* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download CHAPTER 6 A TOUR OF THE CELL
Survey
Document related concepts
Biochemical switches in the cell cycle wikipedia , lookup
Microtubule wikipedia , lookup
Cell encapsulation wikipedia , lookup
Cytoplasmic streaming wikipedia , lookup
Cellular differentiation wikipedia , lookup
Cell culture wikipedia , lookup
Extracellular matrix wikipedia , lookup
Cell growth wikipedia , lookup
Organ-on-a-chip wikipedia , lookup
Signal transduction wikipedia , lookup
Cell membrane wikipedia , lookup
Cytokinesis wikipedia , lookup
Cell nucleus wikipedia , lookup
Transcript
CHAPTER 6 A TOUR OF THE CELL 6.2: Eukaryotic cells have internal membranes that compartmentalize their functions A Panoramic View of the Eukaryotic Cell A Panoramic View of the Eukaryotic Cell • In addition to the plasma membrane, a eukaryotic cell has extensive internal membranes which: Partition the cell into compartments. Participate in the cell’s metabolic reaction since many enzymes are built into the membranes. Have the basic structure of a biological membrane (a double layer of phospholipids) with unique lipid and protein compositions depending upon their specific functions. - For example, those in the membranes of mitochondria function in cellular respiration B- Eukaryotic Cell Eu: True Karyon: Nucleus Animal Cell Plant Cell Compare between Animal and Plant cell? Page 100 - 101 Fig. 7.7 An Animal Cell Fig. 7.8 A Plant Cell Cell Organelles The eukaryotic cell’s genetic instructions are housed in the nucleus and carried out by the ribosomes The Nucleus: Genetic Library of the Cell • The nucleus contains most of the genes in a eukaryotic cell. • The nucleus averages about 5 µm in diameter. • The nucleus is separated from the cytoplasm by a double membrane that is called the “nuclear envelope”: • The nuclear membrane contains pores that allow large macromolecules and particles to pass through. • The nuclear membrane is maintaining the shape of the nucleus Fig. 6.10 • The nucleus contains DNA organized with proteins into a complex called chromatin: • In non-dividing cell chromatin appear as diffuse mass. • when the cell prepares to divide, the chromatin fibers coil up to be seen as separate structures, chromosomes. • Each eukaryotic species has a characteristic number of chromosomes. – A typical human cell has 46 chromosomes, but sex cells (eggs and sperm) have only 23 chromosomes. • Nucleolus is a dark region involved in production of ribosomes. •The nucleus directs protein synthesis by synthesizing messenger RNA (mRNA). • The mRNA travels to the cytoplasm and combines with ribosomes to translate its genetic message into the primary structure of a specific polypeptide: The nucleus controls protein synthesis in the cytoplasm: Messenger RNA (mRNA) synthesized in the nucleus by DNA instructions mRNA passes through nuclear pores into cytoplasm Attaches to ribosomes where the genetic message is translated into primary structure of specific protein Ribosomes: Protein Factories in the Cell • Ribosomes made of rRNA and protein. • Carry out protein synthesis • A ribosome is composed of two subunits. Fig. 7.10 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • In the nucleolus, ribosomal RNA (rRNA) is synthesized and assembled with proteins from the cytoplasm to form large and small ribosomal subunits. • The subunits pass from the nuclear pores to the cytoplasm where they combine to form ribosomes. • Cell types active in proteins synthesis (e.g., pancreas) have large numbers of ribosomes and prominent nucleoli. • Both ribosomes and nucleoli are not enclosed in membrane. • Types of Ribosomes:Ribosomes:1) Free ribosomes are suspended in the cytosol and synthesize proteins that function within the cytosol. 