Gene expression and function | Biomolecules | MCAT | Khan Academy

Introduction

This tutorial provides a step-by-step guide to understanding gene expression and function, key concepts in molecular biology relevant for the MCAT. We will explore the processes that regulate gene expression, the role of different biomolecules, and how these concepts are applied in various biological contexts.

Step 1: Understand the Basics of Gene Expression

Gene expression is the process by which information from a gene is used to synthesize a functional gene product, often proteins. Here’s how it works:

• Transcription:

  • DNA is transcribed into messenger RNA (mRNA).
  • RNA polymerase binds to the promoter region of the gene.
  • The DNA unwinds, and the gene is copied into mRNA.

• Translation:

  • mRNA is translated into a protein at the ribosome.
  • Transfer RNA (tRNA) brings amino acids to the ribosome according to the codon sequence on the mRNA.

Practical Tip

Familiarize yourself with the central dogma of molecular biology: DNA -> RNA -> Protein. This is foundational for understanding gene expression.

Step 2: Explore the Role of Regulatory Elements

Regulatory elements control gene expression. They include:

• Promoters: DNA sequences where RNA polymerase binds to initiate transcription.
• Enhancers: DNA sequences that increase the likelihood of transcription.
• Silencers: DNA sequences that suppress transcription.

Common Pitfalls

• Misunderstanding the difference between enhancers and silencers can lead to confusion. Remember, enhancers boost gene expression while silencers inhibit it.

Step 3: Learn About Post-Transcriptional Modifications

After transcription, mRNA undergoes several modifications before translation:

• Capping: A 5' cap is added to the mRNA, protecting it from degradation.
• Polyadenylation: A poly-A tail is added to the 3' end, aiding in export from the nucleus and stability.
• Splicing: Introns are removed, and exons are joined together to form mature mRNA.

Real-World Application

Understanding these modifications is crucial for gene therapy and biotechnology applications, where manipulating mRNA can alter protein expression.

Step 4: Examine the Role of RNA in Gene Regulation

RNA molecules are not just messengers; they also play regulatory roles:

• MicroRNA (miRNA): Small RNA molecules that can bind to mRNA and prevent its translation or lead to its degradation.
• Long non-coding RNA (lncRNA): Involved in regulating gene expression at various levels.

Practical Advice

Studying the different types of RNA can provide insights into complex gene regulation mechanisms that are critical for advanced biological studies.

Step 5: Recognize the Importance of Gene Expression in Health and Disease

Gene expression is crucial for normal cellular function and is often altered in diseases. Key points include:

• Cancer: Abnormal gene expression can lead to uncontrolled cell growth.
• Genetic Disorders: Mutations that affect gene expression can cause various diseases.

Common Pitfalls

It’s easy to overlook the implications of gene expression in pathology. Always consider how changes in expression can affect health outcomes.

Conclusion

Understanding gene expression and its regulation is essential for grasping fundamental biological processes and their applications in medicine and biotechnology. Review the central dogma, regulatory elements, post-transcriptional modifications, and the role of RNA. As a next step, consider exploring specific case studies of gene expression in health and disease to deepen your understanding.