utf-8''Lecture_05_BIO1003_Cell%20Structure%20and%20Function_DC_2024-2025.pdf

BAU MBG BIO1003 General Biology Lecture 5 Cell Structure and Function Dr. Dilek ÇEVİK © 2021 Pearson Educa...

BAU MBG BIO1003 General Biology Lecture 5 Cell Structure and Function Dr. Dilek ÇEVİK © 2021 Pearson Education Ltd. Figure 7.1a © 2021 Pearson Education Ltd. Figure 7.1b © 2021 Pearson Education Ltd. Concept 7.1: Biologists use microscopes and biochemistry to study cells Cells are usually too small to be seen by the naked eye It is helpful to understand how cells are studied © 2021 Pearson Education Ltd. Microscopy Microscopes are used to visualize cells In a light microscope (LM), visible light is passed through a specimen and then through glass lenses Lenses refract (bend) the light so that the image is magnified © 2021 Pearson Education Ltd.  Three important parameters of microscopy: – Magnification, the ratio of an object’s image size to its real size – Resolution, the measure of the clarity of the image, or the minimum distance of two distinguishable points – Contrast, visible differences in brightness between parts of the sample © 2021 Pearson Education Ltd. Figure 7.2 © 2021 Pearson Education Ltd. Figure 7.3 Exploring microscopy © 2021 Pearson Education Ltd. Cell Fractionation Cell fractionation takes cells apart and separates the major organelles from one another Centrifuges fractionate cells into their component parts (differential centrifugation) © 2021 Pearson Education Ltd. Figure 7.4 Research method: cell fractionation © 2021 Pearson Education Ltd. Concept 7.2: Eukaryotic cells have internal membranes that compartmentalize their functions The basic structural and functional unit of every organism is one of two types of cells: prokaryotic or eukaryotic Only organisms of the domains Bacteria and Archaea consist of prokaryotic cells Protists, fungi, animals, and plants all consist of eukaryotic cells © 2021 Pearson Education Ltd. Comparing Prokaryotic and Eukaryotic Cells Basic features of all cells: – Plasma membrane – Semifluid substance called cytosol – Chromosomes (carry genes) – Ribosomes (make proteins) © 2021 Pearson Education Ltd.  Prokaryotic cells are characterized by having – No nucleus – DNA in an unbound region called the nucleoid – No membrane-bound organelles – Cytoplasm bound by the plasma membrane © 2021 Pearson Education Ltd. Figure 7.5 A prokaryotic cell © 2021 Pearson Education Ltd.  Eukaryotic cells are characterized by having – DNA in a nucleus that is bounded by a double membrane – Membrane-bound organelles – Cytoplasm in the region between the plasma membrane and nucleus Eukaryotic cells are generally much larger than prokaryotic cells © 2021 Pearson Education Ltd.  Metabolic requirements set upper limits on the size of cells The plasma membrane is a selective barrier that allows sufficient passage of oxygen, nutrients, and waste to service the volume of every cell The surface area to volume ratio of a cell is critical As a cell increases in size, its volume grows proportionately more than its surface area © 2021 Pearson Education Ltd. Figure 7.6 © 2021 Pearson Education Ltd. Figure 7.7 © 2021 Pearson Education Ltd. A Panoramic View of the Eukaryotic Cell A eukaryotic cell has internal membranes that divide the cell into compartments—the organelles The cell’s compartments provide different local environments so that incompatible processes can occur in a single cell The basic fabric of biological membranes is a double layer of phospholipids and other lipids Plant and animal cells have most of the same organelles © 2021 Pearson Education Ltd. Figure 7.8 A Panoramic View of the Eukaryotic Cell © 2021 Pearson Education Ltd. BioFlix® Animation: Tour of an Animal Cell © 2021 Pearson Education Ltd. BioFlix® Animation: Tour of a Plant Cell © 2021 Pearson Education Ltd. Concept 7.3: The eukaryotic cell’s genetic instructions are housed in the nucleus and carried out by the ribosomes The nucleus contains most of the DNA in a eukaryotic cell Ribosomes use the information from the DNA to make proteins © 2021 Pearson Education Ltd. The Nucleus: Information Central The nucleus contains most of the cell’s genes and is usually the most conspicuous organelle The nuclear envelope encloses the nucleus, separating it from the cytoplasm The nuclear envelope is a double membrane; each membrane consists of a lipid bilayer © 2021 Pearson Education Ltd. Figure 7.UN01 © 2021 Pearson Education Ltd. Figure 7.9 The nucleus and its envelope © 2021 Pearson Education Ltd.  