Week 2, Lecture 3, A Tour of The Cell 2

Week 2, Lecture 3, A Tour of The Cell 2 - A Tour Of The...

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A Tour Of The Cell Fungal Cell B I O L O G Y 12 2 3 13-Sep-09 Gardiner 2 Cytoplasm Material between the plasma membrane (cell membrane) and the nuclear envelope A fluid that has a variable viscosity Main chemical constituents are water (approx. 80%), nucleic acids, proteins, lipids, carbohydrates, pigments, etc…. . Ribosomes contain rRNA and protein. A ribosome is composed of two subunits that combine to carry out protein synthesis. Ribosomes build 13-Sep-09 Gardiner 4 Cell types that synthesize large quantities of proteins (e.g., pancreas) have large numbers of ribosomes and prominent nuclei. free ribosomes, are suspended in the cytosol and synthesize proteins that function within the cytosol. bound ribosomes, are attached to the outside of the endoplasmic reticulum. Ribosomes can shift between roles depending on the polypeptides they are synthesizing. 13-Sep-09 Gardiner 5 Many of the internal membranes in a eukaryotic cell are part of the endomembrane system . These membranes are either in direct contact or connected via transfer of vesicles , sacs of membrane. The endomembrane system includes the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, and the plasma membrane . Introduction 13-Sep-09 Gardiner 6 The endoplasmic reticulum ( ER ) accounts for half the membranes in a eukaryotic cell. The ER includes membranous tubules and internal, fluid-filled spaces, the cisternae. The ER membrane is continuous with the nuclear envelope. The Endoplasmic Reticulum
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13-Sep-09 Gardiner 7 There are two regions of ER that differ in structure and function. Smooth ER looks smooth because it lacks ribosomes. Rough ER looks rough because ribosomes (bound ribosomes) are attached to the outside, including the outside of the nuclear envelope. B I O L O G Y 12 2 3 13-Sep-09 Gardiner 8 Smooth ER • The smooth ER is rich in enzymes and plays a role in a variety of metabolic processes. • Enzymes of smooth ER synthesize lipids, including oils, phospholipids, and steroids. • The smooth ER also catalyzes a key step in the mobilization of glucose from stored glycogen in the liver. 13-Sep-09 Gardiner 9 Smooth ER • Other enzymes in the smooth ER of the liver help detoxify drugs and poisons. – These include alcohol and barbiturates. – Frequent exposure leads to proliferation of smooth ER, increasing tolerance to the target and other drugs. • Muscle cells are rich in enzymes that pump calcium ions from the cytosol to the cisternae. 13-Sep-09 Gardiner 10 Rough ER • Rough ER is especially abundant in those cells that secrete proteins. – As a polypeptide is synthesized by the
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Week 2, Lecture 3, A Tour of The Cell 2 - A Tour Of The...

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