Core Chemical Principles in Biology

Chemical Bonds and Interactions

Understanding the types and mechanisms of chemical bonds is fundamental to biology, as these interactions determine molecular structure and function.

• Covalent Bonds: Strong bonds formed by the sharing of electron pairs between atoms. Can be nonpolar (equal sharing) or polar (unequal sharing due to differences in electronegativity).

• Ionic Bonds: Formed when electrons are transferred from one atom to another, resulting in oppositely charged ions that attract each other.

• Hydrogen Bonds: Weak attractions between a hydrogen atom covalently bonded to an electronegative atom (like O or N) and another electronegative atom.

• Strength of Bonds: Covalent > Ionic (in dry environments) > Hydrogen > van der Waals interactions.

• Atomic Structure and Electronegativity: The arrangement of electrons and the relative ability of an atom to attract electrons (electronegativity) influence bond formation and strength.

• Example: Water molecules exhibit polar covalent bonds between H and O, and hydrogen bonds between adjacent water molecules.

Bonds in Water Molecules

Water's unique properties arise from its molecular structure and the types of bonds it forms.

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

• Between Water Molecules: Hydrogen bonds form due to partial charges on H and O atoms.

• Electronegativity: Oxygen is more electronegative than hydrogen, creating a dipole.

• Example: The high boiling point of water is due to extensive hydrogen bonding.

Properties of Water and Biological Phenomena

Hydrogen bonding and hydrophobic interactions contribute to water's role in biological systems.

• Cohesion and Adhesion: Water molecules stick to each other (cohesion) and to other surfaces (adhesion), enabling capillary action.

• Surface Tension: Hydrogen bonds create a 'skin' on water's surface.

• Temperature Moderation: Water absorbs and releases heat slowly, moderating climate.

• Hydrophobic Interactions: Nonpolar substances aggregate in water, influencing membrane formation and protein folding.

• Example: Sweating cools the body as water evaporates, absorbing heat.

Acids, Bases, and pH

Acids and bases are defined by their ability to donate or accept protons, and pH quantifies the concentration of hydrogen ions in solution.

• Acid: Substance that donates H+ ions.

• Base: Substance that accepts H+ ions.

• pH Scale: Ranges from 0 (strong acid) to 14 (strong base), with 7 as neutral (pure water).

• Formula:

• Example: Gastric juice (pH ~2), blood (pH ~7.4), bleach (pH ~13).

Chemical Properties of Carbon

Carbon's tetravalency allows it to form diverse and complex molecules essential for life.

• Tetravalency: Carbon forms four covalent bonds, enabling chains, rings, and branching structures.

• Diversity: Carbon can bond with many elements, creating structural and functional diversity in biomolecules.

• Example: Hydrocarbons, carbohydrates, proteins, nucleic acids, and lipids all have carbon backbones.

Chemical Functional Groups

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

• Common Functional Groups: Hydroxyl (-OH), carbonyl (C=O), carboxyl (-COOH), amino (-NH2), sulfhydryl (-SH), phosphate (-PO4), methyl (-CH3).

• Properties: Influence polarity, acidity/basicity, and reactivity.

• Example: Carboxyl groups act as acids; amino groups act as bases.

Polymers and Monomers

Biological macromolecules are polymers built from monomer subunits via condensation reactions and broken down by hydrolysis.

• Polymerization: Monomers are joined by covalent bonds through dehydration (condensation) reactions, releasing water.

• Hydrolysis: Polymers are broken down into monomers by adding water.

• Example: Formation and breakdown of proteins, nucleic acids, and polysaccharides.

Proteins: Structure and Function

Amino Acids and Protein Polymerization

Proteins are polymers of amino acids linked by peptide bonds, with structure determining function.

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

• Peptide Bond: Covalent bond formed between the carboxyl group of one amino acid and the amino group of another via dehydration.

• Example: Polypeptide chains fold into functional proteins.

Core Structural Components of Amino Acids

• 1. Central (alpha) carbon

• 2. Amino group (-NH2)

• 3. Carboxyl group (-COOH)

• 4. Hydrogen atom

• 5. R group (variable side chain)

Chemical Properties of Amino Acid R Groups

The R group determines the chemical behavior of each amino acid.

• Polarity: Polar R groups are hydrophilic; nonpolar R groups are hydrophobic.

• Charge: Acidic (negatively charged), basic (positively charged), or neutral.

• Example: Glutamic acid (acidic), lysine (basic), valine (nonpolar).

Levels of Protein Structure

• Primary: Linear sequence of amino acids (peptide bonds).

• Secondary: Local folding (alpha helices, beta sheets) stabilized by hydrogen bonds.

• Tertiary: 3D folding due to interactions among R groups (hydrophobic, ionic, disulfide bridges).

• Quaternary: Association of multiple polypeptide chains.

• Example: Hemoglobin has quaternary structure with four subunits.

Protein Folding and Function

Proper folding is essential for protein function; misfolding can lead to disease.

• Forces: Hydrogen bonds, ionic bonds, hydrophobic interactions, van der Waals forces, disulfide bridges.

• Denaturation: Loss of structure due to heat, pH, or chemicals disrupts function.

