The DNA-Genetic system also controls cell reproduction
Control exists over growth in the cell and when the cell will divide to form new cells.
Most cells are able to reproducing other cells of their own type, with the exception of RBC, striated muscle, and neurons. In the presence of sufficient nutrition, cells grow larger and larger and then through mitosis divide to form two new cells.
Cellular division begins with the replication of the DNA.
DNA in the chromosome is replicated once, making an exact copy of the entire DNA before mitosis takes place. The replication of DNA is similar to RNA transcription except for the following important differences:
Both strands of DNA are replicated - not only one strand of DNA
Both strands of DNA helix are replicated from end to end rather than small portions of them, as in the transcription of RNA genes.
The principal enzyme for replication of DNA are the complex of several enzymes called DNA polymerase (similar to RNA polymerase).
Each newly formed strand of DNA remains attached by loose hydrogen bonding to the original DNA strand that is used as its template. Two DNA helixes are formed, therefore duplicates of each other are still coiled together.
The two new helixes become uncoiled by action of enzymes that periodically cut each helix along its entire length, rotate each segment sufficiently to cause separation, and then resplice the helix.
DNA strands are "repaired" and then proofread". During the time between replication and mitosis the DNA is repaired and proofread - special enzymes cut the defective DNA and replace them with appropriate complimentary neucleotides. Mistakes are called mutations.
Entire chromosomes are replicated. The human cell contains 46 chromosomes arranged in 23 pairs. In addition to DNA there is a large amount of proteins composed of histones, around which small segments of each DNA helix are coiled.
Mitosis is the process by which the cell splits into two new daughter cells.
Two pairs of centrioles, which are structures that lie at the poles of the nucleus, begin to move apart from each other.
Spindle
mitotic apparatus
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Cell differentiation allows different cells to perform different functions.
Most cells are able to reproducing other cells of their own type, with the exception of RBC, striated muscle, and neurons. In the presence of sufficient nutrition, cells grow larger and larger and then through mitosis divide to form two new cells.
Cellular division begins with the replication of the DNA.
DNA in the chromosome is replicated once, making an exact copy of the entire DNA before mitosis takes place. The replication of DNA is similar to RNA transcription except for the following important differences:
Both strands of DNA are replicated - not only one strand of DNA
Both strands of DNA helix are replicated from end to end rather than small portions of them, as in the transcription of RNA genes.
The principal enzyme for replication of DNA are the complex of several enzymes called DNA polymerase (similar to RNA polymerase).
Each newly formed strand of DNA remains attached by loose hydrogen bonding to the original DNA strand that is used as its template. Two DNA helixes are formed, therefore duplicates of each other are still coiled together.
The two new helixes become uncoiled by action of enzymes that periodically cut each helix along its entire length, rotate each segment sufficiently to cause separation, and then resplice the helix.
DNA strands are "repaired" and then proofread". During the time between replication and mitosis the DNA is repaired and proofread - special enzymes cut the defective DNA and replace them with appropriate complimentary neucleotides. Mistakes are called mutations.
Entire chromosomes are replicated. The human cell contains 46 chromosomes arranged in 23 pairs. In addition to DNA there is a large amount of proteins composed of histones, around which small segments of each DNA helix are coiled.
Mitosis is the process by which the cell splits into two new daughter cells.
Two pairs of centrioles, which are structures that lie at the poles of the nucleus, begin to move apart from each other.
Spindle
mitotic apparatus
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Cell differentiation allows different cells to perform different functions.
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