BIOL 2050 1nd Edition Lecture 27 Outline of Last Lecture I. Translationa. tRNAb. Ribosomesc. Polypeptidesd. Functional proteinOutline of Current Lecture II. Differential Gene Expressiona. Bacteriab. EukaryotesCurrent LectureDifferential Gene Expression- Turning different genes on and off in different places throughout the genome.o In both prokaryotes and eukaryotes- In response to environment- RNA molecules play many roles in regulationBacteriao One mechanism for control of gene expression is the operon model A cluster of functionally related genes can be coordinately controlled by a single “on-off switch” Operator: the “switch” that is usually positioned within the promoter Operon: the entire stretch of DNA that includes the operator, promoter, and the genes they control Repressor: “off switch”- Prevents gene transcription by binding to the operator and blocking RNA polymerase- A product of the a separate regulatory gene- Corepressor: molecule that cooperates with a repressor protein to switch an operon off.o Negative Gene RegulationThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. A repressible operon is one that is usually on and binding of a repressor to the operator shuts of transcription- Tryptophan operon- Anabolic pathways An inducible operon is one that is usually off and a molecule called an inducer inactivates the repressor and turns transcription on.- Lac operon- Usually function in catabolic pathwaysEukaryoteso Gene expression is essential for cell specializationo Signals come into the nucleus and activate gene transcription and RNA processing Transport to cytoplasm for translation Protein processing Transport to cellular destination - Or protein can be degradedo Chemical modifications to histones and DNA of chromatin influence both chromatin structure and gene expression Histone Acetylation: acetyl groups are attached to positively charged lysines in histone tails- Promoting the initiation of transcription DNA Methylation: addition of methyl groups to certain bases in DNA and reduces transcription in some specieso Chromatin-modifying enzymes provide initial control of gene expression by making a region of DNA more or less able to bind to transcription machinery. Control elements: segments of noncoding DNA that serve as binding sites for transcription factors that help regulate transcription- Transcription factors initiate transcription and are essential for the transcription of all protein-coding
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