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Most cells are only visible under a microscope. Cells emerged on Earth about 4 billion years ago. All cells are capable of replication, protein synthesis, and motility. Cells are broadly categorized into two types: eukaryotic cells, which possess a nucleus, and prokaryotic cells, which lack a nucleus but
Cell division is essential for an organism to grow, but, when a cell divides, it must replicate the DNA in its genome so that the two daughter cells have the same genetic information as their parent. The double-stranded structure of DNA provides a simple mechanism for DNA replication .
The generally accepted parts of modern cell theory include: All known living things are made up of one or more cells [13] All living cells arise from pre-existing cells by division. The cell is the fundamental unit of structure and function in all living organisms. [14] The activity of an organism depends on the total activity of independent ...
The different stages of mitosis all together define the M phase of an animal cell cycle—the division of the mother cell into two genetically identical daughter cells. [3] To ensure proper progression through the cell cycle, DNA damage is detected and repaired at various checkpoints throughout the cycle.
The cell cycle's goal is to precisely copy each organism's DNA and afterwards equally split the cell and its components between the two new cells. Four main stages occur in the eukaryotes. In G1, the cell is usually active and continues to grow rapidly, while in G2, the cell growth continues while protein molecules become ready for separation.
An old standing dynamic problem is how DNA "self-replication" takes place in living cells that should involve transient uncoiling of supercoiled DNA fibers. Although DNA consists of relatively rigid, very large elongated biopolymer molecules called fibers or chains (that are made of repeating nucleotide units of four basic types, attached to ...
Furthermore, the composition and properties of chromatin vary from one cell type to another, during the development of a specific cell type, and at different stages in the cell cycle. The DNA + histone = chromatin definition: The DNA double helix in the cell nucleus is packaged by special proteins termed histones. The formed protein/DNA complex ...
Light micrograph of a moss's leaf cells at 400X magnification. The following outline is provided as an overview of and topical guide to cell biology: . Cell biology – A branch of biology that includes study of cells regarding their physiological properties, structure, and function; the organelles they contain; interactions with their environment; and their life cycle, division, and death.