Fundamentals of Organic Compounds and Cell Structure in Anatomy & Physiology

Organic Compounds

Carbohydrates

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen. They serve as a primary energy source for cells and are classified based on the number of sugar units.

• Monosaccharides: Simple sugars such as glucose and fructose.

• Disaccharides: Composed of two monosaccharide units (e.g., sucrose, lactose).

• Polysaccharides: Long chains of monosaccharides (e.g., starch, glycogen, cellulose).

Lipids

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

• Fatty Acids: Can be saturated (no double bonds), monounsaturated (one double bond), or polyunsaturated (multiple double bonds).

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

• Phospholipids: Major component of cell membranes, consisting of two fatty acids, a phosphate group, and glycerol.

• Cholesterol: Steroid molecule that stabilizes cell membranes and serves as a precursor for steroid hormones.

Proteins

Proteins are polymers of amino acids that perform a wide variety of functions in cells, including catalysis, transport, and structural support.

• Amino Acids and Polypeptides: Amino acids are linked by peptide bonds to form polypeptides.

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

• Organization in Proteins (4 Levels):

  1. Primary Structure: Sequence of amino acids.

  2. Secondary Structure: Local folding (α-helix, β-sheet) stabilized by hydrogen bonds.

  3. Tertiary Structure: Overall 3D shape of a polypeptide.

  4. Quaternary Structure: Association of multiple polypeptide chains.

• Enzymes: Biological catalysts that speed up chemical reactions.

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

• Properties: Specificity, efficiency, and regulation.

• How They Work: Lower activation energy and increase reaction rates.

Nucleic Acids

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

• DNA: Deoxyribonucleic acid; contains genetic instructions for development and function.

• RNA: Ribonucleic acid; involved in protein synthesis (mRNA, rRNA, tRNA).

• Nitrogenous Bases: Adenine, thymine, cytosine, guanine (DNA); uracil replaces thymine in RNA.

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

Adenosine Triphosphate (ATP)

ATP is the primary energy carrier in cells. It stores energy in high-energy phosphate bonds and releases it to power cellular processes.

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

• Function: Provides energy for muscle contraction, active transport, and biosynthesis.

Cell Structure and Function

Main Parts of the Cell

Cells are the basic units of life, consisting of several key components:

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

• Cytoplasm: Gel-like substance containing organelles.

• Nucleus: Contains genetic material (DNA).

Processes Found in Cells

• Metabolism: All chemical reactions occurring in the cell.

• Growth and Division: Cells grow and divide to produce new cells.

• Transport: Movement of substances across membranes.

Plasma Membrane

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

• Components: Phospholipids, cholesterol, proteins, carbohydrates.

• Proteins Associated with Plasma Membrane:

  • Integral Proteins: Span the membrane and function as channels or transporters.

  • Peripheral Proteins: Attached to the surface; involved in signaling and 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.

• Simple Diffusion: Direct movement through the lipid bilayer.

• Facilitated Diffusion: Movement via membrane proteins (channels or carriers).

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

• Concentration Gradients: Difference in concentration across a membrane drives diffusion.

Active Transport

Active transport requires energy (usually from ATP) to move substances against their concentration gradient.

• Primary Active Transport: Direct use of ATP to transport molecules (e.g., sodium-potassium pump).

• Secondary Active Transport: Uses energy from the movement of another substance down its gradient.

Endocytosis and Exocytosis

Cells use vesicular transport to move large particles or volumes across the membrane.

• Endocytosis: Uptake of materials into the cell via vesicles.

• Exocytosis: Release of materials from the cell.

• Types of Endocytosis:

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

  • Pinocytosis: "Cell drinking"; uptake of fluids and small molecules.

Example: Sodium-Potassium Pump

The sodium-potassium pump is a classic example of primary active transport, maintaining cellular ion gradients essential for nerve impulse transmission.

Equation:

$3\,\text{Na}^+_{\text{out}} + 2\,\text{K}^+_{\text{in}} + \text{ATP} \rightarrow 3\,\text{Na}^+_{\text{in}} + 2\,\text{K}^+_{\text{out}} + \text{ADP} + \text{P}_i$

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