Cellular Respiration

Summary Reaction and Key Concepts

Cellular respiration is a catabolic, exergonic process by which cells convert glucose into usable energy (ATP), with the overall reaction involving the oxidation of glucose and the reduction of oxygen.

• Summary Reaction:

• Reactants: Glucose (obtained from food in animals, photosynthesis in plants), Oxygen (from atmosphere via respiration or stomata in plants)

• Products: Carbon dioxide, water, ATP

• Catabolic/Anabolic: Catabolic (breaks down molecules)

• Exergonic/Endergonic: Exergonic (releases energy)

• Oxidized Reactant: Glucose is oxidized to CO2

• Reduced Reactant: Oxygen is reduced to H2O

Electron Carriers in Metabolism

Electron carriers are molecules that transport electrons during cellular respiration, facilitating redox reactions and energy transfer.

• Examples: NAD+ (nicotinamide adenine dinucleotide), FAD (flavin adenine dinucleotide)

• Role: Accept electrons during glycolysis and the Krebs cycle, then donate them to the electron transport chain

Main Steps of Cellular Respiration

Cellular respiration occurs in three main stages, each with distinct locations, reactants, and products.

• 1. Glycolysis: Converts glucose to pyruvate; occurs in the cytoplasm

  • Reactants: Glucose, 2 NAD+, 2 ADP

  • Products: 2 Pyruvate, 2 NADH, 2 ATP

• 2. Pyruvate Oxidation: Converts pyruvate to acetyl-CoA; occurs in mitochondrial matrix

  • Reactants: 2 Pyruvate, 2 NAD+, 2 CoA

  • Products: 2 Acetyl-CoA, 2 NADH, 2 CO2

• 3. Citric Acid Cycle (Krebs Cycle): Acetyl-CoA to CO2; occurs in mitochondrial matrix

  • Reactants: 2 Acetyl-CoA, 6 NAD+, 2 FAD, 2 ADP

  • Products: 4 CO2, 6 NADH, 2 FADH2, 2 ATP

Oxidative Phosphorylation

Oxidative phosphorylation includes the electron transport chain and chemiosmosis, producing the majority of ATP in cellular respiration.

• Location: Inner mitochondrial membrane

• Electron Transport Chain: Transfers electrons from NADH and FADH2 to oxygen, pumping protons to create a gradient

• Chemiosmosis: Protons flow back through ATP synthase, driving ATP production

• Reactants: NADH, FADH2, O2, ADP

• Products: NAD+, FAD, H2O, ATP

ATP Yield

• Highest ATP Production: Oxidative phosphorylation produces the most ATP (about 26-28 out of 30-32 total per glucose)

Photosynthesis

Importance of Photoautotrophs

Photoautotrophs, such as plants, algae, and some bacteria, convert solar energy into chemical energy, supporting heterotrophs and maintaining the biosphere's energy flow.

• Heterotrophs: Organisms that rely on consuming other organisms for energy

• Biosphere: The global sum of all ecosystems, dependent on photosynthetic organisms for oxygen and organic molecules

Summary Reaction of Photosynthesis

• Summary Reaction:

• Reactants: CO2 (from atmosphere via stomata), H2O (from soil via roots), light energy (from sun)

• Products: Glucose, O2

• Catabolic/Anabolic: Anabolic (builds molecules)

• Exergonic/Endergonic: Endergonic (requires energy input)

• Oxidized Reactant: H2O is oxidized to O2

• Reduced Reactant: CO2 is reduced to glucose

Stomata Function

• Stomata: Pores on leaf surfaces that allow gas exchange (CO2 in, O2 out)

Chloroplast Structure

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

• Thylakoid: Membranous sacs where light reactions occur

• Location of Reactions: Light reactions in thylakoid membranes; Calvin Cycle in stroma

Photosynthesis and Climate Change

• Reducing CO2 Emissions: Enhances carbon fixation, mitigating climate change by lowering atmospheric CO2 levels

Stages of Photosynthesis

• 1. Light Reactions: Occur in thylakoid membranes

  • Reactants: H2O, light, NADP+, ADP

  • Products: O2, NADPH, ATP

  • Energy Source: Light

• 2. Calvin Cycle (Dark Reactions): Occurs in stroma

  • Reactants: CO2, NADPH, ATP

  • Products: Glucose, NADP+, ADP

  • Energy Source: ATP, NADPH (from light reactions)

Electromagnetic Radiation and Photosynthesis

• Wavelength and Energy: Shorter wavelengths have higher energy; longer wavelengths have lower energy

• Absorbed Wavelengths: Chloroplasts absorb blue (430 nm) and red (660 nm) light; green light (500-550 nm) is reflected, not absorbed

Carbon Fixation

• Definition: The process of incorporating inorganic CO2 into organic molecules during the Calvin Cycle

Cell Reproduction

Eukaryotic Cell Cycle Phases

• Interphase: G1 (growth, unduplicated chromosomes), S (DNA synthesis, chromosomes duplicated), G2 (preparation for division, duplicated chromosomes)

• Mitosis: Division of nucleus (prophase, metaphase, anaphase, telophase)

• Cytokinesis: Physical separation of two daughter cells

Control of Cell Division

• Normal Control: Checkpoints (G1, G2, M) regulate progression; controlled by cyclins and kinases

• Abnormal Division: Loss of control can lead to tumors (uncontrolled cell growth)

Mitosis Characteristics

• Type of Cells: Somatic (body) cells

• Functions: Growth, repair, asexual reproduction

• Daughter Cells: Two genetically identical cells

Chromatin and Chromosomes

• Chromatin: DNA-protein complex (DNA + histones)

• Histones: Proteins that package and organize DNA

• Chromosomes: Condensed chromatin visible during cell division

Chromosome Terminology

• Chromosome: Single DNA molecule with associated proteins

• Sister Chromatids: Identical copies of a chromosome, joined at the centromere

• Homologous Chromosomes: Chromosome pairs with the same genes, one from each parent

• Duplicated Chromosome: Chromosome with two sister chromatids

Structures in Cell Division

• Kinetochores: Protein structures on chromatids where spindle fibers attach

• Centromere: Region joining sister chromatids

• Centrosomes: Organelles organizing microtubules

• Microtubules: Cytoskeletal fibers forming the mitotic spindle

Diploid vs. Haploid

• Diploid (2n): Two sets of chromosomes (somatic cells)

• Haploid (n): One set of chromosomes (gametes)

Mitotic Phase Steps

• Prophase: Chromosomes condense, spindle forms

• Metaphase: Chromosomes align at cell equator

• Anaphase: Sister chromatids separate

• Telophase: Nuclear envelopes reform

• Cytokinesis: Cytoplasm divides, forming two cells

Prokaryotic vs. Eukaryotic Cell Division

• Prokaryotes: Divide by binary fission; no mitosis

• Eukaryotes: Divide by mitosis and cytokinesis

Lab Objectives

Lab 7: Yeast Fermentation

• Aerobic vs. Anaerobic Respiration: Aerobic uses O2, produces more ATP; anaerobic (fermentation) does not use O2, produces less ATP

• Yeast Fermentation Product: CO2 (inflates balloons in lab)

• Experiment Interpretation: Identify variables (independent, dependent, controls), analyze results, draw conclusions

Lab 8: Pigment Chromatography

• Pigment Extraction and Chromatography: Separates plant pigments based on solubility and affinity for paper

• Pigment Functions: Chlorophylls (capture light), carotenoids (protect from excess light, broaden absorption)