Cell Structure and Organelles PDF

Cell Structure and Organelles "Essential Cell Biology" (authored by Bruce Alberts and seven others) Garland Science 2014  mitochondria Chromosome behavior Golgi apparatus cytoskeleton Cell membrane Prokaryotic Cell Structure and Function...

Cell Structure and Organelles "Essential Cell Biology" (authored by Bruce Alberts and seven others) Garland Science 2014  mitochondria Chromosome behavior Golgi apparatus cytoskeleton Cell membrane Prokaryotic Cell Structure and Function Gram-negative The Eukaryotic Cell Eukaryotic cells, in general, are bigger and more elaborate than bacteria and archaea. Some live independent lives as single-celled organisms, such as amoebae and yeasts; others live in multicellular assemblies. All of the more complex multicellular organisms—including plants, animals, and fungi—are formed from eukaryotic cells. "Essential Cell Biology" (authored by Bruce Alberts and seven others) Garland Science 2014 Ref: Prof. Dr. Yekbun Adıgüzel  https://faculty.cc.gatech.edu/~turk/bio_sim/articles/metabolic_pathways.png The complexity of a single cell Ref: Prof. Dr. Yekbun Adıgüzel All Eukaryotic Cells Have the Same Basic Set of Membrane-enclosed Organelles All Eukaryotic Cells Have the Same Basic Set of Membrane-enclosed Organelles All Eukaryotic Cells Have the Same Basic Set of Membrane-enclosed Organelles Eukaryotic Cell Structure and Function:  Cells form tissues in plants and animals (A) Cells in the root tip of a fern. The nuclei are stained red, and each cell is surrounded by a thin cell wall (light blue). (B) Cells in the urine-collecting ducts of the kidney. Each duct appears in this cross section as a ring of closely packed cells (with nuclei stained red). The ring is surrounded by extracellular matrix, stained purple. Ref: Prof. Dr. Yekbun Adıgüzel  Eukaryotic Cells Eukaryotic cells possess a nucleus and other organelles not found in prokaryotes. They probably The nucleus contains the genetic information of the 01 evolved in a series of stages, including the 02 eukaryotic organism, stored in DNA molecules. acquisition of mitochondria by engulfment of aerobic bacteria and (for plant cells) the acquisition of chloroplasts by engulfment of photosynthetic bacteria. The cytoplasm includes all of the cell’s contents Outside the membrane-enclosed organelles in the 03 outside the nucleus and contains a variety of membrane-enclosed organelles with specialized 04 cytoplasm is the cytosol, a very concentrated mixture of large and small molecules that carry out many functions: mitochondria carry out the final oxidation essential biochemical processes. of food molecules; in plant cells, chloroplasts perform photosynthesis; the endoplasmic reticulum and the Golgi apparatus synthesize complex molecules for export from the cell and for insertion in The cytoskeleton is composed of protein filaments that cell membranes; lysosomes digest large molecules. extend throughout the cytoplasm and are responsible for cell shape and movement and for the transport of organelles and other large molecular complexes from one location to another. "Essential Cell Biology" (authored by Bruce Alberts and seven others) Garland Science 2014 Yeasts are simple free-living eukaryotes The cells shown in this micrograph belong to the species of yeast, Saccharomyces cerevisiae, used to make dough rise and turn malted barley juice into beer. As can be seen in this image, the cells reproduce by growing a bud and then dividing asymmetrically into a large mother cell and a small daughter cell; for this reason, they are called budding yeast. How big is a cell and its components? -Most bacterial cells range from about 1 to 10 microns long. They require a relatively good light microscope to see. Viruses and macromolecules are much smaller, in the range of 1 to 100 nm thumb skin cells ribosomes usually beyond the power of the electron microscope  THE EUKARYOTIC CELL The Nucleus Is the Information Store of the Cell Mitochondria Generate Usable Energy from Food to Power the Cell Chloroplasts Capture Energy from Sunlight Internal Membranes Create Intracellular Compartments with Different Functions The Cytosol Is a Concentrated Aqueous Gel of Large and Small Molecules The Cytoskeleton Is Responsible for Directed Cell Movements The Cytoplasm Is Far from Static Eukaryotic Cells May Have Originated as Predators  Membrane-enclosed organelles are distributed throughout the eukaryotic cell cytoplasm The whole system of membrane-enclosed organelles is distributed throughout the cytoplasm. A variety of membrane-enclosed compartments exist in eukaryotic cells, each specialize in a different function. The rest of the cell excluding these organells are called cytosol, many metabolic activities (an aqueous gel of large and small molecules). In bacteria, it is the only intracellular compartment. It is the site of metabolic reactions. Early steps in the breakdown of nutrients takes place here. Lysosomes are small, irregularly shaped organelles, where intracellular digestion occur, releasing nutrients from digested materials. Peroxisomes are another type of organelle, which provide an environment for reactions with hydrogen peroxide (dangerously reactive) Plasma membrane: Sets a boundry for the cell Maintains cell homeostasis Communicates with the outer cell and other cells Maintains and supports cell shape Cytoskeleton: An array of fibrous proteins within the