Gene Expression Basics

Gene Expression

• Gene expression is the process of using a gene's information to create a functional protein.
• Not all genes are expressed in all cells or at all times.
• Gene expression is regulated.
• Certain body parts do not need certain genes, so those genes are not expressed.

Prokaryotic Gene Expression

• Prokaryotic organisms (like bacteria) express genes primarily through transcription and translation happening in the same location (cytoplasm).
• Transcription and translation occur simultaneously.
• Control of gene expression is primarily at the transcription level.

Eukaryotic Gene Expression

• Eukaryotic organisms (like animals and plants) have genes that must be transcribed and translated in different locations (nucleus and cytoplasm).
• Transcription occurs in the nucleus.
• RNA must be processed before translation.
• There are more opportunities for gene regulation in eukaryotes due to having a nucleus and more steps in the process.

Transcription Factors

• Proteins that affect transcription and translation.
• Promoter regions help RNA polymerase start transcription .
• Enhancers are regions that increase transcription.
• Repressors are regions that block RNA polymerase from starting transcription; this is important when the gene is not needed.
• Transcription factors are environmentally affected.
  • UV light
  • Lack of nutrients
  • Too much of something.

Lac Operon Example

• Lactose is a sugar that bacteria want to break down.
• The presence of lactose causes the repressor to be removed.
• Transcription happens.
• mRNA is used to make a protein , the enzyme to break down lactose.
• When lactose is absent, the repressor blocks transcription and no enzyme is created.

Gene Regulation in Eukaryotes (Further Info)

• Transcription: DNA is rewritten into mRNA by DNA polymerase.
• mRNA carries the gene information and travels to the cytoplasm for translation.
• Post-transcriptional modifications: mRNA maturation processes. This includes examining the mRNA strand and removing regions of RNA (Introns) and putting the other useful pieces together (Exons). This is done before leaving the nucleus.
• Introns are non-coding pieces of DNA.
• Exons are the regions that hold the necessary code.

Translation

• Translation uses the mRNA to make a polypeptide chain of amino acids that will become a protein.
• Initiation: mRNA and ribosomes combine.
• Elongation: Amino acids are added to the chain by the ribosome.
• Termination: The polypeptide chain is released.
• Post-translation: Chemical adjustments to protein can change function. This can alter the protein's structure and function.

Why is Gene Expression Important?

• Impacts height
• Impacts eye color
• Impacts blood type
• Impacts hair color
• Affects cell functioning in the body
• Important when cells are not working correctly; e.g., cancer.
• Mutations can increase translation of genes that speed up cell division (e.g., cancer). This increases the division of cancer cells.