Pain sensation Pain receptors are also called as nociceptors They are located at the ends of small 'C unmyelinated or myelinated A delta fibers a) Definition Pain sensation is unpleasant but protective sensation aroused by noxious stimuli that damage or can damage body tissues b) Physiology (properties & reaction) Purpose or importance: Protective Stimulus: noxious (chemicals like- Ach, bradykinin, serotonin, hydrogen ions, potassium ions, prostaglandins or mechanical or thermal) Receptors: free nerve endings (polymodal receptors) Adaptation : non or slow adapting receptors Nerve fibers: fast pain is carried by A-delta nerve fibers while slow pain by 'C' type. Neurotransmitters: glutamic acid (at spinal cord) for fast pain, substance P (at spinal cord) for slow pain and Lewis P factor for muscle pain, Pathway: lateral spinothalamic (specific neo spinothalamic for fast pain and diffuse and non specific paleo spinothalamic for slow pain) Reaction : pain is a
What is Lac Operon:
Lac operon is a unit of gene expression in the bacterial cell.
Lac operon includes structural gene gene (Z,Y,A) , inhibitor gene (i), control elements and promoter and operator area.
In bacterial cell, Z gene is encodes beta-galactosidase. beta-galactosidase is hydrolytic enzyme which hydrolyze lactose into galactose and glucose.
Y gene encodes enzyme permease which transports lactose into cell.
A gene is responsible for production of enzyme thiogalactoside transacetylase.
since, Z,Y and A gene codes for a structure of protein they are called structural gene. these gene are present as contiguous segment of DNA. The RNA polymerase bind to the promoter and transcribes three structural gene as a single mRNA. this type of mRNA call polysistonic RNA.
Transcription in Normally Repressed
Transcription of the structural gene is done under the control of regulator or the "i" (i=inhibitor) gene. It is away from the structural genes.
i gene produce mRNA which encode repressor subunit. Four repressor subunit combines and form repressor tetramer.
The lac repressor has high affinity to the operator site. Repressor tetramer binds with promoter site and so that RNA polymerase cannot do transcription process.
This repressor molecule inhibits transcription process so this type of inhibition called negative inhibition.
Derepression of Lac Operon
When lactose is introduced into the medium, lactose binds to the repressor protein;one molecule on each subunit. And destroy repressor tetramer.
Now RNA polymerase can bind with promoter and do transcription process.
Now a single mRNA. Now translation of this mRNA done and 3 distinct enzyme are produced.
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