cytoplasm Three classes of fibers: A) Microtubules: polymers of tubulin (20 nm in diameter) B) Microfilaments: polymers of actin (7 nm in diameter) C) Intermediate filaments (10 nm in diameter) Maintain shape of the cell; control movement of structures witin the cell Very important function during cell division A B C Microtubules help distribute the chromosomes in a dividing cell Microtubules are thick hollow tubes. In dividing cells, they pull chromosomes in opposite directions to distribute into daughter cells. During division of cell, nuclear envelope disintegrates, DNA condenses to pairs of chromosomes, which are pulled by microtubules. When a cell divides, its nuclear envelope breaks down and its DNA condenses into visible chromosomes, each of which has duplicated to form a pair of conjoined chromosomes that will ultimately be pulled apart into separate cells by microtubules. In the transmission EM (left), the microtubules are seen to radiate from foci at opposite ends of the dividing cell. In the respiratory system, cilia trap and remove dirt (as well as mucous) from the lungs and other parts of this system. In the fallopian tube, on the other hand, cilia serve to move the ovum to the uterus. Flagella and cilia Nucleus: Rough Lumen of endoplasmic endoplasmic Plasma membrane reticulum reticulum Outer nuclear membrane Nuclear pore Ribosomal complex RNA synthesis Nucleolus and Nucleus ribosomal assembly Inner nuclear Ribosome membrane Chromatin Cytosol Nuclear lamina Introduction Extensive system of membrane-enclosed organelles of a typical animal cell The nucleus contains most of the DNA in a eukaryotic cell Nucleus is colored brown, the nuclear envelope is green, and the cytoplasm (the interior of the cell outside the nucleus) is white EM of the nucleus in a mammalian cell. Individual chromosomes are not visible because at this stage of the cell’s growth its DNA Ref: Prof. Dr. Yekbun molecules are dispersed as fine threads throughout the nucleus. Adıgüzel  Nucleus contains most of the DNA, i.e., genome. Organisms vary enormously in genome-size Genome size is measured in nucleotide pairs of DNA per haploid genome, that is, per single copy of the genome. (The body cells of sexually reproducing organisms such as ourselves are generally diploid: they contain two copies of the genome, one inherited from the mother, the other from the father.) Closely related organisms can vary widely in the quantity of DNA in their genomes (as indicated by the length of the green bars), even though they contain similar numbers of functionally distinct genes (that encode proteins)  Chromosomes become visible when a cell is about to divide Three stages of dividing cell cultured from lung. Under light microscope, DNA molecules become visible as chromosomes as they become compact for cell division. Prokaryotes have DNA dispersed in cytosol. As a eukaryotic cell prepares to divide, its DNA molecules become progressively more compacted (condensed), forming wormlike chromosomes that can be distinguished in the light microscope. Photographs show 3 successive steps in this process in a cultured cell from a newt’s lung; note that in the last micrograph on the right, the nuclear envelope has broken down. Endoplasmic Reticulum: a network of membranous tubules within the cytoplasm of a eukaryotic cell, continuous with the nuclear membrane. an extensive network of closed, flattened membrane-bounded sacs called cisternae The endoplasmic reticulum produces many of the components of a eukaryotic cell →EM of a thin section of a mammalian pancreatic cell (specialized for protein secretion) shows a small part of the ER. Note that the ER is continuous with the membranes of the nuclear envelope. The black particles studding the particular region of the ER shown here are ribosomes that translate RNAs into proteins. Ribosome-coated ER is often called “rough ER” to distinguish it from the “smooth ER,” which does not have ribosomes bound to it. Endoplasmic Reticulum Particularly important in the synthesis of lipids, secreted proteins and many types of membrane proteins. Smooth and Rough Endoplasmic Reticulum (SER and RER): SER: not associated with ribosomes. Fatty acid and phospholipid synthesis RER: associated with ribosomes. Synthesis of certain membrane and organelle proteins and all secreted proteins  The Golgi apparatus is composed of a stack of flattened discs Connected to ER, stacked membranes are Golgi apparatus. Golgi apparatus, also called 'Golgi Complex' or simply 'Golgi' is the stack of flattened sacs which are bound by a single membrane also known as cisternae. They are important for packaging and transporting the molecules from one compartment/organelle of the cell to another for secretion from the cell. The proteins are synthesized in ER, then passed to Golgi for modifications and packaged and sent to their destinations. EM that shows the Golgi apparatus from a typical animal cell Golgi complex: secreted and membrane bound proteins undergo a series of enzyme-catalyzed chemical modifications to gain full function.  