General Biology Study Notes: Water, Carbon, and Functional Groups

Water: Structure and Properties

Polar Covalent Bonds in Water

Water (H2O) is a polar molecule due to the unequal sharing of electrons between oxygen and hydrogen atoms. This polarity is fundamental to water's unique properties.

• Polar Covalent Bond: A type of chemical bond where electrons are shared unequally between atoms, resulting in partial charges.

• Electronegativity: Oxygen is more electronegative than hydrogen, pulling shared electrons closer and creating a partial negative charge on oxygen and a partial positive charge on hydrogen.

• Result: Water molecules have a bent shape and a net dipole moment, making them polar.

• Example: The oxygen atom in water attracts electrons more strongly than the hydrogen atoms.

Hydrogen Bonds

Hydrogen bonds are weak attractions between the partial positive charge of hydrogen in one water molecule and the partial negative charge of oxygen in another.

• Hydrogen Bond: A non-covalent interaction important for the structure and properties of water.

• Strength: Individual hydrogen bonds are weak, but collectively they are strong and stabilize water's structure.

• Example: Multiple water molecules can form a network of hydrogen bonds.

Emergent Properties of Water

Water exhibits several unique properties due to hydrogen bonding, which are essential for life.

• Cohesion: Water molecules stick together, creating surface tension.

• Adhesion: Water molecules can cling to other substances, aiding processes like capillary action.

• Example: Water droplets forming on a leaf due to cohesion and adhesion.

Density and Ice Formation

Water's behavior upon freezing is crucial for environmental and biological systems.

• Crystalline Lattice: At 0°C, water molecules form a rigid lattice, making ice less dense than liquid water.

• Expansion: Water expands when it freezes, causing ice to float.

• Maximum Density: Water is most dense at 4°C.

• Example: Lakes freeze from the top down, insulating aquatic life below.

Moderation of Temperature

Water can absorb or release large amounts of heat with only a slight change in its own temperature.

• Specific Heat: The amount of heat required to raise the temperature of water is high due to hydrogen bonding.

• Application: Helps regulate climate and maintain stable environments for organisms.

• Equation: $q = m c \, \Delta T$ (where $q$ is heat energy, $m$ is mass, $c$ is specific heat, and $\Delta T$ is temperature change)

Water as a Solvent

Water's polarity makes it an excellent solvent for ionic and polar substances.

• Solvent: A substance that dissolves other substances (solutes).

• Hydration Shells: Water molecules surround ions and polar molecules, separating and dissolving them.

• Biological Importance: Most cellular reactions occur in aqueous environments.

Carbon: The Backbone of Life

Properties of Carbon

Carbon is the central element in organic molecules due to its versatile bonding capabilities.

• Valence: Carbon has four valence electrons, allowing it to form up to four covalent bonds.

• Versatility: Can form chains, rings, and complex structures.

• Example: Glucose, DNA, proteins all have carbon skeletons.

Isomers: Arrangement Matters

Isomers are compounds with the same molecular formula but different structures, affecting their properties and functions.

• Structural Isomers: Differ in the covalent arrangement of atoms.

• Cis-Trans Isomers: Differ in spatial arrangement around a double bond.

• Enantiomers: Mirror-image isomers important in pharmaceuticals.

Type	Description	Example
Structural Isomer	Different connectivity	Butane vs. isobutane
Cis-Trans Isomer	Different positions around double bond	Cis-2-butene vs. trans-2-butene
Enantiomer	Non-superimposable mirror images	L- and D-glucose

Functional Groups in Organic Molecules

Overview

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

• Importance: Determine the behavior and function of organic molecules.

• Predictable Reactivity: Functional groups participate in chemical reactions in consistent ways.

• Example: The difference between estradiol and testosterone is due to their functional groups.

Major Functional Groups

Functional Group	Structure	Name of Compound	Example	Functional Properties
Hydroxyl	-OH	Alcohols	Ethanol	Polar, forms hydrogen bonds, increases solubility in water
Carbonyl	C=O	Aldehydes (end), Ketones (middle)	Acetone, Propanal	Polar, found in sugars, can be reactive
Carboxyl	-COOH	Carboxylic acids	Acetic acid	Acidic, can donate H+, found in amino acids
Amino	-NH2	Amines	Glycine	Basic, can pick up H+, found in amino acids
Sulfhydryl	-SH	Thiols	Cysteine	Forms disulfide bonds, stabilizes protein structure
Phosphate	-OPO32-	Organic phosphates	Glycerol phosphate	Contributes negative charge, can release energy
Methyl	-CH3	Methylated compounds	5-methyl cytidine	Affects gene expression, modifies molecular shape

Functional Group Examples and Properties

• Hydroxyl Group: Found in alcohols; increases solubility and can form hydrogen bonds.

• Carbonyl Group: Found in sugars; can be an aldehyde or ketone depending on position.

• Carboxyl Group: Acts as an acid; found in amino acids and fatty acids.

• Amino Group: Acts as a base; found in amino acids.

• Sulfhydryl Group: Important in protein structure; forms disulfide bridges.

• Phosphate Group: Key in energy transfer (ATP); adds negative charge.

• Methyl Group: Non-polar; affects gene expression and molecular shape.

Additional info:

• Functional groups are critical in biochemistry for the structure and function of macromolecules.

• Isomerism can affect biological activity, as seen in pharmaceutical enantiomers.