Topic 3: The Chemistry of Life: an Introduction

1. Topic 3: The Chemistry of Life: an Introduction • Corresponding Textbook chapters: • Chapter 2: Chemical Context of Life • Chapter 3: Water and the Fitness of the Environment

2. Chemical Context of Life (skip) • Living things are matter so they are made up of elements that combine to build biological molecules! • Element--a substance that can not be broken down to other substances by chemical reactions. In other words, an element is composed of a single type of Atom • The atom-- smallest unit of matter having the physical and chemical properties of an element.

3. Atomic Structure (skip?) • Nucleus • Protons (+ charge) • Neutrons (no charge) • Electrons (- charge) • Atomic number (# of protons); • mass number (protons + neutrons)

4. Most frequent elements in life! (3.1.1) • Top 4: HONC (Why?) • b/c they are the main elements found in organic molecules in organisms. • Some other necessary elements include: • Sulfur – found in 2 amino acids • Calcium – chemical messenger that helps regulate cell processes… • Phosphorus – ATP and DNA, RNA (as phosphate) • Iron – needed in cytochromes for electron transport chains, hemoglobin. • Sodium – water balance/homeostasis– pumped in to cells to cause water uptake (why does this work?), nerve impulses.

5. Chemical Bonds • Elements bond in order to be stable • Stable = having a full valence energy level • Compound -- two or more elements combined in a fixed ratio.

6. Types of Bonds • Ionic • Covalent • Single,double, triple • Nonpolar covalent • Polar covalent • Hydrogen • Note: The type of bond formed is due to the electronegativity (attraction for electrons) of the atoms involved.

7. Ionic bonding • One atom strips valence electrons away from another atom (due to high electronegativity difference) • Electron transfer creates ions (charged atoms) • Cation (positive ion); anion (negative ion) • Ex: Salts (sodium chloride) Animations

8. Covalent Bonding • Sharing pair of valence electrons • Number of electrons required to complete an atom’s valence shell determines how many bonds will form • Ex: Hydrogen & oxygen bonding in water, bonding in organic molecules • Molecule= when elements covalently bonded Animations

9. Polar/nonpolar covalent bonds • Electronegativity attraction for electrons • Nonpolar covalent •electrons shared equally •Ex: O2 , C-H bonds • Polar covalent •one atom more electronegative than the other (creates partial charges) •Ex: water

10. Polar/nonpolar bonds

11. Hydrogen bond • Attraction between a partially positive hydrogen atom of one polar molecule and a partially negative atom (like oxygen or nitrogen) of another polar molecule. • Be able to draw water, showing its polarity and hydrogen bonds!

12. Properties of Water (How are its characteristics important to living things???) • Note: Water’s properties are due to its POLARITY and the resultant HYDROGEN BONDS. • Thermal Properties: • High Specific heat~ amount of heat absorbed or lost to change temperature by 1°C (water= 1cal/g/°C) • Heat= a type of energy (associated with molecular motion). • High Heat of vaporization~ quantity of heat required to convert 1g from liquid to gas states. Evaporative cooling/ sweat! • High boiling point ~ 100oC

13. Application: Thermal Properties (Water vs. Methane)

14. Cohesive Properties: • Cohesion~ H bonds holding water molecules together • Surface tension~ measurement of the difficulty to break or stretch the surface of a liquid • “Jesus Lizard” https://www.youtube.com/watch?v=45yabrnryXk

15. Properties of Water (continued) • Solvent Properties: • Very good solvent. Sometimes called the “universal solvent” • What types of substances are soluble in water? • Solution= completely homogenous mixture. • Review: Solute… Solvent…

16. Application: Modes of transport in blood depend on solubility • Discuss: Which types of molecules would be easily dissolved and transported in water? • Evaluate these in terms of solubility and hypothesize how they would be transported: • Sodium Chloride • Amino Acids • Glucose • Oxygen gas • Fats • Cholesterol

17. Application: Modes of transport in blood depend on solubility • Sodium Chloride – dissolved in plasma (ions) • Amino Acids – dissolved in plasma (sufficient solubility due to charged regions) • Glucose – dissolved in plasma (polar) • Oxygen gas– carried by hemoglobin (nonpolar) • Fats – transported in lipoprotein complexes (nonpolar) • Cholesterol -- transported in lipoprotein complexes (nonpolar)

18. Other properties: • Adhesion~ H bonds holding molecules to another substance • Density…

19. Density • Less dense as solid than liquid • Due to hydrogen bonding • Crystalline lattice keeps molecules at a distance

20. Water’s Uses in Organisms • Journal: Explain the relationship between the properties of water and its uses in living organisms as a coolant, medium for metabolic reactions, transport medium, and habitat (see question 4 of journals). • Do the above for each property… • 8 marks

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22. Chemical Reactions • Making and breaking of chemical bonds leading to the changes in the composition of matter • A chemical reaction is represented by a chemical equation • 6 CO2+ 6 H2O  C6H12O6+ 6 O2 reactants  products

23. Acid/Base & pH • Acid: increases the hydrogen concentration of a solution • Base: reduces the hydrogen ion concentration of a solution • pH scale • Buffers: substances that minimize H+ and OH- concentrations (accepts or donates H+ ions)