BIOL 103_Fa24.08.23_carbsLipids

Discussion Questions

Some key discussion questions include: Why can single-cell amoebas grow larger than cells in multicellular organisms? Where does ATP breakdown occur - in the nucleus, mitochondria, or cytoplasm? What is the function of membrane-bound organelles in organizing metabolic pathways? Additionally, why are fats (triglycerides) more energy-dense than carbohydrates?

Surface Area to Volume Ratio

A critical concept is that the ratio of surface area to volume decreases as volume increases. For example, with a Unit 1 Cube having a surface area of 6 and a volume of 1, the ratio is 6:1, while a Unit 2 Cube has a surface area of 24 and a volume of 8, with a ratio of 3:1. This decreased ratio restricts a cell's ability to absorb nutrients efficiently, necessitating an increased density of ribosomes and mitochondria to meet resource demands as volume grows.

Structural Differences in Cells

Constraints on cell size are influenced by environmental and internal factors. Environmental constraints can be seen in large unicellular organisms (e.g., eggs) versus limitations in multicellular organisms. Internal constraints include the surface to volume ratio and variations in ribosome and mitochondria density in reproductive and dividing cells. The distinction between prokaryotes and eukaryotes also highlights structural differences that impact size and capability.

Origin and Evolution of Cells

Prokaryotic cells lack a nuclear envelope, whereas eukaryotic cells possess a nucleus housing genetic material. Within eukaryotic cell structure, several organelles, such as the nucleus, rough and smooth endoplasmic reticulum, Golgi apparatus, mitochondria, and lysosomes, are present. The nuclear envelope, which is part of the endomembrane system, surrounds the nucleus and regulates entry and exit to/from it. The roles of the endoplasmic reticulum (ER) include processing and transporting proteins, synthesizing lipids, and regulating cellular calcium levels.

Energy Production in Cells

The main energy currency in cells includes ATP and other nucleotides (like GTP). Disruption and the role of ATP in chemical reactions are essential, especially during phosphate bond breaking for energy transfer. Glycolysis, which occurs in the cytosol without oxygen, produces ATP and NADH, while the citric acid cycle occurs within the mitochondria under aerobic conditions. When comparing energy yields, fats provide double the energy when metabolized compared to carbohydrates.

Conclusion

In summary, the composition of cells includes carbohydrates, lipids, proteins, and nucleic acids, which play significant roles in energy production, structural integrity, and the regulation of biological activities within cellular processes.