A1: enzyme protein.
Q2: why does expresion of gene need to be regulated?
A2: to perform right role in body; to regulate life acticity.
Q3: what is the different between positive and negative gene regulation?
A3: negative redulation control of gene: the operons are switched off by the active form of th erepression protein. positive only when a regulatory protein interacts direactly with the genome to switch transcription on.
Five Facts:
1. bacteria often respond to environmental change by regulating transcription.
2. eukaryotic gene expression can be regulated at any stage
3. noncoding RNAs play multiple roles in controling gene expression
4. a program of differential gene expression leads to the different cell types in a multicellular organism
5. cancer results from genetic changes that affect cell cycle control
Figure:
overwhole view of eukaryotic gene expression.
Summary:
Every cell in a human contains exactly the same sequences of DNA. One way in which cells with Identical DNA become different is by regulationg gene expression through the activatio of only selected genes. The DNA of bacteria contain sequence of DNA, called operons.
1. a regulatory gene produces a repressor protein, a substance that can prevent gene expression by blocking the action of RNA polymerase.
2.promoter region is a sequence of DNA to which the RNA polymerase attaches to begin transcription
3. operator region can block action of the RNA polymerase if teh regionis occupied by a repressor protein
4. structual genes contain DNAsequences that code for several related enzymes that direct the production of some particular end product
The lac operon controls the breakdown of lactos. The regulatory gene in the lac operon produces an active repressor that binds to the operator region. When the operator region is occupied by the repressor, RNA polymerase is unable to transcribe several strnctural genes that code for enzymes that control the uptake and subsquent breakdown of lactose. When lactose is available, however, some of the lactose combines with the repressor to make it inactive. When the repressor is inactived, RNA polymerase is able to transcribe the genes. Since a substance is required to induce the operon, the enzymes that the operon produces are said to be inducible enzymes.
Another operon is trp operon, produces enzymes for the synthesis of the amino acid tryptophan. The regulatory gene produces an inactive repressor that does not bind to the operator. As a result, the RNA polymerase proceeds to transcribe the structural genes necessary to pruoduce enzymes that synthesis tryptophan. When tryptophan is available from environment, the bacteria no longer eed to manufacture its own tryptophan. In this case, rising levels of tryptophan is acting as a corepressor. The active repressor now binds to th e operator region, which, in turn, prevents the transcription of the stuctural genes. Since these structural genes stop producing enzymes only in the presence of an active repressor, they are called repressible enzymes.
Video:
No comments:
Post a Comment