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Transcript
10/1/2008 Chapter 3 Cells Under the Microscope Electron microscopes have much higher magnifying and resolving powers than light microscopes. Ch 3 – Cell Structure Biology – Periods 2, 3, 4, & 6 Mrs. Stolipher • Cell size and shape relate to function Figure 4.2 Chapter 3 Natural laws limit cell size The Cell Theory The Cell Theory has three parts: 1. All living things are made of one or more cells. • At minimum, a cell must be large enough to house the parts it needs to survive and reproduce • The maximum size of a cell is limited by the amount of surface needed to obtain nutrients from the environment and dispose of wastes 2. Cells are the basic units of structure and function in organisms. 3. All cells arise from existing cells. 1 10/1/2008 • A small cell has a greater ratio of surface area to volume than a large cell of the same shape Cell Size Small cells function more efficiently than large cells. If a cell’s surface area–to-volume ratio is too low, substances cannot enter and leave the cell well enough to meet the cell’s needs. 30 µm 10 µm Surface area of one large cube = 5,400 µm2 Total surface area of 27 small cubes = 16,200 µm2 Figure 4.3 Common Cell Features Prokaryotes ALL Cells share common structural features, including: • • • • • an outer boundary called the cell membrane, interior substance called cytoplasm, structural support called the cytoskeleton, genetic material in the form of DNA cellular structures that make proteins, called ribosomes Prokaryotes are single-celled organisms that lack a nucleus and other internal compartments. They have a cell wall, may have cilia or flagella, and have a single circular molecule of DNA. Eukaryotic cells are partitioned into functional compartments Two Groups of Prokaryotes • Early in the history of life, two different groups of prokaryotes evolved—eubacteria (which are commonly called bacteria) and archaebacteria. • Eubacteria are prokaryotes that contain a chemical called peptidoglycan in their cell walls. • All other life forms are made up of one or more eukaryotic cells • These are larger and more complex than prokaryotic cells • Eukaryotes are distinguished by the presence of a true nucleus • Archaebacteria are prokaryotes that lack peptidoglycan in their cell walls and have unique lipids in their cell membranes. 2 10/1/2008 Eukaryotic Cells Eukaryotic cells have: • A nucleus which contains the cell’s DNA • Other internal compartments called organelles. Eukaryotic Cells • The cytoskeleton provides the interior framework of a cell. There are three basic kinds of cytoskeletal fibers. 1. Microfilaments: long slender filaments made of the protein actin 2. Microtubules: hollow tubes made of the protein tubulin. 3. Intermediate fibers: thick ropes made of protein. The Cell Membrane • The cell (plasma) membrane controls the cell’s contact with the environment • The cell membrane is a selectively permeable barrier that determines which substances enter and leave the cell. • The selective permeability of the cell is mainly caused by the way phospholipids interact with water. Chapter 3 Section 2 Cell Features Comparing Prokaryotes and Eukaryotes Watch video clip Ch 3 – Sect 2 – vc10 Eukaryotic Cells, continued The cytoskeleton’s network of protein fibers anchors the cell’s organelles and other components of the cytoplasm. The Cell Membrane, continued Cell membranes are made of a double layer of phospholipids, called a bilayer. • A phospholipid is a lipid made of a phosphate group and two fatty acids. 3 10/1/2008 The Cell Membrane, continued The Nucleus - cell’s genetic control center • Generally the largest organelle • The nucleus is an internal compartment that houses the cell’s DNA. Most functions of a eukaryotic cell are controlled by the cell’s nucleus. • is surrounded by a double membrane called the nuclear envelope, which separates the nucleus from the cytoplasm • Scattered over the surface of the nuclear envelope are many small channels called nuclear pores. Chapter 3 The Nucleus, continued Overview: Many cell organelles are related through the endomembrane system • The endomembrane system is a collection of membranous organelles – These organelles manufacture and distribute cell products – The endomembrane system divides the cell into compartments – Endoplasmic reticulum (ER) is part of the endomembrane system Section 3 Cell Organelles Nucleus of a Cell Ribosomes and the Endoplasmic Reticulum • Ribosomes are the cellular structures on which proteins are made. • The Endoplasmic Reticulum or ER is an extensive system of internal membranes that move proteins and other substances through the cell. 4 10/1/2008 Ribosomes and the Endoplasmic Reticulum, continued The ER moves proteins and other substances within eukaryotic cells. Ribosomes and the Endoplasmic Reticulum, continued • The part of the ER with attached ribosomes is called the rough ER. • The rough ER helps transport proteins that are made by the attached ribosomes. • New