University:
Glendale Community College
Course:
BIO160 | Introduction to Human Anatomy and Physiology
Academic year:

2020
Views:

243

Pages:

7
Author:

izbra0p

Section 18.3: Gene Expression Figure 18.50 Function of the lac Operon §lac Operon -control element / structural genes that code for enzymes responsible for lactose metabolism §Structural genes Z, Y, and A encode for b-galactosidase, lactose permease, and thiogalactoside transacetylase, respectively §lacI gene encodes for a repressor that binds to the operator of operon as a tetramer §lac operon is repressed when its inducer allolactose is not present due to lac repressor binding Section 18.3: Gene Expression Figure 18.50 Function of the lac Operon §When lactose is present, some of the lactose is converted to allolactose by b-galactosidase §Allolactose binds the repressor, changing its conformation and promoting its dissociation from operator §lac operon becomes active and stays active until lactose is consumed Section 18.3: Gene Expression Genomic Control §Chromatin structure § Structural organization of genome – chromatin remodeling §Transcription factor-regulated RNA polymerase complex formation §Particular set of proteins that assembles on a regulatory DNA sequence §Less common examples include gene rearrangements and gene amplification Section 18.3: Gene Expression RNA processing §Alternative splicing - Joining of different combinations of exons to form cell-specific proteins §Vertebrate tropomyosin gene - 13 to 15 exons; five common in all isoforms §Remaining exons are alternatively used in different mRNAs §RNA editing - After transcription, base changes §RNA stability, translation initiation, alteration of splice sites, and amino acid sequence changes Figure 18.52 RNA Processing Section 18.3: Gene Expression Posttranscriptional Gene Silencing §miRNAs inhibit translation by binding to complementary sequences in the 3′-UTR of target mRNAs §Humans are estimated to have as many as a thousand miRNAs believed to regulate about one-third of human genes §miRNA-mediated gene silencing utilizes components of RNA interference §Limited to protection against viruses & transposons §Cells use small-interfering RNAs (si-RNAs) to recognize and degrade target mRNAs Section 18.3: Gene Expression §mRNA Transport - out of the nucleus requires three phases: processing, docking and passage through nuclear pore complexes (NPC), and release into the cytoplasm §Translational Control—Covalent modification of several translation factors has been shown to alter translation rate in response to various stimuli Section 18.3: Gene Expression Signal Transduction §Cells alter gene expression patterns in response to environmental signals §Initiated by binding of a ligand to a receptor; then initiates a signal transduction cascade §Induce two classes of genes at the end of their signal transduction cascades §Early response genes are rapidly activated (within 15 minutes); often transcription factors §Delayed response genes - induced by activities of transcription factors and proteins produced during the early response phase