Transcription and Gene Expression

Transcription and Gene Expression Transcription Distinguish between the sense and antisense strands The antisense strand IS transcribed into mRNA (it is complementary to the DNA template) ………………………………………………………………………………………………………………………………………………….......... The sense strand is NOT transcribed into mRNA (it is identical to the DNA template - except T = U) ………………………………………………………………………………………………………………………………………………….......... Identify the three sections of a gene Promoter - initiation point (where RNA polymerase binds) ………………………………………………………………………………………………………………………………………………….......... Coding Region - sequence that is transcribed ………………………………………………………………………………………………………………………………………………….......... Terminator - termination point ………………………………………………………………………………………………………………………………………………….......... Explain the process of transcription, including the role of RNA polymerase RNA polymerase attaches to the promoter (requires the presence of transcription factors) ………………………………………………………………………………………………………………………………………………….......... RNA polymerase unwinds the DNA and separates the strands ………………………………………………………………………………………………………………………………………………….......... Nucleoside triphosphates (NTPs) align opposite complementary bases and are joined by RNA polymerase ………………………………………………………………………………………………………………………………………………….......... This continues until the terminator, at which point the enzyme and transcript dissociate from the DNA ………………………………………………………………………………………………………………………………………………….......... List three examples of post-transcriptional modifications Methyl cap added to the 5’-end (protects against degradation and allows recognition by ribosome) 1. …………………………………………………………………………………………………………………………………………………... Polyadenylation occurs at the 3’-end (improves stability and facilitates nuclear export) 2. ………………………………………………………………………………………………………………………………………………….. Splicing occurs (introns are removed) 3. …………………………………………………………………………………………………………………………………………………... Distinguish between introns and exons Introns are intruding sequences within a gene that are removed prior to translation (not expressed) ………………………………………………………………………………………………………………………………………………….......... Exons are the expressing sequences that are translated into protein ………………………………………………………………………………………………………………………………………………….......... Outline how alternative splicing increases the number of different proteins an organism can produce Exons can be selectively removed via alternative splicing to produce different protein variants from the ………………………………………………………………………………………………………………………………………………….......... same gene - this increases the number of proteins an organism can produce relative to the number of genes ………………………………………………………………………………………………………………………………………………….......... ………………………………………………………………………………………………………………………………………………….......... Gene Expression Outline the role of the promoter and transcription factors in the regulation of transcription Transcriptional activity is regulated by transcription factors which mediate binding of RNA polymerase to ………………………………………………………………………………………………………………………………………………….......... the promoter (the initiation point for transcription of a gene sequence) ………………………………………………………………………………………………………………………………………………….......... The presence of certain transcription factors may be tissue-specific (explaining why different genes are ………………………………………………………………………………………………………………………………………………….......... activated in different tissues) and environmentally sensitive (explaining why expression patterns can change) ………………………………………………………………………………………………………………………………………………….......... Discuss, with an example, the role the environment can play in regulating transcription Environmental factors can trigger the production (or change in levels) of transcription factors ………………………………………………………………………………………………………………………………………………….......... Example: Hydrangea flowers change colour according to the pH of the soil ………………………………………………………………………………………………………………………………………………….......... ………………………………………………………………………………………………………………………………………………….......... Describe the role regulatory proteins play in moderating gene expression levels The binding of RNA polymerase to the promoter can be controlled by regulatory proteins ………………………………………………………………………………………………………………………………………………….......... Activators bind to enhancer sequences and make it easier for the enzyme to bind (increases expression) ………………………………………………………………………………………………………………………………………………….......... Repressors bind to silencer sequences and make it harder for the enzyme to bind (decreases expression) ………………………………………………………………………………………………………………………………………………….......... Outline the role of the nucleosome in the regulation of gene expression Nucleosomes are involved in the supercoiling of DNA (supercoiled DNA is inaccessible for transcription) ………………………………………………………………………………………………………………………………………………….......... Acetylation of the histones makes the DNA less tightly coiled (increases gene expression) ………………………………………………………………………………………………………………………………………………….......... Methylation of the histones makes the DNA more tightly coiled (decreases gene expression) ………………………………………………………………………………………………………………………………………………….......... ………………………………………………………………………………………………………………………………………………….......... Describe how DNA methylation patterns may differ between identical twins and the significance of this Direct methylation of DNA also decreases gene expression (prevents binding of transcription factors) ………………………………………………………………………………………………………………………………………………….......... Hence, genes that are methylated are not expressed, while genes that are not methylated are expressed ………………………………………………………………………………………………………………………………………………….......... Because DNA methylation is influenced by environmental factors, identical twins will develop different ………………………………………………………………………………………………………………………………………………….......... methylation patterns over time - this explains why twins may look different despite having identical genomes ………………………………………………………………………………………………………………………………………………….......... …………………………………………………………………………………………………………………………………………………..........