Energy Types and Thermodynamics

Energy Types

• Kinetic energy is the energy of movement.
• Examples of kinetic energy are moving objects, thermal energy (random movement of atoms and molecules), and light.
• Potential energy is stored energy that matter contains based on its location or structure.
• Examples of potential energy are an object waiting to go down a hill and the potential energy in chemical bonds.
• Chemical energy is a type of potential energy in chemical reactions that can be used for work in the cell.

Thermodynamics

• Thermodynamics studies energy transformations.
• The first law of thermodynamics states that energy in the universe is constant and can be transferred or transformed, but not created or destroyed.
• The second law of thermodynamics states every energy conversion increases the disorder in the universe.
• Disorder is also called entropy, which describes the random arrangement of matter and energy.

Cellular Respiration

• Cellular respiration uses oxygen and glucose to produce carbon dioxide and ATP.
• Some energy is released as heat, but the cell uses most in the form of ATP.

Two Types of Chemical Reactions

• Exergonic reactions release energy.
• Example: Wood burning releases light and heat energy.
• Endergonic reactions require energy and their products contain potential energy.
• Example: Photosynthesis converts light energy to chemical energy.

Metabolism

• Metabolism encompasses all the chemical reactions in the body.
• Metabolic pathways are a series of steps taken in a chemical reaction to break down or build complex molecules.
• Cellular respiration is one metabolic pathway.

Energy Coupling

• Energy coupling uses energy released from exergonic reactions to power endergonic reactions.

Adenosine Triphosphate (ATP)

• ATP is made of adenosine and three phosphate groups.
• ATP powers almost all forms of work in the cell.

Making Adenosine Diphosphate (ADP)

• The phosphate groups in ATP are negatively charged and repel each other.
• This repulsion makes the bonds between phosphate groups easily broken by hydrolysis.

Hydrolysis of ATP

• Hydrolysis of ATP releases energy, making it an exergonic reaction.
• The phosphate group released during hydrolysis is used to power other chemical reactions in the cell, a process called phosphorylation.

Functions of ATP

• ATP helps drive chemical, transport, and mechanical work in the cell.

Chemical Work

• ATP can phosphorylate reactants to convert them into products.

Transport Work

• ATP can phosphorylate transport proteins to move molecules against their concentration gradient.

Mechanical Work

• ATP can phosphorylate motor proteins in muscle cells, causing a change in shape that pulls on protein filaments and results in muscle contraction.

ATP Recycling

• ATP is used and regenerated in a cell to be used again.

Stages of Cellular Respiration

• Cellular respiration has three stages: glycolysis, pyruvate oxidation and Citric Acid Cycle, and oxidative phosphorylation.

Glycolysis

• Glycolysis occurs in the cytoplasm, specifically the cytosol.
• It converts glucose into 2 molecules of pyruvate.
• Glycolysis produces a small amount of ATP and provides electrons to the electron transport chain.

Pyruvate Oxidation and the Citric Acid Cycle

• Pyruvate oxidation and the Citric Acid Cycle occur in the mitochondria.
• Pyruvate is oxidized to a 2-carbon compound.
• The Citric Acid Cycle finishes breaking down glucose into carbon dioxide.
• These stages produce some ATP and provide electrons to the electron transport chain.

Oxidative Phosphorylation

• Oxidative phosphorylation relies on electrons carried by NADH and FADH2, which are used to provide electrons to the electron transport chain.
• Energy released from the electron transport chain is used to make ATP in oxidative phosphorylation.
• Electrons are passed to oxygen to make water.

The Electron Transport Chain and ATP

• Energy moving down the ETC by electrons pumps hydrogen ions across the inner membrane of the mitochondria.
• This creates a concentration gradient of hydrogen ions.
• Chemiosmosis uses the potential energy from the hydrogen concentration gradient to make ATP.

Glycolysis in Detail

• Steps 1-4: ATP adds two phosphate groups to a glucose intermediate.
• Step 4: The intermediate is split into two three-carbon molecules called glyceraldehyde-3-phosphate (G3P).
• Steps 5-9 occur twice:
  • Step 5: NAD+ is reduced to NADH and a phosphate group is added to G3P.
  • Steps 6-9: 4 ATP is produced and water is produced in step 8. 2 pyruvate are formed.
• For each molecule of glucose at the beginning of glycolysis, 2 pyruvate are formed.

Glycolysis Summary

• Glycolysis occurs in the cytosol.
• It involves 9 steps, each with a specific enzyme.
• Starts with 1 glucose molecule.
• Products of glycolysis include:
  • 2 ATP
  • 2 pyruvate
  • 2 NADH

Pyruvate Oxidation and the Citric Acid Cycle

• Pyruvate is transported to a mitochondrion for pyruvate oxidation and the Citric Acid Cycle.
• Pyruvate does not enter the mitochondria itself.

Pyruvate Oxidation

• 1. Carboxyl group is removed as CO2.
• 2. Pyruvate is oxidized and NAD+ is reduced to NADH.
• 3. Coenzyme A joins to form Acetyl CoA.
• 2 Acetyl CoA enter the Citric Acid Cycle because 2 pyruvate are produced from glycolysis.

Citric Acid Cycle (Krebs Cycle)

• Coenzyme A splits off from Acetyl CoA and is recycled.
• For each pyruvate, the following products are produced:
  • 2 CO2
  • 3 NADH
  • 1 ATP
  • FADH2 (electron carrier)
• Because each glucose molecule produces 2 pyruvate, these products are doubled for each glucose molecule.

Cellular Respiration Review

• Cellular respiration is crucial for energy production in living organisms.
• It involves three main stages: glycolysis, pyruvate oxidation and the Citric Acid Cycle, and oxidative phosphorylation.
• ATP is the primary energy currency of the cell.
• Understanding these processes is essential for comprehending biological functions.

Fermentation

• Fermentation produces energy without oxygen.
• Aerobic respiration utilizes oxygen to make ATP.
• Anaerobic respiration does not require oxygen to make ATP.

Lactic Acid Fermentation

• Regenerates NAD+
• Step 1: Glycolysis breaks down glucose into 2 pyruvate molecules, producing 2 ATP and reducing 2 NAD+ to 2 NADH.
• Step 2: NADH is oxidized back to NAD+ and pyruvate is reduced to lactate.

When is Lactic Acid Fermentation Used?

• Lactic acid fermentation occurs when oxygen is limited, such as during intense exercise.
• The process allows for the continued production of ATP through glycolysis by recycling NAD+.