The Chemical Context of Life

1. The Chemical Context of Life Chapter 2

2. HCO2H. A Chemical Connection to Biology Methanoic acid • Ex. Ants maintain Duroiahirsuta“devil’s gardens,” in Peru by injecting formic acid into other plants Ants Myrmelachista schumanni This plant is the only species in this tropical rain forest!

3. Formic acid stinging ants  decalcifier; reducer in dyeing for wool; dehairing and plumping hides; tanning; electroplating; coagulating rubber latex; silage and grain preservation; solvents of perfume; lacquers;   Some beekeepers use formic acid as a fumigant to kill a mite which attacks the bees. Most ant species probably use it as a disinfectant

4. Scientific method • Two saplings of a common Amazonian tree, Cedrela odorata, or Spanish cedar, were planted inside each Devil’s garden near the base of a D. hirsuta tree actively patrolled by worker ants. A sticky insect barrier was applied to one cedar sapling to exclude ants, while the other sapling was left untreated. • The results were immediate. Worker ants promptly attacked the untreated saplings by injecting formic acid into the leaves, which began to die within 24 hours. "Most of the leaves on these saplings were lost within five days, and the proportion lost was significantly higher than on ant-excluded saplings,". Cedars treated with the insect barrier fared lived. • Independent variable = • Control group = • Controlled variables = • Dependent variable =

5. Matter, elements, and compounds • matter - anything that takes up space and has mass • Matter is made up of elements • element - substance that cannot be broken down to other substances

6. 25 are essential for life in humans 94 elements occur naturally

7. compound -consists of 2 or more elements in fixed ratio -characteristics different from those of its elements NaCl Na Cl Sodium and water

8. http://youtu.be/m55kgyApYrY

9. Essential Elements of Life About 25 of the 92 elements are essential to life (humans) • CHON =96% of living matter • Also……. • Trace elements required by an organism in minute quantities

10. Copper deficiency prevents full opening of leaves Trace amounts of iodine required for thyroid function (b) Iodine deficiency

11. An element’s propertiesdepend on structure of its atoms • atom =smallest unit of matter that still retains properties of element • subatomic particles • Neutrons (no electrical charge) • Protons (+ charge) • # protons defines the element • Electrons (- charge)

12. Isotopes • Isotopes • Atoms of an element that differ in # of neutrons • Radioactive isotopes • Isotope decays  particles and energy decay • Half life = lifetime for ½ of the isotopes to decay

13. FYI number of protons and neutrons number of protons 12Cis stable , 6 neutrons 14C is radioactive, 8 neutrons 98.89% of carbon

14. FYI • Atomic numbers (# protons) 1 through 40 are considered stable isotopes • Elements 41 through 82 are stable. The half lives of elements 41 through 82 are so long that their radioactive decay has yet to be detected by experiment (100 million times longer than the age of the universe) • 83 through 94 radioactive decay can be detected. • uranium has one or more isotopes with half lives long enough to survive as remnants of the explosive big bang • 94 and higher only observed experimentally – extremely short half life • Tritium (3H) lowenergy beta particle. 12.35 years. Used to tag DNA. No shield necessary. Wear gloves. • Carbon-14 decays into nitrogen-14 by emission of a beta particle. Half life 5730 years. No shield, wear gloves, can penetrate skin. • Phosphorus-32 a beta particle. Half life 14.2 days. Use plexiglass. • Iodine-125 gamma rays. 60 day half life. biological assays, nuclear medicine imaging and in radiation therapy. Thyroid cancer treatment. Use lead shield. • Polonium has 26 isotopes, all radioactive. 250 billion times more toxic than hydrocyanic acid. It is readily soluble in weak acid. It was the first element discovered by Marie Curie, in 1898, and named after her native Poland. Her daughter Irene was contaminated with polonium in a laboratory accident and died of leukemia at the age of 59.

15. FYI • 2006, Litvinenko fell ill. Earlier he had met two former KGB officers in London. Had to do with information on death of journalist killed at her Moscow apartment 2006. • For several days , Litvinenko experienced severe diarrhea and vomiting. Litvinenko's condition worsened as doctors searched for what caused the illness. Litvinenko began to become physically weak, and spent periods unconscious • Shortly after death, it was found Litvinenko had significant amounts of (210Po) in his body. The poison was in Litvinenko's tea cup. • Polonium was identified after Litvinenko's death, on 23 November. Doctors could not detect polonium earlier because it only emits alpha particles that do not penetrate human skin, thus being invisible to hospital radiation detectors . An alpha-emitting substance can cause significant damage only if ingested or inhaled, acting on living cells like a short-range weapon. • The symptoms seen in Litvinenko appeared consistent with an administered activity of approximately (50 mCi which corresponds to about 10 micrograms of 210Po. 200 times the lethal dose

16. radioactive isotopes in biology: • Dating fossils • Medical imaging • Lab research

17. Radiolabeled glucose atom used in PET scans A PET scan (positron emission tomography) detects locations of intense chemical activity. Inject patient with radioactive glucose. A scanner measures collisions of the radioactive glucose with active cells to locate tumor

18. Example: Use of isotopes in research Hypothesis: Cells reproduce faster at higher temperatures 3H-thymidine, building block of DNA Hela cells

19. Add tritiated thymidine to cells. Cells incorporate isotope into new DNA • 1 cells at 10oC • 15oC • 20oC • 25oC • 30oC • 35oC • 40oC • 45oC • 50oC 1 2 3 Cells 7 8 9 Isolated DNA is radioactive

20. Measure radioactivity in counter TECHNIQUE The test tubes are placed in a scintillation counter. 3

21. RESULTS Results 30 Counts per minute ( 1,000) 20 10 0 40 20 30 50 10 Temperature (ºC)

22. Chemical Formulas • Structural formula represents atom bonding H–OH • Molecular formula abbreviation H2O

23. Chemical Bonds 1. Covalent bond – electrons shared by 2 atoms • Ex. O2, H2O • Strong bond

24. 2. Ionic bond – one atom loses an electron • Ionis a charged atom Na+ Cl- • Weaker bond • Salts

25. 3. HydrogenBonds • H atom covalently bonded to electronegative atom is attracted to another atom

26. 4. Van der Waals Interactions • Between molecules of the same substance • Similar to hydrogen bonds but weaker • BBC gecko • Van der waals gecko and synthetic glue

27. Molecular Shape and Function • molecules have specificity/function based on shape • similar shapes can have similar biological effects

28. Key Nitrogen Carbon Sulfur Hydrogen Natural endorphin Oxygen Morphine (a) Structures of endorphin and morphine Natural endorphin Morphine Endorphin receptors Brain cell (b) Binding to endorphin receptors

29. Chemical reactions Chemical reactions make and break chemical bonds • reactants - starting molecules • products - final molecules

30. light Photosynthesis 6 CO2 + 6 H20 →C6H12O6 + 6 O2

31. Chemical reactions are reversible • Chemical equilibrium =when forward and reverse reaction rates are equal (in a closed system)