Cell Respiration and Related Processes

Cell Respiration

  • Definition: The biochemical process by which cells convert nutrients into energy.

    • Oxidation: Loss of electrons (e-) leading to an increase in oxidation state of an atom/molecule.

    • Reduction: Gain of electrons leading to a decrease in oxidation state.

  • Types of Respiration:

    • Aerobic: Requires oxygen (O₂).

    • Anaerobic: Occurs without oxygen.

Glycolysis

  • Location: Cytoplasm

  • Process: Breakdown of glucose into pyruvate.

  • Key Outputs:

    • 2 Pyruvate

    • 2 ATP

    • 2 NADH (NAD+ is reduced to NADH)

Krebs Cycle (Citric Acid Cycle)

  • Location: Mitochondrial Matrix

  • Process Overview: Acetyl-CoA oxidized to CO₂.

  • Key Outputs:

    • CO₂

    • 3 NADH (NAD+ reduced to NADH)

    • 1 FADH₂ (FAD reduced to FADH₂)

    • ATP

  • Important Note: Pyruvate from glycolysis enters as Acetyl-CoA to initiate Krebs Cycle.

Electron Transport Chain (ETC)

  • Location: Mitochondrial inner membrane

  • Process Overview: Electrons from NADH and FADH₂ are passed through a series of protein complexes.

    • Energy released is used to pump protons (H+) out, creating a gradient.

  • Final Outputs:

    • ATP

    • Water (H₂O) (from the reduction of oxygen)

  • ATP Synthase: Uses the proton gradient to produce ATP via oxidative phosphorylation.

Blockers of Cellular Respiration

  • Cyanide:

    • Blocks electron transport chain at cytochrome oxidase.

    • Prevents oxygen utilization, causing cell death.

  • DNP (Dinitrophenol):

    • Uncouples oxidative phosphorylation, leading to heat generation instead of ATP production. It makes the mitochondrial membrane leaky to H+ ions.

Purpose of Anaerobic Pathways

  • Anaerobic Respiration (Fermentation):

    • Occurs without oxygen (e.g., muscle cells and yeast).

  • Products Include:

    • Lactic Acid (in muscle cells)

    • Ethanol (in yeast)

  • Benefits:

    • Rapid energy production

    • Survival in low-oxygen environments

    • Recycling NADH back to NAD+ to sustain glycolysis.

Photosynthesis Overview

  • Light-Dependent Reactions:

    • Location: Thylakoids

    • Products: ATP, NADPH, and O₂ (from water oxidation)

  • Calvin Cycle (Light-Independent Reactions):

    • Location: Stroma

    • Convert CO₂ and ATP/NADPH into glucose.

Photosynthesis Pathways

  • C3 Plants: (e.g., Rice, Wheat, Potato)

    • Uses rubisco for carbon fixation.

    • Operates in cooler, wetter climates.

  • C4 Plants: (e.g., Maize, Sugarcane, Cacti)

    • Uses PEP Carboxylase.

    • Adapted to hot, dry environments with stomata that remain closed to conserve water.

Gene Expression: Transcription and Translation

  • Transcription:

    • Location: Nucleus

    • Process: DNA → mRNA (enzyme: RNA Polymerase)

  • Translation:

    • Location: Ribosome

    • mRNA is translated to proteins.

Mutations

  • Definition: Any change in the DNA sequence.

    • Types of Mutations:

    • A) Substitution (replacing one base)

    • B) Deletion (removing a base)

    • C) Addition (inserting a base)

Lac Operon in E. coli

  • Function: Breaks down lactose (inducible operon).

  • Components:

    • Promoter, Operator, Genes (Z, Y, A), and repressor.

    • Lactose binds to the repressor, allowing transcription to proceed.

Cell Respiration

  • Definition: The biochemical process by which cells convert nutrients into energy. It involves a series of metabolic pathways that produce ATP, the energy currency of the cell.

  • Oxidation: Loss of electrons (e-) leading to an increase in oxidation state of an atom/molecule, often stabilizing the molecule after energy is released.

  • Reduction: Gain of electrons leading to a decrease in oxidation state. This process is crucial for the transfer of energy within biological systems.

  • Types of Respiration:

    • Aerobic: Requires oxygen (O₂) and produces a significant amount of energy (approximately 36-38 ATP molecules per glucose molecule).

    • Anaerobic: Occurs without oxygen, resulting in lower energy production (approximately 2 ATP molecules per glucose molecule).

Glycolysis

  • Location: Cytoplasm.

  • Process: Breakdown of glucose into two molecules of pyruvate through a series of enzyme-catalyzed reactions. Glycolysis can occur with or without oxygen.

