The Chemical Context of Life. Chapter 2

Transcription

1 The Chemical Context of Life Chapter 2

2 A Chemical Connection to Biology HCO 2 H. Methanoic acid Ex. Ants maintain Duroia hirsuta 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 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 =

4 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

5 25 are essential for life in humans 94 elements occur naturally An element is defined by # protons (atomic number)

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

7 The above link is a video on periodic table elements that are reactive and are grouped together on the table.

8 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

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

10 An element s properties depend 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)

11 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 (atom loses particles)

12 FYI uranium has one or more isotopes with half lives long enough to survive as remnants of the explosive big bang Tritium ( 3 H) low energy beta particle 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. There are three main kinds of ionizing radiation: alpha particles, which include two protons and two neutronsm beta particles, which are essentially high-speed electrons gamma rays and x-rays, which are pure energy (photons).

13 radioactive isotopes in biology: Dating fossils Medical imaging Lab research

14 Radiolabeled glucose atom used in PET scans FYI: 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. Gamma rays. PET scan to: Locate site of cancer Determine size of tumor Differentiate benign from malignant growths Discover if cancer has spread Monitor the success of therapy Detect recurrent tumors

15 Chemical Formulas Structural formula represents atom bonding H OH Molecular formula abbreviation H 2 O

16 Chemical Bonds 1. Covalent bond electrons shared by 2 atoms Ex. O 2, H 2 O Strong bond

17 2. Ionic bond one atom loses an electron Ion is a charged atom Na + Cl - Weaker bond Salts

18 3. Hydrogen Bonds H atom covalently bonded to electronegative atom is attracted to another atom

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

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

21 Chemical reactions Chemical reactions make and break chemical bonds reactants - starting molecules products - final molecules

22 Photosynthesis 6 CO H 2 0 C 6 H 12 O O 2 light

23 Many chemical reactions are reversible Chemical equilibrium =when forward and reverse reaction rates are equal (in a closed system) CO 2 + H 2 O H 2 CO 3