Gene Expression
What is gene expression?
Gene expression is the process by which the instructions in our DNA are converted into a functional product, such as a protein. The process begins with DNA being transcribed into a molecule of messenger RNA (mRNA), which is then translated into a protein by the machinery of the cell.
What is the process of transcription?
Transcription is the first step in gene expression. It involves copying a gene's DNA sequence into a complementary RNA sequence. This process is carried out by an enzyme called RNA polymerase. It unzips the DNA and builds a sequence of RNA that matches the DNA.
How is a gene's DNA sequence translated into a protein?
The gene's DNA sequence gets copied into mRNA during transcription. The mRNA then travels to the cell's ribosomes where it gets translated into a chain of amino acids, which is the building block of proteins.
What role does a ribosome play in protein synthesis?
Ribosomes are the sites of protein synthesis in cells. They translate the mRNA's sequence into a specific sequence of amino acids to form a protein, following the instructions carried by the mRNA.
What is an operon in gene expression?
An operon is a functioning unit of genomic DNA containing a cluster of genes under the control of a single promoter. The genes are transcribed together into an mRNA strand and either translated together in the cytoplasm, or undergo splicing to create monocistronic mRNAs that are translated separately.
What are some examples of operons?
The lac operon and trp operon found in E.coli are the two classic examples of operons. They regulate the metabolism of lactose and tryptophan respectively.
What is a promoter in gene expression?
A promoter is a sequence of DNA that starts the transcription of a gene. Promoters direct the enzyme RNA polymerase to where it should start the transcription process.
What happens if a promoter is mutated?
If a promoter is mutated, it can interfere with the binding of the RNA polymerase and other transcription factors, which can decrease or even stop the transcription of the gene it controls.
How does gene expression differ between prokaryotic and eukaryotic cells?
In eukaryotic cells, gene expression involves transcription in the nucleus and subsequent translation in the cytoplasm, and the mRNA undergoes splicing before it exits the nucleus. On the contrary, in prokaryotic cells, both transcription and translation occur in the cytoplasm, and the mRNA does not need to be spliced.
What is mRNA splicing?
Splicing is the editing of the nascent precursor messenger RNA transcript. Basically, it involves removing introns—noncoding sections of an RNA transcript—and joining together exons—coding sections of the RNA transcript—following transcription.
Why is the regulation of gene expression important?
The regulation of gene expression is critical because it allows an organism to respond to changes in the environment, carry out biological functions efficiently, and develop and maintain its complexity. Failure in gene regulation can lead to diseases, notably cancer.
How is gene expression regulated?
Gene expression is regulated at different levels including transcription, RNA processing, and translation. Regulation at transcription involves promoters, enhancers, transcription factors, and methylation of DNA. RNA processing can be regulated by splicing factors, and translation by various proteins and microRNAs.
What are introns and exons?
Introns and exons are parts of genes. Exons are the sections of DNA that are coded into mRNA and then translated into proteins, so they contribute directly to the genetic function. On the other hand, introns are the sections of a gene that are transcribed to mRNA but are removed by splicing before translation.
What is the biological significance of having introns in our genes?
Even though introns are not translated into protein, they play significant roles in gene regulation and evolution. Introns can regulate gene expression levels and influence alternative splicing, thereby increasing variability in protein products.
What is the role of transcription factors in gene expression?
Transcription factors are proteins that control the process of transcription. They do so by binding to specific DNA sequences and helping or preventing RNA polymerase from binding to DNA and producing mRNA. Therefore, transcription factors play a crucial role in gene expression by regulating when and how much mRNA is transcribed.
Can changes in the amount or activity of transcription factors affect gene expression, and how?
Yes, changes in the amount or activity of transcription factors can significantly impact gene expression. For example, if a transcription factor that promotes the transcription of a certain gene is present in lower amounts, the gene may be expressed less. Conversely, if its activity is increased, the gene may be overexpressed.
What is an enhancer in the context of gene expression?
Enhancer is a sequence of DNA that can significantly increase the transcription of genes. Enhancers help increase the transcription rate of genes by facilitating the binding of RNA polymerase and other transcription machinery at the promoter site.
How do enhancers and silencers differ in their function?
Enhancers and silencers both regulate gene expression, but they do so in opposite ways. While enhancers increase the transcription of a gene, silencers reduce it by hindering the binding of RNA polymerase and other transcription machinery.