Mitochondria, Ribosomes, and ER L3 PDF

Mitochondria Prepared By Dr. Hagar Ali Abu Quora Lecturer of Cytology, Histology and Histochemistery Zoology Department- Faculty of Science- Menoufia University 25/10/2023 Mitoc...

Mitochondria Prepared By Dr. Hagar Ali Abu Quora Lecturer of Cytology, Histology and Histochemistery Zoology Department- Faculty of Science- Menoufia University 25/10/2023 Mitochondria  Mitochondria (membranous organelles) Mitochondria (Gr. mitos, thread + chondros, granule) are living organelles present from unicellular organisms to higher animals and plants. Mitochondria are known as the “powerhouses” of cells as oxidation of foodstuffs and energy release occur in them. Mitochondria are membrane-bound organelles occur free in the cytoplasm. Mitochondria are spherical or filamentous organelles 0.5-1 μm wide and can attain a length of up to 12 μm. Mitochondria 25/10/2023  Number of Mitochondria The number of mitochondria is almost constant for each cell type and are numerous in the more specialized cells, such as those of kidney and liver. In Amoeba the number is as high as 500,000, while in liver cells, the number is between 500- 1000 and may reach 2500 per cell. The number became as low as 20 in sperm. Some oocytes contain as many as 300,000, the largest number recorded for a cell. Mitochondria 25/10/2023 Structure of Mitochondria Mitochondria are sac-like structures composed of an outer and an inner mitochondrial membranes each is 5 to 6 nm thickness The outer membrane is smooth-contoured, continuous limiting membrane with the usual trilaminar structure. The inner membrane is similar in appearance to the outer one and generally courses allele to the outer membrane and is folded extends inwards or projects folds called internal ridges or cristae into the interior of the organelle. Mitochondria 25/10/2023 Structure of Mitochondria 5- The two mitochondrial membranes delimit two spaces or compartments: a- The first one located between the two membranes and is known as intermembrane space or membrane space, and including its inward extensions between the leaves of the cristae. These latter clefts are designated as the intracristal spaces. b- The second space is termed the intercristae or matrix space is enclosed by the inner membrane and filled with a fine granular material of variable electron density rich with enzymes. Mitochondria 25/10/2023 Structure of Mitochondria The shape of mitochondrial cristae differs with the function of the cells in which they are located. a- Most mitochondria have flat, shelf-like cristae, whereas they are tubular in steroid- secreting cells (e.g., adrenal gland). b- These cristae increase the internal surface area enough for the intra-mitochondrial activities and they may or may not extend all the way across the mitochondrion interior, and are oriented either perpendicular or parallel to the long axis. Mitochondria 25/10/2023 Mitochondria 25/10/2023  Functions of Mitochondria 1- Metabolites are degraded within. Mitochondria contain the tricarboxylic cycle enzymes which generate reduced nucleotides from the metabolism of citric acid. Mitochondria assist in steroid biosynthesis and nucleic acid synthesis. Mitochondria are strongly engaged in the general metabolism of the cells, especially, fat and amino acids. They are responsible for the formation of the tail sheath of spermatozoa. Mitochondria 25/10/2023  Ribosomes Prepared By Dr. Hagar Ali Abu Quora Lecturer of Cytology, Histology and Histochemistery Zoology Department- Faculty of Science- Menoufia University  Definition of Ribosomes (non-membranous organelles) A ribosome is a complex molecular machine found inside the living cells that produce proteins from amino acids during a process called protein synthesis or translation. The process of protein synthesis is a primary function, which is performed by all living cells. A ribosome is a complex of RNA (ribonucleic acid) and protein and is, therefore, known as a ribonucleoprotein (r protein). It is composed of two subunits – smaller and larger. 25/10/2023 Ribosomes  Site of Ribosomes Ribosomes are formed from the nucleolus from different cytoplasmic proteins and nucleoproteins and pass through the pores of the nuclear membrane to the cytoplasm to perform their functions in the cytoplasm. Structure of Ribosomes Ribosomes consist of two subunits small and large subunits. Small ribosomal RNA, read RNA. Large ribosomal RNA, join amino acids to form a polypeptide chain. 