Answer:
The study of the cell cycle focuses on mechanisms that regulate the timing and frequency of DNA duplication and cell division. As a biological concept, the cell cycle is defined as the period between successive divisions of a cell. During this period, the contents of the cell must be accurately replicated. Microscopists had known about cell division for more than one hundred years, but not until the 1950s, through the pioneering work of Alma Howard and Stephen Pelc, did they become aware that DNA replication took place only at a specific phase of the cell cycle and that this phase was clearly separated from mitosis. Howard and Pelc's work in the broad bean, Vicia faba, revealed that the cell goes through many discrete phases before and after cell division. From this understanding, scientists then identified the four characteristic phases of the cell cycle: mitosis (M), gap 1 (G1), DNA synthesis (S), and gap 2 (G2). The study of these phases, the proteins that regulate them, and the complex biochemical interactions that stop or start DNA replication and cell division (cytokinesis) are the primary concerns of cell cycle biologists.
The most significant progress in this research field came with the demonstration that specific protein complexes involving cyclins were critical for regulating the passage of cells through the cell cycle. These early observations came from biological studies of the cells of rapidly dividing fertilized frog eggs as well as mutant yeast cells that could not divide. The observations suggested that regulation of the cell cycle is conserved throughout eukaryotes, which has since proved to be the case. The mechanism of division in bacteria differs from that of eukaryotes, and the control of their cell cycle is also somewhat different, although again it is linked with DNA replication.
Although the cell cycle is a highly integrated process, distinct areas of interest within this field of study have emerged. For instance, many genes and proteins that influence the passage from one phase of the cell cycle to another have been identified. When their expression is altered by mutation or aberrant regulation, they are usually classed as oncogenes. Other proteins act to hold the cell at distinct points in the cycle (checkpoints) and are known as tumor suppressor genes. Apart from those with a clearly regulatory role, many proteins have important functions in other aspects of the cell cycle; one is replication of DNA and organelles, which is a fascinating process that includes its own repair mechanisms and self-editing. Other fields focus primarily on the mechanical processes of cell cleavage into two daughter cells at the end of mitosis and on the condensation and decondensation of chromatin.
Explanation:
Answer:
"We decided to place the motor to one side of the man, so that in case of a plunge headfirst, the motor could not fall upon him" "To provide against the machine rolling over forward in landing, we designed skids like sled runners, extending out in front of the main surfaces"
Explanation:
The two passages explain the injury preventative measures taken by the brothers to prevent any sort of accident, further proving a point of safety in their design
In 1882, Congress passed the Chinese Exclusion Act, which was a law that prohibited Chinese workers from immigrating to the United States for ten years. This act was designed to halt Chinese immigrants from coming to the United States. However, it also prohibited Chinese immigrants from becoming U.S. citizens.
Explanation:
In the given sentence “In 1882..” the sentence already conveys that the law was passed to bar Chinese workers from immigrating to the US for the next ten years. Thus it would be inappropriate to repeat “act was designed..”.
Hence the revised passage would look like as provided below-
During the mid-1800s, the mid-nineteenth century, many various Chinese labourers came to the U.S. to start the building of the Transcontinental Railroad. After the railroad was completed, Chinese immigrants faced increasing amounts of prejudice and discrimination. Many native-born Americans felt that the Chinese were responsible for unemployment and decreasing wages. <u>In 1882, Congress passed the Chinese Exclusion Act, a law that prohibited Chinese workers from immigrating to the United States for ten years and becoming U.S. citizens.</u> The Chinese Exclusion Act was the first national legislation to restrict free immigration to the United States.
