<h6 id="successmolecular-basis-of-inheritancesuccess"><Success>Molecular basis of inheritance</Success></h6> <h6 id="primaryregulation-of-gene-expressionprimary"><Primary>Regulation of gene expression</Primary></h6> <hr> <main> <div style='float: left; width:100%; text-align: left;font-size:23px'> <p>Regulation of gene expression refers to a very broad term that may occur at various levels. Considering that gene expression results in the formation of a polypeptide, it can be regulated at several levels. In eukaryotes, the regulation could be exerted at</p> <p>(i) Transcriptional level (formation of primary transcript),</p> <p>(ii) processing level (regulation of splicing),</p> <p>(iii) transport of mRNA from nucleus to the cytoplasm,</p> <p>(iv) Translational level.</p> </div> </main> <hr> <footer style="font-size:18px">Introduction$\rightarrow$ The DNA$\rightarrow$ The Search for Genetic Material$\rightarrow$ RNA World$\rightarrow$ Replication$\rightarrow$ Transcription$\rightarrow$ Genetic code$\rightarrow$ Translation$\rightarrow$ <span style="color:blue">Regulation of gene expression</span>$\rightarrow$ Human genome project$\rightarrow$ DNA fingerprinting</footer>

<h6 id="successmolecular-basis-of-inheritancesuccess-1"><Success>Molecular basis of inheritance</Success></h6> <h6 id="primaryregulation-of-gene-expressionprimary-1"><Primary>Regulation of gene expression</Primary></h6> <hr> <main> <div style='float: left; width:100%; text-align: left;font-size:23px'> <p>The genes in a cell are expressed to perform a particular function or a set of functions. For example, if an enzyme called beta-galactosidase is synthesised by E. coli, it is used to catalyse the hydrolysis of a disaccharide, lactose into galactose and glucose; the bacteria use them as a source of energy.</p> <ul> <li>Hence, if the bacteria do not have lactose around them to be utilised for energy source, they would no longer require the synthesis of the enzyme beta-galactosidase. Therefore, in simple terms, it is the metabolic, physiological or environmental conditions that regulate the expression of genes.</li> </ul> </div> </main> <hr> <footer style="font-size:18px">Introduction$\rightarrow$ The DNA$\rightarrow$ The Search for Genetic Material$\rightarrow$ RNA World$\rightarrow$ Replication$\rightarrow$ Transcription$\rightarrow$ Genetic code$\rightarrow$ Translation$\rightarrow$ <span style="color:blue">Regulation of gene expression</span>$\rightarrow$ Human genome project$\rightarrow$ DNA fingerprinting</footer>

<h6 id="successmolecular-basis-of-inheritancesuccess-2"><Success>Molecular basis of inheritance</Success></h6> <h6 id="primaryregulation-of-gene-expressionprimary-2"><Primary>Regulation of gene expression</Primary></h6> <hr> <main> <div style='float: left; width:100%; text-align: left;font-size:23px'> <p>The development and differentiation of embryo into adult organisms are also a result of the coordinated regulation of expression of several sets of genes.In prokaryotes, control of the rate of Transcriptional initiation is the predominant site for control of gene expression.</p> <ul> <li>In a Transcription unit, the activity of RNA polymerase at a given promoter is in turn regulated by interaction with accessory proteins, which affect its ability to recognise start sites. These regulatory proteins can act both positively (activators) and negatively (repressors).</li> </ul> </div> </main> <hr> <footer style="font-size:18px">Introduction$\rightarrow$ The DNA$\rightarrow$ The Search for Genetic Material$\rightarrow$ RNA World$\rightarrow$ Replication$\rightarrow$ Transcription$\rightarrow$ Genetic code$\rightarrow$ Translation$\rightarrow$ <span style="color:blue">Regulation of gene expression</span>$\rightarrow$ Human genome project$\rightarrow$ DNA fingerprinting</footer>

