General Biology Study Guide: Biomolecules, Cell Structure, and Membrane Transport

Biomolecules and Chemical Reactions

Dehydration vs. Hydrolysis Reactions

Dehydration and hydrolysis reactions are fundamental chemical processes in biology, especially in the synthesis and breakdown of macromolecules and ATP production.

• Dehydration Reaction: A chemical reaction that joins two molecules by removing a water molecule. This process is essential for forming polymers such as proteins, carbohydrates, and nucleic acids.

• Hydrolysis Reaction: A chemical reaction that breaks a bond in a molecule by adding water. Hydrolysis is crucial for digestion and cellular metabolism, including ATP utilization.

• ATP Production and Utilization: ATP is synthesized via dehydration reactions and broken down by hydrolysis to release energy for cellular processes.

• Example: The breakdown of starch into glucose monomers during digestion involves hydrolysis.

Monosaccharides and Polysaccharides

Carbohydrates are classified based on the number of sugar units they contain.

• Monosaccharides: Simple sugars such as glucose, fructose, and galactose. They are the building blocks of carbohydrates.

• Polysaccharides: Complex carbohydrates formed by the linkage of multiple monosaccharides. Examples include starch, glycogen, and cellulose.

• Function: Monosaccharides provide immediate energy, while polysaccharides serve as energy storage or structural components.

Glucose

Glucose is a key monosaccharide in biological systems.

• Structure: Six-carbon sugar (C6H12O6), often depicted as a ring in aqueous solutions.

• Function: Primary source of energy for cells; involved in cellular respiration.

• Equation: $\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{energy (ATP)}$

Lipids and Proteins

Lipids and proteins are essential macromolecules with diverse functions.

• Lipids: Hydrophobic molecules including fats, oils, and phospholipids. They are important for energy storage and membrane structure.

• Proteins: Polymers of amino acids with complex three-dimensional structures. Functions include catalysis (enzymes), transport, and structural support.

• Protein Structure: Primary, secondary, tertiary, and quaternary levels of organization.

Nucleic Acids and Genetic Information

Nucleic Acids: A, T, G, C, U

Nucleic acids store and transmit genetic information.

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

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

• Function: DNA stores genetic information; RNA is involved in protein synthesis.

Nucleotide Structure and Sequence

Nucleotides are the building blocks of nucleic acids.

• Structure: Each nucleotide consists of a phosphate group, a five-carbon sugar (deoxyribose in DNA, ribose in RNA), and a nitrogenous base.

• Sequence: The order of bases (e.g., 5'---3') determines genetic information.

• Example: The sequence 5'-ATGC-3' in DNA codes for specific amino acids in proteins.

Cell Structure and Organelles

Prokaryotic vs. Eukaryotic Cells

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

• Prokaryotic Cells: Lack a nucleus and membrane-bound organelles. Example: Bacteria.

• Eukaryotic Cells: Have a nucleus and membrane-bound organelles. Examples: Plant and Animal cells.

• Comparison Table:

Feature	Prokaryotic	Eukaryotic
Nucleus	No	Yes
Organelles	No	Yes
Size	Small	Larger
Examples	Bacteria	Plants, Animals

Cell Organelles: Plant vs. Animal

Organelles perform specialized functions within cells.

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

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

• Common Organelles: Nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes.

Endosymbiosis

The endosymbiotic theory explains the origin of certain organelles in eukaryotic cells.

• Definition: The theory that mitochondria and chloroplasts originated from free-living prokaryotes engulfed by ancestral eukaryotic cells.

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

Cell Membranes and Transport

Biological Membranes: Phospholipid Bilayer

Cell membranes are primarily composed of a phospholipid bilayer with embedded proteins.

• Phospholipid Bilayer: Provides a semi-permeable barrier between the cell and its environment.

• Embedded Proteins: Facilitate transport, signaling, and structural support.

Diffusion

Diffusion is the passive movement of molecules from high to low concentration.

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

• Facilitated Diffusion: Uses membrane proteins to help substances cross the membrane.

• Example: Oxygen and carbon dioxide diffuse across cell membranes.

Osmosis

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

• Definition: Movement of water from an area of low solute concentration to high solute concentration.

• Equation: $\text{Osmosis}: \text{Water moves from hypotonic to hypertonic solution}$

Solute and Solvent

Solutions are composed of solutes dissolved in solvents.

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

• Solvent: The substance doing the dissolving (e.g., water).

• Universal Solvent: Water is called the universal solvent due to its ability to dissolve many substances.

Hypertonic, Hypotonic, Isotonic Solutions

These terms describe the relative concentrations of solutes in solutions separated by a membrane.

• Hypertonic: Higher solute concentration outside the cell; water moves out, cell shrinks.

• Hypotonic: Lower solute concentration outside the cell; water moves in, cell swells.

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

• Example: Red blood cells in different solutions will shrink, swell, or remain unchanged.

Solution Type	Solute Concentration	Effect on Animal Cell
Hypertonic	Higher outside	Shrinks
Hypotonic	Lower outside	Swells
Isotonic	Equal	No change

Sodium-Potassium Pump

The sodium-potassium pump is a vital membrane protein that maintains cellular ion balance.

• Function: Actively transports Na+ out and K+ into the cell against their concentration gradients.

• Equation: $3\text{Na}^+_{\text{out}} + 2\text{K}^+_{\text{in}} + \text{ATP} \rightarrow 3\text{Na}^+_{\text{out}} + 2\text{K}^+_{\text{in}}$

• Importance: Maintains membrane potential and cellular homeostasis.

Phagocytosis vs. Pinocytosis

Both are forms of endocytosis, allowing cells to take in materials from their environment.

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

• Pinocytosis: "Cell drinking"; the cell takes in extracellular fluid and dissolved solutes.

• Similarities: Both involve the formation of vesicles from the plasma membrane.

• Differences: Phagocytosis targets large particles; pinocytosis targets fluids and small molecules.

Process	Material Taken In	Example
Phagocytosis	Large particles	White blood cell engulfing bacteria
Pinocytosis	Fluid and solutes	Cell absorbing nutrients from extracellular fluid