Biology I - Chapter 4

Carbon and Organic Chemistry

Cells consist of 70–95% water, with most of the remaining material composed of carbon-based compounds.
Organic chemistry is the study of carbon compounds regardless of origin, ranging from simple molecules like methane ( $\text{CH}_4$ ) to complex macromolecules.
Historical shift from vitalism to mechanism:
- Vitalism: Proposed that organic compounds could only arise within living organisms.
- Mechanism: Replaced vitalism by establishing that physical and chemical laws govern all biological phenomena.
- Synthetic breakthroughs by Friedrich Wöhler (urea synthesis) and Hermann Kolbe (acetic acid synthesis) disproved vitalism.
- Stanley Miller demonstrated the abiotic synthesis of organic compounds under simulated primitive Earth conditions, such as near volcanoes.

Stanley Miller's experimental apparatus simulating early Earth conditions

Carbon Bonding and Geometry

Carbon has 6 electrons (2 inner shell, 4 valence) and forms 4 covalent bonds to complete its octet.
Molecular spatial geometry depends on bonding pattern:
- Single-bonded carbon atoms form a tetrahedral shape with bond angles of $109.5^\circ$ .
- Carbon-carbon double bonds cause all attached atoms to lie in the same flat plane.
The valences of carbon and its frequent partners—hydrogen, oxygen, and nitrogen—serve as the structural code for biological molecules.

Molecular geometry of methane, ethane, and ethene

Carbon Skeletons and Hydrocarbons

Carbon skeletons form the backbone of organic molecules and vary in:
- Length
- Branching (unbranched vs. branched)
- Double bond placement
- Ring formation
Hydrocarbons consist solely of carbon and hydrogen:
- Nonpolar and hydrophobic (e.g., petroleum, hydrocarbon tails of fats).
- Undergo reactions that release significant quantities of energy.

Isomers

Isomers are compounds sharing the same molecular formula but differing in structure and chemical properties:
- Structural isomers: Differ in the covalent arrangements of atoms or double bond positions.
- Cis-trans isomers (geometric isomers): Differ in spatial arrangements around rigid double bonds (cis = same side, trans = opposite sides).
- Enantiomers: Mirror-image isomers created around an asymmetric carbon attached to 4 distinct groups (designated as L and D, or S and R).

Biological significance of enantiomers:
- Organisms are sensitive to subtle structural variations; typically, only one enantiomer is biologically active.
- Examples in medicine: S-Ibuprofen (effective) vs. R-Ibuprofen (ineffective); R-Albuterol (effective) vs. S-Albuterol (ineffective).

Effective and ineffective enantiomers of Ibuprofen and Albuterol

Functional Groups and Cellular Energy

Functional groups are chemical attachments to carbon skeletons that directly participate in reactions or alter molecular shape and function (e.g., Estradiol vs. Testosterone).
The seven primary chemical groups in biology:
- Hydroxyl group ( $\text{—OH}$ ): Forms alcohols; polar and hydrophilic.
- Carbonyl group ( $\text{>C=O}$ ): Forms ketones (within skeleton) or aldehydes (at the end of skeleton).
- Carboxyl group ( $\text{—COOH}$ ): Forms carboxylic acids; acts as an acid ( $\text{H}^+$ donor).
- Amino group ( $\text{—NH}_2$ ): Forms amines; acts as a base ( $\text{H}^+$ acceptor).
- Sulfhydryl group ( $\text{—SH}$ ): Forms thiols; cross-linking helps stabilize protein structure.
- Phosphate group ( $\text{—OPO}_3^{2-}$ ): Negatively charged anion; plays a primary role in energy transfer.
- Methyl group ( $\text{—CH}_3$ ): Non-reactive; serves as a molecular tag affecting gene expression.

Adenosine Triphosphate (ATP):
- The primary energy-transfer molecule in cellular processes, consisting of adenosine attached to three phosphate groups.
- Hydrolysis releases inorganic phosphate ( $\text{P}_\text{i}$ ) and energy: $\text{ATP} + \text{H}_2\text{O} \rightarrow \text{ADP} + \text{P}_\text{i} + \text{Energy}$

Carbon and Organic Chemistry

Cells consist of 70–95% water, with most of the remaining material composed of carbon-based compounds.
Organic chemistry is the study of carbon compounds regardless of origin, ranging from simple molecules like methane ( $\text{CH}_4$ ) to complex macromolecules.
- Analogy: Think of carbon as the ultimate LEGO backbone of biology—it can assemble simple blocks or colossal molecular structures.
Historical shift from vitalism to mechanism:
- Vitalism: The outdated belief that organic compounds could only arise within living organisms via a mysterious "life force."
- Mechanism: Replaced vitalism by establishing that physical and chemical laws govern all biological phenomena.
- Synthetic breakthroughs by Friedrich Wöhler (urea synthesis) and Hermann Kolbe (acetic acid synthesis) disproved vitalism.
- Stanley Miller demonstrated the abiotic synthesis of organic compounds under simulated primitive Earth conditions (e.g., near volcanoes).
- Tip & Trick: Wöhler & Kolbe = Vitalism Overthrow. Mechanism treats biological chemistry like a clockwork machine governed entirely by chemistry and physics.

