Describe the Biochemical Composition Structure and Replication of Dna Essay

1203 Words Dec 22nd, 2012 5 Pages
Background
DNA is an abbreviation for deoxyribonucleic acid, but it is usually known by its initials alone. DNA is found in practically all living organisms, and it is now known to carry genetic information from one cell to the next, and from one generation to the next. The units of inheritance, called genes, are actually sections of the DNA molecule.
Nuclei of the cells of higher organisms contain thread-like bodies called chromosomes, which consist of DNA, wrapped around proteins.

So understanding how the DNA molecule behaves inside cells helps explain how genetics works at the simplest level.

In the nucleus of every normal cell of the human body there is over 1 metre of DNA, divided between 46 chromosomes.

DNA is a
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It is interesting to note that each "new" double strand is in fact half composed of a section of the previous DNA molecule, together with a completely new section built up from individual bases.
Because of this, it is called semi-conservative replication.

DNA and NUCLEAR DIVISION
These 2 double strands form the 2 sections of chromosomes (called chromatids) that are easily seen when a cell is about to divide. In mitosis the chromosomes are then evenly distributed to different ends of the cell, ready to be incorporated into 2 new cells when the cell itself divides.

Mitosis

For clarity, only 2 pairs of chromosomes are shown in these diagrams | | | | |

In mitosis, the nucleus divides once to produce 2 nuclei, which then form into 2 genetically identical "ordinary" cells, containing the same number of chromosomes as the original cell (46 in human cells)
Because of the reliability of the replication of DNA and mitosis, offspring resulting from asexual reproduction do not usually vary at all, which is the basis of taking cuttings, etc. Similarly, multicellular organisms consists of a harmonious population of identical cells derived from one initial cell, the fertilised egg or zygote. However, in some cases (about 1 in a million) there may be an error in the copying process; an incorrect copy of the DNA will be passed on to any (body) cells produced following cell division.

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