LEC 2. LESSON 1. chemical basis of life

• Matter consists of chemical elements in pure form and in combinations called compounds.
• Elements - A substance that cannot be broken down to other substances by chemical reactions.
• The smallest possible particle of an element that still retains the properties of that element is called an atom (from the Greek atomos, “indivisible”).
• Chemical Bonds Hold Atoms Together

  • The attractive force that holds two or more atoms together in a compound.
• 2 Main Types of Bonds

  1. Ionic Bond 
  2. Covalent Bond 
• Covalent Bond

  •  Polar Covalent Bond
  • Nonpolar Covalent Bond
• Ionic Bond

  • Two atoms are so unequal in their attraction for electrons, and as a result, atoms gain or lose electrons to form this type of bond – Ion (a charged atom or molecule): 
  • Cation (+) when they lose
  • Anion (--) when they gain
  • electron transfer!!
• Covalent Bond

  • The sharing of a pair of electrons by two atoms 
  • Two or more atoms held together by covalent bonds constitute a molecule
  • electron shared!!
• do u get it

  A) atoms

  B) molecules

  C) compounds

  
• nonpolar

  •  The atoms have similar electronegativities 
  • Share the electron equally 
  •  Example: H2 and O2
• polar covalent bond

  • The atoms have differing electronegativities 
  • Share the electrons unequally
• Because oxygen (O) is more electronegative than hydrogen (H), shared electrons are pulled more toward oxygen.

  This results in a partial negative charge on the oxygen and a partial positive charge on the hydrogens.
• • In organisms, most of the strongest chemical bonds are covalent bonds, which link atoms to form a cell’s molecules.
• weak bonds

  • Example: Ionic bond, hydrogen bond, and van der Waals interaction
• Hydrogen Bonds

  • A noncovalent attraction between a hydrogen and an electronegative atom 
  • This can occur in inorganic molecules such as water and in organic molecules like DNA and proteins 
• • In organisms, hydrogen bonding affects the shape and function of protein and nucleic acid molecules and is important in determining the properties of water.
• Van der Waals Interactions

  • Occur only when atoms and molecules are very close together
• Inorganic Compounds

  • Are composed of elements other than carbon 
  • Examples: Water, acids, bases and buffers
• Organic Compounds

  • Contains carbon and usually hydrogen 
  • Many carbon atoms are usually bonded to one another to form a kind of molecular backbone that may consist of a straight chain, branched chain, or rings 
  • Examples: – Carbohydrates, lipids and proteins, Nucleic acids
• Inorganic Compounds

  • Water, Acids, Bases and Buffers
• Water

  •  An inorganic compound essential to plants 
  • It exists as a solid, liquid or vapor 
  • Vital to plants and other organisms because it carries dissolved nutrients and other important materials to cells 
  • All chemical reactions that sustain life occur in aqueous solutions 
  • Water’s polarity causes many of its properties
• 4 Emergent Properties of Water

  • The hydrogen bonds in water are the basis for many of its physical properties:

  1. Cohesive behavior 
  2. Ability to moderate temperature 
  3. Expansion upon freezing 
  4. Versatility as a solvent
• 1. Cohesion of Water Molecules

  • Water molecules stay close to each other as a result of hydrogen bonding. 
  • A phenomenon in which hydrogen bonds hold the substance together is called Cohesion. 
  • The clinging of one substance to another is called Adhesion. 
  • Related to cohesion is surface tension, a measure of how difficult it is to stretch or break the surface of a liquid.
  • Related to cohesion is surface tension, a measure of how difficult it is to stretch or break the surface of a liquid.
• 1. Ability to moderate temperature 

  • Water moderates air temperature by absorbing heat from air that is warmer and releasing the stored heat to air that is cooler. 
  • At sea level, water freezes at 0°C and boils at 100 °C. 
  • Water has a relatively high specific heat (the amount of heat that must be absorbed or lost for 1g of the substance to change its temperature by 1 °C. 
  • As liquid evaporates, the surface of the liquid that remains behind cools down.
• 1. Expansion upon freezing 

  • Water is one of the few substances that are less dense as a solid than as a liquid. 
  • Liquid water expands as it freezes because the hydrogen bonds joining the water molecules in the crystalline lattice of ice keep the water molecules far enough apart to give ice a lower density than the density of liquid water.
• 1. Versatility as a solvent

  • Many materials can be dissolve in water as a result of its polarity. 
  • In nature, water is never completely pure, because it contains dissolved gases from the atmosphere and dissolved mineral salts from Earth. 
  • Water is not a universal solvent; if it were, it would dissolve any container in which it was stored, including our cells.
• Acids and Bases

  • One of the most important aspects of either environment is how acidic or basic (alkaline) it is. 
  • The degree of acidity or alkalinity inside a plant cell must remain fairly stable 
  • Acids and bases dissociate when dissolved in water
• pH Scale

  • Measures the relative concentrations of hydrogen ions and hydroxide ions in a solution. 
  • pH scale extends from 0 (the pH of a strong acid such as HCl) to 14 (the pH of strong base such as NaOH), while pure water has 7 (neutral pH)
  • Example : pure water (pH 7), tomato juice (pH 4), vinegar (pH 3), and lemon juice (pH 2)
• Organic Compound

  • Carbohydrates, Lipids, Nucleic Acids and Proteins
• CARBOHYDRATES

  • It is composed of carbon (C), hydrogen (H), and oxygen (O) atoms in an approximate ratio of 1C:2H:1O. 
  • The general equation for carbohydrates is (CH2O)n , where n refers to any number from 3 to several thousands. 
• • 3 kinds of carbohydrates: Monosaccharides, Disaccharides and Polysaccharides
• 1. Monosaccharides

  • Also known as simple sugars and fuel molecules of cells, the monomer of carbohydrate 
  • Contain 3 to 6 carbon atoms.
  • Glucose (C6H12O6 ) is produced by plants through photosynthesis 
  • Fructose (C6H12O6 ) or fruit sugar
• 1. Disaccharides

  • Also known as double sugar 
  • Consists of two bonded monosaccharide units – Sucrose (C12H22O11) or table sugar 
  • The formation of sucrose from glucose and fructose involves the removal of a molecule of water (condensation reaction) or dehydration reaction.
• 1. Polysaccharides

  • Also known as complex sugar, and composed of many sugar units 
  • 2 major function: 

  1.  Building/structural material ex. Cellulose (major component of plant cell walls) 
  2. Main carbohydrate storage/reserves in plants ex. Starches (potatoes, corn, and rice)
• LIPIDS

  • Have a greasy or oily consistency and do not readily dissolve/mix in water. 
• 1. Phospholipids

  • A group of lipids important as components of cell membranes
• • Suberin is a waxy substance found in the walls of cork cells (the outer bark of woody plants) 
• Cutin and suberin protect the plant’s aerial surfaces from excess water loss
• PROTEINS

  • Are macromolecules composed of carbon, oxygen, hydrogen, nitrogen and usually sulfur that serve as structural components of cells and tissues 
  • It regulate biochemical processes in plants and other organisms 
• proteins are composed of hundreds of units called amino acids