Cellular Respiration

Overview of Cellular Respiration

Cellular respiration is a fundamental metabolic process by which cells convert biochemical energy from nutrients into adenosine triphosphate (ATP), releasing waste products. It is essential for the survival of most organisms, providing the energy required for various cellular activities.

• Goal of Cellular Respiration: To produce ATP by breaking down glucose and other organic molecules.

• Organisms Performing Cellular Respiration: Most eukaryotes (plants, animals, fungi, protists) and many prokaryotes.

• Summary Reaction: The overall reaction is:

• ATP Synthesis: ATP is synthesized via substrate-level phosphorylation and oxidative phosphorylation.

• Associated Organelle: Mitochondria are the primary site of cellular respiration in eukaryotes.

Phases of Cellular Respiration

• Glycolysis: Occurs in the cytoplasm; breaks down glucose (6C) into two pyruvate (3C) molecules.

• Transition Reaction (Pyruvate Oxidation): Converts pyruvate into Acetyl-CoA, producing NADH and CO2.

• Krebs Cycle (Citric Acid Cycle): Occurs in the mitochondrial matrix; Acetyl-CoA is oxidized, producing NADH, FADH2, ATP, and CO2.

• Electron Transport System (ETS): Located in the inner mitochondrial membrane; uses NADH and FADH2 to generate ATP via oxidative phosphorylation.

Fermentation

Fermentation is an anaerobic process that allows ATP production without oxygen. It regenerates NAD+ for glycolysis.

• Lactic Acid Fermentation: Pyruvate is reduced to lactic acid (e.g., in muscle cells).

• Alcoholic Fermentation: Pyruvate is converted to ethanol and CO2 (e.g., in yeast).

• ATP Yield: Fermentation produces much less ATP than aerobic respiration (2 ATP per glucose).

Key Molecules and Carriers

• NAD+ and FAD: Electron carriers that transport electrons to the ETS.

• ATP: The main energy currency of the cell.

• Pyruvate: End product of glycolysis; substrate for the transition reaction.

Electron Transport System (ETS)

• Function: Transfers electrons from NADH and FADH2 to oxygen, forming water and generating ATP.

• ATP Yield: Approximately 34 ATP molecules per glucose are produced in the ETS.

• Proton Gradient: The ETS creates a proton gradient across the inner mitochondrial membrane, driving ATP synthesis via ATP synthase.

Photosynthesis

Overview of Photosynthesis

Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy into chemical energy, producing glucose and oxygen from carbon dioxide and water.

• Summary Reaction:

• Location: Occurs in the chloroplasts of plant cells.

• Two Main Stages: Light-dependent reactions and light-independent reactions (Calvin Cycle).

Light-Dependent Reactions

• Location: Thylakoid membranes of chloroplasts.

• Inputs: Light, water, NADP+, ADP + Pi

• Outputs: Oxygen, ATP, NADPH

• Photosystems: Photosystem II and Photosystem I absorb light and drive electron transport.

• Electron Transport Chain: Generates ATP and NADPH via chemiosmosis.

Light-Independent Reactions (Calvin Cycle)

• Location: Stroma of the chloroplast.

• Function: Uses ATP and NADPH to fix CO2 into glucose.

• Phases: Carbon fixation, reduction, and regeneration of RuBP.

• Key Enzyme: Rubisco catalyzes the first step of carbon fixation.

Specialized Pathways

• C4 Pathway: Adaptation in some plants to minimize photorespiration in hot, dry climates.

• CAM Pathway: Allows plants to fix CO2 at night, reducing water loss.

Mitosis and Meiosis

Mitosis

Mitosis is the process of nuclear division in eukaryotic cells that results in two genetically identical daughter cells, each with the same number of chromosomes as the parent cell.

• Purpose: Growth, repair, and asexual reproduction in multicellular organisms.

• Phases: Prophase, Metaphase, Anaphase, Telophase, followed by Cytokinesis.

• Key Structures: Chromosomes, spindle fibers, centrioles (in animal cells).

• Cell Cycle Checkpoints: Ensure proper division and DNA integrity.

Meiosis

Meiosis is a type of cell division that reduces the chromosome number by half, producing four genetically diverse haploid gametes. It is essential for sexual reproduction.

• Phases: Meiosis I (homologous chromosomes separate) and Meiosis II (sister chromatids separate).

• Genetic Variation: Achieved through crossing over and independent assortment.

• Result: Four non-identical haploid cells (gametes in animals, spores in plants).

Chromosome Structure and Mutations

• Chromatin: DNA-protein complex that condenses to form chromosomes during cell division.

• Chromatid: Each of the two identical halves of a duplicated chromosome.

• Centromere: Region joining sister chromatids.

• Types of Mutations: Deletion, duplication, inversion, translocation.

• Chromosomal Disorders: Down's syndrome (trisomy 21), Klinefelter's syndrome (XXY), Turner's syndrome (XO), etc.

Comparison Table: Mitosis vs. Meiosis

Key Terms and Definitions

• ATP (Adenosine Triphosphate): Main energy carrier in cells.

• NADH/FADH2: Electron carriers in respiration.

• Photosystem: Protein complex in thylakoid membrane that absorbs light.

• Stroma: Fluid-filled space in chloroplasts where the Calvin Cycle occurs.

• Chromosome: DNA molecule with associated proteins, carrying genetic information.

• Haploid: Cell with one set of chromosomes (n).

• Diploid: Cell with two sets of chromosomes (2n).

• Crossing Over: Exchange of genetic material between homologous chromosomes during meiosis I.

• Independent Assortment: Random distribution of homologous chromosomes during meiosis I.

Additional info: The above study guide is based on a comprehensive list of questions covering key General Biology topics, including cellular respiration, photosynthesis, mitosis, meiosis, and related molecular biology concepts. The content has been expanded and organized for clarity and exam preparation.