Organelle

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A typical animal cell. Within the cytoplasm, the major organelles and cellular structures include: (1) nucleolus (2) nucleus (3) ribosome (4) vesicle (5) rough endoplasmic reticulum (6) Golgi apparatus (7) cytoskeleton (8) smooth endoplasmic reticulum (9) mitochondria (10) vacuole (11) cytosol (12) lysosome (13) centriole.
In cell biology, an organelle (pronounced /ɔrɡəˈnɛl/) is a specialized subunit within a cell that has a specific function, and is usually separately enclosed within its own lipid membrane.
The name organelle comes from the idea that these structures are to cells what an organ is to the body (hence the name organelle, the suffix -elle being a diminutive). Organelles are identified by microscopy, and can also be purified by cell fractionation. There are many types of organelles, particularly in eukaryotic cells. Prokaryotes were once thought not to have organelles, but some examples have now been identified.[1]

History and Terminology

In biology, organs are defined as confined functional units within an organism. The analogy of bodily organs to microscopic cellular substructures is obvious, as from even early works, authors of respective textbooks rarely elaborate on the distinction between the two.
Credited as the first[2][3][4] to use a diminutive of organ (i.e. little organ) for cellular structures was German zoologist Karl August Möbius (1884), who used the term "organula" [5] (plural form of organulum, the diminutive of latin organum). From the context, it is clear that he referred to reproduction related structures of protists. In a footnote, which was published as a correction in the next issue of the journal, he justified his suggestion to call organs of unicellular organisms "organella" since they are only differently formed parts of one cell, in contrast to multicellular organs of multicellular organisms. Thus, the original definition was limited to structures of unicellular organisms.
It would take several years before organulum, or the later term organelle, became accepted and expanded in meaning to include subcellular structures in multicellular organisms. Books around 1900 from Valentin Häcker,[6] Edmund Wilson[7] and Oscar Hertwig[8] still referred to cellular organs. Later, both terms came to be used side by side: Bengt Lidforss wrote 1915 (in German) about "Organs or Organells".[9]
Around 1920, the term organelle was used to describe propulsion structures ("motor organelle complex", i.e., flagella and their anchoring)[10] and other protist structures, such as ciliates.[11] Alfred Kühn wrote about centrioles as division organelles, although he stated that, for Vahlkampfias, the alternative 'organelle' or 'product of structural build-up' had not yet been decided, without explaining the difference between the alternatives.[12]
In his 1953 textbook, Max Hartmann used the term for extracellular (pellicula, shells, cell walls) and intracellular skeletons of protists.[13]
Later, the now-widely-used[14][15][16][17] definition of organelle emerged, after which only cellular structures with surrounding membrane had been considered organelles. However, the more original definition of subcellular functional unit in general still coexists.[18][19]
In 1978, Albert Frey-Wyssling suggested that the term organelle should refer only to structures that convert energy, such as centrosomes, ribosomes, and nucleoli.[20][21] This new definition, however, did not win wide recognition

DNA expressed as mRNA transcripts

Which of the following is a marker for regions of the DNA expressed as mRNA transcripts, and characterized by cDNA cloning? EST To characterize sequences from the human genome that are coding regions for mRNAs (i.e. "expressed" sequences), cDNA copies of mixtures of cellular mRNA templates are synthesized with reverse transcriptase. The cDNAs can be converted to double stranded cDNAs, inserted into plasmid vectors using recombinant DNA technology, purified by cloning in bacterial cells, and sequenced.
The term "EST" is now used to describe the DNA sequence of a short fragment of a cDNA. As of October 1996, there were about 450,000 EST sequences from human DNA in public DNA sequence databases. Many are redundant cDNAs from different regions of the same mRNA. Nevertheless, approximately 49,000 unique human ESTs are known, representing half of the predicted 100,000 expressed sequences in the human genome.

DNA expressed as mRNA transcripts

Which of the following is a marker for regions of the DNA expressed as mRNA transcripts, and characterized by cDNA cloning? EST To characterize sequences from the human genome that are coding regions for mRNAs (i.e. "expressed" sequences), cDNA copies of mixtures of cellular mRNA templates are synthesized with reverse transcriptase. The cDNAs can be converted to double stranded cDNAs, inserted into plasmid vectors using recombinant DNA technology, purified by cloning in bacterial cells, and sequenced.
The term "EST" is now used to describe the DNA sequence of a short fragment of a cDNA. As of October 1996, there were about 450,000 EST sequences from human DNA in public DNA sequence databases. Many are redundant cDNAs from different regions of the same mRNA. Nevertheless, approximately 49,000 unique human ESTs are known, representing half of the predicted 100,000 expressed sequences in the human genome.

Tutorial: Inheritance of an X-linked recessive trait

Red-green color blindness is X-linked in humans. If a male is red-green color blind, and both parents have normal color vision, which of the male's grandparents is most likely to be red-green color blind? Parents
If both parents have normal vision, the mother of the affected male must be heterozygous for the X-linked, recessive alleles for red-green color blindness. The father of the affected male could not have been the source of the red-green color blind allele since fathers can only pass X-linked traits to their daughters, and Y chromosomes to their sons. Grandparents
The two possible pedigrees for inheritance from a maternal grandparent are shown in the pedigree charts labeled A andWhich of the mother's parents, the maternal grandmother (pedigree chart B) or maternal grandfather (pedigree chart A), is more likely to both be
1. red-green color blind, 2. the source of the allele inherited by their grandson? Males with only a single X chromosome are more commonly affected by X-linked, recessive traits than are females with two X chromosomes. Why?
A male need only inherit the recessive allele from a heterozygous female carrier. A female would need to inherit the recessive allele from both parents, an affected father and a carrier (or affected) mother. B.

Cell Membranes Tutorial

This exercise introduces the dynamic complexes of proteins, carbohydrates, and lipids that comprise cell membranes. You should learn that membranes are fluid, with components that move, change, and perform vital physiological roles as they allow cells to communicate with each other and their environment. We also show that membranes also are important for regulating ion and molecular traffic flow between cells,and that defects in membrane components lead to many significant diseases.
Instructions: The following problems have multiple choice answers. Correct answers are reinforced with a brief explanation. Incorrect answers are linked to tutorials to help solve the problem.

The cell is a unit of organization

Cells are classified by fundamental units of structure and by the way they obtain energy. Cells are classified as prokaryotes or eukaryotes, which will be covered in more detail in the next two pages of this tutorial.
Living things are classified in six kingdoms based on structure. Within prokaryotes, which appeared 3.5 billion years ago, are the kingdoms Monera (Eubacteria) and Archaea. Within eukaryotes, which evolved 1.5 billion years ago, are the kingdoms Protista, Plantae, Fungae, Animalia.
Cells are also defined according the need for energy. Autotrophs are "self feeders" that use light or chemical energy to make food. Plants are an example of autotrophs. In contrast, heterotrophs ("other feeders") obtain energy from other autotrophs or heterotrophs. Many bacteria and animals are heterotrophs. Multicellular Organisms
Multicellular organisms are created from a complex organization of cooperating cells. There must be new mechanisms for cell to cell communication and regulation. There also must be unique mechanisms for a single fertilized egg to develop into all the different kinds of tissues of the body. In humans, there are 1014 cells comprising 200 kinds of tissues!