2) Bound ribosomes are attached to the outside of the endoplasmic reticulum. – These synthesize proteins that are either included into membranes or for secretion outside the cell. • Ribosomal subunits are structurally identical and can shift between the two roles. CHAPTER 6 A TOUR OF THE CELL The Endomembrane System Regulates protein traffic and Performs metabolic functions in the cell Many of the internal membranes in a eukaryotic cell are part of the endomembrane system. These membranes have diverse functions and structures. The endomembrane system includes: a) b) c) d) endoplasmic reticulum Golgi apparatus lysosomes vacuoles A-The endoplasmic reticulum: (Biosynthetic Factory) The endoplasmic reticulum (ER)includes network of membranous tubules and internal, fluid-filled spaces, the cisternae which separates its internal lumen from the cytosol. There are two, connected, regions of ER that differ in structure and function: • Smooth ER looks smooth because it lacks ribosomes. • Rough ER looks rough because bound ribosomes are attached to the outside of the nuclear envelope. Fig. 6.11 Functions of Smooth ER 1. Synthesis of lipids including phospholipids and steroids : e.g. Vertebrate sex hormones and steroids hormones . 2. Smooth ER in liver cells : a - Contain an embedded enzyme catalyzing the final step in the conversion of glycogen to glucose. b - Contain enzymes which detoxify drugs and poisons. 3. Smooth ER in muscle cells are rich in enzymes that pump calcium ion from the cytosol to the cisternae: i-e, store calcium ion necessary for muscle contraction . Rough ER and synthesis of secretory proteins 1 - Rough ER is continuous with the nuclear envelope. 2 - Manufactures secretory proteins and membrane . 3 - Rough ER makes its own membrane phospholipids. 4- Ribosomes bound to rough ER manufacture the secretory proteins. 5 - These secretory protein departs in transport vesicles from the ER membrane to other parts of the cell. Rough ER and secretory proteins synthesis: Ribosome bound to rough ER synthesize secretory proteins Growing polypeptide is passed from ribosomes through ER membrane into cisternal space Inside cisternal space, new protein folds into its native conformation If the new protein is a glycoprotein, it covalently bonds to an oligosaccharide in the ER Secretory protein departs in transport vesicles from transitional ER to another part of the cell Glycoprotein: = Protein covalently bonded to carbohydrate. Oligosaccharide = Small polymer of sugar units Transport vesicles = Membrane vesicle in transit from one part of the cell to another. Transitional ER = Specialized region of the ER where from transport vesicles are pinched off. B. The Golgi apparatus finishes, sorts, and ships cell products The Golgi apparatus consists of flattened membranous sacs (cisternae). The Golgi apparatus is abundant in cells specialized for secretion. Many transport vesicles from the ER travel to the Golgi apparatus for the modification of their contents. The function of Golgi apparatus • It is a center of manufacturing, warehousing, sorting, and shipping materials outside the cell. • It alters some membrane phospholipids. • It modifies the oligosaccharide portion of the glycoproteins. Fig. 6.12 C. Lysosomes: Digestive compartments The lysosome is a membrane-bounded sac of hydrolytic enzymes that digests all macromolecules.Fig.6.13 . Hydrolytic enzymes (including; lipases, carbohydrases, proteases and nucleases ) are synthesized in the rough ER and processed further in the Golgi apparatus then to the lysosomes. The optimal pH of these lysosomal enzymes is about pH 5 (acidic). Functions of Lysosomes: 1- Intracellular digestion Lysosomes may fuse with food-filled vacuoles, and their hydrolytic enzymes digest the food by a process called phagocytosis. Phagocytosis = Cellular process of ingestion, where the plasma membrane engulfs particulate substances and pinches off to form a particle-containing vacuole. Fig. 6.14 2. Recycle cell's own organic material (autophagy). Autophagy = A process by which lysosomes engulf other cellular organelles or part of the cytosol and digest them with hydrolytic enzymes. The resulting monomers are released into the cytosol where they can be recycled into new macromolecules. Fig. 6.14 Fig. 6.14 D-Vacuoles: Diverse Maintenance Compartments Vacuoles are membrane-bound sacs that is larger than a vesicle (transport vesicle). A plant or fungal cell may have one or several vacuoles. Vacuole Types and Functions: • Food vacuoles are formed by phagocytosis, fuse with the lysosomes and it is the site of the intracellular digestion in some protists . • Contractile vacuoles are found in freshwater