Biology Overview: ATP and Photosynthesis

ATP - The Energy Currency of the Cell

• ATP is the primary energy molecule used by cells.
• ATP is a nucleotide consisting of adenine, ribose, and three phosphate groups.
• The breakdown of ATP into ADP and inorganic phosphate releases energy that cells use to carry out various functions.
• ATP powers processes like the Na+-K+ pump, movement of cell parts, and muscle contraction.
• Cells store energy in glucose, which is a more efficient energy source than ATP.

Photosynthesis - Converting Sunlight to Energy

• Photosynthesis is the process of using sunlight, water, and carbon dioxide to build glucose.
• Photosynthesis is a key process for life on Earth as it produces oxygen as a byproduct.
• The overall photosynthesis equation is: 6CO2 + 6H2O → C6H12O6 + 6O2.
• Chlorophyll is a pigment essential for photosynthesis, absorbing sunlight and exciting electrons.
• Photosynthesis occurs in chloroplasts, specifically in the thylakoids and stroma.

Photosynthesis Reactions

• Photosynthesis is divided into two sets of reactions: light-dependent reactions and light-independent reactions.
• Light-dependent reactions occur in the thylakoids and require sunlight to produce ATP and NADPH.
• Light-independent reactions, also known as the Calvin Cycle, occur in the stroma and use ATP and NADPH to create glucose from carbon dioxide.

Light-Dependent Reactions

• Photosystem II captures light energy, splitting water molecules, and releasing oxygen as a byproduct.
• The electrons released from water are passed down an electron transport chain, releasing energy and pumping protons into the thylakoid space.
• The proton gradient drives ATP synthase, producing ATP.
• Photosystem I captures light energy again, boosting electrons to a higher energy level and producing NADPH.

Cellular Respiration - Decomposing Glucose for Energy

• Cellular respiration is the process by which organisms convert glucose into ATP to power cellular functions.
• Cellular respiration utilizes oxygen and releases carbon dioxide and water, which are the products of photosynthesis.
• The equation for cellular respiration is: C6H12O6 + 6 O2 → 6CO2 + 6 H2O.

Steps of Cellular Respiration

• Cellular respiration occurs in three stages: glycolysis, Krebs cycle, and electron transport chain.

Glycolysis

• Glycolysis occurs in the cytoplasm and splits glucose into two molecules of pyruvic acid.
• It requires two ATP molecules but produces four ATP molecules, resulting in a net gain of two ATP.
• Glycolysis also produces two molecules of NADH, another electron carrier.
• Glycolysis does not require oxygen and can occur in both prokaryotic and eukaryotic cells.

Krebs Cycle

• The Krebs cycle, also known as the citric acid cycle, takes place in the mitochondrial matrix.
• The cycle breaks down pyruvic acid into CO2, producing NADH, FADH2, and ATP.

Electron Transport Chain

• The electron transport chain takes place in the inner mitochondrial membrane.
• NADH and FADH2, produced in glycolysis and the Krebs cycle, donate high-energy electrons to a chain of proteins.
• The electrons move down the chain, releasing energy that pumps protons into the intermembrane space, creating a proton gradient.
• The proton gradient powers ATP synthase, which generates ATP.
• Oxygen acts as the final electron acceptor, combining with electrons and protons to form water.

Anaerobic Respiration: Fermentation

• In the absence of oxygen, cells utilize fermentation, which is a less efficient way to generate energy.
• Lactic acid fermentation occurs in muscle cells during strenuous exercise when oxygen supply is limited.
• It regenerates NAD+, allowing glycolysis to continue, but produces lactic acid as a byproduct.
• Alcohol fermentation is a form of anaerobic respiration that occurs in yeast and some bacteria.

Exercise and Cellular Respiration

• During short bursts of intense exercise, muscles primarily use stored ATP and then engage in lactic acid fermentation for energy.
• Lactic acid accumulation contributes to muscle soreness.
• Aerobic exercise, which relies on cellular respiration, requires a steady supply of oxygen and is more efficient in the long term.
• Training can increase muscle fibers, stored ATP/glucose, and mitochondria to improve performance.