<h6 id="successmolecular-basis-of-inheritancesuccess-3"><Success>Molecular basis of inheritance</Success></h6> <h6 id="primaryregulation-of-gene-expressionprimary-3"><Primary>Regulation of gene expression</Primary></h6> <hr> <main> <div style='float: left; width:100%; text-align: left;font-size:23px'> <ul> <li> <p>The accessibility of promoter regions of prokaryotic DNA is in many cases regulated by the interaction of proteins with sequences termed operators. The operator region is adjacent to the promoter elements in most operons and in most cases the sequences of the operator bind a repressor protein.</p> </li> <li> <p>Each operon has its specific operator and specific repressor. For example, lac operator is present only in the lac operon and it interacts specifically with lac repressor only.</p> </li> </ul> </div> </main> <hr> <footer style="font-size:18px">Introduction$\rightarrow$ The DNA$\rightarrow$ The Search for Genetic Material$\rightarrow$ RNA World$\rightarrow$ Replication$\rightarrow$ Transcription$\rightarrow$ Genetic code$\rightarrow$ Translation$\rightarrow$ <span style="color:blue">Regulation of gene expression</span>$\rightarrow$ Human genome project$\rightarrow$ DNA fingerprinting</footer>

<h6 id="successmolecular-basis-of-inheritancesuccess-4"><Success>Molecular basis of inheritance</Success></h6> <h6 id="primaryregulation-of-gene-expressionprimary-4"><Primary>Regulation of gene expression</Primary></h6> <hr> <main> <div style='float: left; width:100%; text-align: left;font-size:23px'> <p><strong>The Lac operon</strong></p> <p>The elucidation of the lac operon was also a result of a close association between a geneticist, Francois Jacob and a biochemist, Jacque Monod. They were the first to elucidate a Transcriptionally regulated system. In lac operon (here lac refers to lactose), a polycistronic structural gene is regulated by a common promoter and regulatory genes.</p> <ul> <li>Such arrangement is very common in bacteria and is referred to as operon. To name few such examples, lac operon, trp operon, ara operon, his operon, val operon, etc.</li> </ul> </div> </main> <hr> <footer style="font-size:18px">Introduction$\rightarrow$ The DNA$\rightarrow$ The Search for Genetic Material$\rightarrow$ RNA World$\rightarrow$ Replication$\rightarrow$ Transcription$\rightarrow$ Genetic code$\rightarrow$ Translation$\rightarrow$ <span style="color:blue">Regulation of gene expression</span>$\rightarrow$ Human genome project$\rightarrow$ DNA fingerprinting</footer>

<h6 id="successmolecular-basis-of-inheritancesuccess-5"><Success>Molecular basis of inheritance</Success></h6> <h6 id="primaryregulation-of-gene-expressionprimary-5"><Primary>Regulation of gene expression</Primary></h6> <hr> <main> <div style='float: left; width:100%; text-align: left;font-size:23px'> <p>The lac operon consists of one regulatory gene (the i gene – here the term i does not refer to inducer, rather it is derived from the word inhibitor) and three structural genes (z, y, and a). The i gene codes for the repressor of the lac operon.</p> <p>The z gene codes for beta-galactosidase (β-gal), which is primarily responsible for the hydrolysis of the disaccharide, lactose into its monomeric units, galactose and glucose. The y gene codes for permease, which increases permeability of the cell to β-galactosides. The a gene encodes a transacetylase.</p> </div> </main> <hr> <footer style="font-size:18px">Introduction$\rightarrow$ The DNA$\rightarrow$ The Search for Genetic Material$\rightarrow$ RNA World$\rightarrow$ Replication$\rightarrow$ Transcription$\rightarrow$ Genetic code$\rightarrow$ Translation$\rightarrow$ <span style="color:blue">Regulation of gene expression</span>$\rightarrow$ Human genome project$\rightarrow$ DNA fingerprinting</footer>

<h6 id="successmolecular-basis-of-inheritancesuccess-6"><Success>Molecular basis of inheritance</Success></h6> <h6 id="primaryregulation-of-gene-expressionprimary-6"><Primary>Regulation of gene expression</Primary></h6> <hr> <main> <div style='float: left; width:49%; text-align: left;font-size:23px'> <p>Hence, all the three gene products in lac operon are required for metabolism of lactose. In most other operons as well, the genes present in the operon are needed together to function in the same or related metabolic pathway (Figure 5.14).</p> </div> <div style='float: right; width:45%; text-align: left;font-size:21px'> <img src="https://imagedelivery.net/YfdZ0yYuJi8R0IouXWrMsA/1e96d9bf-c988-4bb8-b510-ae326355bd00/public" width="80%"> </div> </main> <hr> <footer style="font-size:18px">Introduction$\rightarrow$ The DNA$\rightarrow$ The Search for Genetic Material$\rightarrow$ RNA World$\rightarrow$ Replication$\rightarrow$ Transcription$\rightarrow$ Genetic code$\rightarrow$ Translation$\rightarrow$ <span style="color:blue">Regulation of gene expression</span>$\rightarrow$ Human genome project$\rightarrow$ DNA fingerprinting</footer>