• Cellular Mechanisms: Chaperone proteins assist in proper folding and prevent misfolding.

• Example: Prion diseases result from misfolded proteins.

Nucleic Acids: DNA and RNA

Nucleotide Structure and Polymerization

Nucleic acids are polymers of nucleotides, which consist of a sugar, phosphate group, and nitrogenous base.

• Polymerization: Nucleotides are joined by phosphodiester bonds between the 3' hydroxyl and 5' phosphate groups.

• Example: DNA and RNA strands.

Base Pairing and Double Helix Structure

Complementary base pairing enables the double-helix structure of DNA.

• Base Pairs: Adenine (A) pairs with Thymine (T), Guanine (G) pairs with Cytosine (C) via hydrogen bonds.

• Antiparallel Strands: DNA strands run in opposite 5' to 3' directions.

• Secondary Structure: Stabilized by hydrogen bonds between complementary bases.

• Example: If one DNA strand is 5'-ATGC-3', the complementary strand is 3'-TACG-5'.

Lipids and Membranes

Types and Structures of Lipids

Lipids are hydrophobic molecules including fats, phospholipids, and steroids, each with distinct structures and functions.

• Fats (Triglycerides): Glycerol + 3 fatty acids; energy storage.

• Phospholipids: Glycerol + 2 fatty acids + phosphate group; major component of cell membranes.

• Steroids: Four fused carbon rings; hormones and membrane components (e.g., cholesterol).

• Saturation: Saturated fats have no double bonds; unsaturated fats have one or more double bonds (kinks).

Phospholipid Bilayers and Membrane Properties

Phospholipids spontaneously form bilayers in aqueous environments, creating the basis of biological membranes.

• Hydrophilic Head: Interacts with water.

• Hydrophobic Tails: Avoid water, face inward.

• Bilayer Formation: Drives membrane structure and function.

• Fluidity and Permeability: Influenced by fatty acid saturation and cholesterol content.

• Example: More unsaturated fatty acids increase membrane fluidity.

Membrane Transport

Diffusion, Osmosis, and Facilitated Diffusion

Cells regulate the movement of substances across membranes through various transport mechanisms.

• Diffusion: Passive movement of molecules from high to low concentration.

• Osmosis: Diffusion of water across a selectively permeable membrane.

• Facilitated Diffusion: Passive transport via membrane proteins (channels/carriers).

• Example: Glucose transport into cells via GLUT proteins.

Passive and Active Transport

• Passive Transport: No energy required; includes diffusion and facilitated diffusion.

• Active Transport: Requires energy (ATP); moves substances against concentration gradients via pumps (e.g., Na+/K+ pump).

Membrane Proteins and Transport

• Integral Proteins: Span the membrane; involved in transport and signaling.

• Peripheral Proteins: Attached to membrane surface; support and signaling.

• Carbohydrates and Lipids: Contribute to cell recognition and membrane structure.

Permeability of Ions and Molecules

• Nonpolar Molecules: Cross membranes easily (e.g., O2, CO2).

• Polar/Ionic Molecules: Require transport proteins due to low permeability.

• Relative Rates: Small nonpolar > small polar > large polar > ions.

• Example: Water crosses via aquaporins; Na+ requires channels.

Carbohydrates: Structure and Function

Monosaccharides and Polymerization

Carbohydrates are polymers of monosaccharides linked by glycosidic bonds.

• Monosaccharides: Simple sugars (e.g., glucose, fructose).

• Polymerization: Glycosidic bonds form via condensation reactions.

• Example: Starch, glycogen, cellulose.

Roles of Carbohydrates in Cells

• Energy Storage: Starch (plants), glycogen (animals).

• Structural Support: Cellulose (plants), chitin (fungi, arthropods).

• Cell Recognition: Glycoproteins and glycolipids on cell surfaces.

Comparison of Biological Macromolecules

Biological macromolecules differ in monomer subunits, chemical composition, and function.

Cell Structure and Function

Prokaryotic vs. Eukaryotic Cells

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

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

• Eukaryotes: Nucleus and membrane-bound organelles (e.g., plants, animals, fungi, protists).

• Example: E. coli (prokaryote), yeast (eukaryote).

Significance of Organelles

• Advantages: Compartmentalization increases efficiency and specialization.

• Disadvantages: Requires complex transport and regulation.

• Organelles: More common in eukaryotes due to larger cell size and complexity.

Plant vs. Animal Cells

• Plant Cells: Have cell walls, chloroplasts, and large central vacuoles.

• Animal Cells: Lack cell walls and chloroplasts, have smaller vacuoles.

Organelle Structure and Function

• Unique Functions: Each organelle (e.g., mitochondria, Golgi apparatus) has specialized roles.

• Coordination: Organelles work together in systems (e.g., endomembrane system for protein synthesis and transport).

Endomembrane System and Protein Transport

• Process: Proteins are synthesized in the rough ER, modified in the Golgi, and transported via vesicles.

• Dysfunction: Non-functional organelles disrupt protein sorting and cell function.

Cytoskeletal Elements

The cytoskeleton provides structural support and mediates cell movement.

Additional info: These notes synthesize and expand upon the provided learning objectives, offering definitions, examples, and comparisons to support exam preparation in General Biology.