MBB 201 Lecture Notes - Lecture 15: Start Codon, Xist (Gene), Transgenerational Epigenetic Inheritance
29 May 2018
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Chapter 8: Control of Gene Expression
An Overview of Gene Expression
Gene Expression
• Process by which cells selectively direct synthesis of proteins
• Experiments transplanted the nucleus of an organism into the younger version and
placed it into the younger version of that animal. The organism still developed normally
confirming that the genes are not different in different cells, they are just expressed
differently
• Can be altered due to extracellular cues
Mass Spectrometry
• Determines amount of protein in cell
• Sensitive to electrophoresis
Regulation
• Control when and how often a gene is transcribed
• Control how an RNA transcript is spliced and processed
• Select which mRNAs are exported from the nucleus to cytosol
• Regulate how quickly certain mRNA molecules degrade
• Select which mRNAs are translated by ribosomes
• Regulate how rapidly specific proteins are destroyed
How Transcriptional Switches Work
Transcriptional Regulators
• Regulatory DNA Sequences
o Switch genes on and off
o May respond to a single signal
o Micropressors- integrate information from several sources
• Transcriptional Regulators are proteins that recognize regulatory DNA sequences
• Transcription regulator binds to DNA sequence to control transcription
• Surface features of protein fit tightly to surface features of DNA
• Usually TR fit into the large groove of the DNA and makes molecular contact within the
groove
• Tightest interactions in biology
• Most bind as dimers
Tryptophan (in bacteria)
• Operons- rare in eukaryotes, genetic regulator, set of similar genes all transcribed from a
single promoter
• When tryptophan is low the operon is transcribed producing a set of enzymes
• When tryptophan is high it enters cells and shuts down the production
• Within the operon is the operator, a short DNA sequence. When transcription regulators
are bound transcription is inhibited
o Regulator is called the tryptophan repressor
o Can only bind to DNA if it is also bound to several tryptophan
o Allosteric protein
o When tryptophan levels drop the repressor dissociates from DNA
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Document Summary
Gene expression: process by which cells selectively direct synthesis of proteins, experiments transplanted the nucleus of an organism into the younger version and placed it into the younger version of that animal. The organism still developed normally confirming that the genes are not different in different cells, they are just expressed differently: can be altered due to extracellular cues. Mass spectrometry: determines amount of protein in cell, sensitive to electrophoresis. When transcription regulators are bound transcription is inhibited: regulator is called the tryptophan repressor, can only bind to dna if it is also bound to several tryptophan, allosteric protein, when tryptophan levels drop the repressor dissociates from dna. Repressors and activators: repressors turn a gene off, activators turn genes on, help promoters that are inefficient at binding to dna, often have to interact with other molecules to bind to dna.
