Lecture 4 Cell Structure and Function Part 1.pptx

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 vis...

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. 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 • 0nly organisms of the domains 8acteria 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 • 8asic 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 © 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. 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 © 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 7.9 © 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) - 0 n the outside of the endoplasmic reticulum or the nuclear envelope (bound ribosomes) © 2021 Pearson Education Ltd. Figure 7.10 © 2021 Pearson Education Ltd. Concept 7.4: The endomembrane system regulates protein traffi c 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 © 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 © 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 © 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 re ositor of inorganic ions, including potassium andchloride • The central vacuole plays a major role in the growth of plant cells © 2021 Pearson Education Ltd. Figure 7.14 © 2021 Pearson Education Ltd.