1.2 - Elements of Life

All living organisms and their environments are composed of the same basic chemical elements.

Constant Exchange of Matter

Living things must continually exchange matter with their environment to maintain life processes:

• Intake

  • Oxygen (O₂) for cellular respiration

  • Nutrients (e.g., glucose) for energy and building blocks

  • Water (H₂O) as a solvent and for many reactions

  • Ions (e.g., sodium, potassium) for various cellular functions

• Output

  • Carbon dioxide (CO₂) as a waste product of respiration

  • Wastes (e.g., urea) to remove metabolic byproducts

  • Water (H₂O) through respiration, excretion, and other processes

  • Ions to maintain proper balance

Key Life Processes

• Respiration: Converting nutrients into energy

• Synthesis: Building complex molecules from simpler ones

• Growth: Increasing in size and complexity

• Division: Creating new cells for reproduction and repair

Carbon: The Backbone of Life

Besides water, most biological molecules are carbon-based. Carbon's unique ability to form four covalent bonds allows for the creation of a vast diversity of organic compounds.

Major Classes of Biological Molecules

• Carbohydrates: Composed of carbon, hydrogen, and oxygen (CHO); provide energy and structural support

• Lipids: Composed of carbon, hydrogen, and oxygen (CHO); include fats, oils, and waxes; store energy, insulation, and cell membrane components

• Proteins: Composed of carbon, hydrogen, oxygen, nitrogen (CHON), and sometimes sulfur; diverse functions including enzymes, structural components, and transport

• Nucleic Acids: Composed of carbon, hydrogen, oxygen, nitrogen, and phosphorus (CHONP); store and transmit genetic information (DNA and RNA)

All living organisms and their environments are composed of the same basic chemical elements. However, the arrangement of these atoms within molecules can lead to an astonishing diversity of compounds.

Isomers: Variations on a Theme

Isomers are molecules with the same chemical formula (same number and types of atoms) but different structural arrangements. This variation in structure often leads to differences in function.

Types of Isomers

• Structural Isomers: These have different arrangements of their atoms. For example, glucose and fructose both have the formula C₆H₁₂O₆ but different atom connectivity.

• Cis-trans Isomers (Geometric Isomers): These occur when a molecule has a double bond, preventing free rotation. If the same groups are on the same side of the double bond, it's called "cis." If they're on opposite sides, it's called "trans." These isomers can have distinct biological effects.

• Enantiomers (Optical Isomers): These are mirror images of each other, like your left and right hands. They have a central carbon atom bonded to four different groups. Enantiomers often interact differently with other molecules in biological systems, like enzymes.

Importance of Isomers in Biology

• Enzyme Specificity: Enzymes are highly specific and often only recognize one specific isomer of a molecule. This is crucial for many metabolic processes.

• Drug Design: Different isomers of drugs can have varying effects on the body, with some being beneficial and others harmful.

• Biological Activity: Enantiomers can have different biological activities. For instance, one enantiomer of a drug might be effective, while its mirror image might be inactive or even toxic.