are much more complex in eukaryotes than in prokaryotes. In bacteria, genes are clustered into operons (gene clusters that encode the proteins necessary to perform coordinated function).
During normal growth on a glucose-based medium, the lacrepressor is bounded to the operator region of the lac operon, preventing transcription. However, in the presence of an inducer of the lac operon, the repressor protein binds the inducer and is rendered incapable of interacting with the operator region of the operon.
The trp operon encodes the genes for the synthesis of tryptophan. Since the activity of the trp repressor is enhanced in the presence of tryptophan, the rate of expression of the trp operon is graded in response to the level of tryptophan in the cell.
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