### Carbon Bonding and Geometry

Carbon has 6 electrons (2 inner shell, 4 valence) and forms 4 covalent bonds to complete its octet.
- Analogy: Carbon is like a 4-handed molecule reaching out to hold hands with 4 other atoms to feel complete.
Molecular spatial geometry depends on bonding pattern:
- Single-bonded carbon atoms form a tetrahedral shape with bond angles of $109.5^\circ$ .
  - Analogy: A single-bonded carbon atom forms a 3D tripod with one arm pointing straight up.
- Carbon-carbon double bonds cause all attached atoms to lie in the same flat plane.
  - Analogy: Double bonds act like rigid handcuffs that lock all attached atoms into a flat, non-rotatable plane.
The valences of carbon and its frequent partners—hydrogen, oxygen, and nitrogen—serve as the structural code for biological molecules.
- Acronym / Trick: Remember the valence rules with HONC 1234:
  - Hydrogen = 1 bond
  - Oxygen = 2 bonds
  - Nitrogen = 3 bonds
  - Carbon = 4 bonds

### Carbon Skeletons and Hydrocarbons

Carbon skeletons form the backbone of organic molecules and vary in:
- Length
- Branching (unbranched vs. branched)
- Double bond placement
- Ring formation
Hydrocarbons consist solely of carbon and hydrogen:
- Nonpolar and hydrophobic (e.g., petroleum, hydrocarbon tails of fats).
  - Analogy: Hydrocarbons are like water-repellent slickers—they refuse to mix with water because they lack polar charges.
- Undergo reactions that release significant quantities of energy.
  - Analogy: Hydrocarbons serve as biological fuel tanks storing vast energy.

### Isomers

Isomers are compounds sharing the same molecular formula but differing in structure and chemical properties.
- Analogy: Isomers are like using the exact same box of LEGO bricks to construct two entirely different models.
Types of Isomers:
- Structural isomers: Differ in the covalent arrangements of atoms or double bond positions.
- Cis-trans isomers (geometric isomers): Differ in spatial arrangements around rigid double bonds.
  - Tip & Trick: Cis = "Close / Same side" (functional groups on the same side). Trans = "Transcontinental / Across" (functional groups on opposite sides).
- Enantiomers: Mirror-image isomers created around an asymmetric carbon attached to 4 distinct groups (designated as L and D, or S and R).
  - Comparison / Analogy: Enantiomers are like your left and right hands. They are mirror images, but non-superimposable—a right glove won't fit on your left hand!

- Biological significance of enantiomers: - Organisms are sensitive to subtle structural variations; typically, only one enantiomer is biologically active. - Lock-and-Key Analogy: Just as a right hand only fits comfortably into a right-handed glove, cellular receptors only fit one specific enantiomer key. - Examples in medicine: S-Ibuprofen (effective against pain) vs. R-Ibuprofen (ineffective); R-Albuterol (effective asthma medication) vs. S-Albuterol (ineffective/counters treatment).

### Functional Groups and Cellular Energy

Functional groups are chemical attachments to carbon skeletons that directly participate in reactions or alter molecular shape and function (e.g., Estradiol vs. Testosterone).
- Analogy: The carbon skeleton is a basic car chassis, and functional groups are custom attachments (like a spoiler, turbo engine, or snow tires) that completely redefine what the car can do.
The seven primary chemical groups in biology (Acronym: CBS MAPS):
- Hydroxyl group ( $\text{-OH}$ ): Forms alcohols; polar and hydrophilic (increases water solubility).
- Carbonyl group ( $\text{>C=O}$ ): Forms ketones (within skeleton) or aldehydes (at the end of skeleton).
  - Tip & Trick: Aldehyde is at the All-the-way end of a chain; Ketone is Kaught in the middle.
- Carboxyl group ( $\text{-COOH}$ ): Forms carboxylic acids; acts as an acid ( $\text{H}^+$ donor).
- Amino group ( $\text{-NH}_2$ ): Forms amines; acts as a base ( $\text{H}^+$ acceptor).
- Sulfhydryl group ( $\text{-SH}$ ): Forms thiols; cross-linking creates disulfide bridges that stabilize protein structures.
- Phosphate group ( $\text{-OPO}_3^{2-}$ ): Negatively charged anion; plays a primary role in energy transfer.
- Methyl group ( $\text{-CH}_3$ ): Non-reactive; serves as a molecular tag affecting gene expression.

- Adenosine Triphosphate (ATP): - The primary energy-transfer molecule in cellular processes, consisting of adenosine attached to three phosphate groups. - Analogy: ATP is like a coiled spring or a rechargeable battery. Removing a phosphate group uncoils the spring and releases usable cellular energy! - Hydrolysis reaction: $\text{ATP} + \text{H}_2\text{O} \rightarrow \text{ADP} + \text{P}_\text{i} + \text{Energy}$