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

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.

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

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.

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.

Types of Bonds Ionic Covalent Hydrogen 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.

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

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

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

Polar/nonpolar bonds

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!

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

Application: Thermal Properties (Water vs. Methane) Specific Heat Capacity 4.2 J/g/oC 2.2J/g/oC Heat of vaporization 2257 J/g 760 J/g Melting Point 0 oC -182 oC Boiling Point 100oC -160oC

Cohesion~ H bonds holding water molecules together 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

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…

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

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)

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

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

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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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

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)