Cell Respiration

ATP: The Universal Energy Currency

  • Adenosine triphosphate (ATP) is the primary molecule used by cells to transfer energy for various processes.

  • It's an RNA nucleotide composed of:

    • Nitrogenous base: Adenine

    • 5-carbon sugar: Ribose

    • Tail of three phosphate molecules

  • ATP acts as the "universal energy currency" because it's utilized in biochemical processes like:

    • Transport of substances

    • Muscle contraction

    • Synthesis of macromolecules

ATP in Cellular Processes

  • Active Transport:

    • Molecules moved against their concentration gradient require active transport.

    • ATP binds to transport proteins, releasing a phosphate group and energy.

    • This energy enables the transport protein to move the molecule across the membrane.

  • Macromolecule Synthesis (Anabolism):

    • Forming bonds between amino acids (proteins) or nucleotides (DNA) requires energy.

    • ATP provides this energy, and enzymes use ATP to catalyze bond formation.

  • Movement:

    • Cell movement or movement of components within the cell requires ATP.

    • ATP fuels the growth of cytoskeleton filaments (protein filaments).

    • The polymerization and depolymerization cause changes in cell shape, leading to movement.

    • Example: A phagocyte engulfing a bacterium uses ATP to extend its membrane.

ATP Hydrolysis and Synthesis

  • ATP Hydrolysis:

    • Breaking the bond between the second and third phosphate in ATP releases energy.

    • This is a hydrolysis reaction because it involves the addition of a water molecule (H2OH_2O).

    • The reaction is exergonic (energy-releasing).

    • ATP is converted to adenosine diphosphate (ADP).

  • ATP Synthesis:

    • Adding a phosphate to ADP to form ATP stores energy.

    • This is an endergonic reaction (energy-requiring).

    • The process of adding a phosphate group is called phosphorylation.

    • Water molecule is removed.

  • The energy released during ATP hydrolysis and stored during ATP synthesis is sufficient for many cellular tasks.

Cell Respiration and Respiratory Substrates

  • Cell respiration is the primary process for producing ATP.

  • Organisms use respiratory substrates to generate ATP via cell respiration.

  • Respiratory Substrates:

    • Any molecule broken down in respiration to release energy.

    • Glucose is the primary substrate for most cells.

    • Lipids and fatty acids are used when glucose is depleted.

    • Cells can also use other sugars and carbohydrates.

    • Proteins and amino acids are used as a last resort because proteins have other crucial functions.

  • Cell respiration involves metabolic pathways that break down carbon compounds, releasing energy to produce ATP.

  • Cell respiration is distinct from gas exchange (external respiration) in the lungs (oxygen in, carbon dioxide out).

Aerobic vs. Anaerobic Cell Respiration

  • Aerobic Respiration:

    • Occurs in the presence of oxygen.

    • Starts in the cytoplasm, but most steps occur in the mitochondria.

    • Can use any respiratory substrate.

    • Produces a large amount of ATP (approximately 36-38 molecules).

    • Waste products are carbon dioxide and water.

    • Word equation: glucose+oxygen→carbondioxide+water(+ATP)glucose + oxygen \rightarrow carbon dioxide + water (+ATP)

  • Anaerobic Respiration:

    • Occurs in the absence of oxygen.

    • Occurs only in the cytoplasm.

    • Only glucose and other carbohydrates can be used.

    • Produces a small amount of ATP (net gain of 2 molecules).

    • Waste product is lactate/lactic acid.

    • Word equation: glucose→lactate(+ATP)glucose \rightarrow lactate (+ATP)

Feature

Aerobic Respiration

Anaerobic Respiration

Oxygen

Present

Absent

Location

Cytoplasm and mitochondria

Cytoplasm only

Respiratory Substrates

All

Carbohydrates only

ATP Yield

High (36-38 ATP)

Low (2 ATP)

Waste Products

Carbon dioxide and water

Lactate/lactic acid

Factors Affecting Cell Respiration Rate

  • Variables affecting respiration rate:

    • Temperature

    • pH

    • Substrate concentration

    • Oxygen concentration

  • Respiration involves enzyme-controlled reactions, so factors affecting enzyme activity also affect respiration.

Respirometer

  • A respirometer is used to measure the rate of respiration.

  • Measures oxygen consumption, as aerobic respiration uses oxygen and produces carbon dioxide and water.

  • Setup:

    • Tube A: Contains organisms (e.g., insects, germinating seeds).

    • Tube B: Control (no organisms).

    • Alkaline solution (e.g., potassium hydroxide) absorbs CO2CO_2 in both tubes.

    • Capillary tube (manometer) connects the tubes.

  • Process:

    • Organisms in Tube A respire, consuming O2andproducingand producingCO2.

    • Alkaline solution absorbs the CO2CO_2, reducing the gas volume in Tube A.

    • The pressure in Tube A decreases, causing the liquid in the manometer to move towards Tube A.

    • The movement of the liquid indicates the amount of oxygen consumed, allowing calculation of the respiration rate (oxygen consumed per unit time).