25/10/2023 Ribosomes  Structure of Ribosomes L/M E/M Appeared as minute basophilic granules Appeared as electron-dense granules The cause of this shape Diffuse in the cytoplasm e.g. embryonic cells Free either single or groups connected together by mRNA form clusters or spiral chains called (polyribosomes/polysomes) Localized in a certain area of cytoplasm e.g. basal Attached is arranged on the membrane surface of the rough pancreatic secretory cells endoplasmic reticulum (rER). Spotty appeared as small aggregation as spots e.g. Nissl granules in nerve cells 25/10/2023 Ribosomes  Free and Attached Ribosomes 25/10/2023 Ribosomes  Functions of Ribosomes Free ribosomes are concerned with the synthesis of protein in cell growth and regeneration of organelles. Attached ribosomes are concerned with the synthesis of protein from rER and Golgi apparatus to form secretory granules that synthesized secretions. Ribosomes act as catalysts in two extremely important biological processes called peptidyl transfer and peptidyl hydrolysis. 25/10/2023 Ribosomes  Functions of Ribosomes During protein biosynthesis, the tRNA traverses the intersubunit by going through three primary binding positions termed:  The A site (i.e. the binding site of the aminoacylated tRNA).  The P site (the site of peptidyl tRNA, or the tRNA bound to the polypeptide).  The E site (exit site, where the deacylated P-site tRNA moves after peptide bond formation). 25/10/2023 Ribosomes  Functions of Ribosomes N.B. At any time, only two of these sites are occupied: A and P (in the pretranslocational state) or P and E (in the posttranslocational state). N.B. the Nobel Prize in Chemistry 2009 (STRUCTURE AND FUNCTION OF THE RIBOSOME) https://sites.google.com/site/proteinsynthesistranslation/home/terms  (Please check) 25/10/2023 Ribosomes Endoplasmic Reticulum (ER) Prepared By Dr. Hagar Ali Abu Quora Lecturer of Cytology, Histology and Histochemistery Zoology Department- Faculty of Science- Menoufia University Cytology and Histology- First semester 2022-2023  Definition of Endoplasmic Reticulum (ER) ER was discovered by Emilio Veratti in the year of 1902 as a Sarcoplasmic Reticulum in muscle fibers which is similar to ER in other cells (Veratti, 1961). Fifty years later, this new organelle was first visualized through EM by Keith Porter who termed it as an “endoplasmic reticulum” (Porter, 1953). Structure of ER The general structure of the endoplasmic reticulum is a network of membranes called cisternae. These sac-like structures are held together by the cytoskeleton. The phospholipid membrane encloses the cisternal space (or lumen), which is continuous with the perinuclear space but separate from the cytosol. 25/10/2023 Endoplasmic Reticulum  Site and types of ER ER is the largest organelle in the cell. ER is present in the cytoplasm. It is a system of communicating membrane-bound tubules, vesicles, and flattened cisternae. There are two types: Rough ER (rER) / granular. Smooth ER (sER)/ agranular. 25/10/2023 Endoplasmic Reticulum  Rough ER (rER) / granular It is well developed in protein-forming cells, e.g. plasma cells. The surface of the membranes has specific glycoproteins receptors (ribophorins) to which the large subunits of ribosomes bind. L/M E/M Its sites appear as It appears as a membrane- basophilic areas, due to bound sheets of flattened the present of ribosomes cisternae with ribosomes on the surface. attached to its outer surface. 25/10/2023 Endoplasmic Reticulum  Rough ER (rER) / granular Functions: 1. Synthesis of protein by the ribosomes on their surfaces. 2. Accumulation of the formed protein within their cavities. 3. Transfer vesicles, containing protein, bud off from the ER, to transfer this protein to the Golgi apparatus. 4. The interconnected cavities of the reticulum act as an intracellular pathway for the transport of protein to the site of the Golgi apparatus. 25/10/2023 Endoplasmic Reticulum  Smooth ER (sER)/ agranular It is well developed in fat and steroid hormones forming cells. L/M E/M It can not be It appears as demonstrated. membrane-bound tubules and vesicles, with no ribosomes on surface. 25/10/2023 Endoplasmic Reticulum  Smooth ER (sER)/ agranular Functions: 1. Synthesis and storage of lipids and cholesterol. 2. Synthesis of steroid hormones, such as testosterone and cortisone. 3. Helps muscular contraction, by acting as a calcium pump. 4. Storage and breakdown of glycogen in liver and muscle cells. 5. Detoxifications of drugs and hormones. 6. Has a role in intracellular transport system science it is continuous with rER and Golgi apparatus. 25/10/2023 Endoplasmic Reticulum  Differentiate between rER and sER? https://www.youtube.com/watch?v=iLmp9SKtXuU (PLZ check) 25/10/2023 Endoplasmic Reticulum Mitochondria 25/10/2023