CSB325 Lecture 4 Review Notes

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Cell and Systems Biology
David Lovejoy

CSB325 Lecture 4 – Hormone Evolution Prebiotic synthesis of biogenic molecules - Extraterrestrial origins o Meteorites with organic material  Gases  oxygen (O2), water (H2O), carbon monoxide (CO), carbon dioxide (CO2), methane (CH4), nitrogen (N2), ammonia (NH3)  Sugars  formaldehyde, dihydroxyacetone, glyceraldehyde  Amino acids  glycine, alanine, aspartic acid, glutamic acid  Fatty acids  Alcohols  methanol, glycerol  Urea - Terrestrial origins o Methane (CH4), ammonia (NH3), water (H2O), nitrogen (N2) will readily form amino acids, sugars, and purines - Energy sources that could have been used o Sunlight o Lightning o Cosmic radiation o Geothermal vents o Volcanic activity Pre-requisites of life - A living system is characterized by an ability to reduce entropy - Physiological requirements = Internal conditions o Energy o Raw materials - Environmental conditions = External conditions o Acceptable conditions (growth/metabolism) o Poor conditions (quiescence) - When cells can coordinate these signals, they begin to live in a community either singly or communal and begin to establish a division of labor and therefore specialization of function Protocells  partitioning of biotic (life) and non-biotic (non-life) environments in the form of a plasma membrane created the need for signalling networks - Evolution of protocells o Association of organic material on inorganic substrate o Concentration of organic material o Partitioning of hydrophilic and hydrophobic molecules o Formation of hydrophobic membrane o Separation of protocell from substrate - Structure of protocells o Ion gradients across membrane and energy production o Signaling capacity  Membrane diffusion  Membrane pores  Protein channels  Early adhesion proteins - First signalling networks o Random and intermittent signaling capacity o Little coordination between the excreted molecule and the regulation of activity of another protocell First true cells  metabolic and genetic replication ability - Requirements for the evolution of multicellularity o Stable membrane o Cytoskeleton  Adhesion, Signaling system, Endocytosis and exocytosis o Reasonably accurate replication - Evolution o Over 2 billion years ago from first cell to first multicellular animal o Elaboration of membranes  Membranes act as a substrate for biosynthetic enzymes required for exocytosis and endocytosis o Symbiosis with other organisms  increase in complexity  Transformation from anaerobic to aerobic  Anaerobic organism ingested an aerobic organism  Ingested aerobic cell became the ancestor of modern mitochondria  Formation of organelles  Signaling pathways are required to coordinate the actions of the new organelle with the actions of the rest of the cell - Problems associated with the development of multicelluarity o Adhesion  cells need to be physically connected or attached o Signaling systems  coordination of function between cells o Increased energy requirements  Transport of nutrients, ion, water, and oxygen to inner cells  Procurement of nutrient sources Types of signaling molecules - Amino acids o Among first amino acids synthesized o Acid/base ability (buffering capacity) o Form elongated chains (polymers) - Peptides and proteins o Structural and signaling ability o Several types of structural organization o Can carry and transmit information - Lipids o Pass through membrane o Early prebiotic synthesis - Gases and ions o Present in prebiotic Earth - Nucleic acids o Common as signaling molecule o Evolutionary origins are not clear - Sugars o Not common as signaling molecule because too hydrophilic o More likely to be selected as an energy source because lots of energy Types of signaling processes - Earliest cells o Intracrine o Exocrine - More evolved systems o Autocrine o Paracrine o Juxtacrine - Membrane mechanisms o Simple and facilitated diffusion o Channel and transporter mediated diffusion Phylogeny of metazoans - Metazoa o Placozoa (e.g., Trichoplax adherens)  the most basal metazoan o Porifera (sponges) o Eumetazoa  nerve cells and tissue layer construction  Radiata  radial symmetry  Ctenophora (comb jellies)  Cnidaria (sea anemones, corals, hydra)  Bilatera  bilateral symmetry  Protostomia  mouth formed first, followed by the anus o Ecdysoza o Lophotrochozoa  Deuterostomia  anus formed first, followed by the mouth o Chordata  Vertebrate o Echinodermata Signaling in the Placozoa - No symmetry - No endocrine or nervous system - Autocrine and paracrine signaling only - Two tissue types Signaling in the Porifera - No symmetry - No true nervous system with axons and action potentials - Capable of transmitting