Pores, lined with a structure called a pore complex, regulate the entry and exit of molecules from the nucleus The nuclear side of the envelope is lined by the nuclear lamina, which is composed of proteins and maintains the shape of the nucleus There is evidence for a nuclear matrix, a framework of protein fibers throughout the interior of the nucleus © 2021 Pearson Education Ltd.  In the nucleus, DNA is organized into discrete units called chromosomes Each chromosome contains one DNA molecule associated with proteins, called chromatin Chromatin condenses to form discrete chromosomes as a cell prepares to divide The nucleolus, located within the nucleus, is the site of ribosomal RNA (rRNA) synthesis © 2021 Pearson Education Ltd. Ribosomes: Protein Factories Ribosomes are complexes made of ribosomal RNA and protein Ribosomes build proteins in two locations: – In the cytosol (free ribosomes) – On the outside of the endoplasmic reticulum or the nuclear envelope (bound ribosomes) © 2021 Pearson Education Ltd. Figure 7.10 Ribosomes © 2021 Pearson Education Ltd. Concept 7.4: The endomembrane system regulates protein traffic and performs metabolic functions The endomembrane system consists of – Nuclear envelope – Endoplasmic reticulum – Golgi apparatus – Lysosomes – Vacuoles – Plasma membrane These components are either continuous or connected via transfer by vesicles © 2021 Pearson Education Ltd. The Endoplasmic Reticulum: Biosynthetic Factory The endoplasmic reticulum (ER) accounts for more than half of the total membrane in many eukaryotic cells The ER membrane is continuous with the nuclear envelope There are two distinct regions of ER: – Smooth ER, which lacks ribosomes – Rough ER, whose surface is studded with ribosomes © 2021 Pearson Education Ltd. Figure 7.11 Endoplasmic reticulum (ER) © 2021 Pearson Education Ltd. Functions of Smooth ER The smooth ER – Synthesizes lipids – Detoxifies drugs and poisons – Stores calcium ions © 2021 Pearson Education Ltd. Functions of Rough ER The rough ER – Has bound ribosomes, which secrete glycoproteins (proteins covalently bonded to carbohydrates) – Distributes transport vesicles, secretory proteins surrounded by membranes – Is a membrane factory for the cell © 2021 Pearson Education Ltd. The Golgi Apparatus: Shipping and Receiving Center The Golgi apparatus consists of flattened membranous sacs called cisternae The Golgi apparatus – Modifies products of the ER – Manufactures certain macromolecules – Sorts and packages materials into transport vesicles © 2021 Pearson Education Ltd. Figure 7.12 The Golgi apparatus © 2021 Pearson Education Ltd. Lysosomes: Digestive Compartments A lysosome is a membranous sac of hydrolytic enzymes that can digest macromolecules Lysosomal enzymes work best in the acidic environment inside the lysosome Hydrolytic enzymes and lysosomal membranes are made by rough ER and then transferred to the Golgi apparatus for further processing Some lysosomes probably arise by budding from the trans face of the Golgi apparatus © 2021 Pearson Education Ltd.  Some types of cell can engulf another cell by phagocytosis; this forms a food vacuole A lysosome fuses with the food vacuole and digests the contents Lysosomes also use enzymes to recycle the cell’s own organelles and macromolecules, a process called autophagy © 2021 Pearson Education Ltd. Figure 7.13 Lysosomes © 2021 Pearson Education Ltd. Vacuoles: Diverse Maintenance Compartments Vacuoles are large vesicles derived from the ER and Golgi apparatus Vacuoles perform a variety of functions in different kinds of cells © 2021 Pearson Education Ltd.  Food vacuoles are formed by phagocytosis Contractile vacuoles, found in many freshwater protists, pump excess water out of cells Central vacuoles, found in many mature plant cells, contain a solution called sap It is the plant cell’s main repository of inorganic ions, including potassium and chloride The central vacuole plays a major role in the growth of plant cells © 2021 Pearson Education Ltd. Figure 7.14 © 2021 Pearson Education Ltd. The Endomembrane System: A Review The endomembrane system is a complex and dynamic player in the cell’s compartmental organization © 2021 Pearson Education Ltd. Figure 7.15 © 2021 Pearson Education Ltd. BioFlix® Animation: Endomembrane System © 2021 Pearson Education Ltd. 