General Biology Study Guide: Macromolecules, Cell Structure, Membranes, and Metabolism

Chapter 5: Biological Macromolecules

Monomer vs Polymer

Biological macromolecules are large molecules composed of smaller subunits called monomers. When monomers join together, they form polymers through specific chemical reactions.

• Monomer: A small molecule that can bind to other similar molecules to form a polymer (e.g., glucose, amino acids, nucleotides).

• Polymer: A large molecule made up of repeating monomer units (e.g., starch, proteins, DNA).

Synthesis and Breakdown of Polymers

• Dehydration (Condensation) Reaction: Joins monomers by removing a water molecule.

• Hydrolysis: Breaks polymers into monomers by adding a water molecule.

Example: Formation of a peptide bon`qaz d between amino acids releases water (dehydration); breaking the bond requires water (hydrolysis).

Carbohydrates

Carbohydrates are organic molecules consisting of carbon, hydrogen, and oxygen, typically in a 1:2:1 ratio. They serve as energy sources and structural components.

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

• Disaccharides: Two monosaccharides joined by a glycosidic linkage (e.g., sucrose = glucose + fructose).

• Oligosaccharides: Short chains of monosaccharide units.

• Polysaccharides: Long chains of monosaccharides.

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

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

• Linkage: Glycosidic bonds connect monosaccharide units.

Example: Starch is a polymer of glucose used for energy storage in plants.

Lipids

Lipids are hydrophobic molecules, including fats, phospholipids, and steroids. They function in energy storage, membrane structure, and signaling.

• Fats (Triglycerides): Composed of glycerol and three fatty acids.

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

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

• Linkage: Ester bonds between glycerol and fatty acids.

Example: Butter contains saturated fats; olive oil contains unsaturated fats.

Phospholipids

Phospholipids are major components of cell membranes, consisting of two fatty acids, a phosphate group, and glycerol.

• Amphipathic: Contain both hydrophobic (fatty acid tails) and hydrophilic (phosphate head) regions.

• Bilayer formation: In water, phospholipids arrange into bilayers, forming the basis of biological membranes.

Steroids

Steroids are lipids with a characteristic four-ring structure. They function as hormones and membrane components.

• Examples: Cholesterol (membrane fluidity), steroid hormones (e.g., estrogen, testosterone).

Proteins

Proteins are polymers of amino acids that perform a wide range of functions, including catalysis, structure, transport, and signaling.

• Structure: Composed of one or more polypeptide chains folded into specific shapes.

• Monomer: Amino acid (20 standard types).

• Linkage: Peptide bonds between amino acids.

• Amino acid categories: Non-polar, polar, acidic, basic, aromatic.

• Abbreviations: Each amino acid has a 3-letter and 1-letter code.

Example: Hemoglobin is a protein that transports oxygen in blood.

Nucleic Acids

Nucleic acids (DNA and RNA) store and transmit genetic information.

• Monomer: Nucleotide (composed of a sugar, phosphate, and nitrogenous base).

• DNA vs RNA:

  • DNA: Deoxyribose sugar, double-stranded, bases A, T, C, G.

  • RNA: Ribose sugar, single-stranded, bases A, U, C, G.

• Bases: Purines (A, G) vs Pyrimidines (C, T, U).

• Base pairing: A-T (or A-U in RNA), C-G.

• Gene expression: DNA → RNA → Protein (Central Dogma).

Chapter 6: Cell Structure

Cell Theory

All living organisms are composed of cells, which are the basic units of life.

• Eukaryotic vs Prokaryotic: Eukaryotes have a nucleus and membrane-bound organelles; prokaryotes do not.

Cell Components

• Nucleus: Contains genetic material; surrounded by nuclear envelope.

• Ribosomes: Sites of protein synthesis; found free in cytoplasm or bound to rough ER.

• Endomembrane System: Includes nuclear envelope, endoplasmic reticulum (rough and smooth), Golgi apparatus, lysosomes, and vacuoles.

• Mitochondria: Sites of cellular respiration; produce ATP.

