Energy at the Cellular Level

Photosynthesis

6 CO2 + 6 H2O + Energy = Glucose + 6 O2

• Plants harness the sun’s energy, storing it in glucose

• Requires energy; anabolic and endergonic

Cellular respiration

Glucose + O2 = 6 CO2 + 6 H2O + Energy

• The cell stores energy as a molecule called ATP and transfers energy through phosphorylation

• Releases energy; catabolic and exergonic

• Aerobic (oxygen-requiring) process

Thermodynamics

The study of energy and energy transfer through physical matter

The First Law of Thermodynamics

The energy in the universe is constant; energy cannot be created nor destroyed, only transformed or transferred

The Second Law of Thermodynamics

With every transformation or transfer of energy, some energy is lost to the surroundings as heat; “Law of Entropy”

Entropy

A measure of disorder

Kinetic energy

Energy of motion

Potential energy

Energy of position or structure

Mitochondria

Performs cellular respiration; breaks down glucose down one carbon at a time, and the chemical energy is used to make ATP

Exergonic reactions

Release chemical energy

Endergonic reactions

Consumes and stores chemical energy

Metabolic pathways

A series of chemical reactions that either builds or breaks down a complex molecule

Enzymes

Proteins that catalyze chemical reactions; decrease the activation energy required for a reaction

Substrate

The chemical reactants to which an enzyme binds to

Phosphorylation

The process of adding a phosphate group from ATP to another molecule

Glycolysis

• Splitting glucose into 2 pyruvate in the cytosol

• Results in 2 ATP, 2 pyruvate, and 2 electron carriers

Pyruvate Oxidation and Citric Acid Cycle

• Pyruvate enters the mitochondria from the cytosol and is transformed into Acetyl CoA after it is oxidized

• Transfers electrons and hydrogen ions to the electron carriers and releases CO2 (to be breathed out)

• Acetyl CoA enters the Citric Acid Cycle to be broken down even further

• Produces 4 electron carriers and 12 ATP per Acetyl CoA

Oxidative Phosphorylation

• Chemiosmosis occurs in the electron transport chain

• Hydrogen ions are pumped against the concentration gradient by the ETC

• Electrons generate energy as they travel through the ETC

• Hydrogen ions then diffuse through the ATP synthase, providing the energy to phosphorylate ADP

• O2 we breathe in acts as the final electron acceptor

• 30-34 ATP is produced from one glucose molecule

Chemiosmosis

The mechanism that uses the energy from the concentration gradient involving hydrogen ions on the opposite side of the cell membrane

Light Dependent Reactions

• In the membrane of the thylakoid inside a chloroplast, chlorophyll becomes chemically excited by light, causing it to release electrons

• Electrons travel through photosystem II, ETC, photosystem I, and finally NADP+ (electron carrier), making NADPH

• A hydrogen ions gradient is created and they diffuse through ATP synthase at the end of the ETC, providing energy for the Calvin Cycle

• Energy is generated as electrons pass through the ETC

Photosystem

Protein-based components that hold chlorophyll molecules

The Calvin Cycle

• Electron carriers and ATP from the light reactions are used to reduce carbon (from CO2) into a sugar (becomes glucose)

• Takes place in the stroma (internal space) inside the chloroplast