7.3.7Unit 5: Respiration, Internal Environment, Coordination and Gene Technology
Control of Gene Expression — IAL Edexcel Linear Revision Notes & Topical Questions
5 min read 4 parts Lesson 35 of 36 Unit quiz
Section 1 of 4Transcription Factors
Definition
- Proteins that control transcription of a gene by binding to a specific region of DNA.
Activators
- Transcription factors that increase the rate at which a gene is expressed.
Repressors
- Transcription factors that decrease the rate of expression.
Role
- They make sure that genes are expressed in the right cells, at the right time and to the correct level.
Environment
- They allow organisms to alter protein production when conditions change.
Section 2 of 4Hormones That Enter Cells
1
Steroid and thyroid hormones are lipid soluble, so they pass through the cell surface membrane and enter the nucleus.
2
In warm conditions a thyroid hormone receptor bound to DNA near a gene reduces its expression.
3
The gene codes for a protein that raises the metabolic rate and so generates heat.
4
In cold conditions thyroxine binds to the receptor, and the complex allows RNA polymerase to attach and transcribe the gene.
5
More protein is made, metabolic rate rises, more heat is released and body temperature increases.
Section 3 of 4Hormones That Stay Outside Cells
Hormones That Stay Outside Cells
Examples
- Adrenaline, insulin and glucagon cannot cross the membrane.
Receptor
- They bind to receptors on the cell surface membrane.
Second messenger
- Binding triggers formation of cyclic AMP from ATP in the cytoplasm.
Cascade
- Cyclic AMP activates protein kinases, starting a cascade that can change transcription factor activity.
Section 4 of 4Exam Checklist & Tips
7.3.7 – Key Points for the Exam
- Transcription factor A protein that regulates transcription by binding to DNA.
- Second messenger A molecule that relays a signal inside the cell, such as cyclic AMP.
- Protein kinase An enzyme activated by a second messenger that triggers a cascade.
- Gene expression The use of a gene's information to make a protein.
Common Mistakes
- Stating that hormones like adrenaline enter the nucleus;
- they stay outside and work through second messengers.
- Saying transcription factors translate mRNA; they act on transcription.
- Thinking a gene is always completely on or off; expression is often just raised or reduced.
- Mixing up thyroxine, which enters cells, with peptide hormones.
Last updated:
\n