• Chloroplasts: Sites of photosynthesis in plants and algae.

• Peroxisomes: Break down fatty acids and detoxify harmful substances.

The Cytoskeleton

The cytoskeleton provides structural support, cell shape, and facilitates movement.

• Microtubules: Hollow tubes; involved in cell division, organelle movement, and structure (e.g., cilia, flagella).

• Microfilaments: Thin filaments of actin; involved in muscle contraction and cell movement.

• Intermediate filaments: Provide mechanical support for the cell.

Extracellular Components

• Cell wall: Provides structure and protection (plants, fungi, some protists).

• Extracellular matrix (ECM): Network of proteins and carbohydrates outside animal cells; provides support and signaling.

• Cell junctions: Connections between cells (e.g., plasmodesmata in plants).

Chapter 7: Membranes and Transport

Passive vs Active vs Bulk Transport

• Passive transport: Movement of substances down their concentration gradient without energy input (e.g., diffusion, osmosis, facilitated diffusion).

• Active transport: Movement against the concentration gradient; requires energy (e.g., Na+/K+ pump).

• Bulk transport: Movement of large particles via vesicles (e.g., endocytosis, exocytosis).

Plasma Membrane Structure

• Phospholipid bilayer: Amphipathic structure with hydrophilic heads and hydrophobic tails.

• Fluid mosaic model: Membrane is a fluid structure with proteins embedded in or attached to the bilayer.

• Membrane fluidity: Affected by temperature, fatty acid composition, and cholesterol content.

Selective Permeability

• Solute vs Solvent: Solute is dissolved in solvent; water is the universal solvent in biology.

• Permeability: Small, nonpolar molecules cross easily; large or charged molecules require transport proteins.

Membrane Proteins

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

• Peripheral proteins: Loosely attached to the membrane surface.

Transport Mechanisms

• Diffusion: Movement of molecules from high to low concentration.

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

• Facilitated diffusion: Passive transport via specific proteins.

• Tonicity: Effect of solute concentration on cell volume (hypotonic, isotonic, hypertonic).

• Active transport: Requires energy; moves substances against their gradient.

• Cotransport: Coupled transport of two substances (e.g., sodium-glucose cotransport).

• Bulk transport: Endocytosis (phagocytosis, pinocytosis, receptor-mediated), exocytosis.

Chapter 8: Metabolism and Enzymes

Metabolic Pathways

Metabolism is the sum of all chemical reactions in a cell, organized into metabolic pathways.

• Anabolic pathways: Build complex molecules from simpler ones; require energy.

• Catabolic pathways: Break down complex molecules; release energy.

Energy and Thermodynamics

• First Law of Thermodynamics: Energy cannot be created or destroyed, only transformed.

• Second Law of Thermodynamics: Every energy transfer increases the entropy (disorder) of the universe.

• Free energy ($\Delta G$): The portion of a system's energy that can perform work.

• Exergonic reactions: Release energy ($\Delta G < 0$).

• Endergonic reactions: Require energy input ($\Delta G > 0$).

ATP: The Cell's Energy Currency

• ATP (Adenosine Triphosphate): Stores and transfers energy for cellular processes.

• Energy coupling: Use of exergonic processes to drive endergonic ones.

• ATP regeneration: ATP is regenerated from ADP and inorganic phosphate.

Enzymes

Enzymes are biological catalysts that speed up chemical reactions by lowering activation energy.

• Substrate specificity: Each enzyme acts on a specific substrate.

• Enzyme-substrate complex: Temporary association between enzyme and substrate.

• Active site: Region on the enzyme where the substrate binds.

• Induced fit model: Enzyme changes shape to better fit the substrate.

• Enzyme kinetics: Study of reaction rates; affected by substrate concentration, temperature, pH.

• Cofactors: Non-protein helpers (e.g., metal ions, vitamins).

• Regulation: Allosteric regulation (activation/inhibition), feedback inhibition.

• Compartmentalization: Enzymes are often localized within specific cellular compartments.

Example: The enzyme sucrase catalyzes the hydrolysis of sucrose into glucose and fructose.