Gene Expression and Regulation PDF

Gene expression and regulation  **MLO2.**    Explain how DNA is transcribed into mRNA, how mRNA is translated into protein, and how proteins perform biological functions within cells. DNA footprinting - DNA strand is amplified (PCR) - Radioactive label added to localize DNA - DNA ase cuts...

Gene expression and regulation  **MLO2.**    Explain how DNA is transcribed into mRNA, how mRNA is translated into protein, and how proteins perform biological functions within cells. DNA footprinting - DNA strand is amplified (PCR) - Radioactive label added to localize DNA - DNA ase cuts the DNA randomly - One half of the DNA molecule still has a label and is visible, while the other can no longer be detected - This produces a ladder of labelled DNA fragments of every possible size - Using gel electrophoresis, the DNA fragments are separated based on size - \- An electric field is applied to the gel plate, pushing aw the negatively charged DNA from the negative electrode - \- The longer the molecule, the bigger the drag - \- DNA fragments of the same size band together on the plate DNA region ahead of transcription start site called promoter region - Promoter region contains sequences that tell RNA polymerase where to start (called TATA box in eukaryotes) - TATA bind protein binds to TATA box, facilitating the binding of other transcriptional factors, forming a complex that positions RNA polymerase on DNA so transcription can begin. - TATA box is in thr -35 to -25 region Prokaryotic promoters - -35 and -10 boxes in prokaryotic promoters also contain binding sites for sigma factors - Sigma factors recruit in position the RNA polymerase complex Jacob-Monod model of prokaryotic gene expression - Gene expression is controlled by: - Cis-acting elements: they influence the transcription of genes that are right next to them (promoters) - Trans-acting elements: affect gene expression indirectly by creating proteins that bind and activate cis-acting elements anywhere in the genome (transcription factors) Repression means deactivation of gene expression - If a promoter is strong ie. -35 and -100 elements are close to consensus, the promoter can easily bind to sigma factors without other DNA elements - To control these promoters, we need repressors which block gene expression by inactivating the promoter Induction means activation of gene expression - Weak promoters (-35 and -10 elements differ from consensus) cannit bind easily to sigma factors - To switch on these genes we need activators which turn gene expression on: they bind close to sigma factors helping them bind to promoter elements Eukaryotes - TATA bind protein and general transcriptional factors bind near TATA box - Forming main scaffold for binding of RNA polymerase - Enhancers (trans-acting elements) influence expression of genes - These include increased acetylation of histones causing DNA to be less tightly wrapped and making it easier for transcriptional factors to bind, as well as decreased methylation of DNA. Another way the cell can control protein levels is through degredation - The cell can target proteins for rapid degredation by attaching a special chemical signal called ubiquitin Moodle recap quiz Q: Where does gene expression take place?\ A: Nucleus Q: RNA polymerase is responsible for catalyzing which reaction?\ A: DNA transcription Q: Transcription factors bind to which region of a gene?\ A: Promoter Q: Which molecular complex is involved in converting primary mRNA transcripts into mature mRNA transcripts? A: Spliceosome Q: Within a DNA molecule, adenine binds to which other nucleotide?\ A: Thymine Q: Which type of RNA molecule is involved in transferring amino acids to a growing polypeptide chain?\ A: tRNA Q: Differential gene expression can be regulated by which family of proteins?\ A: Transcription factors