CELL BIOLOGY AND SIGNALLING Flashcards
Cell
A semi-independent, living unit within the body, (in unicellular organisms, completely independent) in which are sited the mechanisms for metabolism, growth and replication (by division). It consists of an aqueous solution of organic molecules surrounded by a membrane.
Organelle
A subunit within a cell, with a defined structure and performing specific, integrated activities. Some are bounded by membranes, others are non-membranous e.g. ribosomes
Tissue
An organised assembly of cells and their extracellular products which carry out similar and coordinated activities within the body (connective, lymphoid)
Organ
An assembly of tissues which carry out specific functions within the body (eye, ear, heart)
System
An assembly of organs with specific, related activities, sharing regulatory influences (e.g. respiratory). OR it may be a diffuse functional network of cells situated in many parts of the body, sharing specific activities (e.g. immune)
Prokaryote
A unicellular organism in which the chromosome is a circular strand free floating in the cell (no nucleus) and has no membrane bound organelles (bacteria)
Eukaryote
Unicellular or multicellular organisms in which the chromosomes are enclosed in a nucleus and they typically have cytoplasmic membrane bound organelles. DNA exists as many linear chromosomes and big differences exist between different cells within the same organism (animals, plants, fungi, protozoa)
Virus
An assemblage of nucleic acid (DNA or RNA) and proteins (and often other molecules) which is parasitic on prokaryotes/eukaryotes. Viruses invade cells, subvert their protein synthesis machinery to make more viruses instead of normal cell proteins, then escape to infect other cells. Viruses are not cells or organisms in the strict sense (lack a plasma membrane and only operate chemically within host cells).