Lysosomes: exclusive to animal cells, responsible for degradation of cellular components that are no longer wanted or needed. Autophagy: Autophagy (or autophagocytosis) is the natural, regulated mechanism of the cell that disassembles unnecessary or dysfunctional components. In phagocytosis, large, insoluble particles (e.g., bacteria) are enveloped by the plasma membrane and internalized. Lysosomes contain a group of enzymes that degrade polymers into their monomeric subunits. In plants, vacuoles... Plant Vacuole Most plant cells contain at least one membrane- limited vacuole that accumulates and stores water, ions, and small-molecule nutrients such as sugars and amino acids. A variety of membrane proteins in the vacuolar membrane allow the transport of these molecules from the cytosol and their retention in the vacuole lumen. Like that of a lysosome, the lumen of a vacuole contains degradative enzymes and has an acidic pH, which is maintained by similar transport proteins in the vacuolar membrane. Thus plant vacuoles may also have a degradative function similar to that of lysosomes in animal cells. Glyoxisomes: Oxidases produce hydrogen peroxide; hydrogen peroxide is degraded by catalase to yield water and oxygen.  Mitochondria Generate Usable Energy from Food to Power the Cell It is present in cytoplasm of all eukaryotic cell Animals, fungi , plants depend on mitochondria for energy Only few exceptions: anaerobic eukaryotes lack mitochondria  History 1857 Albert von Kolliker studied mitochondria in muscle cells 1894 Richard Altmann recognized them as organelle; "bioblasts" 1898 Carl Benda coined the term mitochondria "thread bodies" Nucleus is stained blue and mitochondria green in this cultured mammalian cell Figure 1-17 Essential Cell Biology (© Garland Science 2010) Mitochondria can be variable in shape and size This budding yeast cell, which contains a green fluorescent protein in its mitochondria, was viewed in a super-resolution confocal fluorescence microscope. In this 3-dimensional image, the mitochondria are seen to form complex branched networks.  Mitochondria have a distinctive structure 3D representation of arrangement of mitochondrial membranes shows the smooth outer membrane (gray) & the highly convoluted inner membrane (red)→ inner membrane contains most of the proteins responsible for cellular respiration & it is highly folded to provide a large surface area for this activity In this schematic cell, the interior space of the mitochondrion is colored orange EM of a cross section of a mitochondrion reveals the extensive infolding of the inner membrane Double membrane of present-day mitochondria is thought to have been derived from the plasma membrane and outer membrane of the engulfed bacterium Mitochondria: Main site of ATP (i.e. energy) production in aerobic cells In non-photosynthetic cells, the principal fuels for ATP synthesis are fatty acids and glucose.  Chloroplasts Chloroplasts in plant cells capture the energy of sunlight Chloroplasts Chloroplasts are large green organelles. About 5 times bigger than mitochondria. They are found in plant and algae cells, but not in fungi or animals. EM picture shows leaf cell from a moss, contains many green chloroplasts They have double membrane like mitochondria, but additionally internal stacks of membranes containing the green pigment, chlorophylls, that absorb light energy. Chloroplast: interconnected membrane limited vesicles which are flattened to form disks. Thylakoids often form stacks called grana and are embedded in an aqueous matrix termed the stroma. How do we determine the function of an organelle? Observations under microscope give relatively little indications for its function. To discover the function of organelles, cells are disrupted (broken open by homogenization), obtaining a soup of cell fragments. Spinning in a centrifuge, organelles can be separated according to their size and shape. Then, isolated organelle, e.g., mitochondria can be tested for what chemical process they could perform. These kind of experiments revealed that mitochondria oxidize sugars to produce ATP (energy currency of life). Mitochondria consumes O2 and release CO2 during this process. So, it is called respiration. Besides being surrounded by two membranes, chloroplasts and mitochondria have other features in common: Endosymbiosis Both often migrate from place to place within cells, Both contain their own DNA, which encodes some of the key organelle proteins. The proteins encoded by mitochondrial or chloroplast DNA are synthesized on ribosomes within the organelles.  Genes for 4 different rRNAs, 30 different tRNAs, 39 different proteins and 11 other predicted protein coding genes have been located. A comparison of mitochondria and chloroplast structures Animals can obtain energy by feeding on organic materials. But, plants can get energy directly from light. This is essential for life. Chloroplasts traps the energy in (by synthetizing) sugar molecules and release oxygen. So, all life (plants or animals) depends on this sugars and oxygen produced during photosynthesis. Figure 14-27 Essential Cell Biology (© Garland Science 2010)  Eukaryotic cells engage in continual endocytosis and exocytosis Endocytosis and exocytosis Cells obtain materials from outside (import) by capturing them in a vesicle that pinch off from the plasma membrane. These vesicles fuse with lysosomes for digestion. Cells can engulf very large materials like whole cells by this process. Cells export materials by exocytosis. Vesicles fuse with plasma membrane to release contents outside. Hormones, signalling molecules like neurotransmitters are secreted from the cells by exocytosis. In fact, materials are transported inside the cells, from one organell to another, by similar processes.