<span>Cells control cell division in order to maintain normal cell function. If something happens to the control of the cell division, the healthy cells will divide uncontrollably. These new cells are cancer cells. </span>
The mutations in three genes are responsible for development of cancers:
1. Mutation in proto-oncogenes. Proto-oncogenes normally signal cells to grow and differentiate. Proto-oncogenes can become oncogenes due to mutations which result in the uncontrollable division of the cells.
2. Mutation in tumor suppressor genes. In normal cells, tumor suppressor genes suppress genes essential for cell cycle and that way they prevent uncontrollable cell division. However, after a mutation in these genes, suppression is lost and the cell may progress to cancer.
3. Mutation in stability genes. In normal cells, they have no role either in cell death or growth, but they control mutation rate. Mutation in stability genes results in situation where all genes, including proto-oncogenes and tumor suppression genes, are more frequently mutated.
Answer:
b) The nuclear envelope is continuous with the Golgi apparatus.
Explanation:
The nuclear envelope is a nuclear membrane composed of two lipid bilayers: inner and outer membrane and perinuclear space between them. Its outer membrane is continuous with the endoplasmic reticulum. Nuclear pores that are part of this envelope allow the movement of molecules in and from the nucleus (e.g. mRNA formed during transcription should be transported into cytosol through the pores).
Multicellular organisms use different types of cells to function not just one cell. If cells grew larger that cell would be more demanding.
