The elements of life

Carbon, hydrogen, oxygen, and nitrogen make up 96% of living matter.

Most of the remaining 4% consists of calcium, phosphorus, potassium, and sulfur.

Trace elements are those required by an organism in minute quantities.

Figure 1. the elements of life

The formation and function of molecules depend on chemical bonding between atoms.

  • Covalent Bonds: strong chemical bonds
  • Ionic Bonds
  • Hydrogen Bonds
  • Van der Waals Interactions

Chemical reactions make and break chemical bonds.

  • The starting molecules of a chemical reaction are  called reactants.
  • The final molecules of a chemical reaction are called products.

Figure 2. chemical reactions

Photosynthesis is an important chemical reaction.

Sunlight powers the conversion of carbon dioxide and water to glucose and oxygen.

6 CO2 + 6 H20 → C6H12O6 + 6 O2

water and life

  • Water is the biological medium on Earth.
  • Most cells are surrounded by water, and cells themselves are about 70–95% water.
  • The abundance of water is the main reason the Earth is habitable.
  • Water: The Solvent of Life
  • Acidic and basic conditions affect living organism.
  • Water is in a state of dynamic equilibrium in which water molecules dissociate at the same rate at which they are being reformed.

Figure 3. water dissociation

Carbon and Molecular Diversity of Life

Living organisms consist mostly of carbon-based compounds.

Proteins, DNA, carbohydrates, and other molecules are all composed of carbon compounds.

Isomers

Isomers are compounds with the same molecular formula but different structures and properties.

  • Structural isomers have different covalent arrangements of their atoms
  • Cis-trans isomers have the same covalent bonds but differ in spatial arrangements
  • Enantiomers are isomers that are mirror images of each other

The Structure and Function of Large Biological Molecules

Macromolecules are polymers, built from monomers.

  • A polymer is a long molecule consisting of many similar building blocks
  • These small building-block molecules are called monomers
  • Three of the four classes of life’s organic molecules are polymers

Carbohydrates

Proteins

Nucleic acids

Dehydration reaction: synthesizing a polymer

Figure 4. dehydration

Hydrolysis: breaking down a polymer

Figure 5. hydrolysis

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