Properties of Water

Emergent Properties of Water

Water exhibits several unique properties that are essential for life. These properties arise from its molecular structure and hydrogen bonding.

• Cohesion and Adhesion: Water molecules stick to each other (cohesion) and to other surfaces (adhesion), facilitating transport in plants.

• Moderation of Temperature: Water has a high specific heat, allowing it to buffer temperature changes in organisms and environments.

• Expansion Upon Freezing: Ice is less dense than liquid water, so it floats, insulating aquatic life in cold climates.

• Versatility as a Solvent: Water dissolves many substances, making it an excellent medium for biochemical reactions.

Bonds in Water

Water molecules are held together by covalent bonds, while interactions between molecules are due to hydrogen bonds.

• Within a Water Molecule: Polar covalent bonds between oxygen and hydrogen atoms.

• Between Water Molecules: Hydrogen bonds form due to partial charges, leading to water's unique properties.

Isomers

Isomers are molecules with the same chemical formula but different structures. They are important in biology because structural differences can lead to different biological functions.

• Structural Isomers: Differ in the arrangement of atoms.

• Cis-trans Isomers: Differ in spatial arrangement around double bonds.

• Enantiomers: Mirror images, important in pharmaceuticals and metabolism.

Relevance: Isomers can have drastically different effects in biological systems (e.g., glucose vs. fructose).

Biological Molecules

Functional Groups

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

• Hydroxyl (-OH): Found in alcohols; increases solubility in water.

• Carbonyl (C=O): Found in aldehydes and ketones; reactive in sugars.

• Carboxyl (-COOH): Found in acids; acts as an acid by donating H+.

• Amino (-NH2): Found in amino acids; acts as a base by accepting H+.

• Sulfhydryl (-SH): Found in thiols; forms disulfide bonds in proteins.

• Phosphate (-PO4): Found in nucleic acids; involved in energy transfer.

• Methyl (-CH3): Nonpolar; affects gene expression.

Major Classes of Biological Molecules

Biological macromolecules are classified based on their structure and function.

Cellulose vs. Starch

Both are polysaccharides made of glucose, but differ in structure and digestibility.

• Cellulose: Found in plant cell walls; beta-glucose linkages; indigestible by humans.

• Starch: Energy storage in plants; alpha-glucose linkages; digestible by humans.

• Nutrient Extraction: Humans lack enzymes to break beta linkages in cellulose.

Saturated, Unsaturated, and Trans Fats

Fats differ in the presence and configuration of double bonds in their fatty acid chains.

• Saturated Fats: No double bonds; solid at room temperature.

• Unsaturated Fats: One or more double bonds; liquid at room temperature.

• Trans Fats: Unsaturated fats with trans double bonds; artificially produced; associated with health risks.

Cell Membranes and Transport

Membrane Permeability

Saturation and chain length of fatty acids affect membrane fluidity and permeability.

• Unsaturated chains: Increase fluidity and permeability.

• Saturated chains: Decrease fluidity and permeability.

• Shorter chains: Increase fluidity.

Phospholipids and Membranes

Phospholipids form bilayers due to their amphipathic nature (hydrophilic head, hydrophobic tail). Fats do not form bilayers because they lack this structure.

Semi-Permeable Membranes

The plasma membrane allows selective passage of substances, maintaining homeostasis.

Membrane Transport Categories

• Passive Transport: No energy required (e.g., diffusion, osmosis).

• Active Transport: Requires energy (e.g., pumps, endocytosis).

Osmosis

Osmosis is the diffusion of water across a selectively permeable membrane.

Hypertonic, Hypotonic, Isotonic Solutions

• Hypertonic: Higher solute concentration outside; cell loses water.

• Hypotonic: Lower solute concentration outside; cell gains water.

• Isotonic: Equal solute concentration; no net water movement.

Channel vs. Carrier Proteins

• Channel Proteins: Form pores for passive transport.

• Carrier Proteins: Bind and transport molecules, may require energy.

Proteins and Nucleic Acids

Protein Structure

Proteins have four levels of structure, each stabilized by specific bonds.

• Primary: Amino acid sequence; peptide bonds.

• Secondary: Alpha helices and beta sheets; hydrogen bonds.

• Tertiary: 3D folding; interactions include hydrophobic, ionic, hydrogen, and disulfide bonds.

• Quaternary: Multiple polypeptides; same interactions as tertiary.

Amino Acids

Amino acids differ by their side chains (R groups), which determine their properties and roles in proteins.

Organisms Containing Proteins

All living organisms contain proteins, which perform diverse functions.

Nucleic Acids: Bases and Nucleotides

• Nitrogenous Bases: Adenine (A), Thymine (T), Cytosine (C), Guanine (G), Uracil (U in RNA).

• Base Pairing: A-T (DNA), A-U (RNA), C-G.

• Nucleotide Components: Phosphate group, pentose sugar, nitrogenous base.

• Bonds: Phosphodiester bonds link nucleotides; hydrogen bonds hold DNA strands together.

Macromolecules Not Made of Monomers

Lipids are not true polymers because they are not made from repeating monomer units.

Cell Structure and Function

Prokaryotes vs. Eukaryotes

Cells are classified based on the presence or absence of a nucleus and membrane-bound organelles.

• Prokaryotes: No nucleus, no membrane-bound organelles, smaller size (e.g., bacteria).

• Eukaryotes: Nucleus, membrane-bound organelles, larger size (e.g., plants, animals).

Cell Organelles and Functions

• Nucleus: Stores genetic material; controls cell activities.

• Mitochondria: ATP production via cellular respiration.

• Chloroplasts: Photosynthesis in plants.

• Endoplasmic Reticulum (ER): Protein and lipid synthesis.

• Golgi Apparatus: Modifies, sorts, and ships proteins.

• Lysosomes: Digestion and waste removal; malfunction leads to accumulation of waste.

• Peroxisomes: Breakdown of fatty acids and detoxification.

Cytoskeleton Components

• Microtubules: Cell shape, transport, chromosome movement.

• Microfilaments: Cell movement, muscle contraction.

• Intermediate Filaments: Structural support, cell integrity.

Identifying Biological Molecules

Biological molecules can be identified by their structure and functional groups. For example, the presence of peptide bonds indicates proteins, while glycosidic linkages indicate carbohydrates.

Additional info: Some functional group and molecule identifications were inferred based on standard textbook examples and common biological structures.