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Phys 214. Planets and Life Dr. Cristina Buzea Department of Physics Room 259 E-mail: [email protected] (Please use PHYS214 in e-mail subject) Lecture 12. The nature of life on Earth. Evolution. Defining life. Cells February 1st Contents • Textbook pages 148-164 • • • • • • • • What is life? Evolutionary adaptation The mechanism of evolution Natural selection Cells - basic units of life Earth - Carbon based life Silicon based life Molecular components of cells Movie (13 minutes) Award winning series - Cosmos. Carl Sagan. (Not found online) What is life? 1. Order 2. Reproduction 3. Grows and develops 4. Energy 5. Responds to the environment 6. Evolutionary adaptation Molecules in living organisms exhibit order. They are arranged in patterns that make cell structures. Exception: crystals. The presence of order in living organisms is a necessary condition, but not a sufficient condition for life Spiral patterns in two single celled organism Copyright 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley What is life? 1. Order 2. Reproduction 3. Grows and develops 4. Energy 5. Responds to the environment 6. Evolutionary adaptation Living organisms reproduce or are products of reproduction. All organisms have finite lifetimes and eventually die. Reproduction corrects for this. The type of reproduction that occurs between human beings is referred to as sexual. Bacteria reproduce by the process of cell division (asexual). Exceptions: Mule - is sterile and cannot reproduce even though it is the product of reproduction between a horse and a donkey Viruses - incapable or reproducing on their own, need a living organism. Prions - infectious proteins, mad cow disease. A single-celled organism (amoeba) dividing into two cells. Copyright 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley What is life? 1. Order 2. Reproduction 3. Grows and develops 4. Energy 5. Responds to the environment 6. Evolutionary adaptation Living organisms grow and develop in patterns in part by heredity, traits passed to an organism from its parents. Exception: fire Nile crocodile emerging from its shell. Copyright 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley What is life? 1. Order 2. Reproduction 3. Grows and develops 4. Energy 5. Responds to the environment 6. Evolutionary adaptation Energy utilization in living organisms is one of the most basic requirements of life, without which organisms could not maintain order, grow, and reproduce. Exceptions: Some organisms can survive for very long period of times in dormant state. Tube worms living near deep-sea vents obtain energy from chemical reactions made possible in part by heat released from the volcanic vent. Copyright 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley What is life? 1. Order 2. Reproduction 3. Grows and develops 4. Energy 5. Responds to the environment 6. Evolutionary adaptation Life interacts with the surroundings and responds to environmental changes. Exceptions: human-made devices (thermostat) A jackrabbit’s ears flush with blood, the blood flow adjusts automatically to help the animal maintain a constant temperature by adjusting the heat loss from the ears. Copyright 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley What is life? 1. Order 2. Reproduction 3. Grows and develops 4. Energy 5. Responds to the environment 6. Evolutionary adaptation Life evolves as a result of the interactions between organisms and the environment, leading over time to evolutionary adaptations that make species better suited for the environment. When the adaptations are significant, these organisms may be very different from their ancestors – that they constitute a new species. A pygmy seahorse is camouflaged in its coral surroundings. Copyright 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Evolutionary adaptation Species = groups of organisms that are genetically distinct. • the precise border between the two species is not always clear (especially micro-organisms) Once a species is identified is given a name consisting of two parts: italics Genus (generic) Homo sapiens Horses and donkeys Equus caballus and Equus asinus Species (specific) Evolutionary adaptation Of the six basic properties of life, biologists consider the most fundamental to be evolutionary adaptation. Evolution - ancient idea Anaximander (c. 610-547 B.C.) – life arose in water and evolved to more complex forms Empedocles (c. 429-432 B.C.) – creatures poorly adapted perish Jean Baptiste Lamark – early 1800 – relationship between fossils and living organisms = life forms evolved by gradually adapting to perform successfully in their environments; not able to explain how evolution worked Charles Darwin – “The origin of species” 1859 The mechanism of evolution Charles Darwin – “The origin of species” 1859 Fact 1: Overproduction and competition for survival population has the potential to produce more offspring than the environment can support (food, shelter) = > competition for survival Fact 2. Individual variations: individuals vary in many heritable traits; some traits make them better to compete for survival Conclusion: unequal reproductive success = natural selection Individuals whose traits best enable them to survive and reproduce will, on average, leave the largest number of offspring that in turn