Overview
This lecture reviews the cell cycle, DNA and protein synthesis, and cellular respiration, detailing the steps of ATP production and the roles of major macronutrients.
The Cell Cycle & DNA Replication
- Somatic cells mainly remain in interphase, where they grow, replicate organelles, and prepare for division.
- Interphase includes G0 (normal function), G1 (growth and organelle replication), S (DNA replication), and G2 (final preparations).
- DNA structure: double helix, composed of complementary nitrogenous bases (adenine-thymine, guanine-cytosine).
- DNA replication: helicase unzips DNA strands; DNA polymerase adds complementary bases, producing two identical DNA molecules.
Cellular Respiration: Overview & Steps
- Macronutrients (carbs, fats, proteins) are broken down to release energy, primarily as ATP.
- Glucose is the preferred energy source due to rapid ATP yield.
- Cellular respiration includes glycolysis (anaerobic, in cytoplasm), conversion, Krebs cycle, and electron transport chain (aerobic, in mitochondria).
- Equation: C6H12O6 + 6O2 → 6CO2 + 6H2O + ATP.
Glycolysis, Conversion, and Krebs Cycle
- Glycolysis: glucose → 2 pyruvate, 2 NADH, net 2 ATP (requires 2 ATP to start, produces 4 ATP).
- Conversion: pyruvate → acetyl-CoA (in mitochondria, requires O2), releasing CO2 and producing NADH.
- Krebs cycle: acetyl-CoA → citric acid, forms 2 ATP, 6 NADH, 2 FADH2, and CO2.
Electron Transport Chain & ATP Yield
- NADH and FADH2 deliver electrons to mitochondria’s inner membrane.
- Electrons move through protein complexes, pumping protons, creating a gradient.
- Protons flow through ATP synthase, driving ATP synthesis (chemiosmosis).
- Oxygen is the final electron acceptor, forming water.
- ATP yield: 3 ATP per NADH, 2 ATP per FADH2; net ~36 ATP per glucose (theoretical maximum).
Alternative ATP Sources: Fats & Proteins
- Fatty acids (from triglycerides) undergo beta-oxidation to form acetyl-CoA.
- Beta-oxidation is slower, requires O2, and needs glycolysis intermediates.
- Proteins are used for energy only if carbs/fats are insufficient; glucogenic amino acids can be converted to glucose via gluconeogenesis.
- Adequate intake of all macronutrients is necessary for ATP production.
Protein Synthesis: DNA to Protein
- DNA codes for proteins through transcription (DNA → mRNA) and translation (mRNA → protein).
- DNA: double-stranded, codes read as triplets (codons).
- RNA: single-stranded, uracil replaces thymine.
- mRNA carries code to ribosome; tRNA brings correct amino acids; rRNA helps assemble protein.
- Pre-mRNA is edited—introns (non-coding) are removed, exons (coding) are spliced together.
Key Terms & Definitions
- Interphase — cell cycle phase where cells grow and duplicate DNA/organelles.
- Glycolysis — anaerobic breakdown of glucose to pyruvate in cytoplasm.
- Krebs Cycle (Citric Acid Cycle) — series of aerobic reactions in mitochondria producing ATP, NADH, FADH2.
- Electron Transport Chain — mitochondrial process where electron carriers produce ATP.
- ATP Synthase — enzyme producing ATP as protons move down gradient.
- Chemiosmosis — ATP production via proton gradient-driven turbine action.
- Beta-oxidation — breakdown of fatty acids into acetyl-CoA.
- Gluconeogenesis — making glucose from non-carbohydrate sources.
- Transcription — making RNA from DNA.
- Translation — assembling a protein using mRNA at a ribosome.
- Codon — three-base code on mRNA specifying an amino acid.
- Introns/Exons — non-coding/coding regions in RNA.
Action Items / Next Steps
- Complete the cellular respiration worksheet using lecture notes and recommended videos.
- Review and organize notes, especially proteins and organelle functions.
- Study genetic code, transcription, and translation processes.
- Prepare questions for clarification before the next class.