Lecture 6 Flashcards
(7 cards)
What is supercoiling?
Supercoiling compacts DNA to accommodate the genome within the cell. The linear length of DNA is several hundred times longer than cell size.
What are transposable elements?
Transposable elements are segments of DNA that can move between sites on the same or different DNA molecules (chromosomes, plasmids, viral genomes etc.). All organisms have transposable elements.
What are promoter sites?
Promoter sites are specific DNA sequences that allow RNA polymerase to recognize the initiation site for transcription. This process is mediated by sigma factors, which recognize promoter sites and bind to them. Promoters are present on the specific strand of DNA that encodes the gene. Different genes may be encoded on each strand.
What are the two types of transcription factors?
An activator protein turns on transcription by recruiting RNA polymerase or a sigma factor to the promoter region. A repressor protein turns off expression by binding to the operator region of DNA downstream of the promoter.
What are effectors?
Effectors are small molecules that control the binding of activators and repressors. They are typically cell metabolites or molecules with similar structures to cell metabolites.
How do effectors regulate transcription?
When an effector binds to a transcription factor, the conformation of the protein is altered. Transcription factors are allosteric, meaning that a conformational change determines whether it can bind DNA. Inducers turn on transcription, and corepressors turn off transcription.
What is enzyme repression?
Enzyme repression is the prevention of enzyme synthesis unless the product is absent from the culture medium. It acts specifically on a particular enzyme; the synthesis of other enzymes is not affected. Enzyme repression usually affects biosynthetic/anabolic enzymes.
