ANHB1101 Cells PDF

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ANHB1101: The Cell Cells Measurements: 1 centimeter (cm) = 10 mm = 10-2 m 1 millimeter (mm) = 1000 µm = 10-3 m 1 micrometer (µm) = 1000 nm = 10-6 m 1 nanometer (nm) = 10-9 m Membrane: The plasma membrane consists primarily of phospholipid, cholesterol, and protein molecules. The phospholipid molecules form a bilayer. The hydrophobic (water hating) fatty acid chains of phospholipids face each other forming the inner portion of the membrane. The hydrophilic (water loving) polar heads of the phospholipids form the extracellular and intracellular surface of the membrane. Cholesterol molecules are incorporated within the gaps between the phospholipids. Proteins make up approximately 2% of the molecules of the plasma membrane but constitute approximately 50% of the membrane weight. Membrane Proteins: Peripheral proteins adhere to one face of the membrane and do not protrude into the phospholipid bilayer. Peripheral proteins are usually associated with a transmembrane protein. Transmembrane proteins (integral proteins) pass through the cell membrane. Some transmembrane proteins are anchored to the cytoskeleton while others drift feely in the phospholipid layer. Glycoproteins are transmembrane proteins joined with oligosaccharides (carbohydrate chains) on the extracellular side of the membrane. Channel proteins are transmembrane proteins or protein clusters with pores that allow the movement of water and ions through the membrane. Carrier proteins are transmembrane proteins which change shape when a solute binds to the protein, transferring the bound solute across the membrane to the other side. Transport Proteins: There are two major classes of membrane transport proteins: carrier proteins and channel proteins. Channel proteins are transmembrane proteins or protein clusters with pores that allow the movement of water and ions through the membrane. Carrier proteins are transmembrane proteins which change shape when a solute binds to the protein, transferring the bound solute across the membrane to the other side.

Membranous Organelles Endoplasmic Reticulum: The endoplasmic reticulum is a network of interconnecting channels (cisternae) within the cytoplasm. Rough endoplasmic reticulum (RER) is composed of parallel flattened sacs covered with ribosomes and is continuous with the outer membrane of the nuclear envelope. Smooth endoplasmic reticulum (SER) lacks ribosomes and is more extensively branched than RER. The cisternae of SER are tubular shaped and are connected with those of the RER. Golgi Complex: The Golgi complex appears as a small system of curved, flattened cisternae with swollen edges.

The edges of the Golgi complex become the membrane-bounded Golgi vesicles. Some Golgi vesicles become lysosomes, some become secretory vesicles and some migrate to the plasma membrane and fuse with it. Lysosomes and Peroxisomes: Lysosomes are vesicles containing enzymes which are bounded by a single unit membrane. They are produced by the Golgi complex and are usually round or oval in shape. Their contents usually appear dark grey in transmission electron micrographs. Peroxisomes resemble lysosomes but often appear lighter in colour than lysosomes. Peroxisomes are not produced by the Golgi.

Mitochondria: Mitochondria are bounded by a double unit membrane. The inner membrane has folds called cristae. Between the cristae is the matrix which contains ribosomes. Mitochondria are found in a wide variety of shapes. Nucleus: The nucleus is the largest organelle. It is usually spheroid or elliptical in shape (approx. 5μm in diameter). Most cells contain one nucleus though some may be anuclear (no nucleus) or multinucleate (more than one nucleus). The nucleus is surrounded by two unit membranes which form the nuclear envelope (nuclear membrane). The nuclear envelope is perforated with nuclear pores. Immediately inside the nuclear envelope is a narrow densely fibrous zone called the nuclear lamina. Inside the nucleus is the nucleoplasm which contains chromatin and one or more nucleoli. Ribosomes: Ribosomes are small granules of protein and RNA. They are found in the nucleoli, in the cytosol and on the outer surfaces of the rough endoplasmic reticulum and the nuclear envelope. Ribosomes are also found in the matrix of mitochondria. Ribosomes are not visible under a light microscope but appear as very small dark dots on transmission electron micrographs. Cell Surface Extension: Microvilli are extensions of the plasma membrane, approx. 1 - 2 μm long, which increase surface area. Microvilli can be long and dense, appearing as a fringelike brush border, or can be shorter, appearing as small bumps on the surface of the cell.

Cilia are hairlike processes approx. 7 - 10μm long. Cilia may be nonmotile or motile (beating in waves across the surface of an epithelium). Flagella (flagella/flagellum) are longer than cilia. In humans the only functional flagellum is the whip-like tail of sperm cells. Centrioles: A centriole is composed of a short cylinder of nine triplets of microtubules; these triplets are easily seen in a transverse section of the centriole. Centrioles are usually paired, with one centriole lying perpendicular to the other within a small clear area of the cytoplasm called the centrosome. The basal body of a flagellum or a cilium is a single centriole orientated perpendicular to the plasma membrane. The Cytoskeleton: Microfilaments - Microfilaments are approximately 6nm in diameter and are made of the protein actin. Microfilaments form a network on the cytoplasmic side of the plasma membrane forming a membrane skeleton called the terminal web. Actin microfilaments are sometimes found in microvilli attaching to the inside of the plasma membrane at the tip of the microvillus and extending down through the base of the microvillus into the terminal web. Microtubules - A microtubule is a cylinder of 13 parallel strands (protofilaments). Microtubules are 25nm in diameter. Nine microtubule pairs form the axonemes of cilia and flagella. Nine microtubule triplets form each centriole. Microtubules also form basal bodies and mitotic spindles. Intermediate Filaments - Intermediate filaments are 8 - 10nm in diameter. Intermediate filaments line the inside of the nuclear envelope forming the nuclear lamina enclosing the DNA....