General Biology: Biomolecules, Cell Structure, Membranes, and Energy Processing

Biomolecules and Water

Properties of Water and Hydrogen Bonding

Water is a polar molecule, and its structure leads to the formation of hydrogen bonds, which are crucial for many biological processes.

• Polar covalent bonds: Bonds where electrons are shared unequally, creating partial charges.

• Hydrogen bonds: Weak attractions between the hydrogen atom of one water molecule and the oxygen atom of another.

• Solubility: Salt dissolves in water due to its ionic nature, while oil does not dissolve because it is nonpolar.

Example: Water's ability to dissolve salts but not oils is essential for cellular processes and membrane formation.

Functional Groups and Water Interaction

Functional groups determine how molecules interact with water, affecting their solubility and role in biological systems.

• Hydrophilic: Attracted to water (e.g., hydroxyl, carboxyl groups).

• Hydrophobic: Repelled by water (e.g., methyl groups).

Hydrolysis and Dehydration Synthesis

These are key reactions in the formation and breakdown of biological polymers.

• Hydrolysis: Breaking bonds by adding water.

• Dehydration synthesis: Forming bonds by removing water.

Example: Digestion involves hydrolysis of polymers into monomers.

Carbohydrates

Monosaccharides, Disaccharides, and Oligosaccharides

Carbohydrates are classified based on the number of sugar units.

• Monosaccharides: Single sugar units (e.g., glucose).

• Disaccharides: Two sugar units (e.g., sucrose).

• Oligosaccharides: Few sugar units (3-10).

Polysaccharides: Structure and Function

Polysaccharides are long chains of monosaccharides and serve various functions in organisms.

Polysaccharide	Structure	Function	Example/Location
Starch	Glucose monomers, branched	Energy storage	Plants
Glycogen	Highly branched glucose	Energy storage	Animals
Cellulose	Linear glucose chains	Structural support	Plant cell walls
Chitin	Modified glucose units	Structural support	Arthropod exoskeletons

Note: Humans cannot digest cellulose, but cows can due to specialized enzymes.

Proteins

Amino Acids and Protein Structure

Proteins are polymers of amino acids, which have diverse R-groups affecting their properties.

• Primary structure: Sequence of amino acids.

• Secondary structure: Local folding (e.g., alpha helix, beta sheet).

• Tertiary structure: Overall 3D shape.

• Quaternary structure: Multiple polypeptide chains.

Example: Sickle cell anemia results from a single amino acid change affecting protein folding.

Enzymes

Enzymes are biological catalysts that speed up chemical reactions.

• How enzymes work: Lower activation energy, bind substrates.

• Environmental effects: Temperature and pH can denature enzymes, affecting function.

• Enzyme inhibitors: Molecules that decrease enzyme activity.

Lipids

Types and Functions

Lipids are hydrophobic molecules with diverse functions.

• Sterols: Cholesterol, hormones.

• Triglycerides: Energy storage, composed of glycerol and fatty acids.

• Phospholipids: Major component of cell membranes.

Example: Saturated fats have no double bonds; unsaturated fats have one or more double bonds.

Membranes

Fluid Mosaic Model

Cell membranes are composed of a phospholipid bilayer with embedded proteins, creating a dynamic and fluid structure.

• Phospholipids: Hydrophilic heads and hydrophobic tails.

• Membrane proteins: Transport, signaling, structural support.

Membrane Fluidity

Fluidity is affected by temperature, fatty acid composition, and cholesterol.

• Unsaturated fatty acids: Increase fluidity.

• Cholesterol: Stabilizes membrane.

Transport Across Membranes

Cells move substances across membranes via several mechanisms.

• Simple diffusion: Movement down concentration gradient.

• Facilitated diffusion: Uses channel or carrier proteins.

• Osmosis: Water movement across membrane.

• Active transport: Requires energy (e.g., sodium-potassium pump).

• Vesicular transport: Endocytosis and exocytosis for large molecules.

Prokaryotic Cells

Structure and Function

Prokaryotic cells lack a nucleus and membrane-bound organelles.

• Cell wall: Provides structure.

• Plasma membrane: Controls entry/exit of substances.

• Ribosomes: Protein synthesis.

Human Microbiome

The human microbiome consists of all microorganisms living in and on the human body, affecting health and disease.

• Gut-brain axis: Communication between gut microbes and the brain.

• Fecal transplants: Used to restore healthy microbiome.

Eukaryotic Cells

Cellular Components

Eukaryotic cells have a nucleus and various organelles.

• Nucleus: Contains genetic material.

• Endomembrane system: Includes ER, Golgi apparatus, vesicles, lysosomes.

• Cytoskeleton: Microtubules, microfilaments, intermediate filaments.

• Energy organelles: Mitochondria (cellular respiration), chloroplasts (photosynthesis).

Endomembrane System Functions

• Rough ER: Protein synthesis.

• Smooth ER: Lipid synthesis.

• Golgi apparatus: Protein modification and sorting.

• Lysosomes: Digestion and recycling.

Energy Processing Cells

Cellular Respiration

Cells harvest energy from organic molecules through a series of metabolic pathways.

• ATP (adenosine triphosphate): Main energy currency.

• Glycolysis: Breakdown of glucose to pyruvate.

• Pyruvate processing: Conversion to acetyl-CoA.

• Krebs cycle (Citric Acid Cycle): Completes glucose oxidation.

• Oxidative phosphorylation: Electron transport chain and ATP synthesis.

• Fermentation: Energy production without oxygen.

Key Equations:

• $\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{ATP}$

• $\text{ATP} \rightarrow \text{ADP} + \text{P}_i$

Example: Mitochondria are the site of aerobic respiration in eukaryotic cells.

Nucleic Acids and DNA Replication

Structure and Function

Nucleic acids store and transmit genetic information.

• DNA: Double helix, complementary base pairing.

• RNA: Single-stranded, various functions.

DNA Replication

DNA replication is the process by which cells copy their genetic material before division.

• Initiation: Begins at origins of replication.

• Elongation: DNA polymerase synthesizes new strands.

• Leading and lagging strands: Continuous and discontinuous synthesis.

Key Equation:

• $\text{DNA}_{\text{template}} + \text{dNTPs} \xrightarrow{\text{DNA polymerase}} \text{DNA}_{\text{new}}$

Example: Errors in replication can lead to mutations and disease.

Additional info:

• Some content inferred from context and standard biology curriculum (e.g., details on membrane fluidity, DNA replication steps).

• Tables and equations formatted for clarity and completeness.