Levels of Organization, Chemical Level, and Macromolecules

Levels of Organization

• Simplest to most complex:
  • Chemical → Cellular → Tissue → Organ → Organ System → Organismal

Chemical Level

• Matter: Anything with mass that takes up space (e.g., rocks, gases).
  • Composed of elements.

Elements

• Pure substances with unique properties.
  • Can't be broken down by ordinary chemical means.
  • ~90 elements occur naturally.

Essential Elements for Life

• Element composition varies in abundance.

Atoms

• Elements' properties depend on the structure of their atoms.
  • Atom: Smallest unit of an element that retains its properties.

Atomic Components

• Atoms contain:
  • Neutrons: No charge, ~1 atomic mass unit (amu).
  • Protons: +1 charge, ~1 amu.
  • Electrons: -1 charge, negligible mass.
  • Located at varying distances from the nucleus

Atomic Models

• Planetary Model:
  • Electrons orbit the nucleus in fixed paths.
• Electron Cloud Model:
  • Electrons exist in probability clouds around the nucleus.

Periodic Table

• Chemical Symbol: Unique identifier for each element (e.g., C for carbon).
• Atomic Number: Number of protons; defines the element.
  • Located above the element symbol.
• Average Atomic Mass: Mass of protons + neutrons.
  • Shown below the element’s symbol.

Determining Subatomic Particles

• Protons = Atomic Number
• Electrons = Protons (in a neutral atom)
• Neutrons = Atomic Mass - Protons

Atomic Structure Diagrams

• Electrons occupy shells around the nucleus.
  • Innermost shell: max 2 electrons
  • Second shell: max 8 electrons
  • Fill from the inside out.

Chemical Stability & Octet Rule

• Columns in the periodic table relate to valence electrons (outer shell).
• Elements 'want' to achieve a full outer shell (8 electrons, except for some small atoms like Hydrogen and Helium).

Octet Rule

• Atoms gain, lose, or share electrons to get a full outer shell.

Chemical Bonds

• Atoms bond to achieve stability.
  • Ionic Bonds
  • Covalent Bonds

Ionic Bonding

• Electrons are TRANSFERRED.
  • Creates ions (charged atoms).
  • Cations: positive ions (lost electrons)
  • Anions: negative ions (gained electrons)
  • Ions are attracted to each other → ionic bond (salts).

Covalent Bonding

• Electrons are SHARED.
  • Creates molecules.

Single, Double, Triple Covalent Bonds

• Single: 1 shared electron pair (e.g., $H_2$)
• Double: 2 shared pairs (e.g., $O_2$)
• Triple: 3 shared pairs (e.g., $N_2$)

Covalent Bonds & Carbon

• Carbon needs 4 electrons to complete its octet.

Electronegativity

• An atom's ability to attract shared electrons in a bond.

Electronegativity & Partial Charges

• More electronegative atom → partial negative charge (δ–)
• Less electronegative atom → partial positive charge (δ+)
• Polarity: separation of charge.

Polar vs. Nonpolar Covalent Bonds

• Nonpolar: equal sharing of electrons.
• Polar: unequal sharing.

Ionic Bonding & Electronegativity

• Electronegativity difference dictates bond type.

Inorganic vs. Organic Compounds

• Important for structure and function.

Chemical Constituents of Cells

• Inorganic:
  • Usually lack carbon, simple structure.
  • E.g., water, salts
• Organic:
  • Contain carbon and hydrogen, complex.

Water & Electronegativity

• Oxygen is more electronegative than hydrogen in water ($H_2O$).
  • Creates partial charges.

Hydrogen Bonds

• Weak attraction between a hydrogen atom (δ+) and another electronegative atom (δ–).
  • Doesn't form new molecules, affects properties.

Water Properties (Due to Hydrogen Bonds)

• Liquid at room temperature
• Cohesive (sticks to itself)
• High heat capacity (stable temperature)
• Less dense when frozen
• Lubricant
• Solvent for polar molecules (hydrophilic).
  • Hydrophobic = water-repelling.

Water as a Solvent

• Forms hydration shells around ions.

Salts

• Ionic compounds that dissociate into ions in water (not $H^+$ or $OH^−$).
  • Electrolytes: conduct electrical current.

Acids and Bases

• Acid: Releases $H^+$ (protons) in solution.
• Base: Releases $OH^−$ (hydroxide ions) or accepts $H^+$.

Organic Compounds

• Carbon and hydrogen-based, covalent bonds.
  • Large and complex.
  • Monomers vs. Polymers

Water's Role in Reactions

• Dehydration Synthesis: joins monomers, releases water.
• Hydrolysis: breaks polymers, adds water.

Four Organic Molecules

1. Carbohydrates
2. Lipids
3. Proteins
4. Nucleic Acids

Carbohydrates

• C, H, O in 1:2:1 ratio (e.g., glucose $C<em>6H</em>{12}O_6$).
  • Energy source.

Carbohydrate Diversity

1. Monosaccharides: simple sugars (glucose, fructose)
2. Disaccharides: 2 monosaccharides (formed by dehydration synthesis)
3. Polysaccharides: many monosaccharides

• Starches (plant energy storage)
• Glycogen (animal energy storage)

Lipids

• C, H, O (less oxygen than carbs).
  • Triglycerides, phospholipids, steroids.
  • Hydrophobic.

Triglycerides

• Glycerol + 3 fatty acids.
  • Energy storage.

Fatty Acid Shapes

• Saturated: straight chains
• Unsaturated: kinked chains

Other Lipids

• Phospholipids: 2 fatty acids + phosphate group
• Sterols: ring-shaped (cholesterol)
• Prostaglandins: from unsaturated fatty acids

Proteins

• C, H, O, N
  • Amino acid monomers.
  • Peptide bonds link amino acids.
  • Structure: primary, secondary, tertiary, quaternary.
  • Shape dictates function.

Protein Functions

• Support, movement, transport, buffering, metabolic regulation (enzymes), coordination, defense (antibodies), storage.

Amino Acid Structure

• Amino group, carboxyl group, R group.
  • Peptide bonds form between amino acids.

Amino Acid Types

• Nonpolar, polar, electrically charged (acidic, basic).

Protein Structure

• Primary: amino acid sequence
• Secondary: alpha helix or beta sheet (H-bonds)
• Tertiary: 3D folding (R group interactions)
• Quaternary: multiple polypeptide chains

Nucleic Acids

• C, H, O, N, P
  • Nucleotide monomers.
  • Nucleotide = nitrogenous base + pent