Gene Expression P1

Overview of Gene Expression

• Gene Expression: The process by which a gene's information is converted into the structures and functions of a cell, specifically through the synthesis of proteins.

  • mRNA Destruction: If mRNA is destroyed, the gene cannot be expressed, and therefore the specific protein, which can be enzymes or structural proteins, is not synthesized.

Components of Expression

• Gene: A portion of DNA responsible for making a specific protein, which may include:

  • Enzymes

  • Transmembrane proteins

  • Peripheral proteins

• Protein Functionality: The effectiveness of gene expression depends on whether the corresponding protein is produced in its functional form or not.

Examples Illustrating Gene Expression

• Kangaroo Example:

  • Functional vs. Nonfunctional Proteins:

    • Functional protein: Produces a specific trait (e.g., pigment).

    • Nonfunctional protein: May result from structural changes in the protein that affect its active site.

  • This shows how gene expression determines observable traits, such as color in animals.

Cases of Gene Expression

• Case 1: Protein is synthesized but is nonfunctional due to changes in its primary structure (amino acid sequence) affecting its shape and function.

  • Consequences: The gene is not expressed as the protein cannot perform its designated function.

• Case 2: Protein is not synthesized at all due to destruction of mRNA.

  • Consequences: No gene expression occurs; the enzyme is absent, and thus its function is not fulfilled.

Regulation of Expression

• Transcription Factors:

  • These proteins can enhance or inhibit the process of transcription, influencing whether genes are expressed or not.

  • Absence of Transcription Factors: If certain transcription factors are absent, genes may be silenced because mRNA will not be produced.

Specific Examples of Gene Regulation

• E. coli and Tyrosine:

  • E. coli can obtain tyrosine from its host (e.g., human intestines).

    • If enough tyrosine is present, the gene for synthesizing tyrosine in E. coli is silenced to prevent wasteful production.

    • If tyrosine is absent, the gene becomes active, and E. coli synthesizes its tyrosine.

Additional Influencing Factors

• Hormones: Some hormones can regulate gene expression positively or negatively through their presence or absence affecting the transcription machinery.

• Chromatin Structure:

  • The compactness of DNA within chromatin (DNAs and proteins) influences gene accessibility for transcription mechanisms.

  • Modifications of chromatin can inhibit or promote gene expression.

Summary of Mechanisms Affecting Gene Expression

• mRNA and Protein Stability:

  • mRNA can be degraded or proteins can be destroyed, which directly impacts gene expression.

  • Regularly assessing mRNA stability is crucial in understanding how gene expression is controlled at the molecular level.

Conclusion

• Important concepts in gene expression include the distinction between functional and nonfunctional proteins, the role of mRNA, and how external factors such as transcription factors, hormones, and even the inherent properties of DNA such as chromatin structure can influence the overall expression outcomes.