4. Assuming the life of a cell starts as soon as cell division is completed and

ID: 53274 • Letter: 4

Question

4. Assuming the life of a cell starts as soon as cell division is completed and ends when the cell starts a new process of cellular division, how many times in a cell’s life does it replicate its DNA? Explain.
5. When does a multicellular organism undergo mitosis (when it wants to reproduce, all the time, only when injured, when it’s growing, or when)?

6.A) why cell division requires multiple checkpoints and B) what is the role of proto-oncogenes and tumor suppressor genes in normal cells and C) why are proto-oncogenes and tumor suppressor genes related to cancer?

Explanation / Answer

DNA replication is the copying of DNA so that replicating cells will have enough DNA for daughter cells, or the new cells derived from the original cell. Cell division, or the making of one cell into two new cells, occurs through mitosis for non-sex cells, and meiosis for sex cells.

S phase is the DNA replication phase of the life cycle. We will talk more about this later, but if you cannot wait, click ahead. This phase is where the cell doubles the amount of DNA to make enough DNA for thedaughter cells, and the cell goes from 2n to 4n, where n is the number of sets of chromosomes, or ploidy. Most somatic cells are 2n, or diploid, while sex cells are haploid, meaning that they have half as much DNA assomatic cells (regular cells).

5. When does a multicellular organism undergo mitosis (when it wants to reproduce, all the time, only when injured, when it’s growing, or when)?

Cell division and Miosis:

Cell division is the first stage of growth in living organisms whereby cells divide to form new cells. In unicellular organisms cell division is a process of asexual reproduction. It leads to an increase in the total number of individuals. On the other hand, in multicellular organisms the division of all cells, other than the reproductive cells, is known as mitosis. In mitosis is cell division an aspect of growth and is accompanied by cellular enlargement and differentiation.

Mitosis is important for the maintenance of the chromosomal set; each cell formed receives chromosomes that are alike in composition and equal in number to the chromosomes of the parent cell.

Mitosis occurs in the following resons:

1)for Development and growth of the organism

The number of cells within an organism increases by mitosis. This is the basis of the development of a multicellular body from a single cell, i.e., zygote and also the basis of the growth of a multicellular body.

2) Cell replacement during injuries or to replace old cells

In some parts of body, e.g. skin and digestive tract, cells are constantly sloughed off and replaced by new ones. New cells are formed by mitosis and so are exact copies of the cells being replaced. In like manner, red blood cells have short lifespan (only about 4 months) and new RBCs are formed by mitosis.

3) Regeneration

Some organisms can regenerate body parts. The production of new cells in such instances is achieved by mitosis. For example, starfish regenerate lost arms through mitosis.

4) Asexual reproduction

Some organisms produce genetically similar offspring through asexual reproduction. For example, the hydra reproduces asexually by budding. The cells at the surface of hydra undergo mitosis and form a mass called a bud. Mitosis continues in the cells of the bud and this grows into a new individual. The same division happens during asexual reproduction or vegetative propagation in plants.

checkpoints:

requirment and significance of checkpoints:

DNA replication and chromosome distribution are indispensable events in the cell cycle control. Cells must accurately copy their chromosomes, and through the process of mitosis, segregate them to daughter cells. The checkpoints are surveillance mechanism and quality control of the genome to maintain genomic integrity. Checkpoint failure often causes mutations and genomic arrangements resulting in genetic instability. Genetic instability is a major factor of birth defects and in the development of many diseases, most notably cancer. Therefore, checkpoint studies are very important for understanding mechanisms of genome maintenance as they have direct impact on the ontogeny of birth defects and the cancer biology.

B) what is the role of proto-oncogenes and tumor suppressor genes in normal cells and C) why are proto-oncogenes and tumor suppressor genes related to cancer?

Proto-oncogenes are genes that normally help cells grow. When a proto-oncogene mutates (changes) or there are too many copies of it, it becomes a "bad" gene that can become permanently turned on or activated when it is not supposed to be. When this happens, the cell grows out of control, which can lead to cancer. This bad gene is called an oncogene. It may be helpful to think of a cell as a car. For it to work properly, there need to be ways to control how fast it goes. A proto-oncogene normally functions in a way that is much like a gas pedal. It helps the cell grow and divide. An oncogene could be compared with a gas pedal that is stuck down, which causes the cell to divide out of control. A few cancer syndromes are caused by inherited mutations of proto-oncogenes that cause the oncogene to be turned on (activated). But most cancer-causing mutations involving oncogenes are acquired, not inherited. They generally activate oncogenes by:

• Chromosome rearrangements: Changes in chromosomes that put one gene next to another, which allows one gene to activate the other

• Gene duplication: Having extra copies of a gene, which can lead to it making too much of a certain protein

Tumor suppressor genes are normal genes that slow down cell division, repair DNA mistakes, or tell cells when to die (a process known as apoptosis or programmed cell death). When tumor suppressor genes don't work properly, cells can grow out of control, which can lead to cancer. A tumor suppressor gene is like the brake pedal on a car. It normally keeps the cell from dividing too quickly, just as a brake keeps a car from going too fast. When something goes wrong with the gene, such as a mutation, cell division can get out of control. An important difference between oncogenes and tumor suppressor genes is that oncogenes result from the activation (turning on) of proto-oncogenes, but tumor suppressor genes cause cancer when they are inactivated (turned off). Inherited abnormalities of tumor suppressor genes have been found in some family cancer syndromes. They cause certain types of cancer to run in families. But most tumor suppressor gene mutations are acquired, not inherited. For example, abnormalities of the TP53 gene (which codes for the p53 protein) have been found in more than half of human cancers. Acquired mutations of this gene appear in a wide range of cancers.

The cell cycle proceeds by a defined sequence of events where late events depend upon completion of early events . The aim of the dependency of events is to distribute complete and accurate replicas of the genome to daughter cells . To monitor this dependency, cells are equipped with the checkpoints that are set at various stages of the cell cycle. When cells have DNA damages that have to be repaired, cells activate DNA damage checkpoint that arrests cell cycle. According to the cell cycle stages, DNA damage checkpoints are classified into at least 3 checkpoints: G1/S (G1) checkpoint, intra-S phase checkpoint, and G2/M checkpoint. Upon perturbation of DNA replication by drugs that interfere with DNA synthesis, DNA lesions, or obstacles on DNA, cells activate DNA replication checkpoint that arrests cell cycle at G2/M transition until DNA replication is complete. There are more checkpoints such as Spindle checkpoint and Morphogenesis checkpoint. The spindle checkpoint arrests cell cycle at M phase until all chromosomes are aligned on spindle. This checkpoint is very important for equal distribution of chromosomes. Morphogenesis checkpoint detects abnormality in cytoskeleton and arrests cell cycle at G2/M transition.

Navigate

4. Assume you operate a buisness and you are waiting for the first customer to a

4. Assumptions of the Modigliani and Miller proposition Aa Aa Modern capital str

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.

4. Assuming the life of a cell starts as soon as cell division is completed and

Question

Explanation / Answer

Related Questions

Navigate