Ch 2: Chemistry of Life pt. 1 

1. Atoms Ions, and Molecules

Living things consist of atoms and different elements

• atom: the smallest basic unit of matter.
  • everything is made out of atoms.

Atoms and Elements

• Atoms have protons, neutrons, and electrons.
  • Protons and neutrons form the nucleus in the center
  • Electrons circle outside the nucleus.
  • Protons are charged positively, electrons negatively, and neutrons are neutral.
• Element: A type of atom that cannot regularly be broken down into a simpler substance.
  • All atoms of an element have a number of protons that never changes.
  • The number of electrons determines the properties of the element.

Compounds

• Compound: a substance made of atoms of different elements bonded together in a certain ratio.
  • Compounds can be different from the base elements. (Ex. gaseous hydrogen and oxygen make water).

Ions form when atoms gain or lose electrons.

• Ion: an atom that had gained or lost one or more electrons.
  • Certain atoms are more stable when they lose or gain electrons.
  • Ions have an electrical charge, either positive or negative.
• Atoms that lose electrons = positively charged ions
• Atoms that gain electrons = negatively charged ions
• Electrons are usually gained/lost through moving electrons between atoms.
• Ionic Bond: A bond that forms through the electrical force between positively and negatively charged ions.

Atoms share pairs of electrons in covalent bonds

• Some atoms share pairs of electrons between them to be stable.
• Covalent bond: a bond that forms when atoms share a pair of electrons.
• Molecule: two or more atoms held together by covalent bonds.
• Diatomic molecules are molecules that have two of the same type of atom. (Ex. 2 Oxygen as a molecule).

2. Properties of Water

life depends on hydrogen bonds in water.

• water has unique properties like how it expands when frozen.

Water and Hydrogen Bonds

• A polar molecule is a molecule that has a region with a slight positive charge and a region with a slight negative charge.
  • Forms when atoms in a molecule have unequal pulls on shared electrons.
• Water is a polar molecule, with the hydrogen atoms having slight positive charges and the oxygen atom having a slight negative charge.
• A nonpolar molecule is a molecule that does not have charged regions.
• Hydrogen bond: An attraction between a slightly positive hydrogen atom and a slightly negative atom.

Properties related to hydrogen bonds

• Hydrogen bonds give unique properties to water.
  • Water has a high specific heat, which means it takes longer to heat up.
  • Water molecules stick to each other better with cohesion.
  • Water molecules stick to other things better with adhesion.
• Cohesion: The attraction among molecules of a substance.
• Adhesion: The attraction among molecules of different substances.

Many compounds dissolve in water.

• Molecules and ions must dissolve in water to take part in chemical processes in cells.
• Solution: a mixture of substances that is all the same throughout.
  • Called a homogeneous mixture (the same).
  • Requires two parts, the solvent, and the solute.
• Solvent: the substance in a solution that dissolves another substance.
• Solute: a substance in a solution that dissolves in a solvent.
• A solution’s concentration is the amount of solute dissolved in a certain amount of solvent.
• Polar substances dissolve more in water than nonpolar substances.

Some Compounds form acids or bases.

• Acid: a compound that releases a hydrogen ion when it dissolves in water.
• Bases: compounds that remove H ions from a solution.
• pH: A scale that measures the acidity of a solution.
  • Scale usually between 0 to 14.
  • 0 is the most acidic and 14 is the most basic.
• More acid means a higher positive hydrogen ion concentration.
• Most organisms need a specific pH.
  • Buffers help to regulate pH in organisms.

3. Carbon-Based Molecules

Carbon atoms have unique bonding properties.

• Carbon atoms are the basis of most moluecules that make up living things.
  • Carbon’s atomic structure gives it special bonding properties so it can bond with many other atoms.
• Carbon molecules can be straight chains, branched chains, and rings.
• Monomer: a subunit in a complete molecule.
  • A subunit can be a molecule inside a bigger molecule.
• Polymer: a large molecule made of many monomers bonded together
  • Large molecules are called macromolecules.

Four main types of carbon-based molecules are found in living things.

Carbohydrates

• Carbohydrates: molecules made of carbon, hydrogen, and oxygen.
  • Include sugars and starches.
• Simple sugars are the simplest form of carbohydrates.
  • Simple sugars bond to make larger carbohydrates.

Lipids

• Lipids: nonpolar molecules that include fats, oils, and cholesterol.
• Fatty acids: chains of carbon atoms bonded to hydrogen atoms.
  • Lipids contain fatty acids.
• Lipids contain three fatty acids called triglycerides.
• Saturated fats have the most hydrogen atoms while unsaturated fats have the least hydrogen atoms.
• All cell membranes are mostly made of phospholipid, a lipid with a polar head and a nonpolar end.
  • A phospholipid’s polar head contains a phosphate group.
• Cholesterol is a lipid that is needed in the human body.

Proteins

• Proteins: A large molecule (polymer) made out of smaller molecules (monomers) called amino acids.
• Amino acids: molecules that build proteins.
  • Amino acids form covalent bonds called peptide bonds.
  • Through peptide bonds, amino acids form polypeptides.
• One or more polypeptides form a protein.
• The sequence of amino acids effect the structure and function of a protein.
  • Proteins can be bent with certain elements (Sulfur and hydrogen)

Nucleic Acids

• Nucleic Acids: Larger molecules (polymers) that are made out of smaller molecules (monomers) called nucleotides.
  • Nucleic acids store information on how to build proteins.
• A nucleotide is made of a sugar, a phosphate group, and a molecule with nitrogen in it.
• Two types of nucleic acids are DNA and RNA.
  • DNA stores the information to build proteins.
  • RNA helps build the proteins.