Medical Biology Cytology/lec.4 Cytoplasmic organelles part2 03/03/1439 by:Farah E. Ismaeel

Mitochondria Mitochondria (singular, mitochondrion) are membrane-bounded organelles They are usually elongated structures. They are highly plastic, rapidly changing shape, fusing with one another and dividing, and are moved through the cytoplasm along microtubules. 03/03/1439 by:Farah E. Ismaeel

Mitochondria The number of mitochondria is related to the cell’s energy needs: cells with a high-energy metabolism (eg, cardiac muscle, liver cells and cells of some kidney tubules) have abundant mitochondria, whereas cells with a low-energy metabolism have few mitochondria such as small lymphocyte 03/03/1439 by:Farah E. Ismaeel

Mitochondria Mitochondria are often called the powerhouses of the cell. Just as a powerhouse burns fuel to produce electricity, the mitochondria convert the chemical energy of glucose products into the chemical energy of ATP molecules. In the process, mitochondria use up oxygen and give off carbon dioxide. Therefore, the process of producing ATP is called cellular respiration. 03/03/1439 by:Farah E. Ismaeel

The structure of mitochondria 03/03/1439 by:Farah E. Ismaeel

The structure of mitochondria each mitochondrion consists of : Outer membrane: is smooth membrane surrounded that allows entry of molecules and contain enzyme involved in mitochondrial lipid synthesis. Intermembrane space: (perimitochondrial space) Because of channels in the outer membrane of the mitochondria, the content of the intermembrane space is similar to that of the content of the cytoplasm. 03/03/1439 by:Farah E. Ismaeel

The structure of mitochondria Inner membrane: exhibit numerous folds called cristae which maximize internal surface area of mitochondria and contain most of the respiratory chain enzymes and ATP synthase which is responsible for cell respiration (oxidative phosphorylation) and production of cell ATP. Shape of cristea different according type of cells; in protein secreting cells cristea project into the interior of the organelle like shelves. In steroid secreting cells such as the adrenal cortex or interstitial cells in the testes, the mitochondria cristea are tubular. 03/03/1439 by:Farah E. Ismaeel

The structure of mitochondria 4. Mitochondrial matrix: the matrix is the space within the inner membrane; contain enzymes for Krebs cycle, mitochondrial DNA (circular DNA), special ribosome, tRNase and enzymes for gene expression. Mitochondrial DNA is double stranded and has a circular structure very similar to bacterial chromosomes, mitochondrial DNA synthesis and duplication is independent of nuclear DNA replication. Mitochondrial ribosome is smaller than cytosolic ribosome. tRNases are enzymes that degraded the tRNA. 03/03/1439 by:Farah E. Ismaeel

03/03/1439 by:Farah E. Ismaeel

03/03/1439 by:Farah E. Ismaeel

Mitochondria disorders A maternally-inherited mutation in the mitochondrial genome is leading to defective synthesis of respiratory chain proteins which can produce structural abnormal in muscle fibers specially skeletal muscle fibers are very sensitive to mitochondrial defect (muscular dysfunction) and other cells. (This called mitochondrial disorders) 03/03/1439 by:Farah E. Ismaeel

Replication of mitochondria Mitochondria replicate similarly to bacterial cells, when they get large, they undergo fission. This involves furrowing of the inner and then the outer membrane as if someone was pinching the mitochondrion. The two daughter cells of the mitochondria must first replicate the DNA. 03/03/1439 by:Farah E. Ismaeel

Function of mitochondria Mitochondria are primary sites for ATP synthesis (site of Krebs cycle) from organic material so that known as powerhouse of the cell. Cell respiration. Maintain body heat because some energy dissipated as heat. They have key role in apoptosis programmed cell death. Some mitochondrial functions are performed only in specific types of cells, e.g. mitochondria in liver cells contain enzymes that allow them to detoxify ammonia, a waste product of protein metabolism. 03/03/1439 by:Farah E. Ismaeel

Peroxisome Small membrane bounded organelle. Present in all cell type. Named for their enzymes producing and degrading hydrogen peroxide (H2O2), which is potentially damaging to the cell. Similar to lysosome but less dense and contain no hydrolytic enzyme but contain several types of oxidases and catalases enzymes 03/03/1439 by:Farah E. Ismaeel