signals - Photoreception stimulates cilia to propel the organism away from sunlight Signaling in the Radiata - Growth and differentiation pathways comparatively well developed - Wnt/frizzled pathway o Wnt (wingless) ligand  a family of polypeptide ligands o Frizzled receptor  a family of proteins consisting of membrane bound receptors with 7 α-helices  Similar to GPCR, but without the G-protein component - Nuclear receptors o Similar to steroid-thyroid hormone receptors, although ligands are not well understood - Receptor serine/threonine and tyrosine kinase based systems - Sensory type pathways - GPCR are present, but in low numbers and diversity Formation of the nerve net with neurons and neurosecretory cells - Placozoa and Porifera do not have nervous systems - Radiata (Ctenophora and Cnidaria) have nervous systems - No known metazoans that display transitional forms of the nervous system - Phylogenetically older species of deuterostomes and protostomes show the presence of a nerve net - We assume that the first functional neural/neurosecretory system was a nerve net - Nerve net o Neurosecretory cells connected by axons are interspersed between somatic cells o Sensory systems stimulate neurosecretory cells to regulate somatic cells by paracrine signals o Visualize with an anti-vasopressin antiserum - The first neuron/neurosecretory cells may have been derived from early sensory cells - These cells released a chemical signal via a robust depolarizing current resulting from the appropriate sensory input - These cells evolved into a new morphology with extended process that could interact with structures associated with movement and feeding (e.g., cells with cilia) - As movement became more complex, interneurons evolved and bridged the sensory cells with locomotory cells Evolution of signaling pathways - Nervous o Sensory cell o Ionic coupling o Locomotor cell with cilia - Neuroendocrine o Sensory cell o Chemical secretion and paracrine diffusion - Endocrine o Sensory cell o Chemical secretion and paracrine diffusion o Non-nervous (depolarizing) secretory cell Genetic and morphological complexity - Development of nervous and vascular system o Integration of sensory systems with locomotory systems o Formation of nervous system (fast process, short range) and integration with vascular system (slow process, long range)  Complementary systems, such that one cannot exist without the other - Genome duplications increased the physiological and morphological complexity of later evolving metazoan species o Formation of triploblastic organism (ectoderm, endoderm, mesoderm) o Formation of all known bilateral metazoans o Increase in complexity of signaling systems o Presence of nervous system o Presence of vascular system Relationship among symmetry, endocrine system, and nervous system - Location of sensory organs is dependent on how the organism moves - Once bilateral symmetry evolved, the sensory organs could be concentrated in the direction of movement (e.g., head) o Requires less energy o More specialized - Symmetry allowed for structural similarity among individuals of a population - A systemic signaling system could therefore develop in same way in all individuals - This set the foundation for co-ordination among sensory systems, feeding, and locomotory structures - This could not be consistently achieved in a non-symmetrical animal Formation of nervous system in Chordata - Nerve ring and nerve net  ventral nerve chord  segmented nervous system with ganglia and ventral nerve chord o Chordates - Nerve ring and nerve net  ventral nerve chord  segmented nervous system with increased encephalization and dorsal nerve chord o Molluscs Endocrine systems - Any cell that evolved the capability for robust paracrine secretion had the potential to become and endocrine cell - These cells were present in all the basic tissue types of the earliest Metazoans o Therefore, all tissues had the capability of becoming endocrine organs - All tissues and organs have a variety of substances that are secreted into the blood stream o Therefore, all organs may be considered endocrine organs Vertebrate brain - General organization o Forebrain (prosenceophalon)  Diencephalon (hypothalamus)  Telencephalon o Midbrain (mesencephalon) o Hindbrain (rhombencephalon) o Nerve cord (spinal cord) - Ventricles o The brain and nerve chord are hollow, and consists of four ventricles filled with cerebral spinal fluid  Forebrain (ventricles I and II)  Midbrain (ventricle III)  Hindbrain (ventricle IV) o Humans have complex ventricle system, which are all connected and bent over backwards - Cerebrospinal fluid (CSF) o Fluid that surrounds the brain and fills t
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