proteins enter the ER. • The portion of the ER that contains the completed protein pinches off to form a vesicle. • A vesicle is a small, membrane-bound sac that transports substances in cells. Smooth endoplasmic reticulum has a variety of functions • The rough ER manufactures membranes • Ribosomes on its surface produce proteins 4 Transport vesicle buds off Riboso me Sugar chain • Smooth ER synthesizes lipids • In some cells, it regulates carbohydrate metabolism and breaks down toxins and drugs protein inside transport vesicle 3 Glycoprotein 1 Figure 4.8 2 ROUGH ER Polypept ide Ribosomes and the Endoplasmic Reticulum, continued SMOOTH ER ROUGH ER Nuclear envelope Ribosomes SMOOTH ER ROUGH ER Packaging and Distribution of Proteins • Vesicles that contain newly made proteins move through the cytoplasm from the ER to an organelle called the Golgi apparatus. Figure 4.9 5 10/1/2008 The Golgi apparatus finishes, sorts, and ships cell products Chapter 3 Section 3 Cell Organelles Golgi Apparatus – The Golgi apparatus is a set of flattened, membrane-bound sacs that serve as the packaging and distribution center of the cell. – These receive and modify ER products, then send them on to other organelles or to the cell membrane Lysosomes digest the cell’s food and wastes • Lysosomes are sacs of digestive enzymes budded off the Golgi • Lysosomal enzymes LYSOSOME Nucleus – digest food – destroy bacteria – recycle damaged organelles – function in embryonic Connection: Abnormal lysosomes can cause fatal diseases Rough ER Transport vesicle (containing inactive hydrolytic enzymes) Plasma membrane Golgi apparatus • Lysosomal storage diseases are hereditary – They interfere with other cellular functions – Examples: Pompe’s disease - genetic disorder caused by a deficiency or dysfunction of the lysosomal hydrolase which breaks down glycogen. The build-up of glycogen causes progressive muscle weakness throughout the body and affects various body tissues, particularly in the heart, skeletal muscles, liver and nervous system. Engulfment of particle Lysosome engulfing damaged organelle “Food” – Tay-Sachs disease - occurs when harmful quantities of a fatty acid derivative called a ganglioside accumulate in the nerve cells of the brain. It is usually fatal. LYSOSOMES Food vacuole Digestion Figure 4.11B 6 10/1/2008 A review of the endomembrane system • The various organelles of the endomembrane system are interconnected structurally Trans and functionally Transpo Rough ER port vesicl e from ER rt vesicle from Golgi Nuclear envelope Lysoso Golgi me appara tus • Mitochondria are organelles that harvest energy from organic compounds (food) to make ATP. • Mitochondria carry out cellular respiration – This process uses the chemical energy in food to make ATP for cellular work • ATP is the main energy currency of cells. Most ATP is made inside the mitochondria. Vacu ole Nucleus Smo oth ER Plasm a membr ane Mitochondria Figure 4.14 Mitochondria, continued Mitochondria, continued • Mitochondria have two membranes. The outer membrane is smooth. The inner membrane is greatly folded, and has a large surface area. • Mitochondria have their own DNA. – They reproduce independently of the cell. – Mitochondrial DNA is similar to the DNA of prokaryotic cells. • Mitochondria are thought to be descendents of primitive prokaryotes. Structures of Plant Cells Structures of Plant Cells – cell wall Plants have three unique structures that are not found in animal cells: • The cell membrane of plant cells is surrounded by a thick cell wall, composed of proteins and carbohydrates. • Cell Wall • The cell wall • Chloroplasts • helps support and maintain the shape of the cell • protects the cell from damage • Central Vacuole • connects the cell with adjacent cells 7 10/1/2008 Structures of Plant Cells chloroplasts • are organelles that use light energy to make carbohydrates from carbon dioxide and water. • along with mitochondria, supply much of the energy needed to power the activities of plant cells. • like mitochondria, chloroplasts – have their own DNA and reproduce independently of the plant cell. – are thought to be descendents of ancient prokaryotes. Nucleus Structures of Plant Cell – central vacuole • Most of a plant cell’s volume is taken up by a large, membrane-bound space called the central vacuole. • Functions in general maintenance of the cell • The central vacuole stores water and may contain ions, nutrients, and wastes. • Protists (single celled eukaryotes) may have contractile vacuoles – Which work to pump out excess water Rough endoplasmic reticulum An animal cell Ribosomes Rough endoplasmic reticulum Smooth endoplasmic reticulum Golgi apparatus Central vacuole Cytoskeleton Chloroplast Nucleus Flagellum Microtubule Not in animal cells Smooth endoplasmic reticulum Not in most plant cells Lysosome Microfilament Cell wall Ribosomes Mitochondrion Microtubule Cytoskeleton Plasma membrane Figure 4.5B Golgi apparatus Plasma membrane Microfilament Mitochondrion Figure 4.5A Summary of Organelles 8