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MCDB 138 Lecture 4

MCDB 138 Lecture 4 - Notes from lectures Experiments to...

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Notes from lectures - Experiments to show all cells contain the same genetic materials: blastomere isolation and nuclear transplantations. - Maternal mRNAs: in addition to proteins binding, also leave the polyA off of the tails of mRNA, preventing it from being transcribed. - Location of mRNA decides where the gene products will be when the cells divide - Phosphorylation can change the conformation, ex. no longer have catalytic site, affect stability - some proteins, when phosphorylated, are recognized by complex that will degrade them. - Histones: keep RNAs away from transcription factors. When want to express the gene, need to remodel the chromatin. - Positive: factors can unwind chromatin, physically interact with transcriptional complex. - Negative: factors can stabilize chromatin from a wind state, destabilize direct physical interaction of the complex. - Why are transcriptional factors so potent? => Transcriptional synergy - Transcriptional synergy gives very tight control. - Why chain of phosphorylation ? 1) Some transcription factors are away in nucleus, can't shuttle => transmitting the signals to the nucleus. 2) Allow at each step to amplify the signals, big change in gene expression. - Any one gene that needs to be expressed needs to have multiple binding sites for multiple regulatory proteins. What determines overall probability of transcription? Overall balance of regulatory proteins. - Outcome of transcriptional control that is combinatorial: can give rise to an entire organ. Transcriptional factors don't act alone, they're part of complexes. 1. INTRODUCTION Understanding how cells acquire different patterns of gene expression is the central question in developmental biology. In eukaryotes, the expression of a gene requires its transcription into mRNA, processing of the mRNA (splicing and addition of a polyA tail), transport of the mRNA into the cytoplasm where it can be translated, translation, and post-translational modifications. There are many possible post-translational modifications that control both the activity and stability of proteins. Throughout this course, we will encounter examples where gene expression is regulated at each of these stages. In this lecture, we will review the basics of the control of gene expression. We will also consider some of the major techniques used in developmental biology to study differential gene expression in embryos. 2. GENES AND REGULATORY PROTEINS Eukaryotic genes are contained in a complex of DNA and proteins. This complex is known as chromatin , and histones are the main proteins in chromatin. The nucleosome is the basic unit of chromatin structure. Chromatin is often thought of as a string of nucleosome “beads linked by “linkers” of DNA. It is generally thought that the “default” state of chromatin is a repressed state. In this state, a particular protein, histone H1, is bound to the DNA linker regions. Tissue-
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specific genes become activated by interruption of this repression, and this involves removal of histone H1.
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MCDB 138 Lecture 4 - Notes from lectures Experiments to...

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