03/03/1439 by:Farah E. Ismaeel

Peroxisome Oxidases enzyme that oxidized various organic substance to form hydrogen peroxide highly toxic product Catalase enzyme which eliminate excess hydrogen peroxide by breaking it down into water and oxygen molecule. These enzymes also inactivate various potentially toxic molecules, including some prescription drugs. 03/03/1439 by:Farah E. Ismaeel

organic substance OXIDASE H2O2 H2O2 CATALASE H2O + O2 03/03/1439 by:Farah E. Ismaeel

Peroxisome So that the peroxisome protect the cell from the cytotoxic product because the degradation of hydrogen peroxide occur in the same organelle Very abundant in the cell of liver and kidney. 03/03/1439 by:Farah E. Ismaeel

Peroxisome Peroxisomes form in two ways: Budding of precursor vesicles from the ER Or growth and division of preexisting peroxisomes. These organelles lack nucleic acids; their enzymes are synthesized on free cytosolic polyribosomes and bear a small signal sequence of amino acids at the carboxyl terminus. This signal is recognized by receptors located in the peroxisomal membrane and the proteins are imported. by:Farah E. Ismaeel

peroxisomal disoreders Deficiencies of peroxisomal enzymes cause what is called peroxisomal disoreders (exp: Zellweger syndrome) that affects the structure and functions of several organ systems, producing symptoms of the disease. 03/03/1439 by:Farah E. Ismaeel

Non membrane bounded organelles 03/03/1439 by:Farah E. Ismaeel

Ribosomes Ribosomes are membrane naked organelles present in all cells types( prokaryotes and eukaryotes) Ribosomes are small electron-dense particles composed of proteins and rRNA. All ribosomes have two subunits of different sizes and act to catalyze the process of protein translation (Protein synthesis), so that is more abundant in protein secreting cells. 03/03/1439 by:Farah E. Ismaeel

03/03/1439 by:Farah E. Ismaeel

Ribosomes In eukaryotic cells, the rRNA molecules of both subunits are synthesized within the nucleus. Their numerous proteins are synthesized in the cytoplasm but then enter the nucleus and associate with rRNAs. The assembled large and small subunits then leave the nucleus and enter the cytoplasm to participate in protein synthesis. 03/03/1439 by:Farah E. Ismaeel

Ribosomes are often attached to the endoplasmic reticulum; but they also may occur free within the cytoplasm, either singly or in groups called polyribosomes or polysomes. 03/03/1439 by:Farah E. Ismaeel

Attached ribosomes are synthesis any proteins that packaged or release from the cells as secretary product While free polyribosome synthesis protein that use within the cell such as enzymes of peroxisome and enzymes of glycolysis. 03/03/1439 by:Farah E. Ismaeel

Proteasomes Proteasomes are very small abundant protein complexes composed of three subunits : two regulatory particles and one core particle Non membranous organelle that degrades some protein molecules that attached to Upiquitin protein by ATP dependent pathway. 03/03/1439 by:Farah E. Ismaeel

03/03/1439 by:Farah E. Ismaeel

Functions Of Proteasomes degrade excess enzyme Degrade denatured or otherwise nonfunctional polypeptides remove proteins no longer needed by the cell and provide an important mechanism for restricting activity of a specific protein to a certain window of time. Destroy protein infected by viruses. Whereas lysosomes digest organelles or membranes by autophagy, proteasomes deal primarily with free proteins as individual molecules. 03/03/1439 by:Farah E. Ismaeel

Clinical application on proteasomes Failure of proteasomes or other aspects of a cell’s protein quality control can allow large aggregates of protein to accumulate in affected cells. Such aggregates may adsorb other macromolecules to them and damage or kill cells. Aggregates released from dead cells can accumulate in the extracellular matrix of the tissue. In the brain this can interfere directly with cell function and lead to neurodegeneration. Alzheimer disease and Huntington disease are two neurologic disorders caused initially by such protein aggregates. 03/03/1439 by:Farah E. Ismaeel

Thank you for listening 03/03/1439 by:Farah E. Ismaeel