2.5.1

The stages that are present in the cell cycle are Interphase, mitosis and cytokinesis.Interphase is where the cell prepares for mitosis It has three stages: G1, G2, and the S phase *synthesis phase*. The cell begins to reproduce in G1. In the G2 phase the cell goes through growth and it prepares to divide. The S phase is the phase where DNA replication happens. Mitosis is where the cell divides itself. Once the cell is replicated the centrioles take over...


2.5.2

Tumors, or cancerous materiae. If there are too many, apoptosis will occur, and it is basically a cell self destructing to prevent harmful consequ=this apoptosis does not occur, cancerous cell division can occur because it is not regulated.

2.5.1- Outline the stages of the cell cycle, including interphase, mitosis, and cytokinesis.

Interphase:
The cell grows during the G1 phase then replicates its chromosomes during the S phase and finally completes growth during the G2 phase. Within the interpahes stage, the cell remains active and is continuously fulfulling its life processes. The cell is not dormant during this period.

Mitosis:
Once the cell has reached a certain size, it is ready to divide into two daughter cells that are identical to the parent cell. This process consists of five major stages: prophase, prometaphase, metaphase, anaphase, and telophase. Conserves chromosome number by equally allocating replicated chromosomes to each daughter nuclei.

Cytokinesis:
Daughter cells appear shortly after mitosis, during cytokinesis. A cleavage furrow pinches the cell into two parts and the cytoplasm divides.



2.5.2- State that cancers are the result of uncontrolled cell division and that these can occur in any organ or tissue.

Errors can occur during replication or after replication of DNA. These errors usually lead to cancerous tumors or other diseases. There are many environmental factors that can damage DNA including radiation, chemicals, UV rays, and X-rays. When cells are exposed to these factors, they lose control of the cell cycle and the results are often irreversible. This can occur anywhere in the body because cells are present everywhere. Although there are repair systems such as the nucleotide excision repair which includes the enzyme nuclease, these dont always work. This system can make mistakes in DNA that will have profound effects.

2.5.3- State that interphase is an active period in the life of a cell when many metabolic reactions occur including protein synthesis, DNA replication, and an increase in the number of mitochondria and/or chloroplasts.

Interphase takes up most of the time in the cell cycle. Mitosis is only a small part of the life of a cell. The cell is in interphase for the majority of its life, synthesizing proteins, replicating DNA an making more chloroplasts or mitochondria. The cell completes all of its growth during interphase. It also is the time where the cell transcribes genes that code for the production of amino acids which bond in polypeptide chains to make proteins. As the cell grows, it also makes more mitochondria for animal cells and chloroplasts for plant cells to support the increased size of the cell.


2.5.4- Describe the four phases of mitosis (prophase, metaphase, anaphase, telophase).

Prophase:
- Chromatin fibers condense into chromosomes.
- Mitotic spindle begins to form from the two centrosomes.
- Centrosomes move away from each other, propelled by lengthening microtubules.
Metaphase:
- Longest stage of mitosis.
- Nuclear envelope continues to fragment.
- Chromosomes convene on metaphase plate with a kinetochore microtubule attached to a kinetochore on each of the sister chromatids.
- Spindle completes its formation.
Anaphase:
- Sister chromatids are pulled apart becoming eight individual chromosomes.
- Liberated chromosomes move towards respective centrosomes.
- Nonkinetochore microtubules lengthen and elongate the cell.
Telophase:
- Two daughter nuclei begin to form in each daughter cell.
- Nuclear envelopes begin to re-form from fragments of parent cell.
- Chromosomes become less condensed.



external image mitosis_phases.jpg







2.5.5 Explain how mitosis produces two genetically identical nuclei.

Mitosis creates two nuclei. During S phase, each chromosome forms an exact copy of itself. These identical "sister chromatids" are separated during Anaphase, and are moved to each pole. When separated, they are referred to as chromosomes. The result is two nuclei, identical to each other and to the original nucleus.

2.5.6 State that growth, embryonic development, tissue repair and asexual reproduction involve mitosis.

One of the laws of the cell theory is that all cells come from preexisting cells. The process in which this happens is called mitosis. Growth, embryonic development, tissue repair and asexual reproduction, are processes which require new cells. Which have to be obtained through mitosis.

3.4.1
Explain DNA replication in terms of unwinding the double helix and seperation of the strands by helicase, followed by formation of the new complementary strands by DNA polymerase.
1)Helicase unwinds the DNA
2) The laggind and leading strand bond with binding proteins to keep the strands from reattaching.
3) DNA polymerase III starts replcation on the primer on leading strand from 5' - 3'.
4) Rna primase lays down RNA primer, on eon the leading strand and a bunch on the lagging strand.
5) DNA polymerase III lays down the OKAZAKI FRAGMENTS
6) The lagging strand form in pieces called OKAZAKI FRAGMENTS.
7) DNA polymerase I replaces RNA primer with a new DNA on the lagging and leading strand.
8) DNA ligase connects the OKAZAKI FRAGMENTS
9) DNA becomes a helix again

EXAMPLE:::
external image DNA-20replication.gif

3.4.2

3.4.2- Since the nitrogenous bases of DNA can only pair with complementary bases, this allows for the old base sequence to be preserved and built again. The nitrogenous bases pair with their complements, for example- Adenine with Thymine and Cytosine with Guanine. The original base sequence will be preserved because each base only pairs with the its opposite, so when the DNA separates and replicates, it doesnt change at all.

3.4.3 DNA replication is SEMI-CONSERVATIVE, this means that the original pecies of DNA split into TWO strands, leadning and lagging, and then those two individual strands replicate themselves.Each of those strands having their complementary based nucleotides synthesized by DNA polymerase III.If the original DNA is yellow and the copied DNA is blue as shown above, each new DNA would have one yellow strand and one blue strand. In more scientific terms, the resulting 2 DNA after the process of DNA replication are each made up of one strand of the original DNA and one strand of the newly synthesized DNA.


Example::
external image possible.gif
external image possible.gif