Vacuoles Structure-

Vacuoles are eukaryotic organelles that are membrane-bound, bilayer sacs that encase fluids like chemicals, water, proteins, salts, sugars, and other nutrients. Simply put, they are membranes that surroplantcell450.jpgund a mass of fluid. Much of the volume of the cell relies on the materials confined within the organelle. Looking at the image to the right of a mature, plant cell, one can note how a single vacuole in the center of the cell occupies much of that cell's space. In animal cells however, the vacuoles are much smaller and more abundant.

General Function-

The vacuole plays an important role as a mutlifunctional organelle. Its most vital function is acting as the major site for metabolite and protein digestion and recycling, particuarly in animals. They can also hold food or any variety of nutrients the cell may need for survival. Vacuoles have the ability to store and isolate waste products to protect the rest of the cell from contamination. After these waste products accumulate to a certain degree, they are eventually expelled from the cell as a part of the secretory system.

IN PLANTS-

Vacuoles within plant cells have a far more diverse and more prominent roles within the cell. In addition to storing the the red, blue and purple pigments that give certain flowers their colors, the vacuole.jpgcentral vacuole, or tonoplast,also contributes to the structural support of the cell. The structure is controlled by turgor pressure is linked with the difference between the osmotic pressure inside and outside of the cell. Osmotic pressure is the pressure needed to prevent fluid from diffusing through a membrane which is semi- permeable, separating two solutions containing different solute molecule concentrations. The response of the plant cells to water is a perfect example of the importance of turgor pressure. When not enough water available to the plant, the amount of water within the vacuole decreases and wilting of the plant itself occurs. The plant is able to maintain its basic shape however, due to the cell walls. When a sufficient amount of water exists, the central vacuole of the plant cell swells up and exerts a high level of pressure against the cell walls. When a vacuole is filled, it can occupy anywhere from 80% to 90% of the cell's volume.

IN ANIMALS

Vacuoles play a less important role within animal cells. The organelle does function as a storage, digestion and waste removal site, but only to a lesser extent in comparison to its plant cell counterpart. The animal cell utilizes vesicles to perfom the mass of these tasks.

QUIZ TIME!


  1. Vacuoles are found:
    1. where the sidewalk ends
    2. in eukaryotic cells
    3. in prokaryotic cells
    4. in the nucleus

2. Vacuoles contain:
    1. ribosomes
    2. cytoplasm
    3. magic
    4. water and other materials
3. Vacuoles:
  1. hold food and nutrients
  2. perform digestion and recycling
  3. isolate waste
  4. all of the above
4. Plant cell vacuoles can take up up to _ % of the cell's volume
  1. 30%
  2. 90%
  3. -50%
  4. 10%

5. In a plant cell, the vacuole exerts against the cell:
  1. cisternae
  2. tonoplasts
  3. an intervesicular environment
  4. turgor pressure


6. Vacuoles in animal cells are:
  1. small and abundant
  2. inactive
  3. awesome
  4. more important than the vacuoles in plant cell

ANSWERS: 1. - 2; 2. - 4; 3. - 4; 4. - 2; 5. - 4 ; 6. - 1



The Golgi Apparatus

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The Golgi Apparatus
Structure:

The Golgi apparatus (named after Italian biologist Camillo Golgi who discovered the organelle in 1898) is composed of sevaral stacks of membranous sacs called cisternae. The series of membranes resemble a stack of pancakes. Each membrane surrounds an area of fluid where complex molecules are stored and changed.

Function:

The Golgi apparatus can be thought of as a factory where proteins are received, changed, sorted, and sent out into the cell.

The cis face and the trans face are the terms used to refer to the polar ends of a Golgi stack. The cis and trans faces are the "receiving" and "shipping" departments in a cell.
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Parts of the Golgi Apparatus

Commonly, there are four operating regions within the Golgi: the cisGolgi network, the Golgi stack (divided into two subcompartments with a number of layers, medial and trans), and the transGolgi network.

Proteins from the Endoplasmic Reticulum (ER) are brought by transport vesicles into the Golgi apparatus at its cis face. The transport vesicles do this by fusing with the membrane of the Golgi. As seen in the figure to the right, they first pass through the ER-Golgi intermediate compartment, the first layer of the stack of cisternae. The proteins are then transferred through the operating regions of the Golgi, all while being converted and sorted. The most metabolic activities of the Golgi apparatus take place in the medial and trans compartments. The proteins transform into more proteins, lipids, and polysaccharides and then pass on to the transGolgi network, where they are sorted. The modified proteins are targeted at different parts of the cell and are given molecular "identification tags" to help with sorting. Once the modified proteins have transported through the apparatus, they exit from the trans face (as seen in the figure below) and travel to lysosomes, the plasma membrane, or the cell exterior via transport vesicles, which can recognize "docking sites" on the surface of organelles.
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Transport from Golgi Apparatus

The manner in which the proteins are transported through the Golgi is still unknown. Some scientists believe the proteins transport through cisternae progression, in which the apparatus itself moves and builds new cisternae at the cis end while destroying cisternae at the trans end of the apparatus. Another way the proteins may transport is through vesicular transport, where small vesicles move the proteins through the layers of cisternae.

The Golgi apparatus is used in glycosylation (the process of adding glycosyl groups to a protein to form a glycoprotein). It modifies glycoproteins, which are used in cell membranes, by attaching carbohydrates and removing carbohydrates, forming various carbohydrate structures on the proteins. The Golgi apparatus also transports lipids around the cell wall and creates lysosomes,

which are organelles used in digestion.

Overall, the Golgi apparatus is used to finish, sort, and transport cell products.



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VESICLES
exocyt.gif
Vesicle expelling waste from a cell





Structure:
In cell biology, a vesicle is a relatively small and enclosed compartment, separated from the cytosol by at least one lipid bilayer. [If there is only one lipid bilayer, they are called unilamellar vesicles; otherwise they are called multilamellar.] Because it is separated from the cytosol, the intravesicular environment can be made to be different from the cytosolic environment.This biomembrane enclosing the vesicle is similar to that of the plasma membrane.


Function:

Vesicles store, transport, or digest cellular products and waste. Vesicles are a basic tool of the cell for organizing metabolism, transport, enzyme storage, as well as being chemical reaction chambers. Many vesicles are made in the Golgi apparatus, but also in the endoplasmic reticulum.
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Process of making a vesicle to be expelled from the cell














WORKS CITED


<http://www.babylon.com/definition/Vesicle_(biology)/English. >