ATP and Energy Lecture Notes

Introduction

  • The lecture focuses on ATP (adenosine triphosphate) and energy production within the body.
  • It overviews Module 1, which concludes next week.
  • Next week's lectures by Dr. Henry D. Malmantz will cover the central dogma, detailing mRNA transcription from DNA and protein translation from mRNA.
  • Previous lectures covered carbon, macromolecules, nucleic acids, amino acids, proteins, carbohydrates, and lipids.
  • Lecture 6 discussed membrane permeability due to phospholipids and the role of protein channels in molecule transport.
  • Current lecture focuses on how cells harvest and store energy as ATP.

Learning Objectives

  • Cite various ways the body uses energy: protein production, molecule transport across membranes (active transport), transcription, and translation.
  • Explain why oxygen is essential for life and why CO2CO_2 is a metabolic byproduct.
  • Describe the processes cells use to produce ATP.

Textbook Reading

  • Chapter 8: Metabolism, energy, and ATP as the main energy currency of cells.
  • Chapter 9: Stages of respiration.
  • Focus on the stages of respiration, their locations (cytosol or mitochondrion), and the ATP production at each stage.
  • Enzymes involved are not a main focus.

Energy and Reactions

  • Many processes in living things require energy to proceed and are often non-spontaneous.
  • Spontaneous reactions occur when reactants combine without additional energy input, releasing energy.
  • Cells require controlled energy release to prevent damage.

Examples of Cellular Energy Use

  • Cell division (in both eukaryotic and prokaryotic cells).
  • Synthesis of macromolecules (proteins, complex carbohydrates, phospholipids).
  • Light emission by some organisms (bacteria, algae, fireflies).
  • Sound production and movement.
  • Other examples: exercise, hair standing on end, macrophage activity, active transport of ions, and chemical work (e.g., glucose + fructose → sucrose).

ATP: The Energy Currency

  • Cells need a storage molecule for energy (ATP) and a way to harvest energy for use.
  • ATP (adenosine triphosphate) powers reactions through hydrolysis, releasing energy and producing adenosine diphosphate (ADP) and inorganic phosphate.
  • Energy from food is required to convert ADP and inorganic phosphate back into ATP.
  • ATP acts as a universal energy currency for both eukaryotic and prokaryotic cells.
  • Analogy: ATP as a $5 note, purchase (energy use) costs $2, get $3 change (ADP + inorganic phosphate). Earning $2 (energy input) is required to get back the $5 note (ATP).

Molecular Structure of ATP

  • ATP structure is similar to RNA building blocks.
  • It comprises a nucleoside (adenine), a sugar molecule (ribose - a pentose with five carbon atoms and a double-bonded oxygen), and three phosphate molecules.
  • Ribose in RNA has an oxygen on carbon number 2; deoxyribose in DNA lacks this oxygen.
  • RNA building blocks have one phosphate, while ATP has three.
  • Bonds between phosphate groups can be broken to release energy.
  • Phosphate groups have negative charges and repel each other, held together by the oxygen.
  • Hydrolyzing the terminal phosphate bond releases energy as the negatively charged phosphate dissociates.
  • Analogy: ATP is like a compressed spring, where the negatively charged tail is held by "oxygen glue"; hydrolysis releases the spring and energy.

ATP Production and Usage

  • E. coli, a bacterium, requires one ATP molecule to separate each base pair during DNA replication.
  • E. coli has 4,639,000 base pairs in its genome and requires 4,639,000 ATP molecules for DNA replication.
  • In eukaryotic cells, most ATP is generated in the mitochondria.
  • Cells requiring more energy have a larger number of mitochondria.
  • In prokaryotic cells (bacteria), ATP production occurs within the cytoplasm and plasma membrane.

Overview of Cellular Respiration

  • Cellular respiration involves glycolysis (in the cytosol), the citric acid cycle (in the mitochondrion), and oxidative phosphorylation.
  • Electrons are produced during glucose breakdown and transported by electron carriers.
  • The lecture focuses on energy harvesting from glucose.

Glucose and Energy

  • Glucose (a six-carbon molecule) reacts with oxygen in a combustion-like reaction.
  • Overall reaction: glucose + oxygen → 6 carbon dioxide + 6 water + 30-32 ATP molecules.
  • One mole of glucose yields 686 kilocalories or approximately 2,900 kilojoules of energy.
  • A mole of glucose (about 180 grams) provides about a third of the daily energy requirement.

Activation Energy and Enzymes

  • Reactions often require an activation energy barrier to be overcome.
  • Enzymes reduce this activation energy barrier, facilitating reactions.
  • Cellular respiration uses many enzymes to convert energy from glucose gradually.
  • Without controlled steps, glucose reacting with oxygen would cause cells to explode.
  • Cells release energy stored in glucose in small, controlled steps, using electron transport chains for ATP release.

