regulation of gene expression...initiation, elongation and termination in each!!! regulation of a...
TRANSCRIPT
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Regulation of Gene Expression
Chapter 18
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Warm Up
• Explain the difference between a missense and a nonsense mutation.
• What is a silent mutation? QUIZ TOMORROW: Transcription/Translation. Write in your own words, what happens- describing initiation, elongation and termination in each!!!
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Regulation of a Metabolic Pathway
A. Feedback Inhibition- inhibits the activity of the first enzyme in the metabolic pathway.
B. Regulation of Gene
Expression- enzymes are controlled at the transcription level, by turning genes on/off.
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Operons
• Operator- a segment of DNA that controls the access of RNA polymerase to the genes. Found within the promoter sequence. (on/off switch)
• Operon- the operator, promoter, and genes they control- the entire stretch of DNA required for metabolic pathway. (trp operon)
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Types of Operons
• Repressible Operon- usually on but can be inhibited. (Ex: trp operon)
• Inducible Operon- usually off but can be stimulated. (Ex: lac operon)
*Both are examples of negative gene regulation.
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Repressible Operons
• Repressor- protein that can turn off the operon by binding to the operator and blocking the attachment of RNA polymerase, preventing transcription of the genes.
• Regulatory Gene- codes for a repressor or similar protein that controls the transcription of another gene or group of genes.
• Corepressor- a small molecule that cooperates with a repressor protein to switch an operon off.
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• kl
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Inducible Operons
• Inducer- a small specific molecule that binds to the repressor which inactivates it.
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Positive Gene Regulation
• Activator- a protein that binds to DNA and stimulates transcription of a gene.
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Exit Slip
• A certain mutation in E.coli changes the lac operator so that the active repressor cannot bind. How would this affect the cells production of B-galactosidase?
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Warm Up Exercise
• Explain the difference in an inducer and a repressor operon.
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Gene Expression
• Differential Gene Expression- the expression of different genes by cells with the same genome.
• Gene expression typically refers to actions occurring in transcription, but regulation can happen at other stages in more complex organisms.
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Chromosomal Modification
• Epigenetic Inheritance- inheritance of traits transmitted by mechanisms not directly involving the nucleotide sequence. – Ex: histone acetylation and DNA methylation
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Chromosomal Modification
• Histone Acetylation- acetyl groups are attached to lysines in histone tails. – Neutralizes the positive charge on the lysine which
cause histones to not bind to neighboring nucleosomes. Causes chromatin to form a looser structure.
• Deacetylation- removal of acetyl groups.
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Chromosomal Modification
• DNA Methylation- methyl groups are attached to bases in the DNA (usually cytosine). – Inactive DNA is typically more methylated than
regions that are actively transcribed. Individual genes are usually more methylated in cells where they are not expressed.
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Regulation of Transcription Initiation
• Control Elements- segments of noncoding DNA that serve as binding sites for transcription factors (proteins that regulate transcription). – Proximal Control Elements (near promoter) vs.
Distal Control Elements called Enhancers (upstream or downstream of a gene or within an intron)
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Transcription
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INSERT FIGURE 18.10
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Coordinate Control in Eukaryotes
• Genes with the same control elements are activated by the same chemical signals. (Not by a common operator, as in prokaryotes).
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Warm Up Exercise
• Explain how DNA methylation and histone acetylation affect transcription of genes.
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Post-Transcriptional Regulation
• Alternative RNA Splicing- different mRNA molecules are produced from the same primary transcript, depending on which segments are treated as introns or exons.
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Post Transcriptional Regulation
• mRNA Degradation- nucleotide sequences (in UTR) determine how long mRNA remains intact. By degrading mRNA, expression is blocked.
• Initiation of Translation- by preventing the attachment of mRNA on ribosomes, translation is blocked. – Can occur when regulatory proteins bind to
sequences in UTR, when poly-A tail isn’t sufficient in length, or when translation initiation factors are deactivated.
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Post-Transcriptional Regulation
• Chemical modifications to polypeptides to make them functional.
• Transport to target destinations. • Length of time for protein to function in the cell.
– When cells are marked for destruction, a protein called ubiquitin is attached to the protein surface.
– Proteosomes- complexes that recognize ubiquitin and degrade marked proteins.
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Noncoding RNA- Sec. 18.3
• Protein coding DNA = 1.5% of human genome. Very small percent of non-coding DNA codes for genes of rRNA/tRNA. Significant amount of genome may be transcribed into noncoding RNA (ncRNA)
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Noncoding RNA
• MicroRNA (miRNA)- bind to complementary mRNA and degrades or prevents translation.
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Noncoding RNA
• RNA Interference- injecting double-stranded RNA molecules into a cell turns off expression of a gene with the same sequence as the RNA.
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Warm Up Exercise
• Draw a diagram that represents how Alternative RNA Splicing can code for two different proteins.
• How is a protein targeted for degradation, and what cellular component is responsible for degrading it?
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Genetic Programming for Embryonic Development- Sec. 4
• Cell Division- zygote gives rise to a large number or identical cells.
• Cell Differentiation- become specialized in structure and function and organize into tissues and organs.
• Morphogenesis- “creation of form”
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Differential Gene Expression
• Cytoplasmic Determinants- maternal substances in the egg that influence the course of development. (non-homogenous)
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Differential Gene Expression
• Inductive Signals- signals from other nearby embryonic cells that cause a change in gene expression- sending a cell down a specific developmental path.
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Differential Gene Expression
• Determination- events that lead to the observable differentiation of a cell.
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Pattern Formation
• Homeotic Genes- determine pattern formation. – Embryonic Lethals- mutations with phenotypes
causing death at the embryonic stage. • Maternal Effect Gene- when mutant in mother,
results in mutant phenotype in offspring, regardless of offspring’s own genotype.
• Morphogens- establish an embryo’s axis and other features of its form.
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Warm Up Exercise
• Explain the effect of cytoplasmic determinants on cells and cell differentiation.
• Describe what is meant by the term “embryonic lethals”?
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Cancer Control
• p53 Gene- codes for a transcription factor that promotes synthesis of cell-cycle inhibiting proteins. – Mutation is this gene usually leads to excessive cell
growth and cancer. • Tumor-Suppressor Genes- code for proteins
that help prevent uncontrolled cell growth.
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