<h6 id="successmolecular-basis-of-inheritancesuccess-7"><Success>Molecular basis of inheritance</Success></h6> <h6 id="primaryregulation-of-gene-expressionprimary-7"><Primary>Regulation of gene expression</Primary></h6> <hr> <main> <div style='float: left; width:100%; text-align: left;font-size:23px'> <p>Lactose is the substrate for the enzyme beta-galactosidase and it regulates switching on and off of the operon. Hence, it is termed as inducer. In the absence of a preferred carbon source such as glucose, if lactose is provided in the growth medium of the bacteria, the lactose is transported into the cells through the action of permease (Remember, a very low level of expression of lac operon has to be present in the cell all the time, otherwise lactose cannot enter the cells).</p> <p>The lactose then induces the operon in the following manner.</p> </div> </main> <hr> <footer style="font-size:18px">Introduction$\rightarrow$ The DNA$\rightarrow$ The Search for Genetic Material$\rightarrow$ RNA World$\rightarrow$ Replication$\rightarrow$ Transcription$\rightarrow$ Genetic code$\rightarrow$ Translation$\rightarrow$ <span style="color:blue">Regulation of gene expression</span>$\rightarrow$ Human genome project$\rightarrow$ DNA fingerprinting</footer>

<h6 id="successmolecular-basis-of-inheritancesuccess-8"><Success>Molecular basis of inheritance</Success></h6> <h6 id="primaryregulation-of-gene-expressionprimary-8"><Primary>Regulation of gene expression</Primary></h6> <hr> <main> <div style='float: left; width:100%; text-align: left;font-size:23px'> <p>The repressor of the operon is synthesised (all-the-time – constitutively) from the i gene. The repressor protein binds to the operator region of the operon and prevents RNA polymerase from transcribing the operon. In the presence of an inducer, such as lactose or allolactose, the repressor is inactivated by interaction with the inducer. This allows RNA polymerase access to the promoter and Transcription proceeds (Figure 5.14).</p> <p>Essentially, regulation of lac operon can also be visualised as regulation of enzyme synthesis by its substrate.</p> </div> </main> <hr> <footer style="font-size:18px">Introduction$\rightarrow$ The DNA$\rightarrow$ The Search for Genetic Material$\rightarrow$ RNA World$\rightarrow$ Replication$\rightarrow$ Transcription$\rightarrow$ Genetic code$\rightarrow$ Translation$\rightarrow$ <span style="color:blue">Regulation of gene expression</span>$\rightarrow$ Human genome project$\rightarrow$ DNA fingerprinting</footer>

<h6 id="successmolecular-basis-of-inheritancesuccess-9"><Success>Molecular basis of inheritance</Success></h6> <h6 id="primaryregulation-of-gene-expressionprimary-9"><Primary>Regulation of gene expression</Primary></h6> <hr> <main> <div style='float: left; width:100%; text-align: left;font-size:23px'> <p>Remember, glucose or galactose cannot act as inducers for lac operon. Can you think for how long the lac operon would be expressed in the presence of lactose? Regulation of lac operon by repressor is referred to as negative regulation.</p> <p>Lac operon is under control of positive regulation as well, but it is beyond the scope of discussion at this level.In the preceding sections you have learnt that it is the sequence of bases in DNA that determines the genetic information of a given organism.</p> </div> </main> <hr> <footer style="font-size:18px">Introduction$\rightarrow$ The DNA$\rightarrow$ The Search for Genetic Material$\rightarrow$ RNA World$\rightarrow$ Replication$\rightarrow$ Transcription$\rightarrow$ Genetic code$\rightarrow$ Translation$\rightarrow$ <span style="color:blue">Regulation of gene expression</span>$\rightarrow$ Human genome project$\rightarrow$ DNA fingerprinting</footer>