Cell and Molecular Biology BI203 Fall 2018 Dr. Schulman 1 Introduction: Cell Theory • All organisms are composed of one or more cells. • Cells are the smallest living units of all living organisms. • Cells arise only by division of a previously existing cell. 1 Introduction: Cell Size • Most cells are relatively small because as size increases, volume increases much more rapidly. longer diffusion time 1 Introduction: Cell Size David S. Goodsell, The Machinery of Life, Spinger-Verlag. 1 0.1mm 1 ~300mm July 8, 2011 1 2014 2012 ~900mm 2013 2017 1 Introduction: Cell Size David S. Goodsell, The Machinery of Life, Spinger-Verlag. 1 Introduction: Cell Size David S. Goodsell, The Machinery of Life, Spinger-Verlag. 1 Introduction: Cell Size David S. Goodsell, The Machinery of Life, Spinger-Verlag. 1 Evolution • There is a unity and diversity among present-day cells in terms of their evolution from a common ancestor. Prokaryotic cells (bacteria) lack a nuclear envelope. Eukaryotic cells have a nucleus in which the genetic material is separated from the cytoplasm. Streptococcus pnemoniae A testable hypothesis that changed the way we think about things: Miller and Urey Early earth •Reducing atmosphere: much free H •also H2S, NH3, CH4, H2O little, if any, free O2 HOT environment, lightning Does this make organic molecules (molecules based on Carbon chains)? A testable hypothesis that changed the way we think about things: Miller and Urey Early earth •Reducing atmosphere: much free H •also H2S, NH3, CH4, H2O little, if any, free O2 HOT environment, lightning Does this make organic molecules (molecules based on Carbon chains)? Yup, it does. 1 The newly formed organics had to get organized Also possible surfaces: clay, deep sea thermal vents, ice crystals, deep inside the earth 1 The RNA world? RNA makes a good enzyme too! Central dogma of molecular biology: Enzymes (molecular machines) were always thought to be made of protein 1 The RNA world? RNA makes a good enzyme too! Central dogma of molecular biology: Turns out that some enzymes are made of RNA! 1 The RNA world? RNA makes a good enzyme too! The RNA world? RNA makes a good enzyme too! Catalytic RNA: “ribozymes” Tom Cech and Sid Altman (Nobel prize) http://exploringorigins.org/ribozymes.html • self-splicing introns (RNA that cuts itself) • the ribosome (protein making machine) • more examples all the time RNA molecules can be self-replicating therefore may have given rise to life Put it inside a ‘bubble’ made of lipids or proteins (or both) and you have a cell! (well, only sort of- but it’s a start!) 1.2 Self-replication of RNA 1.3 Enclosure of self-replicating RNA in a phospholipid membrane •Phospholipids are the basic components of all present-day biological membranes, including the plasma membranes of both prokaryotic and eukaryotic cells. 1 The First Cell • Amphipathic molecules consist of one portion that is soluble in water and another portion that is not. • Hydrophobic (water-insoluble) hydrocarbon chains form the inside layer of phospholipid molecules. • Hydrophilic (water-loving) head groups containing phosphate form the outside layer of phospholipid molecules. 1 Who were these early cells? No one is sure Certainly, they were prokaryotes (simplest cell type) - clear fossils dating from 3.5 billion years ago (cyanobacteria) Archea: thermophiles, halophiles (it was HOT around here back then) - all kinds of wacky Archea still exist today Even though they have a lot of differences, they are based on the same system of biochemistry. Microfossils of sulphur-metabolizing cells in 3.4billion-year-old rocks of Western Australia David Wacey, Matt R. Kilburn, Martin Saunders, John Cliff & Martin D. Brasier Nature Geoscience 4, 698–702(2011) doi:10.1038/ngeo1238 Published online 21 August 2011 1 Who were these early cells? No one is sure Bacteria: also still exist some can use light to generate food (photosynthesis) cyanobacteria: oxygenated the earth 1 Eukaryotes: 1.5 billion years ago 1 The early cells started working together Endosymbiont Theory 1 Clearly, it’s all connected: Commonalities of Life DNA replication, information storage and expression same amino acids used to make proteins common biosynthetic pathways common utilization of energy (glucose ATP) Descended from single common ancestor Ancestor gave rise to three large “Domains” of life 1.7 Evolution of cells 1 Present-Day Prokaryotes • Escherichia Coli (E. coli) is a typical prokaryotic cell plasma membrane that consists of a bilayer of phospholipids and associated proteins. surrounded by a rigid cell wall that is composed of polysaccharides and peptides. The DNA is a single circular molecule that resides in the organism’s nucleoid. Ribosomes 1 Eukaryotic Cells • Eukaryotic cells contain a variety of membraneenclosed organelles within their cytoplasm. The nucleus is the largest and most prominent organelle of eukaryotic cells and contains the genetic information of the cell in the form of linear DNA molecules, and is the site of DNA replication and RNA synthesis. Structures of animal and plant cells (Part 1) Structures of animal and plant cells (Part 2) 1 Eukaryotic Cells Mitochondria, which are found in almost all eukaryotic cells, are the sites of oxidative metabolism. Chloroplasts, which are found only in the cells of plants and green algae, are the sites of photosynthesis. Lysosomes provide specialized metabolic compartments for the digestion of macromolecules. Peroxisomes reactions. perform various oxidative 1 Eukaryotic Cells Vacuoles perform a variety of functions, including the digestion of macromolecules and the storage of both waste products and nutrients. The endoplasmic reticulum is an extensive network of intracellular membranes that functions not only in the processing and transport of proteins, but also in the synthesis of lipids. The Golgi apparatus sorts and transports proteins destined for secretion. It serves as a site of lipid synthesis, and (in plant cells) is the site of synthesis of some of the polysaccharides that compose the cell wall. 1 Eukaryotic Cells • The cytoskeleton is another level of internal organization of eukaryotic cells. The cytoskeleton provides the structural framework of the cell, is responsible for the movements of entire cells, as well as for the intracellular transport and positioning of organelles and other structures. 1 Eukaryotic Cells Saccharomyces cerevisiae and Amoeba proteus are two commonly studied eukaryotes. 1 The Development of Multicellular Organisms: plants • Volvox, a green alga, associates with other algae cells to form multicellular colonies. • May be similar to the precursor to modern day plants 1.11 Light micrographs of representative plant cells Plant cells are organized into three main tissue systems: ground tissue, dermal tissue, and vascular tissue. The Development of Multicellular Organisms: animals Colonial flagellates (protists) Have a striking morphological similarity to cells in sponges that are called “choanocytes” Ribosomal RNA sequences clearly support this hypothesis 1 The Development of Multicellular Organisms: animals • Animal cells are organized into epithelial tissue connective tissue blood nervous muscle tissue 1.12 Light micrographs of representative animal cells (Part 1) 1.12 Light micrographs of representative animal cells (Part 2)
