ATP and Metabolism

Energy is stored in chemical bonds and can be released + transformed by metabolic pathways

Metabolic Pathways: Coordinated series of biochemical reactions that convert molecules into different molecules

Characteristics of Metabolic Pathways

• A series of separate, intermediate reactions

• Each reaction is catalyzed by a specific enzyme

• Metabolic pathways are similar in all organisms

• Many are compartmentalized

• Each pathway is controlled by one or a few key enzymes that can be inhibited or activated.

Cellular Energy: ATP

• Adenosine Triphosphate (ATP) is the main energy currency in cells

• Energy released by exergonic reactions is stored in the bonds of ATP

• When ATP is hydrolyzed, free energy is released to drive endergonic reactions

Coupling Exergonic and Endergonic Reactions using ADP and ATP

• Exergonic Reaction: releases energy that is used to drive the endrgonic condensation of ADP + Pi to make ATP

• Energy released by the hydrolysis of ATP to ADP + Pi can then be used to drive and endergonic reaction

ATP is Recyclable

• The ADP portion of the molecule stays the same

• Adding a third phosphate group (phosphorylation) adds energy

• Removing the phosphate group (hydrolysis) releases energy

• ATP can also be recharged and reused

• The cell can make and break ATP extremely quickly

  • Muscle cell makes and uses about 10M molecules of ATP every second

ATP Production from Food Metabolism

• Amino acids, monosaccharides and fatty acids are produced from the metabolism of proteins, carbohydrates and fats, respectively

• Pyruvate and/or acetyl-CoA are obtained, which, in turn, are generally metabolized in the Krebs cycle and the oxidative phosphorylation

Pyruvate and Acetyl CoA

• Glucose is metabolized via glycolysis, leading to pyruvate which can then either ber reduced to lactate or alanine

• Enter the tricarboxylic acid (TCA) cucle via pyruvate dehydrogenation (PDH) as acetyl CoA

• Pyruvate is thus an intermediate, common to oxidative phosphorylation and anaerobic glycolysis

ATP Synthesis in Mitochondria

• Energy released during respiration is conserved as ATP

• Mitochondria have an outer membrane, which allows the passage of most small molecules and ions

• The electron-transferring molecules of the respiratory chain and the enzymes responsible for ATP synthesis are located in and on this inner membrane

• Space inside (matrix) contains the enzymes of the TCA cycle

ATP Formation during Photosynthesis

• 6CO2 + 6H2O + light energy → C6H12O6 + 6O2

• Electron carrier molecules are arranged in electron transport chains that produce ATP and NADPH (which temporarily store chemical energy)

• The light reactions capture energy from sunlight, which they change to chemical energy that is stored in molecules of NADPH and ATP

• The light reactions also release oxygen gas as a waste product

• Calvin Cycle reactions use chemical energy from NADPH and ATP that were produced in the light reactions

Two ways of ATP to be generated

1. Substrate Level Phosphorylation

2. Oxidative Phosphorylation

Three Uses of ATP

1. Chemical: Ezymes oversee the transfer of energy from ATP hydrolysis to the formation of another chemical bond

2. Mechanical: Hydrolysis of ATP to ADP causes a conformational change — the protein changes shape — that generates a mechanical force

3. Transport: ATP in the sodium-potassium pump

ATP is a Nucleotide

• ATP not only stores energy, but is also one of the building blocks of RNA (along with UTP, CTP and GTP)

  • GTP can also be used to hold and transfer energy

• RNA polymerases link these building blocks together into long chains to make messenger, transfer, ribosomal and other types of RNA

Electron Carriers in Metabolic Pathways

Cells use coenzyme nicotinamide adenine dinucleotide (NAD) as an elextron carrier in redox reactions

Electron Carriers in Metabolic Pathways have 2 distinct forms; oxidized and reduced

• FAD + FMN can accept 2e- and 2H+