Biology Chapter: Carbon Compounds in Cells

Study Notes

Carbon forms large, diverse molecules due to its four covalent bonds and small atomic size.
Water is the most abundant molecule in cells, constituting 70% or more of cell mass.
Inorganic ions (e.g., Na+, K+, Mg2+, Ca2+, HPO42-, Cl-, HCO3-) make up 1% or less of cell mass, essential for cell metabolism.
Organic compounds are classified into four major families: carbohydrates, lipids, proteins, and nucleic acids.
Macromolecules, formed through polymerization, account for 80-90% of dry weight in cells.

Carbohydrates provide energy and structural support; simple sugars like glucose serve as precursors.
Proteins, composed of 20 amino acids, demonstrate diverse functions including transport, storage, and enzyme catalysis. Cells contain thousands of different proteins.
Fatty acids consist of long hydrocarbon chains ending in carboxyl groups; examples include palmitate and stearate.

Glycolysis, a core ATP-producing pathway, oxidizes glucose to produce pyruvate and generates a net gain of 2 ATP and 2 NADH molecules.
Fermentation occurs under anaerobic conditions, producing ATP without oxygen and relying on organic compounds.
In aerobic cells, pyruvate is transported to mitochondria for further breakdown into CO2 and H2O.

Enzymes, specialized proteins, lower activation energy and increase reaction rates by binding to substrates.
Molecular motions, driven by heat energy, allow enzymes to interact rapidly with substrates.

The citric acid cycle takes place in mitochondria, utilizing compounds like pyruvate and fatty acids, producing energy-rich molecules.
This cycle contributes to biosynthetic reactions by generating carbon-containing intermediates.

Fibrous proteins: long, narrow, stable structures (e.g., keratin, myosin); less sensitive to pH and temperature changes.
Globular proteins: round, functional, and more sensitive to environmental conditions (e.g., enzymes, insulin, hemoglobin); soluble in water.