Gene Expression Responds Dynamically to Environmental Signals
- This is the process where information from a gene is used to synthesize functional products, such as proteins.
- This then determines an organism's traits.
Hormonal Regulation: The Role of Oestrogen
Definition
Hormones
Hormones are chemical messengers that travel through the bloodstream to regulate various physiological processes.
- Oestrogen, a steroid hormone, plays a critical role in the female reproductive system, influencing the expression of specific genes.
- Remember, oestrogen’s ability to regulate gene expression is tissue-specific.
- It affects only cells with oestrogen receptors, such as those in the uterus, breast, and bone.
Biochemical Regulation: The Lac Operon in Bacteria
- In prokaryotes like Escherichia coli, gene expression is tightly regulated to conserve energy and resources.
- A cluster of genes under the control of a single promoter, allowing coordinated regulation.
The Lac Operon is A Model of Gene Regulation
- The lac operon consists of three structural genes:
- lacZ: Encodes β-galactosidase, an enzyme that breaks down lactose into glucose and galactose.
- lacY: Encodes permease, a protein that transports lactose into the cell.
- lacA: Encodes transacetylase, an enzyme with a less well-understood role.
- These genes are controlled by a promoter, an operator, and a regulatory gene ($lacI$) that produces a repressor protein.
How the Lac Operon Works
- No Lactose Present:
- The repressor protein binds to the operator, blocking RNA polymerase from transcribing the structural genes.
- The operon is "off," and the enzymes for lactose metabolism are not produced.
- Lactose Present:
- Lactose acts as an inducer by binding to the repressor protein, causing it to change shape and detach from the operator.
- RNA polymerase can now bind to the promoter and transcribe the genes, enabling the bacterium to metabolize lactose.
- Don't confuse the role of the repressor and RNA polymerase.
- Remember, the repressor blocks transcription by binding to the operator.
- RNA polymerase initiates transcription by binding to the promoter.
Why These Mechanisms Matter
- Efficiency: Cells conserve energy by producing proteins only when needed. For example, E. coli activates the lac operon only in the presence of lactose.
- Adaptation: Hormones like oestrogen enable multicellular organisms to respond to internal and external changes, such as preparing the uterus for pregnancy.
- Survival: These regulatory mechanisms enhance an organism’s ability to survive and reproduce in changing environments.
- How do environmental factors like hormones and nutrients challenge the idea of genetic determinism?
- Could this influence our understanding of human traits and behaviors?
Explain how the presence of lactose in the environment affects the expression of the lac operon in E. coli.
