Fundamental Concepts in General Biology: Cell Structure, Biomolecules, and Cellular Processes

Essential Elements and Biomolecules in Biology

Key Biological Elements

Life is composed of several essential elements, each playing a critical role in biological molecules and processes.

• Carbon: Found in all organic molecules; forms the backbone of biological macromolecules.

• Hydrogen: Present in all biological molecules; involved in energy transfer and structure.

• Oxygen: Found in all major biomolecules; essential for cellular respiration.

• Nitrogen: Key component of proteins and nucleic acids.

• Sulfur: Present in some amino acids and proteins.

• Phosphorus: Found in nucleic acids and phospholipids.

Why is life carbon-based? Carbon's ability to form four covalent bonds allows for the creation of complex and stable molecules necessary for life.

Organic Molecules and Chemical Groups

Organic molecules are represented by letters (elements) and lines (bonds). Recognizing functional groups is essential for understanding molecular function.

• Hydroxyl group: –OH

• Carboxyl group: –COOH or –COO−

• Amino group: –NH2 or –NH3+

• Phosphate group: –PO42−

Types of Molecules and Their Classification

• Monomer: Single subunit (e.g., glucose).

• Dimer: Two subunits joined together (e.g., maltose).

• Oligomer: Few subunits (3–10).

• Polymer: Many subunits (e.g., starch, proteins).

Hydrolysis and Dehydration Reactions

• Hydrolysis: Breaking down polymers into monomers by adding water.

• Dehydration: Joining monomers to form polymers by removing water.

Molecular Properties

• Hydrophobic: Repels water (e.g., lipids).

• Hydrophilic: Attracts water (e.g., sugars).

• Amphipathic: Contains both hydrophobic and hydrophilic regions (e.g., phospholipids).

Amino Acids

Amino acids are the building blocks of proteins. Each has a central carbon, an amino group, a carboxyl group, a hydrogen atom, and an R group (side chain) that determines its properties.

• Drawing and Classification: Given an R group, you should be able to draw the amino acid and classify it as hydrophobic, hydrophilic, or amphipathic.

Major Biological Molecules and Their Functions

Carbohydrates

Carbohydrates are classified by the number of sugar units:

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

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

• Oligosaccharides: Few sugar units.

• Polysaccharides: Many sugar units (e.g., starch, glycogen, cellulose).

Functions: Energy storage (glucose, glycogen), structural support (cellulose), and cell recognition.

Proteins

• Amino acids: Monomers of proteins.

• Polypeptides: Chains of amino acids; proteins may consist of one or more polypeptides.

• Hemoglobin: Example of a protein that transports oxygen in blood.

Nucleic Acids

• Nucleotides: Monomers of DNA and RNA.

• NTPs: Nucleoside triphosphates (ATP, CTP, GTP, UTP) used in energy transfer and nucleic acid synthesis.

• dNTPs: Deoxynucleoside triphosphates (dATP, dCTP, dGTP, dTTP) used in DNA synthesis.

Lipids

• Fatty acids: Saturated (no double bonds) and unsaturated (one or more double bonds).

• Fats and oils: Energy storage and insulation.

• Phospholipids: Major component of cell membranes; amphipathic.

• Glycolipids, steroids, waxes: Various structural and signaling roles.

• Cholesterol: Stabilizes membrane fluidity.

Characteristics of Living Organisms

Defining Features

• Order: Highly organized structure.

• Regulation: Maintenance of homeostasis.

• Growth and Development: Increase in size and complexity.

• Energy Processing: Acquisition and use of energy.

• Response to Environment: Reacting to stimuli.

• Reproduction: Producing offspring.

• Evolutionary Adaptation: Adapting over generations.

Cellular Organization: Eukaryotes vs. Prokaryotes

Major Differences

• Nucleus: Eukaryotes have a membrane-bound nucleus; prokaryotes do not.

• Organelles: Eukaryotes possess membrane-bound organelles (mitochondria, ER, Golgi apparatus); prokaryotes lack these.

• Size: Prokaryotic cells are generally smaller and simpler.

• DNA Structure: Eukaryotic DNA is linear and organized into chromosomes; prokaryotic DNA is typically circular.

Classification Systems

• Kingdoms: Protista, Fungi, Plantae, Animalia (Monera replaced by Domains).

• Domains: Bacteria, Archaea, Eukarya.

Cell Types and Multicellularity

Unicellular vs. Multicellular

• Unicellular: Organisms with one cell.

• Multicellular: Organisms with many cells; humans have ~37 trillion cells and over 200 different cell types.

Cell Membrane Structure and Function

Plasma Membrane Components

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

• Proteins:

  • Integral Proteins: Embedded within the bilayer; involved in transport, cell adhesion, signaling.

  • Peripheral Proteins: Loosely attached to the surface; involved in signaling and structural support.

• Carbohydrates: Attached to proteins (glycoproteins) or lipids (glycolipids); involved in cell recognition and adhesion.

Blood Types

• ABO System: Determines A, B, AB, O types based on antigens.

• Rh System: Determines positive (+) or negative (–) types based on Rh factor.

Plant vs. Animal Cell Membranes

• Cell Wall: Present in plants; provides structural support.

• Plasmodesmata: Channels in plant cells for communication; absent in animal cells.

Membrane Dynamics and Transport

Acquiring Extra Membrane

• Endocytosis: Cell engulfs substances from external environment.

• Membrane Synthesis and Insertion: New membrane components are synthesized and inserted.

Osmotic Environments and Cell Response

Isotonic, Hypertonic, and Hypotonic Solutions

• Isotonic: No net movement of water; cells maintain normal shape.

• Hypertonic: Water moves out; animal cells shrink, plant cells undergo plasmolysis.

• Hypotonic: Water moves in; animal cells may lyse, plant cells become turgid.

Summary Table: Major Biomolecules and Their Functions

Biomolecule	Monomer	Function	Example
Carbohydrate	Monosaccharide	Energy, structure, recognition	Glucose, starch, cellulose
Protein	Amino acid	Catalysis, transport, structure	Hemoglobin, enzymes
Nucleic Acid	Nucleotide	Genetic information, energy transfer	DNA, RNA, ATP
Lipid	Fatty acid	Energy storage, membrane structure	Phospholipid, cholesterol

Key Equations and Chemical Groups

• Hydrolysis reaction: $\text{Polymer} + \text{H}_2\text{O} \rightarrow \text{Monomer}_1 + \text{Monomer}_2$

• Dehydration reaction: $\text{Monomer}_1 + \text{Monomer}_2 \rightarrow \text{Polymer} + \text{H}_2\text{O}$

• Carboxyl group: $\text{COOH}$ or $\text{COO}^-$

• Amino group: $\text{NH}_2$ or $\text{NH}_3^+$

• Phosphate group: $\text{PO}_4^{2-}$

Additional info:

• Some content was expanded for clarity and completeness, including definitions and examples of biomolecules, cell types, and membrane processes.

• Table entries and equations were inferred and formatted for academic clarity.