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We will now begin our discussion of intracellular organelles.docx

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BIL 498
Dr.Shahriar Negahdaripour

We will now begin our discussion of intracellular organelles. As we have mentioned, only eukaryotic cells have intracellular sub-divisions, so our discussion will exclude prokaryotic cells. We will also focus on animal cells, since plant cells have a number of further specialized structures. In this section we will discuss the importance of the cell nucleus, mitochondria, peroxisomes, endoplasmic reticulum, golgi apparatus, and lysosome. The Cell Nucleus The cell nucleus is one of the largest organelles found in cells and also plays an important biological role. It composes about 10% of the total volume of the cell and is found near the center of eukaryotic cells. Its importance lies in its function as a storage site for DNA, our genetic material. The cell nucleus is composed of two membranes that form a porous nuclear envelope, which allows only select molecules in and out of the cell. The DNA that is found in the cell nucleus is packaged into structures called chromosomes. Chromosomes contain DNA and proteins and carry all the genetic information of an organism. The nucleus gains support from intermediate filaments that both form the surrounding nuclear lamina and makes direct contact with the endoplasmic reticulum. The nucleus is also the site of DNA and RNA synthesis. Figure %: Location of the cell nucleus, mitochondria, and peroxisomes in a cell. Mitochondria The mitochondria, with its specialized double-membrane structure, generate adenosine triphosphate (ATP), a molecule that provides organisms with energy. Figure %: Mitochondrial structure The outer and inner membranes of the mitochondria form two sub- compartments: the internal matrix space and the intermembrane space. Those few proteins found withn the mitochondria are located within the inner membrane. Mitochondria synthesize ATP with energy supplied by the electron transport chain and a process called oxidative phosphorylation. Peroxisomes Peroxisomes are single-membrane structures found in all eukaryotic cells. They are small, membrane-bound structures that use molecular oxygen to oxidize organic molecules. The structure is one of the major oxygen utilizing organelles, the other being the mitochondria. Peroxisomes contain oxidative enzymes and other enzymes that help produce and degrade hydrogen peroxide. Because of their varying enzymatic compositions, peroxisomes are diverse structures. Their main function is to help breakdown fatty acids. They perform specific functions in plant cells, which we will discuss later. The Endoplasmic Reticulum The endoplasmic reticulum, or ER, is a very important cellular structure because of its function in protein synthesis and lipid synthesis. For example, the ER is the site of production of all transmembrane proteins. Since nearly all proteins that are secreted from a cell pass through it, the ER is also important in cellular trafficking. In addition to these major roles, the ER plays a role in a number of other biological processes. There are two different types of ER: smooth ER and rough ER (RER). The rough ER has its na
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