Cellular+Organelles

Organelles means "little organs" and each has a specialised job to do.

We will discuss the following organs in turn on this page (locate each of them on the generalised cell below):

Endoplamic reticulum (Smooth and Rough) Ribosomes Mitochondira Golgi Apparatus Lysosomes Peroxisomes

The cytoplasm is the site of most cellular activities. It consists of three major elements: The cytosol, organelles and inclusions. Organelles are suspended in cytosol. Cytosol is a viscous, semi transparent fluid composed of mostly water, salt, sugars and solutes. It is not homogenous. **__ Endoplasmic Reticulum (ER) __** Endo means within, plasmic is within the plasma, reticulum means network…so……the endolplasmic reticulum is a network within the plasma. A series of tubules running through the cytoplasm, continuous with the nuclear membrane. There are two (2) kinds of ER: __Rough ER__ – bumps called ribosomes on the surface. __Smooth ER__ – no bumps.

The major job of the __rough ER__ is to serve as a transportation network and participate in membrane synthesis. Its attached ribosomes manufacture all of the proteins that are secreted from the cell. __Smooth ER__ does no protein synthesis. It catalyses reactions involved with lipid metabolism, steroid based hormones, fats, breaks down stored glycogen to form free glucose (in liver especially). __**Ribosomes**__ Are granules composed of proteins and ribosomal RNA, they serve as sites of protein synthesis (assembling of amino acids). There are two (2) kinds of ribosomes that we are concerned with: //Free ribosomes// float freely in the cytoplasm, they make proteins for cell domestic use; and  //Rough ribosomes// make proteins for export or for cellular membranes.

Ribosomes can switch between being free or rough depending on the type of protein they are making at any given time. __** Mitochondria **__ Mitochondria are involved with aerobic cellular respiration. In cellular respiration food fuels (glucose) are broken down to water and carbon dioxide by enzymes and this releases energy that is used to attach phospate groups of ADP to form Adenosine triphosphate (ATP). In essence mitochondria are the power house of the cell.

Mitochondria contain their own DNA, RNA, and ribosomes and multiply when needed by fission (asexual division by splitting off ones self), they are found in high levels in the muscles. Interestingly mitochondrial DNA is identical to a persons mother. [|Maternal DNA] Mitochondria are oblong shaped with a double membrane, the inner membrane has folds that have their point to the middle. These folds are called cristae (kristi) meaning crestsATP production takes place here.

__** Golgi Apparatus **__ Golgi apparatus are traffic directors for cellular proteins; they sort, modify and package proteins.

The Golgi apparatus consists of 4 to 8 sacs that are stacked. They receive proteins from the ER, modifies the proteins with sugars and phosphates, sorts and packages into vesicles that are then addressed for exo/trans cytosis. A high number of these organelles are found in areas known for secretion. __**Lysosomes: "**__ The suicide packs". A lysosome is a package of enzymes bounded by a single membrane. Each lysosome contains digestive enzymes and are highly acidic.

The enzymes hydrolyse proteins, nucleic acids, complex carbohydrates, phospholipids and other substances. For example; in the liver, lysosomes break down stored glycogen to release glucose into the blood stream. Lysosomes perform phagocytosis (Phag = digest and osis = process) which aids in the safe digestion of ingested molecules within the cell. High levels of lysosomes are found within white blood cells (WBCs). WBCs use their lysosomes to digest phagocytosed bacteria. __**Peroxisomes**__ Are peroxide bodies. Peroxisomes resemble lysosomes but contain different enzymes and are not produced by the golgi complex (apparatus). Peroxisomes are sacs of oxidases and catalases (they are enzymes – whenever you see the ending ‘-ase’ it suggests an enzyme). Oxidases convert free radicals to hydrogen peroxide and catalases convert hydrogen peroxide into water. Free radicals and hydrogen peroxide are normal by products of cellular metabolism. Free radicals are reactive chemicals with unpaired electrons that can scramble the structure of molecules if they are allowed to accumulate. Peroxisomes are very active in detoxification especially alcohol, hence we find high levels in the liver and kidney. Organelles Summary The Cell: Contents Nucleus