Describe cell division, including the process of mitosis and cytokinesis. be sure to describe the mitotic steps.

Answer and Explanation:

Mitosis occurs at the sites of growth and development of new tissues. The stages of mitosis include;

This is the initial phase. The chromosomes in the nucleus become visible as thin coiled threads. In animals, the centrosome found in the cytoplsm divdes to form two centrioles. The chromosomes become tightly coiled and shorter. From each centriole, fine fibres develop and elongate to form spindle apparatus. The nucleolus becomes dispersed in the nucleus and disappears. The nuclear membrane also break and disappears.

The pairs of chromatids align along the equator of the spindle apparatus and are attached to it at their centromeres.

The centromere of each chromosome splits and the chromatids separate. Each chromatid moves to the opposite poles of the cell. The chromatids appear as V--shaped.

The spindle fibres disintegrate and disappear. New nuclear membrane forma around each set of chromatids. A nucleolus develops in the nucleus of each daughter cell. The cytoplasm now divides in a process caled cytokinesis. In animals, an invagination develops at the plasmalemma near the equator of the cell.

step 1: initiation

initiation is the beginning of transcription. it occurs when the enzyme rna polymerase binds to a region of a gene called the promoter. this signals the dna to unwind so the enzyme can ‘‘read’’ the bases in one of the dna strands. the enzyme is now ready to make a strand of mrna with a complementary sequence of bases.

step 2: elongation

elongation is the addition of nucleotides to the mrna strand. rna polymerase reads the unwound dna strand and builds the mrna molecule, using complementary base pairs. there is a brief time during this process when the newly formed rna is bound to the unwound dna. during this process, an adenine (a) in the dna binds to an uracil (u) in the rna.

step 3: termination

termination is the ending of transcription, and occurs when rna polymerase crosses a stop (termination) sequence in the gene. the mrna strand is complete, and it detaches from dna.

a- all cells come from pre-existing cells