Cell Biology PDF - Endoplasmic Reticulum (2023-2024)

Q 5.2.5 (i) ENDOPLASMIC RETICULUM (ER) uestion 1. Fill in the gaps in the following table illustrating differences between prokaryotic and eukaryotic cells. Prokaryotic Cell Eukaryotic Cell 1. Size : generally small ( 1-10 µm) 1 µm = 10–6 m 1. Size: generally large ( 5-100 µm) 2. Nuclear region: ___...

Q 5.2.5 (i) ENDOPLASMIC RETICULUM (ER) uestion 1. Fill in the gaps in the following table illustrating differences between prokaryotic and eukaryotic cells. Prokaryotic Cell Eukaryotic Cell 1. Size : generally small ( 1-10 µm) 1 µm = 10–6 m 1. Size: generally large ( 5-100 µm) 2. Nuclear region: _______________ _______________ and known as__ 2. Nuclear region: well defined and surrounded by a nuclear membrane 3. Chromosome: single 3. More than one chromosome 4. Membrane-bound 4. _______________ cell organelles _______________ absent _______________ The endoplasmic reticulum (ER) is a large network of membrane-bound tubes and sheets. It looks like long tubules or round or oblong bags (vesicles). The ER membrane is similar in structure to the plasma membrane. There are two types of ER– rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER). RER looks rough under a microscope because it has particles called ribosomes attached to its surface. The ribosomes, which are present in all active cells, are the sites of protein manufacture. The manufactured proteins are then sent to various places in the cell depending on need, using the ER. The SER helps in the manufacture of fat molecules, or lipids, important for cell function. Some of these proteins and lipids help in building the cell membrane. This process is known as membrane biogenesis. Some other proteins and lipids function as enzymes and hormones. Although the ER varies greatly in appearance in different cells, it always forms a network system. 5.2.5 CELL ORGANELLES Every cell has a membrane around it to keep its own contents separate from the external environment. Large and complex cells, including cells from multicellular organisms, need a lot of chemical activities to support their complicated structure and function. To keep these activities of different kinds separate from each other, these cells use membrane-bound little structures (or ‘organelles’) within themselves. This is one of the features of the eukaryotic cells that distinguish them from prokaryotic cells. Some of these organelles are visible only with an electron microscope. We have talked about the nucleus in a previous section. Some important examples of cell organelles which we will discuss now are: endoplasmic reticulum, Golgi apparatus, lysosomes, mitochondria and plastids. They are important because they carry out some very crucial functions in cells. THE FUNDAMENTAL UNIT OF Fig. 5.5: Animal cell Thus, one function of the ER is to serve as channels for the transport of materials (especially proteins) between various regions of the cytoplasm or between the cytoplasm and the nucleus. The ER also functions as a cytoplasmic framework providing a surface LIFE 55 Rationalised 2023-24