"Specialized" organelles or parts means that these parts have been modified to carry out a specific function that is unique to them.
Organelles are literally "little organs" and each of them in the cell has a specific and distinct function.
For example the nucleus is an organelle. It is arguably the most important organelle in the cell. Its specific overall function is that it acts as the cell control center, directing the activities of all the other organelles .i.e. what they need do and when to do it.
The nucleus also contains all of the cell's genetic material (DNA).
Insect populations can develop resistance to insecticides over time. The evolution of resistance is associated with an increase in the frequency of adaptive genes in the population.
- In the case above described it is expected that a few mosquitoes in the population were resistant to DDT before it was ever used (Option a is correct).
- Dichlorodiphenyltrichloroethane (DDT) is a pesticide used in agriculture.
- After exposure to DDT, those individuals in the mosquito population that didn't carry gene variants (i.e., alleles) associated with the resistance to this pesticide died.
- Subsequently, insects having adaptive alleles associated with DDT resistance survived and reproduced, thereby increasing the frequency of adaptive genes/alleles in the population.
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Answer:
For both actin and microtubule polymerization, nucleotide hydrolysis is important for decreasing the binding strength between subunits on filaments.
Explanation:
Cytoskeletal filaments are common to eucaryotic cells and are impotartant to the spatial organization of cells. Intermediate filaments provide mechanical strength and resistance to shear stress. Microtubules determine the positions of membrane-enclosed organelles and direct intracellular transport. Actin filaments determine the shape of the cell's surface and are necessary for whole-cell locomotion. A large number of accessory proteins are present that link the filaments to other cell components, as well as to each other. Accessory proteins are essential for the assembly of the cytoskeletal filaments in particular locations, and it includes the motor proteins that either move organelles along the filaments or move the filaments themselves.
Actin filaments and microtubules are assembled with expenditure of energy i.e the ATP/GTP tightly bound to actin/tubulin is irreversibly hydrolyzed to ADP/GTP during the assembly process, and liberation of Pi in the medium occurs subsequent to the incorporation of subunits in the polymer. Pi release acts as a switch, causing the destabilization of protein-protein interactions in the polymer, therefore regulating the dynamics of these fibres. The progress is made in four areas: the chemistry of the NTPase reaction; the structure of the intermediates in nucleotide hydrolysis and the nature of the conformational switch; the regulation of parameters involved in dynamic instability of microtubules; and the possible involvement of nucleotide hydrolysis in the macroscopic organization of these polymers in highly concentrated solutions, compared with the simple case of a equilibrium polymers.
