Transcript 37000 genes
Astronomy 3040 Astrobiology Spring_2016 Day-11 Cells: Basic Units of Life Cells – microscopic units separated from the outside by a “membrane.” Basic structure of larger organisms. Can have one cell organisms. Life on Earth is Carbon-based - everywhere. Molecules linked by chemical bonds. Carbon molecules = organic Carbon + Hydrogen = hydrocarbon Silicon Based Life Silicon and Carbon are the only elements that can form 4 bonds. Significantly weaker than carbon bonds. Fragile, especially in water. Silicon does not normally form double bonds. Limits the reactions and molecular structures. Carbon can be in a gaseous state (CO2). SiO2 is a solid. Major Groupings Leeuwenhoek – 1674 – microscope 5 Kingdoms Plants Animals Protista Monera Fungi Is there a biochemical classification? Microscopic Life Plants and Animals are different Cell walls (plants) Cell Nucleus Prokaryotes Eukaryotes All prokaryotes are single celled. They lack a cell nucleus. Eukaryotes – single or multi-celled. Domains of Life Based on biochemistry and genetics: Bacteria Archaea Eukarya Tree of life. Kingdom – Phylum – Class – Order – Family – Genus – Species The Tree of Life Extremely valuable organizational tool. 3 key ideas 1. Domains based on biochemistry & genetics is fundamentally different from the older KPCOFGS based on structural & physiological differences. 2. New and fundamentally different view of microbes - lipid structure of cell membranes. 3. True diversity almost entirely in microbes. Metabolism: Chemistry of Life Metabolic needs: 1. Source of raw materials. 2. Source of energy. ATP: adenosine triphosphate Used by every living cell for internal energy. Outside energy needed only to produce ATP. Carbon sources – form basic materials. Energy sources – run the metabolism. Classification by Metabolism To obtain carbon: 1. Heterotrophs: Consume preexisting organic compounds (i.e. eating). 2. Autotrophs: Direct uptake from the environment (selffeeding, plants) Classification by Metabolism To obtain energy: 1. Photosynthesis: sunlight 2. chemosynthesis: chemical energy Ingested food Inorganic reactions 4 Metabolic Classifications Based on energy and carbon acquisition. 1. Photoautotrophs 2. Chemoautotrophs 3. Photoheterotrophs 4. Chemoheterotrophs Liquid Water on Earth All living cells on Earth depend on liquid water because metabolism requires: 1. Organic chemicals are readily available for reactions. 2. A means of transporting chemicals to and within cells; waste products away. 3. Water plays a role in many of the reactions. DNA and Heredity 3 key features of life on Earth 1. structural units – cells 2. metabolic processes – energy production 3. owner's manual – data storage for how a cell is constructed, how it works, and how to build another one, and pass it on to the next generation - heredity. DNA Structure Double helix DNA bases – 4 Adenine Guanine Thymine Cytosine Pair as AT & CG Replication Unzip & each strand acts as a template. Use RNA in the rebuild process. Genome Humans have ~3 X 10^9 bases 46 chromosomes (23 pairs) Sequences for individual instructions are called genes. Most of DNA is “noncoding” (junk 95%) Complete sequence – genome. Some bacteria – 10^5 bases, few 10^2 genes Humans – 20,000 – 25,000 genes Rice – 37,000 genes (smaller DNA sequence) Genetic Code Words consist of 3 DNA bases. Sequence has a start and stop word. Used to build proteins. Redundancy (64 codes, 20 amino acids) Most amino acids are coded with the first 2 base letters only (16). Does this give a clue to evolution of complex organisms? Nearly all living organisms have mostly similar genetic code. RNA Uses ACG & Uracil mRNA – transcription (carries the instr.) tRNA – transfer (gathers the AAs) rRNA – backbone of building structure. Mutations - <1:10^9, but can have dramatic consequences. Provide the basis for evolution. Genetic Engineering. RNA was probable precursor.