13BIS101S2013GeneRegulLect13-1

Lrodriguez 2013

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: the time of birth. hemoglobin BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 4 Evidence for Gene Expression* Selective Gene Expression: The proteins found in a cell at any particular The time represent only a fraction of the total number of proteins encoded by the cell. For example, although the E. coli genome has the capacity to encode about 6000 genes, only about 600 to 800 proteins are present at any instant in the life cycle of the cell. Differential Gene Expression: Within the same cell, different proteins Within are present in different amounts. Responsive Gene Expression: By changing the environment of the cell, By it is possible to selectively increase the amount of one protein over another. another. Selective, differential, and responsive gene expression is accomplished through specific protein/DNA and protein/protein interactions involving regulatory DNA sequences such promoters, interactions operators and ribosome binding (SD) sites, enhancers. Protein/DNA interactions can be negative (i.e., repress transcription or Protein/DNA negative translation) or positive (i.e, enhance transcription or translation). positive BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 5 Examples of Positive and Negative Control For most genes, a combination of positive and negative For regulation is used to achieve the precise level of gene expression for the cell. expression Positive Control p p gene gene Negative Control p gene p BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez gene 6 Lactose Operon One of the best examples of regulated gene expression is found in E. coli One and involves the metabolism (or fermentation) of the milk sugar, lactose. lactose E. coli is capable of utilizing various carbon sources for energy. When grown on the disaccharide lactose, E. coli produces the enzyme β galactosidase (β -gal), which breaks lactose down into the simple which monosaccharides, glucose and galactose. monosaccharides, BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 7 Lactose Operon E. coli cells grown in the presence of glucose contain about 3 β -gal -gal molecules/cell. However, molecules/cell However, when cells are switched from glucose to lactosefrom containing medium, the containing number of β-gal molecules -gal increases to about 3000 molecules/cell. molecules/cell This in shown in the graph This at the left. IPTG is an at analog of lactose and can induce β-gal without being -gal metabolized. IPTG is a gratuitous inducer. gratuitous β-gal enzyme β-gal mRNA 0 IPTG 10 IPTG BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 15 20 min 8 Genetics of the Lactose...
View Full Document

This note was uploaded on 02/12/2014 for the course BIS 101 taught by Professor Simonchan during the Spring '08 term at UC Davis.

Ask a homework question - tutors are online