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Transcript
The Amazing Cell, Part 2 Cytoplasm • The inner substance of the cell, excluding the nucleus. • Components include: • • • • Cytosol Cytoskeleton Organelles Inclusions Cytosol • The fluid of the cell • Viscous (thick, sticky consistency), • Semi-transparent liquid composed of dissolved electrolytes, amino acids, and simple sugars. • Proteins suspended within fluid give fluid its thick, jellylike consistency. • Proteins within the cytosol are enzymes that are important in metabolic activities of the cell. Cytoskeleton • Three dimensional frame/structure for the cells • It is neither rigid or permanent. • Flexible and fibrous; changes in accordance to activities of the cell. • Gives support and shape to the cell, enables cell to move and provides direction for metabolic activity. • Also anchors organelles • These fibers are not enclosed in a membrane • Types of fibers that comprise cytoskeleton: • Microtubules • Intermediate fibers • Microfilaments Microtubules • • • • Thickest fibers, protein, and are long and hollow Grow out from the cell center, near nucleus Form cables that organelles attach too. Proteins move these organelles along microtubules throughout cell, like a railroad track for the organelles • Can be easily disassembled and re-asembled to form new paths or take on new direction • Composed of a pair of spherical molecules -tubulins, which are linked together in a spiral chain Intermediate Fibers • Woven, ropelike fibers that possess high tensile strength • Are able to resist pulling forces on the cell by acting as internal guy wires • Toughest and most permanent part of the cytoskeleton • Composed of proteins - variable depending on cell function • May take on different names: • Tonofilaments-in epithelial cells, mostly keratin • Neurofilaments- in nerve cells Microfilaments •Located near cell surface on the cytoplasmic side of the plasma membrane. •Are arranged in bundles and meshworks. •Provide tensional support like cables on a bridge •Composed of the contracticle protein actin and the motor protein myosin •Play key role in cell’s ability to change shape, break apart during cell division and form outpouchings and involutions. •Are assembled where and when needed. •Cell’s activity determines how many and where microfilaments are position Organelles • “little organs” • Membrane bound structures within cytoplasm that have specialized functions. • Is separated from cytoplasm it’s own membrane so can maintain own internal environment. • Do not have glycocaylx coating • Compartmentalization is good for metabolic processes such as food absorption, energy production, and excretion. • • • • • • Mitochondria Ribosomes Golgi Apparatus Endoplasmic Reticulum Lysosomes Peroxisomes Mitochondria POWERHOUSE • One of largest organelles • Called “powerhouse of the cell” because produces up to 95% of energy that fuels the cell. • Nutrient molecules (i.e. glucose) are broken down to produce intracellular fuel. • Location of many biochemical reactions. • Amino acid and fat catabolism • Where respiration takes place • Oxygen consumed • Carbon Dioxide released Mitochondria • Active cells have higher energy demands so have more mitochondria. • Heart cells • Mitochondria can divide through fission-or the pinching themselves in half. • Tend to be located at portion of cell where energy requirements are the greatest. • Contain DNA, RNA and enzymes. • DNA and RNA are similar to those found in bacteria • Provide selves with 13 proteins while nucleus provides the remaining 50. Where are the Mitochondria Mitochondrial shape • Tend to be elliptical and round • Outer smooth membrane • Inner involuted membrane. • Inner membrane forms cristae which increase internal working area and matrix (enzyme-rich liquid housed in mitochondria). • Cristae are site of ATP production • Active mitochondria possess more cristae than inactive ones. Ribosomes • Most common organelle in the cell. • Made of two globular subunits that fit together. • Composed of protein and rRNA. • Small, but important in the synthesis of proteins for intracellular use. • Can attach and detach from membranes and move freely within the cell. • Move back and forth between endoplasmic reticulum and cytoskeleton depending on type of protein they are making. Endoplasmic Reticulum Endoplasmic Reticulum (ER) - Factory • Series of flattened membranes stacked on one another and bent into crescent shape. • Composed of single lipid bi-layer • Continuous with the membranes of the nucleus and golgi apparatus • May be rough or smooth depending on if it contains ribosomes or not. • Rough ER is involved in production of protein assembled by ribosomes • New Proteins are moved inside ER into passageways. • Cisternae -Location of protein modification before being moved to Golgi. • Smooth ER is connected to Rough ER and is active in synthesis and storage of lipids (phospholipids and steroids) • In liver may also break down drugs and break down glycogen into glucose => detoxification • Proportion of smooth to rough ER varies depending on the cell’s synthetic activities. Golgi Apparatus – Shipping! • Found near nucleus and is similar in structure to ER (composed of cisternae) • Receives proteins produced by ER via transfer sacs. • Proteins are modified (add carbohydrates) here as they move from fold to fold. • Once completed they are packaged into vesicles and travel out into other parts of the cell or to cell membrane. • Act as the modification, packaging and distribution center. • Also functions to synthesize polysaccharides. Lysosomes • Specialized vesicle formed by Golgi apparatus. • Contains hydrolytic or digestive enzymes • Lysosome fuses with other vesicles and digests them. • Principal responsibility to breakdown nutrient molecules and digestion of cellular debris. • Considered “stomach of the cell”. • When cells die, lysosomes are triggered to burst, release digestive enzymes and digest other portions of the cell. • This is called autolysis. • May also release enzymes outside of cell to assist with breakdown of extracellular material. • Increase in numbers as cell ages. Lysosome Action 1. Material from outside is drawn into a forming vesicle. 2. Plasma membrane pinches off vesicle 3. Vesicle transports material into cell 4. Lysosome approaches 5. Lysosome fuses with vesicle and inserts its digestive enzymes 6. Contents of vesicle are digested and transported to other regions of the cell. Peroxisomes • Membranous sacs containing enzymes found throughout the cell. • Reproduce through pinching in half. • Common in liver and Kidney cells • Important in detoxification of various molecules. • Remove free radicals- normal products of cellular metabolism but can be harmful in large numbers • Carry two major enzymes: • Peroxidases-assist in conversion in free radicals to hydrogen peroxide. • Catalases-reduce hydrogen peroxide to water. Inclusions • Packaged units of metabolic products or substances that the cell has engulfed. • May or may not be membrane-bound. • Vacuoles are larger than vesicles but are of similar structure. Centrioles • Small, hollow-like cylinders composed of microtubules. • Found in pairs perpendicular to one another. • Visible during cell division near nuclear envelope • Help to organize spindle fibers during cell division. • May also form bases of cilia and flagella (basal bodies). Nucleus • Largest organelle in the cell. • Control center or “brain” of the cell. • Primary functions are to maintain hereditary information of the species and to control cellular activities through protein synthesis. • Some cells may be multi-nucleated while some are anucleated. • What is this and where is it found? • What is a disadvantage to no nucleus? Nuclear Anatomy • Divided into four parts: • • • • Nuclear Envelope or membrane Nucleoplasm Chromatin Nucleoli Nuclear Envelope and Nucleoplasm • Separated from cytosol by a nuclear envelope composed of two lipid bilayers • Outer layer is continuous with Rough ER. • Contains nuclear poreschannel through entire thickness. • Allow transport of protein and RNA. • Area between bilayers is space called perinuclear space. Nucleoplasm • The gel-like substance that fills the nucleus. • Resembles cytosol. DNA, RNA and Chromatin • DNA and RNA are composed of nucleotides. • What are they? • How do they pair? • What does DNA form? • Chromatin-fibers made up of DNA and globular proteins called histones • Nucleosome- single strand of DNA wound around 8 histone molecules. • During cell divison, chromatin condenses into super-coiled, x-shaped structure called chromosomes. Nucleoli • Not membrane bound • Where ribosomal subunits are made • Contain DNA that governs synthesis of rRNA.