protozoa, pump excess water out of the cell. • Central vacuoles are found in many mature plant cells.Fig.6.14 Fig. 6.15 Other membranous Organelles A – Mitochondria: Mitochondria are organelles that convert energy acquired from the surroundings into forms useable for the cellular work. They are the sites of cellular respiration, generating ATP from the catabolism of sugars, fats, and other fuels in the presence of oxygen. Almost all the eukaryotic cells have mitochondria. Structure of the Mitochondrion: Enclosed by two membranes that are not part of the endomembrane system . Their membranes are made by the free ribosomes in the cytosol and also by their own ribosomes. The outer membrane is smooth. The inner membrane is convoluted with infoldings called cristae. The inner membrane encloses the matrix , a fluid-filled space that contains mitochondrial DNA , ribosomes and enzymes . Fig. 6.17 Fig. 6.17 B - Peroxisomes: They are specialized metabolic compartments bounded by a single membrane,contain enzymes that transfer hydrogen from various substrates to oxygen. An intermediate product of this process is hydrogen peroxide (H2O2), a poison, but the peroxisome has another enzyme that converts H2O2 to water. Some peroxisomes break fatty acids down to smaller molecules that are transported to mitochondria for fuel. Peroxisomes in the liver detoxify alcohol and other harmful compounds.Fig.6.18 Fig. 6.18 The Cytoskeleton • The cytoskeleton is a network of fibers extending throughout the cytoplasm. • The cytoskeleton organizes the structures and activities of the cell . Fig. 6.21 The cytoskeleton Role: Support, Motility and Regulation • The cytoskeleton provides mechanical support and maintains shape of the cell. • The cytoskeleton provides anchorage for many organelles and cytosolic enzymes. The cytoskeleton is dynamic, dismantling in one part and reassembling in another to change cell shape. The cytoskeleton interacts with motor proteins. • • Fig. 6.21a • • • • In cilia and flagella motor proteins pull components of the cytoskeleton past each other. This is also true in muscle cells. Motor protein molecules also carry vesicles or organelles to various destinations along “monorails’ provided by the cytoskeleton. Interactions of motor proteins and the cytoskeleton circulates materials within a cell via streaming. There are three main types of fibers in the cytoskeleton: microtubules, microfilaments, and intermediate filaments. Fig. 6.21 b Centrosomes and Centrioles • In animal cells, the centrosome has a pair of centrioles, each with nine triplets of microtubules arranged in a ring. • In many cells, microtubules grow out from a centrosome near the nucleus. • During cell division the centrioles replicate. Fig. 6.22 Cilia and Flagella Locomotor organelles protrude from some eukaryotic cells formed from microtubules • Microtubules are the central structural supports in cilia and flagella. • Both cilia and flagella can move unicellular(protista) and small multicellular organisms (sperms) by moving water past the organism. • If these structures are anchored in a large structure, they move fluid over a surface. cilia sweep mucus carrying trapped debris from the lungs. Fig. 6.2 Flagella • • • There are usually just one or a few flagella per cell. A flagellum has an undulatory movement. Flagella are the same width as cilia, but 10-200 microns long. • Force is generated parallel to the flagellum’s axis. Fig. 6.23a Cilia • • • • Cilia usually occur in large numbers on the cell surface. They are about 0.25 microns in diameter and 2-20 microns long. Cilia move more like oars with alternating power and recovery strokes. They generate force perpendicular to the cilia’s axis. Fig. 6.23b Ultrastructure of a eukaryotic flagellum or cilium • Both have similar ultrastructure core of microtubules sheathed by the plasma membrane. • Nine doublets of microtubules arranged around a pair at the center, the “9 + 2” pattern. • The structure of cilium and flagellum is identical to that of centriole centriole.. Fig. 6.24 Microfilaments (Actin filaments) Fig. 6.26 The shape of the microvilli in this intestinal cell are supported by microfilaments, anchored to a network of intermediate filaments.