Dehydration and Hydrolysis Reactions

Overview of Chemical Reactions in Biology

Biological macromolecules are assembled and broken down through two key types of reactions: dehydration synthesis and hydrolysis. These reactions are fundamental to metabolism, including ATP production and utilization.

• Dehydration Reaction: Also called condensation, this process joins two molecules by removing a water molecule. It is essential for building polymers from monomers (e.g., forming proteins, polysaccharides).

• Hydrolysis Reaction: This process breaks polymers into monomers by adding water. It is crucial for digestion and energy release, such as ATP hydrolysis.

• ATP Utilization: ATP is hydrolyzed to ADP and inorganic phosphate, releasing energy for cellular processes.

• Example: Hydrolysis of sucrose into glucose and fructose.

Monosaccharides and Polysaccharides

Carbohydrate Structure and Function

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen. They serve as energy sources and structural components.

• Monosaccharides: Simple sugars (e.g., glucose, fructose) with the general formula .

• Polysaccharides: Long chains of monosaccharides linked by glycosidic bonds (e.g., starch, glycogen, cellulose).

• Example: Starch is a storage polysaccharide in plants; glycogen in animals.

Glucose

Central Role in Metabolism

Glucose is a six-carbon monosaccharide that is the primary energy source for cells.

• Structure: C6H12O6; can exist in linear or ring forms.

• Function: Used in cellular respiration to produce ATP.

• Example: Glycolysis is the metabolic pathway that converts glucose into pyruvate, generating ATP.

Lipids and Proteins

Structure and Biological Importance

Lipids are hydrophobic molecules, including fats, oils, and steroids. Proteins are polymers of amino acids with complex 3D structures.

• Lipids: Composed of fatty acids and glycerol; function in energy storage, insulation, and membrane structure.

• Proteins: Made of amino acids; structure determined by four levels (primary, secondary, tertiary, quaternary).

• Example: Enzymes are proteins that catalyze biochemical reactions.

Nucleic Acids

DNA and RNA Structure

Nucleic acids are polymers of nucleotides, responsible for genetic information storage and transfer.

• DNA: Contains bases A (adenine), T (thymine), G (guanine), C (cytosine).

• RNA: Contains bases A, U (uracil), G, C.

• Example: DNA double helix; RNA single-stranded.

Nucleotides and DNA/RNA Directionality

Structure and Sequence Orientation

Nucleotides consist of a phosphate group, a five-carbon sugar (deoxyribose or ribose), and a nitrogenous base. DNA and RNA sequences are read from the 5' to 3' direction.

• 5' End: Phosphate group attached to the fifth carbon of the sugar.

• 3' End: Hydroxyl group attached to the third carbon of the sugar.

• Example: DNA replication proceeds in the 5' to 3' direction.

Prokaryotic vs. Eukaryotic Cells

Cellular Organization Comparison

Cells are classified as prokaryotic or eukaryotic based on their structure and complexity.

Cell Organelles

Names and Functions in Plant and Animal Cells

Organelles are specialized structures within cells that perform distinct functions.

• Nucleus: Contains genetic material (DNA).

• Mitochondria: Site of ATP production.

• Chloroplasts: Site of photosynthesis (plants only).

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

• Golgi Apparatus: Modifies and packages proteins.

• Lysosomes: Digestion of cellular waste (mainly animal cells).

• Vacuole: Storage and structure (large central vacuole in plants).

Endosymbiosis

Origin of Eukaryotic Organelles

The endosymbiotic theory explains the origin of mitochondria and chloroplasts as formerly free-living prokaryotes engulfed by ancestral eukaryotic cells.

• Evidence: Double membranes, own DNA, ribosomes similar to prokaryotes.

• Example: Mitochondria and chloroplasts replicate independently within cells.

Biological/Cell Membranes

Phospholipid Bilayer and Embedded Proteins

Cell membranes are composed of a phospholipid bilayer with embedded proteins, providing selective permeability and structural support.

• Phospholipids: Hydrophilic heads and hydrophobic tails.

• Proteins: Integral and peripheral; involved in transport, signaling.

• Example: Channel proteins facilitate movement of ions.

Diffusion

Types of Molecular Movement

Diffusion is the passive movement of molecules from high to low concentration. It can be simple or facilitated, and is distinct from active transport.

• Passive Diffusion: No energy required; molecules move down concentration gradient.

• Facilitated Diffusion: Uses membrane proteins to help molecules cross.

• Active Transport: Requires energy (ATP) to move molecules against gradient.

Osmosis

Movement of Water Across Membranes

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

• Direction: Water moves from low solute concentration to high solute concentration.

• Example: Water uptake by plant roots.

Solute and Solvent

Definitions and Examples

A solute is a substance dissolved in a solvent. In biological systems, water is the universal solvent, and salts like NaCl are common solutes.

• Solvent: The liquid in which solutes are dissolved (usually water).

• Solute: The dissolved substance (e.g., NaCl).

• Example: Saltwater solution: water (solvent), salt (solute).

Hypertonic, Hypotonic, Isotonic Solutions

Effects on Animal and Plant Cells

Cells respond differently to solutions based on solute concentration relative to their cytoplasm.

Sodium-Potassium Pump

Mechanism and Function

The sodium-potassium pump is a membrane protein that actively transports Na+ out of and K+ into the cell, maintaining electrochemical gradients.

• Location: Plasma membrane of animal cells.

• Function: Maintains cell potential and volume.

• Mechanism: Uses ATP to move 3 Na+ out and 2 K+ in per cycle.

Phagocytosis vs. Pinocytosis

Types of Endocytosis

Cells ingest material via endocytosis, which includes phagocytosis and pinocytosis.

• Phagocytosis: "Cell eating"; cell engulfs large particles or cells.

• Pinocytosis: "Cell drinking"; cell engulfs extracellular fluid and dissolved solutes.

• Similarities: Both are forms of active transport requiring energy.

• Differences: Phagocytosis involves solid particles; pinocytosis involves liquids.

• Example: White blood cells use phagocytosis to ingest bacteria.