Redox Reactions and Electron Carriers

  • Electrons are released during glucose breakdown and transferred via electron carriers: NADH and FADH2FADH_2.
  • NADH can hold two electrons and one proton.
  • NADH is the cell's universal electron carrier with a structure similar to ATP (adenine, ribose sugar, two phosphates, nicotinamide).
  • NADH alternates between oxidized and reduced forms by accepting or releasing electrons.

Stages of Respiration: Glycolysis

  • Glycolysis occurs in the cytosol, breaking down glucose into two pyruvate molecules.
  • Glucose comes from the blood into the cell.
  • Two phases: energy investment and energy payoff.
  • Requires two ATPs initially to kick-start the reaction.
  • Overall, glucose (6 carbons) becomes two pyruvates (3 carbons) plus water.
  • Net production: two ATPs and two NADHs (each carrying two electrons and two protons).
  • The energy investment phase involves five enzymes; ATP is used in two steps. The next phase needs five additional enzymes.
  • Overall, glycolysis involves 10 enzymes required to turn a glucose molecule into two pyruvate molecules.

Pyruvate Production and ATP Yield in Glycolysis

  • The important output at the end is two pyruvate molecules.
  • Electrons are released and picked up by NADH. The four electrons are picked up by two NADH molecules.
  • The gross output of ATP in this process is the production of four ATP molecules.
  • However, we have to subtract the initial two ATPs that were used so that is a net of 2 ATP being produced.
  • This step produces comparatively a little ATP when related to the overall ATP target goal (30 - 32 ATP molecules).

Pyruvate Transport and Acetyl CoA Formation

  • Pyruvate is transported into the mitochondrion via a transport protein.
  • Carbon dioxide is released as a waste product (the first step in breathing out CO2CO_2).
  • A two-carbon molecule binds to coenzyme A, forming acetyl CoA.
  • More NADH is produced.

Citric Acid Cycle (Krebs Cycle or TCA Cycle)

  • Each glucose molecule entering glycolysis produces two acetyl CoA molecules that feed into the citric acid cycle.
  • Occurs within the mitochondrion.
  • Produces more carbon dioxide, NADHs, ATP, and FADH2FADH_2.
  • Output: CO<em>2CO<em>2, electron carriers (NADH, FADH</em>2FADH</em>2), and a small amount of ATP.

Electron Transport Chain and Oxidative Phosphorylation

  • Occurs in the inner membrane of the mitochondrion.
  • Inner membrane has invaginations for maximum surface area to accommodate proteins.
  • Prokaryotes use their plasma membrane for this process.
  • NADH and FADH2FADH_2 transfer electrons to proteins in the electron transport chain (proteins I, II, III, IV).
  • Electrons are transferred between proteins, which alternate between oxidized and reduced states.
  • Oxygen accepts the electrons, forming water.
  • Proteins pump protons out into the space between the inner and outer mitochondrial membranes, creating a proton gradient.

The Importance of Oxygen

  • Oxygen accepts electrons to turn them into water.

ATP Synthase: The Molecular Mill

  • ATP is produced by ATP synthase, a protein embedded in the inner mitochondrial membrane.
  • Protons flow through ATP synthase, driven by the concentration gradient.
  • Protons enter rotor-like grooves, spinning the rotor within the membrane.
  • Rotation of the rotor drives the rotation of an internal rod and a catalytic knob.
  • The catalytic knob combines ADP and inorganic phosphate, forming ATP in the last step.
  • This entire process is facilitated by the prior movement of carried electrons. If the electron carriers are removed then the power required to start this process is nullified.

Summary of Respiration

  • Glycolysis: two ATPs

  • Citric acid cycle: two ATPs

  • Oxidative phosphorylation: 26-28 ATPs

  • Total: approximately 30-32 ATPs per glucose molecule.

  • Electron carriers (NADH, FADH2FADH_2) are crucial for oxidative phosphorylation.

  • Glycolysis occurs in the cytoplasm, converting glucose to pyruvate.

  • Pyruvate is shuttled into the mitochondrion for the citric acid cycle and oxidative phosphorylation.

Proteins And Fats

  • Proteins and fats can also serve as source of energy.
  • Proteins are funneled into the respiration cycle and fats also join at a later juncture in the cycle.
  • Glycerol (from fats) enters the glycolysis cycle, while fatty acids enter at the acetyl CoA step.
  • Typically, it takes more energy to extract the energy from protein and fats than carbohydrates. That's why carbohydrates are the ideal food source when trying to lose weight.

Conclusion

  • Key takeaways: the stages of respiration and the ATP production at each stage, so memorize these items, particularly.