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| 11.1 Gene Expression Through Time and Tissue 1. Discovery of the globin proteins that transport oxygen in the blood over half a century ago provided Geneticists with an excellent example of the control of gene expression. 2. Changes in gene expression occur over time at the molecular level (globin switching), at the tissue level (blood plasma), and at the organ/gland level (pancreas development). Globin Chain Switching 1. Hemoglobin provides a classic example of a change in gene expression that accompanies development. 2. The subunit composition of hemoglobin changes in the embryo, fetus, and after birth. Building Tissues and Organs 1. Globin chains affect one type of molecule, hemoglobin. 2. Stem cell biology is beginning to shed light on how genes are turned on and off during the development of an organ or gland. 3. As a pancreas forms, progenitor cells diverge from shared stem cells and their daughters specialize. Proteomics 1. Proteomics uses analytical chemistry techniques and gene expression DNA microarrays to catalog the types of proteins in particular cells, tissues, organs, or entire organisms under specified conditions. 2. Comparing gene expression profiles over time is particularly useful clinically, to chart disease progression and response to therapy. 11.2 Mechanisms of Gene Expression 1. Combinations of signals instruct cells to activate combinations of transcription factors, and these in turn, control which genes are transcribed. The Histone Code 1. Histones play a major role in exposing DNA when it is to be transcribed, and shielding it when it is to be silenced. 2. Nucleosomes control gene expression through the acetylation of specific amino acids on specific histone proteins. 3. Acetylation contorts the histone so that transcription of a nearby gene can begin. RNA Interference 1. Short, double-stranded RNA molecules locate and bind to specific mRNAs, marking them for destruction; they also add methyls to DNA at the nucleus, blocking transcription. 11.3 Proteins Outnumber Genes 1. Differential intron splicing and exon shuffling explain how one gene can produce more than one protein. 2. Intron sequences of one gene may contain the coding sequences for another protein. 11.4 The "Other" 98.5 Percent of The Human Genome 1. Ninety eight percent of the human genome does not code for protein. What is its function? Noncoding (nc) RNAs 1. About 1/3 of the human genome produces non-coding RNAs (i.e. rRNA, tRNA, snRNA, snoRNA, etc.). 2. Part of the human genome is composed of pseudogenes. These may or may not be transcribe, and are never translated into protein. 3. A large part of the human genome is composed of repeat sequences such as SINEs and LINEs. |