survive to reproduce. Evidence for evolution by natural selection Darwin backed up his claim by documenting cases of related organisms adapted to different environments or lifestyle. The different species of finches found on the Galapagos islands are evidence of Darwin’s theory of natural selection because they have all evolved adaptations from a common ancestor to suit the environmental conditions found on different islands. Evidence for evolution by natural selection Darwin discovered fossils of extinct organisms clearly related to modern organisms (giant armadillos). Darwin realized that natural selection explains differences not only between closely related modern species (finches), but larger changes can occur over a long time -> extinction of some species and appearance of others. Artificial selection – selective breeding of domesticated plants and animals by humans over the few thousands of years. Dogs breeds with common ancestors – Rottweilers and Chihuahuas Evolution by natural selection Evolutionary adaptations are related to changes that occur through time in DNA The most basic definition of life which takes account of the relative importance of the six fundamental properties of living things is that life is something that can reproduce and evolve through natural selection. Evolution by natural selection Movie (13 minutes) Award winning series - Cosmos. Carl Sagan. Disk 2. Ch. 1-4. [0:00 – 13:00] Natural selection, artificial selection. Cells - the basic units of life The basic biological structures of life on Earth are called cells. • • Some organisms consist of single cells, others are complex structures with trillions of cells working cooperatively, having specialized tasks. Life elsewhere might be composed of cells, might not have the same biochemistry as Earth cells. The fact that all cells used in life on Earth are based on the same biochemistry suggests that all life on Earth shares a common ancestor. only left-handed amino acids; the same molecule - ATP - to store and release energy; passes hereditary information in the same way with DNA. Earth life is carbon based • Life on Earth made of more than 20 elements • More than 96% of the mass of living cells are made of carbon, hydrogen, oxygen, and nitrogen • The molecule that accounts for cell structure and function - Carbon Earth life is carbon based • • • • Carbon - ideal as a fundamental building block of biological molecules It readily forms chemical bonds with itself and other elements, allowing a wide variety of complex molecules to form! 4 = Maximum number of atoms that carbon can bond Single and double bonds Chemists refer to molecules containing carbon atoms as organic. Complex organic molecule. One bond links C to an amino group (green) Silicon based life? Is silicon an obvious alternative to carbon as a building block for biological molecules? It has a similar electronic structure to carbon, forming a maximum of four bonds and, hence, but does it have a similar chemistry? Silicon forms its strongest chemical bonds with oxygen. Silicon based life - unlikely! Reason why silicon is unsuitable as a building block for life compared to carbon 1. Silicon–silicon bonds are much weaker than carbon–carbon bonds 2. Silicon does not form multiple bonds with itself, limiting the complexity of molecules it can form 3. SiO2 is a high melting point solid and, hence, cannot be used to transfer silicon atoms like gaseous CO2 can be used to transport carbon atoms!! Silicon ~ 1000 times more abundant in Earth crust than carbon Life on Earth is based on carbon Why? Carbon (organic) molecules found in space - meteorites, interstellar dust, Jovian satellites Molecular components of cells Carbohydrates • MOST important role - shortterm energy storage • Provide energy to cells (sugars and starches) • Make important cellular structures (celulose - fibers of cotton and linen, main constituent of wood) Lipids • MOST IMPORTANT - Major ingredient of cell membrane (Membrane forming role critical in the origin of life spontaneously form membranes in water) • Long term energy storage (known as fats) Nucleic acids Most important - the storage and transfer of information DNA - The basic hereditary material on Earth RNA (ribonucleuc acid) - helps carry out instructions contained in DNA More on DNA later Proteins • basic functioning of living organisms • Vast array of functions • Structural elements • Enzymes - important to almost all biochemical reactions, including copying genetic material, serving as catalysts • Most important - enzymes - facilitate replication of DNA and the reading of the genetic code Amino acids The basic molecular building blocks of proteins are amino acids. • • Amino refers to the amino group (one nitrogen and 2 hydrogen); also contain a carboxyl group (CCOH). Different amino acids - distinguished by different sets of atoms bonded to the central carbon More than 70 amino acids identified, but life on Earth uses only 20! => all life on Earth has a common ancestor. Amino acids found in protein in life on Earth are all left-handed molecules. Next lecture • February 4th. Midterm exam review Common mistakes Calculations Marking of calculations I encourage you to solve the quantitative problems from the textbook! February 6th - Midterm exam! 1 hour, multiple choice questions + images description + calculations