Without a centrosome, cells would not be able to

Without a centrosome, cells would not be able to move organelles around the cytoplasm. The centrosome is part of the nucleus that interacts with the chromosomes to build the mitotic spindle. It is typical for the animal cells. This organelle is also responsible for cell division and the stages in the cell division process.

I like to think of the DNA molecule strand as a ladder, rather than a spiral staircase. The siderail of the DNA ladder (The DNA "Backbone") consists of the Sugar and Phosphate molecules. The rungs of the ladder (the inner bases) consist of the pairs of Nitrogen Bases - Adenine, Guanine, Cytosine and Thymine. 

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