Answer:
Chromosomes were first named by cytologists viewing dividing cells through a microscope. The modern definition of a chromosome now includes the function of heredity and the chemical composition. A chromosome is a DNA molecule that carries all or part of the hereditary information of an organism. In eukaryotic cells, the DNA is packaged with proteins in the nucleus, and varies in structure and appearance at different parts of the cell cycle.
Explanation:
Cells reproduce genetically identical copies of themselves by cycles of cell growth and division. The cell cycle diagram on the left shows that a cell division cycle consists of 4 stages:
G1 is the period after cell division, and before the start of DNA replication. Cells grow and monitor their environment to determine whether they should initiate another round of cell division.
S is the period of DNA synthesis, where cells replicate their chromosomes.
G2 is the period between the end of DNA replication and the start of cell division. Cells check to make sure DNA replication has successfully completed, and make any necessary repairs.
M is the actual period of cell division, consisting of prophase, metaphase, anaphase, telophase, and cytokinesis.
Answer:
Explanation:
Proteins in the plasma membrane have several functions based on their components, location etc. For instance, if the protein transcends the entire plasma membrane it could be a transport protein, responsible for the import and export of certain molecules between the cell and the extracellular matrix (ECM). If the proteins are resting at the surface of the cell, facing the ECM, their role could be to detect components in the ECM, relaying a series of messages back to the nucleus so that the cell can ‘decide’ what it should do with this information (is it being told it should undergo apoptosis, should it begin to divide, should it migrate?). As well as this, it could be involved in the detection of foreign bodies such as pathogens. This is an extremely job for these proteins because if the cell does come in contact with a pathogen, the cell can use these proteins to engulf the pathogen and through a series of steps, present the antigen on their major histocompatibility complexes (either 1 or 2 depending on the cell type) or HLA’s for human cells. Thus it can be concluded that protein functions vary widely in the plasma membrane and due to the vast number of proteins that can be found there, it’s difficult to narrow down the exact main of functions of all these proteins put together.
Answer:
Oldest fossils ever found show life on Earth began before 3.5 billion years ago.
Explanation:
