Why does release (the rate of release of minus ends from the nucleation site of the centrosome, allowing the depolymerization of minus ends) cause the decrease of the number and length of microtubules?
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.
Why does release (the rate of release of minus ends from the nucleation site of the centrosome, allowing the depolymerization of minus ends) cause the decrease of the number and length of microtubules?
The microtubules are cylindrical structures composed of tubulin proteins. These tubulin proteins are heterodimers composed of alpha and beta-tubulin subunits. The tubulin heterodimers associate in a linear array to form a protofilament. The protofilaments having the same polarity are aligned with each other to form a hollow-structure known as the microtubule.
- The alpha-tubulin subunit forms the minus end and the beta-tubulin subunit forms the plus end of the microtubule. Both the alpha and beta-tubulin subunits are bound to GTP (guanosine triphosphate). However, the beta-tubulin subunit undergoes hydrolysis upon its incorporation into a microtubule chain.
- The assembly of microtubules includes an initial step of nucleation, the tubulin heterodimers associate with each other to form a hollow ring known as microtubule seed. All the beta-tubulin subunits of the tubulin heterodimer face one end known as the plus end and the alpha-tubulin subunits face the other end known as the minus end. This step is very slow and is called the rate-limiting step of microtubule assembly.
- The centrosome is the microtubule-organizing center in the animal cells. It contains a gamma-tubulin ring complex that by-passes the rate-limiting nucleation step. It speeds-up the microtubule assembly process by acting as a scaffold on which tubulin heterodimers are assembled in a spiral fashion. The plus end containing the beta-tubulin subunit is the growing end to which tubulin heterodimers are added. The minus-end containing the alpha-tubulin subunits remains associated with the gamma-tubulin ring complex in the centrosome. The growth of microtubule occurs only at the plus end as the minus end is blocked and hydrolyzed tubulin heterodimers bound to GDP (guanosine diphosphate) cannot dissociate from the minus end. Therefore, polymerization at the centrosomes takes place at a rapid rate than anywhere else in the cell.
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