Organic Compounds

Carbohydrates

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen, and serve as a primary energy source for cells.

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

• Disaccharides: Formed by joining two monosaccharides via a dehydration reaction. Examples include sucrose (glucose + fructose), lactose (glucose + galactose), and maltose (glucose + glucose).

• Polysaccharides: Long chains of monosaccharides. Examples include glycogen (animal storage), starch (plant storage), and cellulose (plant cell walls).

Lipids

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

• Fatty Acids: Long hydrocarbon chains with a carboxyl group. They can be:

  • Saturated: No double bonds; solid at room temperature (e.g., animal fats).

  • Monounsaturated: One double bond; liquid at room temperature (e.g., olive oil).

  • Polyunsaturated: Two or more double bonds (e.g., fish oils).

• Triglycerides: Composed of three fatty acids and one glycerol; main form of stored energy in animals.

• Phospholipids: Contain two fatty acids, a glycerol, and a phosphate group; major component of cell membranes.

• Cholesterol: A steroid important for membrane fluidity and as a precursor for steroid hormones.

Proteins

Proteins are polymers of amino acids linked by peptide bonds, performing structural, enzymatic, and regulatory functions.

• Amino Acids: The building blocks of proteins; 20 standard amino acids exist.

• Polypeptides: Chains of amino acids joined by peptide bonds.

• Peptide Bonds: Covalent bonds formed between the amino group of one amino acid and the carboxyl group of another.

• Levels of Protein Organization:

  • Primary: Sequence of amino acids.

  • Secondary: Local folding (α-helix, β-sheet) due to hydrogen bonding.

  • Tertiary: 3D folding due to side chain interactions.

  • Quaternary: Association of multiple polypeptide chains.

Enzymes

Enzymes are biological catalysts that speed up chemical reactions without being consumed.

• Groups: Classified by the type of reaction they catalyze (e.g., hydrolases, oxidoreductases).

• Properties: Highly specific, reusable, and sensitive to temperature and pH.

• Mechanism: Lower activation energy by binding substrates at the active site.

Nucleic Acids

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

• DNA (Deoxyribonucleic Acid): Double-stranded helix containing genetic instructions.

• RNA (Ribonucleic Acid): Single-stranded; types include:

  • mRNA (messenger RNA): Carries genetic code from DNA to ribosomes.

  • rRNA (ribosomal RNA): Structural component of ribosomes.

  • tRNA (transfer RNA): Brings amino acids to ribosomes during protein synthesis.

• Nitrogenous Bases: Adenine (A), Thymine (T, in DNA), Uracil (U, in RNA), Cytosine (C), Guanine (G).

• Crick and Watson: Discovered the double helix structure of DNA.

Adenosine Triphosphate (ATP)

ATP is the primary energy currency of the cell, providing energy for cellular processes.

• Structure: Adenine base, ribose sugar, and three phosphate groups.

• Energy Release: Hydrolysis of the terminal phosphate bond releases energy:

The Cell

Three Main Parts of the Cell

All eukaryotic cells share three basic structural components:

• Plasma Membrane: Outer boundary that regulates entry and exit of substances.

• Cytoplasm: Jelly-like fluid (cytosol) containing organelles and inclusions.

• Nucleus: Contains genetic material (DNA) and controls cellular activities.

Cellular Processes

Cells perform various processes essential for life, including metabolism, transport, communication, and reproduction.

• Metabolism: All chemical reactions in the cell (anabolism and catabolism).

• Transport: Movement of substances across membranes.

• Communication: Signal transduction and response to stimuli.

• Reproduction: Cell division (mitosis and meiosis).

Plasma Membrane

The plasma membrane is a selectively permeable barrier composed mainly of lipids and proteins.

• Structure: Phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates.

• Main Molecule: Phospholipids form the basic structure, with hydrophilic heads and hydrophobic tails.

• Associated Proteins:

  • Integral Proteins: Span the membrane; function as channels, carriers, or receptors.

  • Peripheral Proteins: Attached to membrane surface; involved in signaling or structural support.

  • Receptors: Bind signaling molecules and initiate cellular responses.

  • Enzymes: Catalyze reactions at the membrane surface.

  • Carriers: Transport specific substances across the membrane.

Membrane Transport Mechanisms

Cells use various mechanisms to move substances across the plasma membrane.

• Diffusion: Movement of molecules from high to low concentration (down the concentration gradient).

• Simple Diffusion: Direct movement of small, nonpolar molecules (e.g., O2, CO2).

• Facilitated Diffusion: Movement of larger or polar molecules via membrane proteins (channels or carriers).

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

• Concentration Gradient: Difference in concentration of a substance across a space or membrane.

• Primary Active Transport: Uses ATP to move substances against their concentration gradient (e.g., Na+/K+ pump).

• Secondary Active Transport: Uses energy from the movement of another substance down its gradient (often Na+) to transport a different substance against its gradient.

• Endocytosis: Uptake of materials by engulfing them in vesicles.

  • Phagocytosis: "Cell eating"; uptake of large particles.

  • Pinocytosis: "Cell drinking"; uptake of fluid and dissolved substances.

• Exocytosis: Release of substances from the cell via vesicles fusing with the plasma membrane.

Example Table: Types of Membrane Transport

Additional info: Academic context and examples have been added to expand on the brief points in the original review sheet, ensuring the notes are self-contained and suitable for exam preparation.