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. The Evolutionary Origins of Mitochondria and Chloroplasts Mitochondria and chloroplasts have similarities with bacteria These similarities led to the endosymbiont theory It suggests that an early ancestor of eukaryotes engulfed an oxygen-using nonphotosynthetic prokaryotic cell The engulfed cell formed a relationship with the host cell, becoming an endosymbiont © 2021 Pearson Education Ltd.  The endosymbionts evolved into mitochondria At least one of these cells may have then taken up a photosynthetic prokaryote, which evolved into a chloroplast Similarities between mitochondria and chloroplasts that support this theory: – Enveloped by a double membrane – Contain free ribosomes and circular DNA molecules – Grow and reproduce somewhat independently in cells © 2021 Pearson Education Ltd.  The endosymbiont theory of the origins of mitochondria and chloroplasts in eukaryotic cells © 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. Figure 7.17 © 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. Figure 7.18 The chloroplast, site of photosynthesis © 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 7.20 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. 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. Figure 7.22 © 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. Figure 7.23 © 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.  Structure of a flagellum or motile cilium © 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.  Microfilaments that function in cellular motility contain the protein myosin in addition to actin Cells crawl along a surface by extending pseudopodia (cellular extensions) and moving toward them Cytoplasmic streaming, in plant cells, is a circular flow of cytoplasm within cells, driven by actin- protein interactions © 2021 Pearson Education Ltd. Figure 7.26 © 2021 Pearson Education Ltd. Video: Cytoplasmic Streaming © 2021 Pearson Education Ltd. Intermediate Filaments Intermediate filaments range in diameter from 8 to 12 nanometers, larger than microfilaments but smaller than microtubules Intermediate filaments are more permanent cytoskeleton fixtures than the other two classes They support cell shape and fix organelles in place © 2021 Pearson Education Ltd. © 2021 Pearson Education Ltd. Concept 7.7: Extracellular components and connections between cells help coordinate cellular activities Most cells synthesize and secrete materials to the outside of the cell These extracellular materials and structures are involved in many essential cellular functions © 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. Figure 7.27 © 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. Figure 7.28 Extracellular matrix (ECM) of an animal cell © 2021 Pearson Education Ltd.  The ECM has an influential role in the lives of cells ECM can regulate a cell’s behavior by communicating with a cell through integrins The ECM around a cell can influence the activity of genes in the nucleus Mechanical signaling may occur through cytoskeletal changes that trigger chemical signals in the cell © 2021 Pearson Education Ltd. Cell Junctions Neighboring cells in tissues, organs, or organ systems often adhere, interact, and communicate through direct physical contact © 2021 Pearson Education Ltd. Plasmodesmata in Plant Cells Plasmodesmata are channels that connect plant cells Through plasmodesmata, water and small solutes (and sometimes proteins and RNA) can pass from cell to cell © 2021 Pearson Education Ltd. Figure 7.29 © 2021 Pearson Education Ltd. Tight Junctions, Desmosomes, and Gap Junctions in Animal Cells Three types of cell junctions are common in epithelial tissues – At tight junctions, membranes of neighboring cells are pressed together, preventing leakage of extracellular fluid – Desmosomes (anchoring junctions) fasten cells together into strong sheets – Gap junctions (communicating junctions) provide cytoplasmic channels between adjacent cells © 2021 Pearson Education Ltd. Figure 7.30 © 2021 Pearson Education Ltd. Animation: Cell Junctions © 2021 Pearson Education Ltd. Concept 7.8: A cell is greater than the sum of its parts None of the cell’s components work alone For example, a macrophage’s ability to destroy bacteria involves the whole cell, coordinating components such as the cytoskeleton, lysosomes, and plasma membrane © 2021 Pearson Education Ltd. Figure 7.31 © 2021 Pearson Education Ltd.