Lecture 5 Cell Structure and Function Part 3.pptx
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Imam Mohammad Ibn Saud Islamic University
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Concept 7.5: Mitochondria and chloroplasts change energy from one form to another • Mitochondria are the sites of cellular respiration, the metabolic process that uses oxygen to generate ATP • Chloroplasts, found in plants and algae, are the sites of photosynthesis • Peroxisomes are oxidative organe...
Concept 7.5: Mitochondria and chloroplasts change energy from one form to another • Mitochondria are the sites of cellular respiration, the metabolic process that uses oxygen to generate ATP • Chloroplasts, found in plants and algae, are the sites of photosynthesis • Peroxisomes are oxidative organelles © 2021 Pearson Education Ltd. Mitochondria: Chemical Energy Conversion • Mitochondria are found in nearly all eukaryotic cells • They have a smooth outer membrane and an inner membrane folded into cristae • The inner membrane creates two compartments: intermembrane space and mitochondrial matrix • Some metabolic steps of cellular respiration are catalyzed in the mitochondrial matrix • Cristae present a large surface area for enzymes that synthesize ATP © 2021 Pearson Education Ltd. Chloroplasts: Capture of Light Energy • Chloroplasts contain the green pigment chlorophyll, as well as enzymes and other molecules that function in photosynthesis • Chloroplasts are found in leaves and other green organs of plants and in algae © 2021 Pearson Education Ltd. • Chloroplast structure includes – Thylakoids, membranous sacs, stacked to form a granum – Stroma, the internal fluid • The chloroplast is one of a group of plant organelles, called plastids © 2021 Pearson Education Ltd. Peroxisomes: Oxidation • It is not known how peroxisomes are related to other organelles • Peroxisomes are specialized metabolic compartments bounded by a single membrane • They contain enzymes that remove hydrogen atoms from various substances and transfer them to oxygen • This forms hydrogen peroxide • These reactions have many different functions © 2021 Pearson Education Ltd. • Functions of peroxisomes – Some use oxygen to break fatty acids into smaller molecules, eventually used for fuel for respiration – In the liver, they detoxify alcohol and other harmful compounds – Glyoxysomes in the fat-storing tissues of plant seeds, convert fatty acids to sugar to feed the emerging seedling © 2021 Pearson Education Ltd. Figure 7.19 © 2021 Pearson Education Ltd. Roles of the Cytoskeleton: Support and Motility • The cytoskeleton helps to support the cell and maintain its shape • It interacts with motor proteins to produce cell motility • Inside the cell, vesicles and other organelles can use motor protein “feet” to travel along tracks provided by the cytoskeleton © 2021 Pearson Education Ltd. Figure 7.21 © 2021 Pearson Education Ltd. Components of the Cytoskeleton • Three main types of fibers make up the cytoskeleton – Microtubules are the thickest of the three components of the cytoskeleton – Microfilaments, also called actin filaments, are the thinnest components – Intermediate filaments are fibers with diameters in a middle range © 2021 Pearson Education Ltd. Table 7.1 © 2021 Pearson Education Ltd. Microtubules • Microtubules are hollow rods about 25 nm in diameter and about 200 nm to 25 microns long • Microtubules are constructed of dimers of tubulin • Functions of microtubules: – Shaping the cell – Guiding movement of organelles – Separating chromosomes during cell division © 2021 Pearson Education Ltd. Centrosomes and Centrioles • In animal cells, microtubules grow out from a centrosome near the nucleus • In animal cells, the centrosome has a pair of centrioles, each with nine triplets of microtubules arranged in a ring • Other eukaryotic cells organize microtubules in the absence of centrosomes with centrioles © 2021 Pearson Education Ltd. Cilia and Flagella • Microtubules control the beating of flagella and cilia, microtubule-containing extensions that project from some cells • Many unicellular protists are propelled through water by cilia or flagella • Motile cilia are found in large numbers on a cell surface, whereas flagella are limited to one or a few per cell • Cilia and flagella differ in their beating patterns © 2021 Pearson Education Ltd. • Cilia and flagella share a common structure – A group of microtubules sheathed in an extension of the plasma membrane – Nine doublets of microtubules are arranged in a ring with two single microtubules in the center – A basal body that anchors the cilium or flagellum – A motor protein called dynein, which drives the bending movements of a cilium or flagellum © 2021 Pearson Education Ltd. Microfilaments (Actin Filaments) • Microfilaments are solid rods about 7 nm in diameter, built as a twisted double chain of actin subunits • A network of microfilaments helps support the cell’s shape • They form a cortex just inside the plasma membrane to help support the cell’s shape • Bundles of microfilaments make up the core of microvilli of intestinal cells © 2021 Pearson Education Ltd. Figure 7.25 © 2021 Pearson Education Ltd. Cell Walls of Plants • The cell wall is an extracellular structure that distinguishes plant cells from animal cells • Prokaryotes, fungi, and some protists also have cell walls • The cell wall protects the plant cell, maintains its shape, and prevents excessive uptake of water • Plant cell walls are made of cellulose fibers embedded in other polysaccharides and protein © 2021 Pearson Education Ltd. • Plant cell walls may have multiple layers: – Primary cell wall: Relatively thin and flexible, secreted first – Middle lamella: Thin layer between primary walls, containing polysaccharides called pectins – Secondary cell wall (in some cells): Added between the plasma membrane and the primary cell wall © 2021 Pearson Education Ltd. The Extracellular Matrix (ECM) of Animal Cells • Animal cells lack cell walls but are covered by an elaborate extracellular matrix (ECM) • The ECM is made up of glycoproteins such as collagen, proteoglycans, and fibronectin • Fibronectin and other ECM proteins bind to receptor proteins in the plasma membrane called integrins © 2021 Pearson Education Ltd.