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LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson Chapter 6 A Tour of the Cell Lectures by Erin Barley Kathleen Fitzpatrick © 2011 Pearson Education, Inc. Cells: The Fundamental Units of Life • first cell observed – Robert Hooke in 1665 • • thin slices of bottle cork saw a network of “cells” that a monk would live in • first living cell (Spirogyra) observed by Anton van Leeuwenhoek in 1674 • also described bacteria he found in his mouth (1676) Anton van Leeuwenhoek Cells: The Fundamental Units of Life • the cell is the simplest collection of matter that can be alive • the Cell Theory: • 1. all organisms are made of at least one type of cell • 2. all cells come from pre-existing cells by this cell dividing in two • 3. the cell is the basic, fundamental unit of life • attributed to: Theodor Schwann, Matthias Jakob Schleiden, and Rudolf Virchow Concept: Eukaryotic cells have internal membranes that compartmentalize their functions • the basic structural and functional unit of every organism is the cell • two types of cells: prokaryotic or eukaryotic • protists, fungi, animals, and plants all consist of eukaryotic cells Cells • Basic features of all cells – Plasma membrane – Semifluid substance called cytoplasm – organized DNA in the form of Chromosomes (carry genes) – Ribosomes (make proteins) Comparing Prokaryotic and Eukaryotic Cells • Prokaryotic cells: – no nucleus – DNA in a region of the cytoplasm called the nucleoid – no membrane-bound organelles – a Cytoplasm bound by the plasma membrane – smaller ribosomes • Eukaryotic cells – membrane – bound nucleus containing DNA – membrane-bound organelles – a Cytoplasm in the region between the plasma membrane and nucleus – larger ribosomes The Eukaryotic Cell • 1. Plasma membrane • 2. Nucleus • 3. Cytoplasm – a. cytosol – b. cytoskeleton • 4. Cytoplasmic organelles – membrane-bound – non-membrane bound Plants and fungus have a Cell Wall outside of the plasma membrane – not the same composition The Plasma Membrane • the plasma membrane is a semipermeable barrier – 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 – known as a phospholipid bilayer – membrane proteins embedded within it or found attached to one layer Outside of cell Inside of cell 0.1 m (a) TEM of a plasma membrane Carbohydrate side chains Hydrophilic region Hydrophobic region Hydrophilic region Phospholipid Proteins (b) Structure of the plasma membrane The Cytoplasm • Comprised of – 1. The cytosol – 2. The cytoplasm • Cytoskeleton = a“skeleton” of protein filaments found prokaryotic and eukaryotic cells • Cytosol = intracellular fluid of the prokaryotic or eukaryotic cell The Cytosol • also known as the intracellular fluid or ICF – about 55% of the cell’s volume – about 70-90% water PLUS • • • • • • ions dissolved nutrients – e.g. glucose soluble and insoluble proteins waste products macromolecules and their components - amino acids, fatty acids ATP • unique composition with respect to extracellular fluid (ECF) • fluid found outside of a cell The Eukaryotic Nucleus: Information Central • the nucleus contains most of the eukaryotic cell’s genes and is usually the most conspicuous organelle • the nuclear envelope encloses the nucleus, separating it from the cytoplasm – not found in prokaryotic cells – so NO nucleus in prokaryotic cells • the nuclear envelope is comprised of two phospholipid bilayers • the nucleolus is located within the nucleus and is the site of ribosomal synthesis – a prominent dark region inside the nucleus • nuclear pores exist for import and export Nucleus Nucleolus Chromatin Nuclear envelope: Inner membrane Outer membrane Nuclear pore Rough ER Pore complex Ribosome Close-up of nuclear envelope Chromatin Eukaryotic DNA: Chromatin & Chromosomes histone DNA helix nucleosome - organized form of DNA in the nucleus = chromatin described as “beads on a string” model DNA helix is wrapped around complexes of proteins called histones the histone-DNA complex is called a nucleosome described by Roger Kornberg – Nobel Prize 2006 Eukaryotic DNA: Chromatin & Chromosomes • eukaryotic DNA needs to be condensed when the cell divides • done just after the cell “copies” its DNA before mitosis • cell “compacts” its chromatin into a duplicated chromosome – histones play an important role Membranous Organelles •surrounded by one or two phospholipid bilayers that are similar to the plasma membrane •major functions of the membranous organelles •1. protein synthesis – ER and Golgi •2. energy production – mitochondria •3. waste management – lysosomes & peroxisomes 1. Endoplasmic reticulum (ER) = multiple membrane-bound compartments called cisterna (plural = cisternae) -often attached to the nucleus -responsible for: 1. protein synthesis 2. lipid & phospholipid synthesis 3. calcium storage -two types: Rough ER vs. Smooth ER -Rough ER (RER) – ribosomes “docked” onto their surface protein synthesis -Smooth ER (SER) – no ribosomes: lipid synthesis & calcium storage 2. Golgi Apparatus = multiple stacks of cisternae next to the ER -described by Camillo Golgi in 1897 -responsible for: 1. protein modifications – sugar addition, trimming 2. protein sorting and targeting 3. Mitochondria -singular = mitochondrion -surrounded by a two phospholipid bilayers • an outer mitochondrial membrane • an inner mitochondrial membrane • a fluid-filled space = matrix -the inner membrane is folded into folds called cristae -these increase the membrane surface area for the enzymes of ATP synthesis (via Oxidative phosphorylation) 4. Lysosomes = “garbage disposals” -dismantle debris, eat foreign invaders/viruses internalized by the cell -cell biologists not really sure exactly how the lysosome forms -contain powerful enzymes to breakdown substances into their component parts -these enzymes are collectively known as acid hydrolases e.g. nucleases = breakdown RNA & DNA into nucleotides e.g. proteases = breakdown proteins into amino acids 5. Peroxisomes: found in all cells but abundant in liver and kidney cells -only identified in 1954 -major function is breakdown of fatty acids - but this reaction generates hydrogen peroxide (H2O2) - so peroxidases contain an enzyme (called catalase) that catalyzes the breakdown of the H2O2 into H2O and O2 Non-membranous Organelles A. Centrioles: short cylinders of a protein called tubulin - 9 microtubule triplets called a 9+0 array (9 peripheral triplets, 0 in the center) -found in cells capable of division (in an area of the cell called the centrosome) -has a role in mitosis - spindle and chromosome alignment -duplicate just prior to the onset of mitosis -migrate to opposite ends of the replicating cell -mitotic spindle grows in between centriole spindle B. Cilia & Flagella • cilia = projections off of the plasma membrane of eukaryotic cells • flagella = larger cilia • made of hollow “straws” of tubulin called microtubules • beat rhythmically to transport material – power & recovery strokes • found in linings of several major organs covered with mucus where they function in cleaning • e.g. trachea, lungs Trachea Tubulin in a microtubule B. Cilia & Flagella • cilia and flagella = 9+2 array 9 doublets around the periphery + 2 singlets in the center of the cilia C. Ribosomes: Protein Factories • Ribosomes are particles made of ribosomal RNA (rRNA) and protein • comprised of two subunits – large – small • ribosomes carry out protein synthesis 0.25 m Free ribosomes in cytosol Endoplasmic reticulum (ER) Ribosomes bound to ER Large subunit Small subunit TEM showing ER and ribosomes Diagram of a ribosome