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Transcript
Cell Structure Karl A. Bettelheim Cell Structure Some statistics about cells. Estimated number of cells in the human body: 35 Trillion. Estimated number of different types of cells in the human body: 200. But this estimate is considered much to low. Cell Structure Definition of a Cell. A cell is a group of self sustaining biochemical reactions, that are isolated from the environment by a selectively permeable lipid membrane. Among the key reactions are those t hat maintain a stable intracellular concentration of ions. Cell Structure Sizes of Cells. Most plant and animal cells are visible only under a microscope, with dimensions between 1 and 100 micrometers They contain many organelles, which are distinct units of function. Cell Structure Contents of Cells. Water 80% Proteins 15% Structural Proteins Globular Proteins Remainder Lipids : Cellular membrane Energy source Carbohydrates Energy source Ions :potassium, magnesium, phosphate, sulphate & bicarbonate. Cell Structure Organelles. Within the cell are highly organized physical structures – organelles- which carry out specific functions. Cell Structure Organelles. The Cell Nucleus. Generally cells contain one nucleus, which contains the DNA, which carries the code of the proteins to be made by the cells. The DNA code is read and exits the nucleus as messenger RNA. Muscle cells have many nuclei. Cell Structure Organelles. The Nuclear Membrane/envelope. These two membranes surround the nucleus. They contain pores that regulate the entry and exit of molecules. Cell Structure Organelles. The Nucleolus . The nucleoli are not surrounded by a nuclear membrane. They contain RNA and protein components. Cell Structure Organelles. The Ribosomes(1). There are many ribosomes in the cell. They process the information in the messenger RNA and thus produce the encoded protein, which is then edited as required. The amount of a given protein to be made is regulated. Only proteins specifically required are made. Cell Structure Organelles. The Ribosomes(2). The ribosomes are large particles composed of about 70 proteins arranged in two subunits. They combine the amino acids into the proteins as required by the cell. Cell Structure Organelles. The Endoplasmic Reticulum (ER). The ER forms a network of membranes within the cell. There are two types: 1) The rough ER. 2) The smooth ER. Cell Structure Organelles. The Rough ER (1). The rough ER carries surface ribosomes. On these proteins are synthesized and they enter the lumen of the ER and they are either distributed within the cell or secreted to other cells. Cell Structure Organelles. The Smooth ER (2). The smooth ER does not carry ribosomes. On these fatty acids are synthesized and they regulate the cellular levels of Calcium ions, whi h i tur regulate a y of the ell’s activities. Cell Structure Organelles. The Golgi apparatus. These membranous sacs sort and modify proteins arriving from the granular ER, packaging them into vesicles before sending them to other organelles or secreting them. Cell Structure Organelles. The Mitochondria. These are double-membraned elongated ovoid elongated structures. The outer membrane is smooth and the inner is folded into tubes to increase surface area. Inside is DNA for mitochondrial protein synthesis. They make energy available to the cell. Cell Structure Organelles. The Lysosomes. These single-membraned oval organelles contain highly acidic digestive enzymes that break down bacteria, cell debris and dead organelles. Cell Structure Organelles. The Peroxysomes. These single-membraned oval organelles destroy the highly toxic compound hydrogen peroxide (H2O2), which is a by-product of some cellular activities. In the liver and kidney cells manufacture H2O2 and use it to destroy various ingested molecules. Cell Structure Organelles. The Filaments. The cytoplasm of most cells contains filaments –the cytoskeleton-, whi h ai tai the ell’s shape and produce cell movement. Cell Structure Cell Structure Cell Structure Similar to a bacterium. Muscle Cell Structure Muscle Cell Structure Nerve-fibre connection Muscle Cell Structure Muscle Cells. The basis of muscle movement is the interaction of two entities: Actin Myosin These operate within a structure called the Sarcomere. Muscle Cells. Nomenclature Muscle Cell Other Organismal Cells Sarcoplasm Cytoplasm Sarcoplasmic Reticulum Smooth Endoplasmic Reticulum Sarcosome Mitochondrion Sarcolemma Cell Membrane Muscle Cells. A sarcomere is the basic unit of striated muscle tissue. Skeletal muscles are composed of tubular muscle cells (myocytes called muscle fibers) which are formed in a process known as myogenesis. Muscle fibers are composed of tubular myofibrils. Muscle Cells. Muscle Cells. Muscle contraction based on sliding filament hypothesis. Muscle Cells. The Actin filament. Tropomysin and troponin are part of the actin filament. Muscle Cells. The Actin filament. The binding of the myosin heads to the muscle actin is a highly regulated process. The thin filament is made of actin, tropomyosin, and troponin. The contraction of skeletal muscle is triggered by nerve impulses that in turn stimulate the release of Ca2+ Troponin is attached to the protein tropomyosin and lies within the groove, between actin filaments in muscle tissue. In a relaxed muscle, tropomyosin blocks the attachment site for the myosin crossbridge, thus preventing contraction. Muscle Cells. Dystrophin a-DG Dystroglycan b-SG Sarcoglycan N Nitric oxide synthase ST Syntrophin a-, b- DG & SG: Dystroglycans & Sarcoglycan are glycosilated proteins in the surface membrane. NOS: Nitric oxide synthase synthesizes nitric oxide. ST: Syntrophin binds signalling molecules, such as NOS to dystrophin and dystrobrevin. Muscle Cells. Muscle Cells (1) Dystrophin is a protein located between the sarcolemma and the outermost layer of myofilaments in the muscle fiber (myofiber). It is a cohesive protein, linking actin filaments to another support protein that resides on the inside surface of each muscle fi er’s plasma membrane (sarcolemma). This support protein on the inside surface of the sarcolemma in turn links to two other consecutive proteins for a total of three linking proteins. The final linking protein is attached to the fibrous endomysium of the entire muscle fiber. Muscle Cells (2) Dystrophin supports muscle fiber strength, and the absence of dystrophin reduces muscle stiffness, increases sarcolemmal deformability, and compromises the mechanical stability of costameres and their connections to nearby myofibrils; as shown in recent studies where biomechanical properties of the sarcolemma and its links through costameres to the contractile apparatus were measured, and helps to prevent muscle fiber injury. Movement of thin filaments (actin) creates a pulling force on the extracellular connective tissue that eventually becomes the tendon of the muscle. Muscle Cells Thank you for your Attention.