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Lac

Lac

a resinous substance produced mainly on the banyan tree, but to some extent on other trees, by the coccus lacca, a scale-shaped insect, the female of which fixes herself on the bark, and exudes from the margin of her body this resinous substance.

Stick-lac is the substance in its natural state, incrusting small twigs. When broken off, and the colouring matter partly removed, the granular residuum is called seed-lac. When melted, and reduced to a thin crust, it is called shell-lac or shellac. Lac is an important ingredient in sealing wax, dyes, varnishes, and lacquers. Ceylon lac, a resinous exudation of the tree Croton lacciferum, resembling lac. Lac dye, a scarlet dye obtained from stick-lac. Lac lake, the colouring matter of lac dye when precipitated from its solutions by alum. Mexican lac, an exudation of the tree Croton draco.

Origin: Per. Lak; akin to Skr. Laksha: cf. F. Lague, It. & NL. Lacca. Cf. Lake a colour, lacquer, litmus.


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Gene Upregulation/Overexpression

... a promoter WILL express your gene - that's what a promoter does. It's just that a lot of promoters aren't active all the time. For example, the lac promoter is not active if the bacterium doesn't have a CAP protein. I'm sorry, did i totally confuse you just there? This is kinda the nitty-gritty ...

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by MrMistery
Sat May 09, 2009 9:32 pm
 
Forum: Molecular Biology
Topic: Gene Upregulation/Overexpression
Replies: 5
Views: 194

Re: Really puzzled with gene expresseion!!!!

The bacterial system controlling expression of the genes needed to take up and use lactose is a classic example of the regulation of genes in response to an organism's environment. It is also a dangerous example, as it is a system your instructor is likely very familiar ...

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by jonmoulton
Mon Apr 27, 2009 3:07 pm
 
Forum: Genetics
Topic: Really puzzled with gene expresseion!!!!
Replies: 4
Views: 230

When are parts of prokaryotic operons seperated?

... gene(Watson et al. Molecular biology of the gene 6th edition. page 460). However, this is not always true. sometimes an ORF(open reading frame) lacks a ribosome binding site and is only actively transcribed by virtue of the being downstream of a gene with a strong RBS. in these cases, the start ...

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by MrMistery
Wed Dec 10, 2008 4:09 am
 
Forum: Genetics
Topic: When are parts of prokaryotic operons seperated?
Replies: 5
Views: 888

Re: Plasmid question

pUC18 is not an expression vector. It is used for cloning. It has a lac promoter for the expression of lacZ, but not a T7 (or such) promoter for specific expression of cloned sequences. In the absence of an insert, colonies are blue when grown on IPTG/X-gal ...

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by blcr11
Tue May 27, 2008 9:17 am
 
Forum: Molecular Biology
Topic: Plasmid question
Replies: 3
Views: 793

Re: IBO 2003 questions- please help me out

... β-galactosidase, lacY encodes galactosidepermease which carries out lactose transport to the cell, lacA encodes galactoside-transacetylase. Lac operon is under the control of LacI (repressor), which is inactive in the presence of lactose (inductor). There is a wide diversity of the chemical ...

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by tittu
Mon May 12, 2008 2:41 pm
 
Forum: Cell Biology
Topic: IBO 2003 questions- please help me out
Replies: 9
Views: 1377
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