Cell Organelles, Membrane Transport & Cellular Respiration
Advertisement
Custom Network In-Article
1. Organelle Functions Reference
- Nucleus: Houses linear genomic DNA, surrounded by a double membrane with nuclear pores; site of transcription and ribosome subunit assembly (nucleolus).
- Mitochondria: Double-membrane organelle; inner membrane contains cristae and electron transport chain complexes; produces majority of ATP via oxidative phosphorylation.
- Rough Endoplasmic Reticulum (RER): Studded with ribosomes; synthesizes and post-translationally modifies proteins destined for secretion or membranes.
- Smooth Endoplasmic Reticulum (SER): Lipid synthesis, steroid hormone production, calcium storage in muscle (sarcoplasmic reticulum), and drug detoxification.
- Golgi Apparatus: Modifies, packages, and sorts proteins and lipids received from the ER into vesicles for lysosomal delivery or exocytosis.
- Lysosomes: Acidic interior (pH $\approx$ 4.5–5.0) containing hydrolytic enzymes for intracellular digestion and autophagy.
2. Cellular Respiration Summary: Glucose to ATP
$$\text{C}6\text{H}$$}\text{O}_6 + 6\text{O}_2 \longrightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \sim 30\text{--}32\text{ ATP
| Pathway Stage | Cellular Location | Key Inputs | Net Direct Yield | Reduced Coenzymes |
|---|---|---|---|---|
| Glycolysis | Cytosol | 1 Glucose, $2\text{ NAD}^+$ | 2 Pyruvate, $2\text{ ATP}$ | $2\text{ NADH}$ |
| Pyruvate Decarboxylation | Mitochondrial Matrix | 2 Pyruvate | $2\text{ Acetyl-CoA}, 2\text{ CO}_2$ | $2\text{ NADH}$ |
| Citric Acid (Krebs) Cycle | Mitochondrial Matrix | 2 Acetyl-CoA | $4\text{ CO}_2, 2\text{ ATP/GTP}$ | $6\text{ NADH}, 2\text{ FADH}_2$ |
| Oxidative Phosphorylation | Inner Mitochondrial Membrane | Electrons from NADH & $\text{FADH}_2$, $\text{O}_2$ | $\sim 26\text{--}28\text{ ATP}, 6\text{ H}_2\text{O}$ | Oxidizes coenzymes |
3. Membrane Transport Mechanisms
- Simple Diffusion: Down concentration gradient; small, nonpolar molecules (e.g., $\text{O}_2, \text{CO}_2$, steroid hormones). No ATP required.
- Facilitated Diffusion: Down electrochemical gradient via protein channels or carrier proteins (e.g., GLUT glucose transporters, aquaporins). No ATP required.
- Primary Active Transport: Moves solutes against their concentration gradient using direct ATP hydrolysis (e.g., $\text{Na}^+/\text{K}^+\text{-ATPase}$ pumping $3\text{ Na}^+$ out and $2\text{ K}^+$ in per ATP).
- Secondary Active Transport (Cotransport): Couples the downhill movement of one ion to the uphill movement of another substance (e.g., $\text{Na}^+/\text{glucose}$ symporter SGLT1).