Answer:
A Mutation is an agent of substance that can bring about a permanent alteration to the physical composition of a DNA gene such that the genetic message is changed.
Explanation:
<h2>Lac operon </h2>
Explanation:
Lac operon present in prokaryotic chromosomes whose product involves in transportation and catabolism of lactose
- Lac operon consists of three structural genes called Lac Z,Lac Y and Lac A and a regulatory element(promoter and operator)
- Lac I gene is present outside the Lac operon,act as regulatory gene and control the expression of Lac operon genes
- Lac Z codes for β galactosidase which converts lactose into allolactose
- Lac Y codes for Lac permease which act as a membrane transporter and transport lactose into the cells
- Lac A codes for transacetylase which neutralize the toxic effects of lactose
Lac operon in absence of lactose
- In absence of lactose Lac operon exists in switch off state
- Lac I gene produces Lac repressor which binds to operator region and prevent binding of RNA Polymerase thus blocks transcription
Lac operon in presence of lactose
- In presence of lactose Lac operon exists in switch on state
- In presence of lactose few molecules of Lac operon enzyme catalyse conversion of lactose to allolactose
- Allolactose act as an inducer,binds to the Lac repressor and induce conformational changes causing dissociation of Lac repressor from operator
- In absence of Lac repressor RNA Polymerase binds to the promoter and starts transcription of genes which catabolize lactose
Lac promoter is a weak promoter and direct transcription of Lac operon genes in very low level in presence of lactose
- For higher level expression of Lac operon genes,operon system require conversion of weak promoter to strong promoter which is always mediated by catabolite protein-cAMP complex(CAP-cAMP complex)
- CAP cAMP complex binds to the upstream of promoter called CAP binding site and stimulate expression of Lac operon genes by facilitating binding of RNA Polymerase
- Catabolite activator protein(CAP) or cAMP receptor protein(CRP) activate when cAMP binds
- cAMP is a secondary messenger synthesized from ATP and act as co-activator of CRP
- With respect to CAP cAMP complex Lac operon system is positively controlled
- In prokaryotic cell cAMP is very low when glucose concentration is relatively high and vice versa
- At high concentration of glucose the growth rate is maximum and lactose catabolism is repressed called catabolite repression
Answer:
cell membrane, cytoplasm, nucleus
The lack of centrioles in nerve cells prevents them from undergoing mitosis and meiosis, which prevents them from dividing. Nerve cells do not divide throughout their lives and do not lengthen without doing so.
<h3>
</h3><h3>
What is nerve cells?</h3>
The central nervous system is constantly receiving information about the external and internal environment (in the form of sequences of action potentials) from nerve cells, also known as neurons.
Nerve cells are “excitable” cells that may convert a range of stimuli into electrical impulses (CNS). Despite the complexity of the nervous system, neurons and glial cells are the only two types of nerve cells that make up nervous tissue.
The structural and operational components of the nervous system are called neurons. Nerve impulses are electrical signals that are transmitted by them. Neuronal support is provided by glial cells.
Therefore, nerve cells do not reproduce and, if damaged by injury or disease, are lost forever.
Learn more about nerve cells here:
brainly.com/question/15642720
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