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Lecture 3

BI236 lecture 3.docx

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Renuka Karunagoda

BI236 : Cell and Molecular Biology Lecture 3 • GolgiApparatus o AGolgi complex is composed of flat sacs known as cisternae. The sacs are stacked in a bent, semicircular shape. o Each stacked grouping has a membrane that separates its insides from the cell's cytoplasm. Golgi membrane protein interactions are responsible for its unique shape. o Molecules synthesized in the ER exit via special transport vesicles which carry their contents to the Golgi complex. o The vesicles fuse with Golgi cisternae releasing their contents into the internal portion of membrane. o The molecules are modified as they are transported between cisternae layers o Part of the cellular endomembrane system system o Packages proteins inside the cell before they are sent to their destination o Particulary important in the processing of proteins for secretion. • Lysosomes o Membranous sacs containing digestive enzymes found in animal cells o Digest excess or worn-out organelles, food particles, and engulf viruses or bacteria. o Sacs of enzymes, typically hydrolytic and can digest cellular macromolecules. o They are made by the ER and Golgi apparatus. o They are active in recycling the cell's organic material and in the intracellular digestion of macromolecules. o The membrane around a lysosome allows the digestive enzymes to work at the 5 pH they require. o Frequently nicknamed “suicide-bags” or “suicide-sacs” by cell biologists due to their autolysis. o In humans, a variety of inherited conditions can affect lysosomes. o These defects are called storage diseases and include Pompe's disease and Tay- Sachs disease. People with these disorders are missing one or more of the lysosomal hydrolytic enzymes. • Peroxisomes o Also called microbodies -are organelles found in virtually all eukaryotic cells  Important in getting rid of toxic substances o Amajor function of peroxisome is the breakdown of the very long chain fatty acids through (Beta)-oxidation. o In animal cells – the very long fatty acids are converted to medium chain fatty acids, which are shuttled to mitochondria where they are broken down to carbon dioxide and water. o In yeast and plants cells, this process is exclusive for peroximes • Vacuoles o Membrane bound storage sacs o Has no basic shape or size; its structure varies according to the needs of the cell. o More common in plants than animals o Contents  Water  Food  Wastes o Mature plant cells have one large central vacuole o Animal vacuoles are smaller than their plant vacuoles but also usually greater in number. o There are animal cells that do not have any vacuoles o A vacuole is surrounded by a membrane called the tonoplast or vacuolar membrane, separating the vacuolar contents from the cell’s cytoplasm. o Tonoplast  Mainly involved in regulating the movements of ions around the cell,  Isolating materials that might be harmful to the cell. • Bacteria – Like organelles o Release and store energy o Types  Mitochondria (release energy) • Amembrane double) enclosed organelle found in most eukaryotic cells. • Have their own DNA • Described as “cellular power plants” because they gene
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