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AP Biology Unit 1- The Chemistry Of Life Review

Topic 1.1: Structure of water and hydrogen bonding

Properties of Water

Hydrogen Bonds + Polarity

  • Polar: Oxygen has a partial negative charge, hydrogen has a positive charge

  • Hydrogen bond: Weak bond between hydrogen in a polar molecule and a small electronegative atom, forms due to the two atoms’ opposite charges

  • Cohesion: Hydrogen bonds hold a substance together

  • Adhesion: Clinging of one substance to another-- especially between water and another polar substance

  • Both adhesion and cohesion allow water to move against gravity

  • Surface temperature: How difficult it is to break or stretch the surface of a liquid, water has a high surface tension due to hydrogen bonds

Temperature Moderation

  • High specific heat: Water is able to absorb/release a lot of heat without its own temperature changing much, water absorbs warm air and releases it to cooler air. Allows climate moderation
  • High heat of vaporization: Water has to absorb a lot of heat to change from a liquid to a gas and water cools when its molecules evaporate. Allows evaporative cooling

Ice Floats

  • Water expands (becomes less dense) in its solid form, so ice floats

Floating ice insulates water below it

Solvent

  • Solvent: The substance that dissolves other molecules in a solution
  • H2O is a versatile solvent due to its polarity
  • Water can carry many chemicals, nutrients, and minerals throughout an ecosystem and the organisms within it

Topic 1.2-1.6: Macromolecules and the elements of life

Carbon

  • Carbon: Has 4 valence electrons so can form 4 covalent bonds, allowing it to be the backbone for many complex and diverse molecules

  • Organic compounds: Compounds containing carbon

    Examples of various structures carbon helps form

Functional Groups (not required course content but definitely helpful to know)

  • Functional groups change function by being directly involved in chemical reactions
  • Hydroxyl (OH-): Alcohol, make substance more basic (raises pH)
  • Carboxyl (-COOH): Acid, contributes H+ (lowers pH)
  • Amino group (-NH2)
  • Phosphate group: Add negative charge to a molecule

Polymers and Monomers

  • Polymer: A molecule made of similar building blocks

  • Monomer: One of the units making up a polymer

  • Dehydration reaction: Monomers connected and covalently bonded by removing a hydrogen from both molecules and an oxygen from one (making H2O)

    Dehydration reaction example

Hydrolysis: Bond between monomers of a polymer is broken by adding H2O

Hydrolysis example

Carbohydrates

  • Contain elements: Carbon, hydrogen, and oxygen
  • Monomer: Monosaccharide
  • Polymer: Polysaccharides (chain of monosaccharides linked by covalent bonds called glycosidic linkages)
  • Functions: Provide and store energy, provide structural support

Important polysaccharides (all are glucose polymers)

  • Starch: Stores glucose in plants
  • Glycogen: Glucose storage in animals
  • Chitin: Structural polysaccharide in fungi cell wells and arthropod exoskeletons
  • Cellulose: Cell wall component for plant cells

Lipids

  • Elements: Carbon, hydrogen, oxygen (sometimes N or P)

  • No true monomers of lipids

  • Have little to no affinity for water (hydrophobic)

  • Function: Energy storage and structure

  • Saturated: No double bonds between carbon atoms, atoms tightly packed

  • Unsaturated: Double bonds between some carbons creating a kink in the chain

Trigylcerol: 3 fatty acids attached to one glycerol, energy storage

Phospholipid: Form phospholipid bilayer, have a hydrophilic head and hydrophobic tail

Cholesterol: Steroid that contributes to cell membrane integrity

Nucleic Acids

  • Elements: Carbon, hydrogen, oxygen, phosphorus

  • Monomers: Nucleotides, consist of a 5 carbon sugar, a phosphate, and a nitrogenous base

  • Polymers: Nucelic acids, linear sequences of nucleotides

  • Nitrogenous base pairs: Adenine pairs with thymine (or uracil in RNA), and cytosine pairs with guanine

  • Purines: Have a 2 ring structure (A and G)

  • Pyrmidines: Have a 1 ring structure ( C and T/U)

  • C and G are joined by 3 bonds, A and T are joined by 2

  • Directionality: Determined by orientation of sugars (hydroxyl = 3´ and phosphate = 5´)

  • Base pairs are joined by hydrogen bonds, nucleotides joined by covalent bonds

  • DNA: Antiparallel double helix (2 strands running in opposite directions), has deoxyribose

  • RNA: Single stranded, has ribose

Proteins

  • Elements: Carbon, hydrogen, oxygen, nitrogen, sulfur

  • Monomers: Amino acids, consist of carboxyl group + amino group + R group

  • Different amino acids have different R groups

  • Polymer: Polypeptide

    STRUCTURE

    • Primary: Linear sequence of covalently bonded amino acids

    • Secondary: Structure formed by interactions between polypeptide´s ¨Backbone¨ ( carboxyl and amino groups)

    • Tertiary: 3d structure formed by interactions ( hydrogen bonds, ionic bonds, disulfide bridge, hydrophobic, etc.) between R groups

    • Quaternary: More than one polypeptide chain joined together