  • Key Outputs:

    • 2 Pyruvate (which can enter the Krebs Cycle for further oxidation).

    • 2 ATP (net gain) through substrate-level phosphorylation.

    • 2 NADH (NAD+ is reduced to NADH) used in the electron transport chain for ATP production.

Krebs Cycle (Citric Acid Cycle)

  • Location: Mitochondrial Matrix.

  • Process Overview: Acetyl-CoA (derived from pyruvate) is oxidized to carbon dioxide (CO₂) in a series of reactions that also regenerate oxaloacetate, enabling the cycle to continue.

  • Key Outputs:

    • CO₂ (released as a waste product).

    • 3 NADH (NAD+ reduced to NADH), which carry electrons to the electron transport chain.

    • 1 FADH₂ (FAD reduced to FADH₂), contributing to ATP production.

    • 1 ATP (produced by substrate-level phosphorylation).

  • Important Note: Pyruvate from glycolysis is converted into Acetyl-CoA before entering the Krebs Cycle.

Electron Transport Chain (ETC)

  • Location: Mitochondrial inner membrane.

  • Process Overview: Electrons from NADH and FADH₂ are passed through a series of protein complexes (Complexes I-IV), leading to the pumping of protons (H+) out of the mitochondrial matrix, forming a proton gradient.

  • Final Outputs:

    • 32-34 ATP produced via oxidative phosphorylation, powered by the proton gradient.

    • Water (H₂O) is formed from the reduction of oxygen at the end of the chain, acting as the final electron acceptor.

  • ATP Synthase: A protein complex that utilizes the proton gradient to facilitate ATP synthesis as protons flow back into the matrix.

Blockers of Cellular Respiration

  • Cyanide:

    • Blocks electron transport chain at cytochrome oxidase, inhibiting oxygen utilization and halting ATP production, leading to cell death.

  • DNP (Dinitrophenol):

    • Uncouples oxidative phosphorylation, causing protons to flow back into the mitochondrial matrix without producing ATP, leading to heat generation instead of energy production. This disrupts normal cellular metabolism and can cause overheating.

Purpose of Anaerobic Pathways

  • Anaerobic Respiration (Fermentation):

    • Occurs in conditions where oxygen is scarce (e.g., in active muscle cells and certain microorganisms like yeast).

  • Products Include:

    • Lactic Acid (in muscle cells) which can accumulate causing fatigue.

    • Ethanol (in yeast and some bacteria) as a waste product.

  • Benefits:

    • Provides rapid energy production in situations where oxygen is limited.

    • Allows for survival in low-oxygen environments by recycling NADH back to NAD+ to sustain glycolysis and ATP production.

Photosynthesis Overview

  • Light-Dependent Reactions:

    • Location: Thylakoids in chloroplasts.

    • Products: ATP, NADPH, and molecular oxygen (O₂ from the oxidation of water).

  • Calvin Cycle (Light-Independent Reactions):

    • Location: Stroma of chloroplasts.

    • Process: Uses ATP and NADPH to convert CO₂ into glucose through a series of reactions, including carbon fixation and reduction phases.

Photosynthesis Pathways

  • C3 Plants:

    • Examples: Rice, Wheat, Potato.

    • Uses rubisco for carbon fixation, primarily in cooler, wetter climates.

  • C4 Plants:

    • Examples: Maize, Sugarcane, Cacti.

    • Employs PEP Carboxylase for carbon fixation, adapted to hot, dry environments; stomata remain closed to minimize water loss.

Gene Expression: Transcription and Translation

  • Transcription:

    • Location: Nucleus of eukaryotic cells.

    • Process: DNA is transcribed into messenger RNA (mRNA) with the help of the enzyme RNA Polymerase, which assembles nucleotides in the 5' to 3' direction.

  • Translation:

    • Location: Ribosome (cytoplasm or on the rough endoplasmic reticulum).

    • Process: mRNA is translated into a polypeptide chain (protein) through the association of tRNA molecules with ribosomes, following the genetic code for amino acid sequence.

Mutations

  • Definition: Any change in the DNA sequence that can result in variations in gene expression and potentially lead to disease or adaptation.

  • Types of Mutations:

    • A) Substitution (replacing one base with another, which can be silent, missense, or nonsense).

    • B) Deletion (removing one or more bases, which can lead to frameshifts and altered protein production).

    • C) Addition (inserting one or more bases, which may also result in frameshifts).

Lac Operon in E. coli

  • Function: Breaks down lactose and is an example of an inducible operon, where genes are activated in response to the presence of lactose.

  • Components:

    • Promoter, Operator, Genes (Z, Y, A), and repressor protein (lacI).

    • When lactose is present, it binds to the repressor and inactivates it, allowing transcription of the operon's genes to