CE

Cellular Respiration Overview

Overview of Cellular Respiration

  • Cellular respiration involves a series of chemical reactions that convert food energy into ATP.

  • Emphasizes that energy cannot be created or destroyed (law of conservation of energy).

    • ATP (adenosine triphosphate) is a molecule that stores energy, not energy itself.

Key Concepts
ATP Structure

  • Each ATP molecule consists of:

    • Three phosphate groups

    • A five-carbon sugar (ribose)

    • A nitrogen base (adenine)

  • Energy is stored in the bonds between the phosphates.

  • Breakdown of ATP releases energy for cellular processes.

Cellular Metabolism

  • Cellular respiration is the process by which cells extract energy from food to generate ATP, through a process called glucose metabolism.

  • Every time we eat, our bodies extract energy from food to produce ATP.

  • Two main processes for organisms to get energy:

    1. Photosynthesis (for autotrophs)

    2. Cellular respiration (for heterotrophs)

Types of Organisms
Autotrophs

  • Organisms that can produce their own food using sunlight (photosynthesis):

    • Examples: Plants, algae, cyanobacteria

    • Photoautotrophs convert solar energy into chemical energy for growth and reproduction.

Heterotrophs

  • Organisms that cannot make their own food:

    • Examples: Animals, fungi, most bacteria

    • Acquire nutrients from consuming other organisms.

Energy Transfer in Biological Systems
Energy Flow in Food Chains

  • Energy transfer between organisms at different trophic levels:

    • Predators (e.g., lions) receive only about 10% of the energy from their prey (e.g., deer).

    • The remaining energy is lost through metabolic processes and heat.

Redox Reactions
Definition

  • Redox reactions (oxidation-reduction reactions):

    • Oxidation: Loss of electrons

    • Reduction: Gain of electrons

Reaction Examples

  • Methane (CH4) loses electrons and becomes carbon dioxide (CO2); this is an oxidation reaction.

  • Carbon dioxide gains electrons to revert back to methane in a reduction reaction.

Role of Electron Carriers

  • Electron carriers (molecules that transport electrons) are crucial for cellular respiration:

    • Examples include NAD+, FAD, NADP+, NADPH.

    • Primarily focused on NAD and FAD in cellular respiration.

    • In cellular respiration, electron carriers like NAD+ and FAD act as oxidizing agents, accepting high-energy electrons and storing energy in their reduced forms (NADH and FADH2).

    • NAD+ accepts electrons during glycolysis (becomes NADH) and can donate them later in oxidative phosphorylation; NADH and FADH2 are utilized in the electron transport chain to produce ATP.

ATP Production Processes
Phosphorylation

  • Process of adding a phosphate group to a molecule:

    • Phosphorylation increases molecule reactivity and energy potential.

    • ADP can be phosphorylated to form ATP using energy either from substrate-level or oxidative phosphorylation.

Two Types of Phosphorylation

  1. Substrate-level phosphorylation:

    • Direct transfer of a phosphate group to ADP from a substrate.

    • Occurs in glycolysis and citric acid cycle.

  2. Oxidative phosphorylation:

    • Indirect method of ATP production that requires electron transport chain and chemiosmosis.

    • Predominantly occurs in mitochondria in the presence of oxygen.

Steps of Cellular Respiration

  1. Glycolysis (occurs in cytoplasm)

    • Breakdown of glucose into two pyruvate molecules. Can occur with or without oxygen (O_2), providing initial steps for ATP production.

    • Input: 1 glucose, 2 ATP (energy).

    • Output: 2 pyruvate, 2 NADH, 4 ATP (net gain of 2 ATP).

  2. Pyruvate Oxidation (occurs in mitochondria if oxygen is present)

    • Converts pyruvate into acetyl-CoA.

    • Byproducts include 2 CO_2 and 2 NADH for every glucose oxidized.

  3. Citric Acid Cycle (Krebs Cycle) (occurs in mitochondria)

    • Acetyl-CoA enters the cycle.

    • Outputs per glucose molecule: 6 NADH, 2 FADH2, 2 ATP, and 4 CO_2 (twice for 1 glucose).

    • Harnesses energy by oxidizing acetyl-CoA.

  4. Electron Transport Chain and Chemiosmosis (occurs in inner mitochondrial membrane)

    • Electron Transport Chain:

      • Series of proteins that transport electrons; proteins are located in the inner mitochondrial membrane.

      • NADH and FADH2 donate electrons; protons are pumped to create a gradient.

      • Oxygen acts as the final electron acceptor, forming water.

    • Chemiosmosis:

      • ATP synthase uses the proton gradient (created by the electron transport chain) to synthesize ATP.

      • Approximately 3 protons required for each ATP produced.

      • Approximately 30-36 ATP molecules are created from one glucose molecule via the entire process.

Fermentation

  • Occurs when oxygen is absent (anaerobic conditions).

  • Two types:

    1. Lactic Acid Fermentation:

      • Pyruvate converted to lactic acid; generates NAD+ to sustain glycolysis.

      • Common in muscle cells during intense activity when oxygen supply is limited.

    2. Alcoholic Fermentation:

      • Pyruvate converted to ethanol and CO_2; primarily used by yeast.

Regulation of Cellular Respiration

  • Regulated to maintain energy balance:

    • Hormonal control of glucose entry into cells; enzymes sensitive to pH changes due to lactic acid buildup.

  • Feedback inhibition ensures homeostasis in energy production.

Conclusion

  • Cellular respiration is essential for energy production in both autotrophs and heterotrophs.

  • Understanding each step and its regulation is vital in biology.