Ch 3 Cell Structure 10/1/2008. Cells Under the Microscope. Natural laws limit cell size. Biology Periods 2, 3, 4, & 6 Mrs.

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1 Ch 3 Cell Structure Cells Under the Microscope Electron microscopes have much higher magnifying and resolving powers than light microscopes. Biology Periods 2, 3, 4, & 6 Mrs. Stolipher Cell size and shape relate to function Figure 4.2 The Cell Theory The Cell Theory has three parts: 1. All living things are made of one or more cells. Natural laws limit cell size 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

2 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. A small cell has a greater ratio of surface area to volume than a large cell of the same shape 30 µm 10 µm Figure 4.3 Surface area of one large cube = 5,400 µm 2 Total surface area of 27 small cubes = 16,200 µm 2 Common Cell Features ALL Cells share common structural features, including: an outer boundary called the cell membrane, interior substance called cytoplasm, structural support called thecytoskeleton, genetic material in the form of DNA cellular structures that make proteins, called ribosomes Prokaryotes Prokaryotes are single-celled organisms that lack a nucleus and other internal compartments. They have a cell wall, may havecilia or flagella, and have a single circular molecule of DNA. 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. Archaebacteriaare prokaryotes that lack peptidoglycan in their cell walls and have unique lipids in their cell membranes. Eukaryotic cells are partitioned into functional compartments 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 2

3 Eukaryotic Cells Eukaryotic cells have: A nucleuswhich contains the cell s DNA Other internal compartments called organelles. Section 2 Cell Features Comparing Prokaryotes and Eukaryotes Watch video clip Ch 3 Sect 2 vc10 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. Eukaryotic Cells, continued The cytoskeleton s network of protein fibers anchors the cell s organelles and other components of the cytoplasm. 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. 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

4 The Cell Membrane, continued The Nucleus -cell s genetic control center Generally the largest organelle Thenucleus 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. The Nucleus, continued Section 3 Cell Organelles Nucleus of a Cell 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 () is part of the endomembrane system Ribosomesand the Endoplasmic Reticulum Ribosomes are the cellular structures on which proteins are made. The Endoplasmic Reticulum or is an extensive system of internal membranes that move proteins and other substances through the cell. 4

5 Ribosomesand the Endoplasmic Reticulum, continued The moves proteins and other substances within eukaryotic cells. Ribosomesand the Endoplasmic Reticulum, continued The part of the with attached ribosomes is called the rough. The rough helps transport proteins that are made by the attached ribosomes. New proteins enter the. The portion of the that contains the completed protein pinches off to form a vesicle. A vesicle is a small, membrane-bound sac that transports substances in cells. The rough manufactures membranes Ribosomes on its surface produce proteins Transport vesicle buds off Riboso me Sugar chain 4 3 protein inside transport vesicle Smooth endoplasmic reticulum has a variety of functions Smooth synthesizes lipids In some cells, it regulates carbohydrate metabolism and breaks down toxins and drugs Figure Polypept ide 2 Glycoprotein ROUGH SMOOTH ROUGH Nuclear envelope Ribosomesand the Endoplasmic Reticulum, continued Packaging and Distribution of Proteins SMOOTH Ribosomes ROUGH Vesicles that contain newly made proteins move through the cytoplasm from the to an organelle called the apparatus. Figure 4.9 5

6 The apparatus finishes, sorts, and ships cell products Section 3 Cell Organelles Apparatus The apparatus is a set of flattened, membrane-bound sacs that serve as the packaging and distribution center of the cell. These receive and modify 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 Lysosomal enzymes LYSOSOME Nucleus digest food destroy bacteria recycle damaged organelles function in embryonic Food Plasma membrane Engulfment of particle Rough Transport vesicle (containing inactive hydrolytic enzymes) LYSOSOMES apparatus Lysosome engulfing damaged organelle Connection: Abnormal lysosomes can cause fatal diseases Lysosomal storage diseases are hereditary They interfere with other cellular functions Examples: Pompe sdisease - genetic disorder caused by a deficiency or dysfunction of the lysosomalhydrolasewhich 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, liverand nervous system. Tay-Sachs disease - occurs when harmful quantities of a fatty acidderivative called a gangliosideaccumulate in the nerve cells of the brain. It is usually fatal. Food vacuole Digestion Figure 4.11B 6

7 A review of the endomembrane system The various organelles of the endomembrane system are interconnected structurally and functionally Rough Nucleus Smo oth Trans port vesicl e from Nuclear envelope Transpo rt vesicle from Lysoso me appara tus Vacu ole Plasm a membr ane Figure 4.14 Mitochondria 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 ATPis the main energy currency of cells. Most ATP is made inside the mitochondria. 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. Mitochondriahave their own DNA. They reproduce independently of the cell. Mitochondrial DNA is similar to the DNA of prokaryotic cells. Mitochondriaare thought to be descendents of primitive prokaryotes. Structures of Plant Cells Plants have three unique structures that are not found in animal cells: Cell Wall Chloroplasts Central Vacuole Structures of Plant Cells cell wall The cell membrane of plant cells is surrounded by a thickcell wall, composed of proteins and carbohydrates. The cell wall helps support and maintain the shape of the cell protects the cell from damage connects the cell with adjacent cells 7

8 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. 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 apparatus Nucleus Rough endoplasmic reticulum Ribosomes Smooth endoplasmic reticulum An animal cell Rough endoplasmic reticulum Smooth endoplasmic reticulum Nucleus Not in animal cells Central vacuole Chloroplast Cell wall Microtubule Microfilament Cytoskeleton Not in most plant cells Flagellum Lysosome Ribosomes Mitochondrion Microtubule apparatus Plasma membrane Cytoskeleton Microfilament Mitochondrion Plasma membrane Figure 4.5B Figure 4.5A Summary of Organelles 8