Search results
Results from the WOW.Com Content Network
An oocyte (/ ˈ oʊ ə s aɪ t /, oöcyte, or ovocyte is a female gametocyte or germ cell involved in reproduction.In other words, it is an immature ovum, or egg cell.An oocyte is produced in a female fetus in the ovary during female gametogenesis.
Oogenesis starts with the process of developing primary oocytes, which occurs via the transformation of oogonia into primary [oocyte]s, a process called oocytogenesis. [11] From one single oogonium, only one mature oocyte will rise, with 3 other cells called polar bodies. Oocytogenesis is complete either before or shortly after birth.
There are two main types of bacterial cell walls, those of Gram-positive bacteria and those of Gram-negative bacteria, which are differentiated by their Gram staining characteristics. For both these types of bacteria, particles of approximately 2 nm can pass through the peptidoglycan. [3]
The zona pellucida is a translucent matrix of cross-linked glycoprotein filaments that surrounds the mammalian oocyte and is 6.5–20 μm thick depending on the species. Its formation, which depends on a conserved zona pellucida-like (ZP) module that mediates the polymerization of egg coat components, [2] is critical to successful fertilization. [3]
The three-domain system adds a level of classification (the domains) "above" the kingdoms present in the previously used five- or six-kingdom systems.This classification system recognizes the fundamental divide between the two prokaryotic groups, insofar as Archaea appear to be more closely related to eukaryotes than they are to other prokaryotes – bacteria-like organisms with no cell nucleus.
Cells are broadly categorized into two types: eukaryotic cells, which possess a nucleus, and prokaryotic cells, which lack a nucleus but have a nucleoid region. Prokaryotes are single-celled organisms such as bacteria, whereas eukaryotes can be either single-celled, such as amoebae, or multicellular, such as some algae, plants, animals, and fungi.
Bacteria which are the etiological cause for a disease are often referred to by the disease name followed by a describing noun (bacterium, bacillus, coccus, agent or the name of their phylum) e.g. cholera bacterium (Vibrio cholerae) or Lyme disease spirochete (Borrelia burgdorferi), note also rickettsialpox (Rickettsia akari) (for more see [124]).
The eukaryotic cell cycle consists of four distinct phases: G 1 phase, S phase (synthesis), G 2 phase (collectively known as interphase) and M phase (mitosis and cytokinesis). M phase is itself composed of two tightly coupled processes: mitosis, in which the cell's nucleus divides, and cytokinesis, in which the cell's cytoplasm and cell membrane divides forming two daughter cells.