Question

Gene expression in eukaryotes is regulated at steps beyond transcription. Briefly, describe these steps and give the mechanism of regulation.

Answer 1

Gene regulation is the process of controlling which genes in a cell's DNA are expressed (used to make a functional product such as a protein).

Gene expression in eukaryotic cells is regulated by repressors as well as by transcriptional activators. eukaryotic repressors bind to specific DNA sequences and inhibit transcription

Eukaryotic gene expression involves many steps, and almost all of them can be regulated. Different genes are regulated at different points, and it’s not uncommon for a gene to be regulated at multiple steps.

• Chromatin accessibility. The structure of chromatin (DNA and its organizing proteins) can be regulated. More open or “relaxed” chromatin makes a gene more available for transcription.

• Transcription. Transcription is a key regulatory point for many genes. Sets oftranscription factor proteins bind to specific DNA sequences in or near a gene and promote or repress its transcription into an RNA.

• RNA processing. Splicing, capping, and addition of a poly-A tail to an RNA molecule can be regulated, and so can exit from the nucleus. Different mRNAs may be made from the same pre-mRNA by alternative splicing.

• RNA stability. The lifetime of an mRNA molecule in the cytosol affects how many proteins can be made from it. Small regulatory RNAs called miRNAs can bind to target mRNAs and cause them to be chopped up.

• Translation. Translation of an mRNA may be increased or inhibited by regulators. For instance, miRNAs sometimes block translation of their target mRNAs (rather than causing them to be chopped up).

• Although all stages of gene expression can be regulated, the main control point for many genes is transcription. Later stages of regulation often refine the gene expression patterns that are "roughed out" during transcription.

• Protein activity. Proteins can undergo a variety of modifications, such as being chopped up or tagged with chemical groups. These modifications can be regulated and may affect the activity or behavior of the protein.