ASTR-3040: Astrobiology Day 11 The Nature of Life on Earth Chapter 5

Homework - 4 Due Tues. Feb. 22 Chapter 5:  4, 6, 14, 20, 25, 27, 33, 37, 42, 47, 48, 49, 51

Molecular Components Carbohydrates – energy sources  Sugars and starches Lipids – energy stores, barriers  Fats Nucleic Acids – DNA and RNA

Molecular Components Proteins – structure & chemistry  Structural materials  Enzymes – catalysts for reactions  Amino Acids (20 used in most life forms)‏  Left-handed in biological entities.

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 (self-feeding, 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.

Extreme Life - Extremophiles Thermophiles – heat lovers Hyperthermophiles  Black smokers (350˚C)‏  Hot springs

Extreme Life - Extremophiles Psychrophiles – cold lovers  Antarctica ice pack (-20˚C)‏  Also very dry Radiation hardened

Extreme Life - Extremophiles Endoliths – within rocks  Up to several km below ground Endospores (resting) – found on moon  Could these survive interplanetary journeys?