Cell Replication
Kathryn - Blue

Mitosis is the division of a cell giving rise to two genetically identical daughter cells. It is seperated into five different phases which are interphase, prophase, metaphase, anaphase, and telophase. There is also the phase in which a cell spends most of its life in which is interphase. Interphase divided into three phases which are the G1 phase, S phase, and G2 phase. During the G1 phase the cell will increase in mass to prepare for cell division, there is also the little fact that the G means gap and the 1 mean first so the G1 phase is the first gap phase. The next phase in Interphase is the S phase which is the period in which the DNA synthesized, in most cells there is only a narrow window of time for DNA to be synthesized. The S in the S phase means synthesis. The third phase in Interphase is the G2 phase which is the final phase in Interphase before the beginning of prophase. In the G2 phase the cell will synthesize more proteins and will continue to grow in size, this phase is also known as the second gap phase. One of the last phases in cell divison is Cytokinesis which is the stage in which the cytoplasm of a cell will split resulting in two daughter cells.
Malignant tumors, also known as cancer are the result of uncontrolled cell division and this can occur in organ or tissue. Cells through some form of mutation lose their regulatory functions and begin to divide uncontrollably this can be caused by inheritance, certain infections, and diet and immunity weakness. The reason why it can be present in organs or tissues is because those things are made of cells and in reality tumors is just one big concentration of malfunctioning cells so that means that cancer can show up in any area of the body that is made up of cells such as tissues and organs.

Interphase is an active period in the life of a cell when man metabolic reactions occur. These include protein synthesis specifically ribosomes, DNA replication and an increase in the number of mitochondria and/or chloroplast. This is so the cell is capable of producing more ATP because interphase requires a lot of energy.


The Four Stages of Mitosis

Prophase: The chromosomes become visible and the nuclear membrane begins to break down, spindle fibers also start extending from both poles of the cell.
Metaphase: Centrosomes are at opposite poles with spindles extending across cell. Duplicated chromosomes align with the spindle fibers on a middle line called the equator.

Anaphase: Duplicated sets of chromosomes separate and two identical groups move to opposite poles of the cell.
Telophase: Nuclear membrane is formed around each new group of chromosomes and the cytoplasm divides (cytokinesis) forming two daughter cells.
3.4.1- Explain DNA replication in terms of unwinding the double helix and separation of the strands by helicase, followed by formation of the new complementary strands of DNA polymerase.
  1. Stage 1: The DNA double helix is unwound and separated into strands by helicase breaking the hydrogen bonds holding the strands together and creating a replication bubble.
  2. Stage 2: The single strands act as blueprints for new strands. Free nucleotides are present in large numbers. The enzyme primase places primers on the new strand, allowing DNA Polymerase III to add to the strand in a 5-carbon to 3-carbon direction. Several small strands are made within the replication bubble formed by helicase that are known as Okazaki fragments. DNA Polymerase III is then removed, and DNA polymerase I replaces primers with corresponding base pairs. The enzyme ligase then binds these new base pairs to the rest of the strand. The bases of these nucleotides form hydrogen bonds with the bases of the parent strand. The nucleotides are connected to form a new strand.
  3. Stage 3: The daughter DNA molecules each rewind into a double helix.
The two daughter DNA molecules are identical in base sequence to each other and to the parent molecule, because of complementary base pairing (Adenine pairs with Thymine and Cytosine with Guanine). Each of the new strand is complementary to the template on which it was made and identical to the other template.

3.4.2- Explain the significance of complementary base pairing in the conservation of the base sequence of DNA.
Because the nitrogenous bases that compose DNA can only pair with complementary bases, any two linked strands of DNA are complementary. This ensures that the old base sequence is conserved.

3.4.3- State that DNA replication is semi-conservative.
DNA replication copies DNA to produce new molecules with the same base sequence. It is semi-conservative because each new molecule formed by replication uses one new strand and one old strand which is conserved from the parent DNA molecule.

2.5.5 -
Explain how mitosis produces two genetically identical nucleus.
The result of the process of mitosis is two nuclei. During S phase, each chromosome replicates (forms an exact copy of itself). These copies are called sister chromatids. These identical sister chromatids are separated during Anaphase, and are moved to each pole. When they are separated they are referred to as chromosomes. The result is two nuclei, identical to each other and to the original nucleus.
State that growth, tissue repair, and asexual reproduction involve mitosis.
  1. During growth.
  2. When a tissue is damaged.
  3. Asexual reproduction when a single parent cell divides into two identical daughter cells.