Cellular Respiration & ATP

• Cellular respiration is an metabolic process essential for life
• Photosynthesis and cellular respiration are complementary processes involving glucose

Energy

• Defined as the capacity to do work, encompassing kinetic (motion) and potential (stored) forms
• The law of Conservation of Energy states energy is neither created nor destroyed
• Entropy measures disorder or randomness
• Chemical energy is stored in molecular bonds
• ATP (adenosine triphosphate) powers cellular work directly

ATP

• ATP is composed of adenosine and three phosphate groups
• ATP releases stored energy to become ADP (adenosine diphosphate) by breaking a phosphate bond
• The breaking of bonds releases energy, while the creation of bonds stores energy
• ATP can be used for mechanical, transport, and chemical work within cells
• ATP is a renewable resource, cycling between ATP and ADP

Cellular Respiration

• An aerobic process requiring oxygen, differing from respiration (breathing)
• The overall equation for cellular respiration involves glucose and oxygen, producing carbon dioxide, water, and energy

Oxidation-Reduction

• Crucial reactions as electrons are transferred from sugar to oxygen
• Oxidation involves the loss of electrons, while reduction involves the gain of electrons
• The rapid fall of electrons releases energy, harnessed by cells in small amounts
• Electrons from glucose reduce NAD+ to NADH
• During the electron transport chain, electrons pass through Redox Reactions until oxygen is a final electron acceptor, forming water
• Energy released during the electron transport chain is funneled into ATP production

Steps of Cellular Respiration

• Glycolysis, the Citric Acid Cycle, and the Electron Transport Chain are the key stages

Glycolysis

• Glycolysis splits glucose into two molecules of pyruvic acid in the cell cytoplasm, generating a small amount of ATP directly
• It is an anaerobic process that does not require oxygen
• Electrons are donated to the electron carrier NAD+

Intermediate Step

• Pyruvic acid converts to Acetyl-CoA for use in the Krebs cycle
• The breaking of pyruvic acid bonds stored the electrons in NADH and will be later used for ATP production

Krebs Cycle

• Acetyl-CoA enters the Krebs cycle within the mitochondria, completing sugar breakdown into CO2 and generates a small amount of ATP directly
• Captures more energy in the form of NADH and FADH2 for electron transport chain conversion

Electron Transport Chain

• Electrons from glucose by NADH travel down the electron transport chain to oxygen, occurring in the inner membranes of the mitochondria
• Released energy pumps H+ ions across the inner mitochondrial membrane, creating a concentrated gradient that fuels ATP synthase to produce ATP from ADP
• This stage generates the most ATP for the cell, both directly and from electron carriers

Metabolism

• Metabolism refers to all chemical processes in cells
• Cellular respiration serves as an example of metabolism and includes Glycolysis, Intermediate Step, Krebs Cycle, and the Electron Transport Chain

Versatility

• Cellular respiration breaks down diverse foods as energy sources

Aerobic vs Anaerobic

• Cellular respiration requires oxygen whereas fermentation does not
• Facultative anaerobes use either pathway
• Obligate anaerobes cannot be in the presence of oxygen, while obligate aerobes require oxygen

Anaerobic Respiration Types

• Lactic Acid Fermentation and Alcoholic Fermentation are the two types

Lactic Acid Fermentation

• Occurs with no oxygen or low oxygen, which commonly occurs in muscle cells
• Glycolysis supplies the ATP, but is not efficient when compared to cellular respiration
• Lactic acid is a waste product and is why muscles fatigue

Alcoholic Fermentation

• Features yeast fermentation to produce ethyl alcohol and CO2
• The produced CO2 makes beer and champagne bubbly and bread rise

Methane

• Produced by cows, methane is a greenhouse gas linked to climate change