The amount of time it takes for one cell to completely divide in most mammals, including the human body, is about 24 hours. Some cells take more or less time, depending on their purpose; a fly embryo takes only eight minutes to divide, for example, while a human liver cell could take more than a year. Gametes, cells used in sexual reproduction, can take decades to divide. Abnormal cell division can also occur, resulting in cancerous cells that multiply much more rapidly.embryo

Regulation and Asexual Reproduction

Factors of Regulation There are two types of factors that regulate the cell cycle External Internal

External factors External factors that regulate the cell cycle can be divided into two types Physical and chemical signals One example of a physical signal is Cell contact One example of a chemical signal is growth factors

External Factors Cell Contact is simple basically a cell divides until it is surrounded by other cells as long as there is empty space around it a cell will continue to divide Growth factors are a broad group of proteins that stimulate cell division Some examples of this are platelets, and various hormones.

Internal Factors Two of the most important internal factors are kinases and cyclins A kinase is an enzyme that transfers a phosphate group to a specific target molecule which either increases its energy or changes its shape. Cyclins activate the kinases that help control the cell cycle

Apoptosis Programmed cell death Occurs when internal or external signals activate genes that help produce self destructive enzymes During apoptosis the nucleus shrinks and breaks apart, the cell is recognized by specialized cells in your immune system, these cells consume the dead cell and recycle its components to other cells

Cancer Uncontrolled cell division Two types benign and malignant Benign-cells remain clustered together they do not spread and can be removed relatively easily Malignant-cells break away, this is called metastasize, they are carried in the blood stream or lymph system where it can spread throughout the body

Cancer Cancer is caused by normal cells suffering damage to the genes that make proteins useful to cell cycle regulation Some cancer can be inherited ex: some types of breast cancer Some cancer is caused by exposure to radiation or chemicals ex. UV radiation, tobacco smoke Any substance that promotes the development of cancer is called a carniogen

Asexual Reproduction Creation of offspring from a single parent The offspring that result are genetically identical to each other and to the parent Binary fission- is the reproduction of a single celled organism by division into two roughly equal parts

Advantages and Disadvantages More efficient No genetic diversity in a population