Ribosome+and+Vacuole

**Ribosomes **

Ribosomes are organelles that synthesize proteins and are composed of protein and rRNA (ribosomal RNA). They are found on the rough endoplasmic reticulum (ER) and floating in the cytoplasm. The ones connected to the rough ER are called bound ribosomes, while those suspended in cytosol (the fluid which makes up the cytoplasm) are called free ribosomes. Both are structurally the same, with a large subunit and a smaller one, called 60-S and 40-S respectively in eukaryotic cells, or 50-S and 30-S in prokaryotic cells, though in both types of cells they perform the same function.

Overview of Protein Synthesis: Messenger RNA, or mRNA, provides a template for the synthesis of specific proteins. The mRNA binds with the smaller subunit of a ribosome and determines what amino acids are delivered by the tRNA (transport RNA), and in what order they are attached. Once the first tRNA binds to a codon on the mRNA, the larger subunit of the ribosome attaches to the smaller subunit. The individual amino acids are linked by peptide bonds, releasing their tRNA as they're added to the growing polypeptide chain, until a stop codon, or red light, on the mRNA is reached. Then the completed protein isb released by the ribosome and sent where it is needed. Proteins synthesized by free ribosomes are generally the ones that will be used inside a cell, while proteins created by bound ribosomes might be used either by that cell or exported for use outside the cell. The ribosome can now bind to another mRNA molecule and create another protein.

Video of Protein Synthesis: media type="custom" key="2370765"

A giant sculpture of ribosomes by Mara Haseltine. Click on photo to see source on flickr.com.

An interactive tour of a cell- http://www.nsf.gov/news/overviews/biology/interactive.jsp
 * Other Fun Links: **

molecular model of a ribosome- http://www.wellcome.ac.uk/en/wia/gallery.html?image=7

ribosome info on biology4kids- http://www.biology4kids.com/files/cell_ribos.html

A more in depth explanation with cool pictures- http://cellbio.utmb.edu/CELLBIO/ribosome.htm

=**Vacuole ** =

**Plant**
Vacuoles help keep the structure of a plant cell; this structure is controlled by turgor pressure. Turgor pressure determines the rigidity of the cell structurebased on the difference between osmotic pressure inside and outside the cell. Osmotic pressure is needed to prevent liquids from defusing outside the partly permeable membrane. Water is the best example when trying to explain this process. As a plant takes in water it is collected inside the central vacuole. As more and more water is accumulated the vacuole expands to hold all of liquid causing turgor pressure to increase, which keeps the structure of the cell and the plant. The central vacuole is normally fifty percent of the volume of the cell, but when it expands it can become up to ninety percent! However, when the central vacuole inside the cell does not have enough water it decreases in turgor pressure and the plant starts to wilt. The pressure is no longer creating a firm stricture. In addition to keeping the cell's structure, the vacuole is also a storage container. It holds nutrients, waste products and other things such as pigments for flower color or poisonous molecules so the cell doesn't get eaten.  //Plant cell ^//

**Animal**
In animal cells vacuoles are much smaller and more plentiful. Contractile vacuoles slowly accumulate nutrients, waste, and water and pump them to the outside of the cell. This makes sure the cell will not burst from the build up. Digestion takes place in food vacuoles with help from lysosome. During phagocytosis the food vacuole encloses the nutrients and fuses with a lysosome and hydrolytic enzyme, which digests the food. After digestion the undigested waste gets pushed out of the cell. That process is part of exocytose and endocitosi, exocytose is the expelling process of proteins which is how animal cells get rid of the waste and endocitosi is the opposite. They also help digest nutrients with help from lysosome; when doing this they are called food vacuoles.

//Animal cell ^//

media type="custom" key="2367959" //Contractile Vacuole ^//

For interesting interactive sites choose one of the following: http://www.cellsalive.com/cells/cell_model.htm http://www.cells.de/cellseng/1medienarchiv/Zellstruktur/Endosomen_u_Vakuolen/Vakuolen/Vacuole,_Plant_Cell/index.jsp http://www.tvdsb.on.ca/WESTMIN/science/sbi3a1/Cells/cells.htm

works cited

__contractile vacuoles__. Dir. ajcann. video. Davidson, Michael. "plant cells vacuoles." 2008. molecular expressions. 27 Oct 2008 . " vacuole." __cell anatomy__. cellupedia. 27 Oct 2008 .