The figure at the beginning of this chapter showsthe binding of both a Lac repressor tetramer and aCRP-cAMP complex to the regulatory region of thelac operon.a. What is the key feature of a regulatory protein suchas the Lac repressor or CRP that allows it to regulate specifically the genes or operons it is supposedto control?b. On the figure, show the positions of the followingcomponents: (i) A Lac repressor monomer; (ii) a Lacrepressor dimer; (iii) all four DNA binding domains ofthe Lac repressor tetramer; (iv) a single helix-turnhelix motif; (v) the o1 part and either the o2 or o3 partsof the lac operator (assume the operon would be transcribed from right to left on the figure); (vi) themultimerization domains of the four Lac repressormonomers; (vii) an inducer-interacting domain; (viii)the CRP-cAMP complex; and (ix) a DNA loop.c. What is the physical basis for the formation of theDNA loop shown in the figure?d. On the figure, show the position of two axes ofsymmetry in the sequence of DNA. How do youknow, only on the basis of the figure and withoutprior information about the precise DNA sequence,that these two axes of symmetry are likely to bepresent in the DNA and that the sequences aroundthese axes are rotationally symmetrical?
Gene Interactions
When the expression of a single trait is influenced by two or more different non-allelic genes, it is termed as genetic interaction. According to Mendel's law of inheritance, each gene functions in its own way and does not depend on the function of another gene, i.e., a single gene controls each of seven characteristics considered, but the complex contribution of many different genes determine many traits of an organism.
Gene Expression
Gene expression is a process by which the instructions present in deoxyribonucleic acid (DNA) are converted into useful molecules such as proteins, and functional messenger ribonucleic (mRNA) molecules in the case of non-protein-coding genes.
The figure at the beginning of this chapter shows
the binding of both a Lac repressor tetramer and a
CRP-cAMP complex to the regulatory region of the
lac operon.
a. What is the key feature of a regulatory protein such
as the Lac repressor or CRP that allows it to regulate specifically the genes or operons it is supposed
to control?
b. On the figure, show the positions of the following
components: (i) A Lac repressor monomer; (ii) a Lac
repressor dimer; (iii) all four DNA binding domains of
the Lac repressor tetramer; (iv) a single helix-turnhelix motif; (v) the o1 part and either the o2 or o3 parts
of the lac operator (assume the operon would be transcribed from right to left on the figure); (vi) the
multimerization domains of the four Lac repressor
monomers; (vii) an inducer-interacting domain; (viii)
the CRP-cAMP complex; and (ix) a DNA loop.
c. What is the physical basis for the formation of the
DNA loop shown in the figure?
d. On the figure, show the position of two axes of
symmetry in the sequence of DNA. How do you
know, only on the basis of the figure and without
prior information about the precise DNA sequence,
that these two axes of symmetry are likely to be
present in the DNA and that the sequences around
these axes are rotationally symmetrical?
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