General Biology Study Guide: Carbon, Biomolecules, and Cell Structure

Chapter 4: Carbon

Properties and Importance of Carbon

Carbon is a fundamental element in biological molecules due to its unique chemical properties. Its versatility allows it to form a wide variety of compounds essential for life.

• Versatility of Carbon: Carbon can form four covalent bonds, allowing for complex molecules with various shapes and sizes.

• Isomers: Isomers are compounds with the same molecular formula but different structures. Types include:

  • Structural isomers: Differ in the arrangement of atoms.

  • Geometric isomers: Differ in spatial arrangement around a double bond.

  • Enantiomers: Mirror-image isomers, important in biological systems.

• Functional Groups: Groups of atoms that confer specific chemical properties to molecules. Key functional groups include:

  • Carboxyl (-COOH)

  • Carbonyl (C=O)

  • Hydroxyl (-OH)

  • Sulfhydryl (-SH)

  • Methyl (-CH3)

  • Phosphate (-PO4)

  • Amino (-NH2)

Example: Glucose and fructose are structural isomers; both have the formula C6H12O6 but different structures.

Chapter 5: Biomolecules

Polymers and Monomers

Biological macromolecules are often polymers, made by joining smaller units called monomers through chemical reactions.

• Monomers: Small molecules that can join to form polymers (e.g., amino acids, nucleotides, monosaccharides).

• Polymers: Large molecules made from repeating monomer units (e.g., proteins, nucleic acids, polysaccharides).

• Dehydration (Condensation) Reactions: Chemical reactions that join monomers by removing water.

• Hydrolysis: Breaking polymers into monomers by adding water.

Carbohydrates

Carbohydrates are energy-rich organic molecules composed of carbon, hydrogen, and oxygen.

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

• Polysaccharides: Complex carbohydrates made of monosaccharide monomers (e.g., starch, glycogen, cellulose).

• Glycosidic Bond: Covalent bond that links monosaccharides together.

• Monomer of Polysaccharides: Usually glucose.

• Functions: Energy storage (starch, glycogen), structural support (cellulose).

Example: Starch is a polysaccharide made of glucose monomers joined by glycosidic bonds.

Lipids

Lipids are hydrophobic molecules important for energy storage, membrane structure, and signaling.

• Structure: Most lipids are made of fatty acids and glycerol.

• Triglycerides: Composed of three fatty acids linked to glycerol.

• Saturated vs. Unsaturated Fats: Saturated fats have no double bonds; unsaturated fats have one or more double bonds.

• Functions: Energy storage, insulation, cell membrane structure.

Example: Phospholipids form the bilayer of cell membranes.

Proteins

Proteins are polymers of amino acids and perform a wide range of functions in cells.

• Amino Acids: Monomers of proteins; 20 different types found in proteins.

• Peptide Bond: Covalent bond joining amino acids.

• Levels of Protein Structure:

  • Primary: Sequence of amino acids.

  • Secondary: Local folding (α-helix, β-sheet).

  • Tertiary: Overall 3D shape.

  • Quaternary: Association of multiple polypeptides.

• Functions: Enzymes, structural support, transport, signaling.

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

Nucleic Acids

Nucleic acids store and transmit genetic information. The two main types are DNA and RNA.

• Nucleotides: Monomers of nucleic acids, composed of a phosphate group, a sugar (ribose or deoxyribose), and a nitrogenous base.

• Purines: Adenine (A) and Guanine (G).

• Pyrimidines: Cytosine (C), Thymine (T), and Uracil (U).

• DNA vs. RNA: DNA contains deoxyribose and thymine; RNA contains ribose and uracil.

Example: DNA encodes genetic instructions; RNA is involved in protein synthesis.

Chapter 6: Cells and Organelles

Cell Types and Characteristics

Cells are the basic units of life. They can be classified as prokaryotic or eukaryotic based on their structure.

• Prokaryotic Cells: Lack a nucleus and membrane-bound organelles (e.g., bacteria).

• Eukaryotic Cells: Have a nucleus and membrane-bound organelles (e.g., plants, animals).

• Common Features: Plasma membrane, cytoplasm, ribosomes.

Example: Escherichia coli is a prokaryotic cell; human cells are eukaryotic.

Cell Structure and Organelles

Cells contain specialized structures called organelles that perform specific functions.

• Nucleus: Contains genetic material (DNA); controls cell activities.

• Plasma Membrane: Phospholipid bilayer that regulates entry and exit of substances.

• Endomembrane System: Includes the nuclear envelope, endoplasmic reticulum (ER), Golgi apparatus, lysosomes, and vesicles.

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

• Endoplasmic Reticulum (ER): Rough ER has ribosomes (protein synthesis); smooth ER (lipid synthesis, detoxification).

• Golgi Complex: Modifies, sorts, and packages proteins and lipids.

• Mitochondria: Site of cellular respiration; produces ATP.

• Lysosomes: Contain digestive enzymes; break down waste.

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

• Central Vacuole (plants): Stores water, nutrients, and waste; maintains cell turgor.

• Chloroplasts (plants): Site of photosynthesis; contain stroma, thylakoids, and grana.

Example: The mitochondrion has folded inner membranes called cristae, increasing surface area for ATP production.

Cell Membrane Structure

The plasma membrane is a selectively permeable barrier composed of a phospholipid bilayer with embedded proteins.

• Phospholipid Bilayer: Hydrophilic heads face outward; hydrophobic tails face inward.

• Membrane Proteins: Integral and peripheral proteins serve as channels, receptors, and enzymes.

• Fluid Mosaic Model: Describes the dynamic nature of the membrane.

Example: Transport proteins facilitate movement of ions and molecules across the membrane.

Cell Junctions and Cytoskeleton

Cells are connected and supported by junctions and the cytoskeleton.

• Cell Junctions: Structures that connect cells (tight junctions, gap junctions, desmosomes, plasmodesmata in plants).

• Cytoskeleton: Network of protein filaments (microfilaments, intermediate filaments, microtubules) that provide shape, support, and movement.

• Order of Cytoskeletal Elements (largest to smallest): Microtubules > Intermediate Filaments > Microfilaments.

Example: Flagella and cilia are composed of microtubules and are involved in cell movement.

Comparison of Prokaryotic and Eukaryotic Cells

Prokaryotic and eukaryotic cells differ in several key aspects.

Feature	Prokaryotic Cells	Eukaryotic Cells
Nucleus	Absent	Present
Membrane-bound Organelles	Absent	Present
Size	Smaller	Larger
Examples	Bacteria, Archaea	Plants, Animals, Fungi

Functions of Major Organelles

Organelle	Function
Nucleus	Stores DNA, controls cell activities
Mitochondria	ATP production via cellular respiration
Chloroplast	Photosynthesis (plants)
Golgi Complex	Protein and lipid modification, sorting, packaging
Lysosome	Digestion of macromolecules
Peroxisome	Breakdown of fatty acids, detoxification
Central Vacuole	Storage, turgor pressure (plants)

Key Equations

• General Formula for Carbohydrates: $C_n(H_2O)_n$

• Peptide Bond Formation: $\text{Amino acid}_1 + \text{Amino acid}_2 \rightarrow \text{Dipeptide} + H_2O$

Additional info: Some content was inferred and expanded for clarity and completeness, including definitions, examples, and tables.