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The Discovery of the Cell What is the cell theory? The cell theory states: - All living things are made up of cells. - Cells are the basic units of structure and function in living things. - New cells are produced from existing cells. Fig. 6-3cd TECHNIQUE (c) Phase-contrast (d) Differential-interferencecontrast (Nomarski) RESULTS Comparing Prokaryotic and Eukaryotic Cells • Basic features of all cells: – Plasma membrane – Semifluid substance called cytosol – Chromosomes (carry genes) – Ribosomes (make proteins) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Eukaryotic cells are characterized by having – DNA in a nucleus that is bounded by a membranous nuclear envelope – Membrane-bound organelles – Cytoplasm in the region between the plasma membrane and nucleus • Eukaryotic cells are generally much larger than prokaryotic cells Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • The plasma membrane is a selective barrier that allows sufficient passage of oxygen, nutrients, and waste to service the volume of every cell • The general structure of a biological membrane is a double layer of phospholipids Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-7 Outside of cell Inside of cell 0.1 µm (a) TEM of a plasma membrane Carbohydrate side chain Hydrophilic region Hydrophobic region Hydrophilic region Phospholipid Proteins (b) Structure of the plasma membrane • The logistics of carrying out cellular metabolism sets limits on the size of cells • The surface area to volume ratio of a cell is critical • As the surface area increases by a factor of n2, the volume increases by a factor of n3 • Small cells have a greater surface area relative to volume Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-8 Surface area increases while total volume remains constant 5 1 1 Total surface area [Sum of the surface areas (height width) of all boxes sides number of boxes] Total volume [height width length number of boxes] Surface-to-volume (S-to-V) ratio [surface area ÷ volume] 6 150 750 1 125 125 6 1.2 6 A Panoramic View of the Eukaryotic Cell • A eukaryotic cell has internal membranes that partition the cell into organelles • Plant and animal cells have most of the same organelles Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings BioFlix: Tour Of An Animal Cell Fig. 6-9a Nuclear envelope ENDOPLASMIC RETICULUM (ER) Flagellum Rough ER NUCLEUS Nucleolus Smooth ER Chromatin Centrosome Plasma membrane CYTOSKELETON: Microfilaments Intermediate filaments Microtubules Ribosomes Microvilli Golgi apparatus Peroxisome Mitochondrion Lysosome Concept 6.3: 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. • The DNA is organized into long strands called chromosomes which are the genetic information Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Nucleus: Information Central •Ribosomes use the information from the DNA to make proteins Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • In the nucleus, DNA and proteins form genetic material called chromatin • Chromatin condenses to formchromosomes • The nucleolus is located within the nucleus and is the site of ribosomal RNA (rRNA) synthesis Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Ribosomes: Protein Factories • Ribosomes carry out protein synthesis in two locations: – In the cytosol (free ribosomes) – On the outside of the endoplasmic reticulum or the nuclear envelope (bound ribosomes) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-11 Cytosol Endoplasmic reticulum (ER) Free ribosomes Bound ribosomes Large subunit 0.5 µm TEM showing ER and ribosomes Small subunit Diagram of a ribosome The Endoplasmic Reticulum: Biosynthetic Factory • The endoplasmic reticulum (ER) accounts for more than half of the total membrane in many eukaryotic cells • There are two distinct regions of ER: – Smooth ER, which lacks ribosomes – Rough ER, with ribosomes studding its surface Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-12 Smooth ER Rough ER ER lumen Cisternae Ribosomes Transport vesicle Smooth ER Nuclear envelope Transitional ER Rough ER 200 nm Functions of Smooth ER • The smooth ER – Synthesizes lipids – Metabolizes carbohydrates – Detoxifies poison – Stores calcium Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Functions of Rough ER • The rough ER – Has bound ribosomes, which secrete proteins – Distributes transport vesicles, proteins surrounded by membranes – Is a membrane factory for the cell Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Golgi Apparatus: Shipping and Receiving Center • The Golgi • Functions of the Golgi apparatus: – Sorts and packages materials made in the ER into transport vesicles Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-13 cis face (“receiving” side of Golgi apparatus) 0.1 µm Cisternae trans face (“shipping” side of Golgi apparatus) TEM of Golgi apparatus Lysosomes: Digestive Compartments • A lysosome is a membranous sac of enzymes that can digest macromolecules • Lysosomal enzymes can digest proteins, fats, polysaccharides, and nucleic acids Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • 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 molecules • Lysosomes also use enzymes to recycle the cell’s own organelles and macromolecules, a process called autophagy Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-14a Nucleus 1 µm Lysosome Lysosome Digestive enzymes Plasma membrane Digestion Food vacuole (a) Phagocytosis Concept 6.5: Mitochondria and chloroplasts change energy from one form to another • Mitochondria are the sites of cellular respiration, a metabolic process that generates ATP or ENERGY Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings MITOCHONDRIA Concept 6.6: The cytoskeleton is a network of fibers that organizes structures and activities in the cell • The cytoskeleton is a network of fibers extending throughout the cytoplasm • It organizes the cell’s structures and activities, anchoring and supporting many organelles Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-20 Microtubule 0.25 µm Microfilaments Roles of the Cytoskeleton: Support, Motility, and Regulation • The cytoskeleton helps to support the cell and maintain its shape • It interacts with motor proteins to produce motility • Inside the cell, vesicles can travel along “monorails” provided by the cytoskeleton • Recent evidence suggests that the cytoskeleton may help regulate biochemical activities Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Centrioles • In many 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 and function to help separate chromosomes during cell division (Mitosis) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-22 Centrosome Microtubule Centrioles 0.25 µm Longitudinal section Microtubules Cross section of one centriole of the other centriole Cilia and Flagella • Cilia and Flagella, are appendages of some cells that help them move or to move substances on their surfaces Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings