Chemistry of Life

Elements Essential to Life

Living organisms are primarily composed of a few key elements that are crucial for biological processes.

• Key Elements: Hydrogen, Oxygen, Nitrogen, and Carbon are the four most common elements in living organisms.

• Example: Sodium is not one of the four most common elements in living organisms.

Trace Elements

Trace elements are required by organisms in minute quantities but are essential for proper physiological functioning.

• Common Trace Elements: Iodine is a trace element commonly added to table salt to prevent iodine deficiency.

Atomic Structure

Atoms consist of protons, neutrons, and electrons. The atomic number equals the number of protons, while the atomic mass is the sum of protons and neutrons.

• Neutrons Calculation: Number of neutrons = Atomic mass - Atomic number.

• Example: Boron (atomic number 5, atomic mass 11) has 6 neutrons.

Isotopes and Radioactivity

Isotopes are atoms of the same element with different numbers of neutrons. Some isotopes are radioactive and decay over time.

• Radioactive Isotopes: Undergo decay; have more neutrons than protons.

• Applications: Used in PET scans to diagnose diseases.

Chemical Bonds and Water

Covalent and Ionic Bonds

Atoms form chemical bonds to achieve stable electron configurations.

• Covalent Bonds: Atoms share pairs of electrons.

• Ionic Bonds: One atom donates electrons to another, forming charged ions.

• Example: In NaCl, sodium donates an electron to chlorine.

Electron Shells

Electron shells are energy levels where electrons reside around the nucleus.

• Innermost Shell: Holds up to 2 electrons.

• Outer Shell: Holds up to 8 electrons.

• Nitrogen: Atomic number 7; electron configuration is 2 in the first shell, 5 in the second shell.

Water Properties

Water is vital for life due to its unique chemical and physical properties.

• Cohesion: Water molecules stick together via hydrogen bonds.

• Adhesion: Water molecules stick to other surfaces, aiding movement in plant tubes.

• Temperature Moderation: Water absorbs and releases heat slowly, helping regulate temperature.

• Ice Density: Ice is less dense than liquid water, allowing it to float.

• Solvent Properties: Water dissolves a wide range of substances due to its polarity.

Acids, Bases, and pH

Acids and bases affect the pH of solutions, which is a measure of hydrogen ion concentration.

• Bases: Contribute OH- ions, raising pH (making solution more basic).

• Ocean Acidification: Dissolving CO2 gas lowers ocean pH.

Biological Molecules

Isomers

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

• Example: Propanol and isopropanol have the same molecular formula but different chemical properties.

Functional Groups

Functional groups are specific groups of atoms within molecules that confer particular chemical properties.

• Carboxyl Group: Consists of a hydroxyl group and a carbonyl group.

Macromolecules: Carbohydrates

Carbohydrates are energy-rich organic compounds made of monosaccharide units.

• Monosaccharide Formula:

• Glucose: A monosaccharide and primary energy source for cells.

• Disaccharides: Composed of two monosaccharides.

• Polysaccharides: Long chains of monosaccharides; e.g., starch (storage in plants), cellulose (structural in plants), glycogen (storage in animals), chitin (structural in arthropods and fungi).

Macromolecules: Lipids

Lipids are hydrophobic molecules including fats, oils, and phospholipids.

• Triglycerides: Composed of glycerol and three fatty acids.

• Phospholipids: Major component of cell membranes; form bilayers with hydrophilic heads and hydrophobic tails.

• Phospholipid Behavior: In water, phospholipids form spheres (micelles) with tails inside and heads outside.

Macromolecules: Proteins

Proteins are polymers of amino acids, which have diverse functions in cells.

• Amino Acid Structure: Central carbon, amino group, carboxyl group, R group (side chain).

• Peptide Bonds: Formed by dehydration reactions between amino acids.

• Protein Structure: Primary, secondary, tertiary, and quaternary levels.

• Tertiary Structure: Involves bonding between R groups of amino acids.

• Denaturation: Loss of protein structure affects function.

Macromolecules: Nucleic Acids

Nucleic acids (DNA and RNA) store and transmit genetic information.

• DNA Structure: Composed of deoxyribose sugar, phosphate group, and nitrogenous base.

• Base Pairing: Adenine (A) pairs with Thymine (T); Cytosine (C) pairs with Guanine (G).

• Flow of Genetic Information: DNA → RNA → Protein

Cell Membranes

Phospholipid Bilayer

The plasma membrane consists of a phospholipid bilayer with embedded proteins.

• Phospholipid Heads: Hydrophilic, face outward toward aqueous solutions.

• Phospholipid Tails: Hydrophobic, face inward, shielded from water.

• Membrane Function: Selective barrier, compartmentalization, communication.

Membrane Proteins

Proteins embedded in the membrane perform various functions such as transport, signaling, and structural support.

• Example: Transport proteins facilitate movement of substances across the membrane.

Additional info:

• Some questions reference PET scans, which use radioactive isotopes to visualize metabolic processes.

• Ocean acidification is a result of increased atmospheric CO2 dissolving in seawater, forming carbonic acid and lowering pH.

• Isomers are important in biology because structural differences can lead to different biological activities.