cellular respiration

Anabolism and Energy

• Sugars are combined through dehydration reactions to form carbohydrates.
• Anabolism, where smaller molecules combine to form larger ones, requires energy.
• ATP (adenosine triphosphate) provides this energy, converting to ADP (adenosine diphosphate) as it loses a phosphate group.
• The release of the phosphate group from ATP is what provides energy for reactions.

ATP as an Energy Currency

• ATP supplies energy for anabolism, such as when amino acids combine to form proteins.
• ATP is converted to ADP when it loses a phosphate group, thereby releasing energy.
• ATP's role as an energy provider depends on the presence of its phosphate group. Removal or oxidation of this group renders ATP unable to provide energy.

Cellular Respiration Overview

• Cellular respiration involves multiple phases.
• Key concepts include oxidation (loss of electrons) and reduction (gain of electrons), summarized by the mnemonic "OIL RIG" (Oxidation Is Loss, Reduction Is Gain).

Background Knowledge Requirement

• Cellular respiration has nine steps, while the Krebs cycle has approximately ten steps.

Cellular Respiration - Amoeba Sisters Video

• Cells constantly perform processes, including active transport, requiring ATP (adenosine triphosphate) for energy.
• ATP is a type of nucleic acid composed of adenosine and three phosphates.
• Cells, whether prokaryotic or eukaryotic, must produce ATP through various processes.
• Aerobic cellular respiration occurs in eukaryotic cells, which contain membrane-bound organelles like the nucleus and mitochondria.
• Mitochondria play a central role in aerobic cellular respiration.

Goal of Aerobic Cellular Respiration

• The primary goal of aerobic cellular respiration is to produce ATP.
• The overall equation for aerobic cellular respiration involves reactants (inputs) on the left side and products (outputs) on the right side.
• This equation is similar to that of photosynthesis, with reactants and products on opposite sides.
• In photosynthesis, organisms produce glucose, while in cellular respiration, glucose is broken down to generate ATP.
• A germinating bean seed relies on stored glucose and cellular respiration to produce ATP for growth until it develops leaves and can perform photosynthesis.
• Plants perform both photosynthesis (to make glucose) and cellular respiration (to break down glucose).
• Non-photosynthetic organisms, like humans and amoebas, must obtain glucose from food sources to initiate cellular respiration.

Step 1: Glycolysis

• Glycolysis occurs in the cytoplasm and does not require oxygen (anaerobic).
• During glycolysis, glucose is converted into pyruvate, a more usable form.
• Glycolysis requires a small amount of ATP to initiate.
• The net yield from glycolysis is approximately two pyruvate molecules, two ATP molecules, and two NADH molecules.
• NADH is a coenzyme that transfers electrons, which are used to produce more ATP later.

Intermediate Step: Pyruvate Oxidation

• Pyruvate molecules are transported into the mitochondrial matrix via active transport.
• In the mitochondria, pyruvate is oxidized and converted to acetyl CoA, which is used in the next step (Krebs cycle).
• Carbon dioxide is released, and two NADH molecules are produced during this step.

Step 2: Krebs Cycle (Citric Acid Cycle)

• The Krebs cycle occurs in the mitochondrial matrix and is considered an aerobic process.
• While the cycle does not directly consume oxygen, some events within it require oxygen to continue.
• During the Krebs cycle, carbon dioxide is released, and two ATP molecules, six NADH molecules, and two FADH2 molecules are produced.
• FADH2, like NADH, is a coenzyme that assists in transferring electrons to produce more ATP.

Step 3: Electron Transport Chain and Chemiosmosis

• In eukaryotic cells, the electron transport chain and chemiosmosis occur in the inner mitochondrial membrane and require oxygen (aerobic).
• Electrons are transferred from NADH and FADH2 to protein complexes and electron carriers.
• The electrons are used to generate a proton gradient by pumping protons (H+) across the intermembrane space, creating an electrical and chemical gradient.
• Protons travel down their electrochemical gradient through ATP synthase, an enzyme that produces ATP by adding a phosphate to ADP.
• Oxygen acts as the final electron acceptor. When oxygen combines with two hydrogens, water (H2O) is produced.

ATP Production

• The electron transport chain and chemiosmosis produce significantly more ATP than the previous steps.
• The number of ATP molecules produced per glucose molecule varies depending on factors like the proton gradient across the mitochondrial membrane.
• Estimates range from 26 to 34 ATP molecules produced by the electron transport chain and chemiosmosis alone.
• Including the other two steps (Krebs cycle and glycolysis), the total ATP production ranges from 30 to 38 net ATP molecules per glucose molecule.

Alternative ATP Production: Fermentation

• In the absence of oxygen, some cells perform fermentation to produce ATP, although it is less efficient.

Importance of ATP Production and Mitochondrial Diseases

• ATP production is crucial for cells.
• Substances like cyanide can block steps in the electron transport chain, inhibiting ATP production and potentially causing death.
• Mitochondrial diseases are an area of increased research due to the mitochondria's central role in ATP production.

Glycolysis Explained

• The first step of cellular respiration is glycolysis.
• The word glycolysis means “cutting the sugar”.
• The glucose is snipped in half in your cells.
• The snipping of sugar gives two smaller pieces called pyruvate.
• Glucose \rightarrow 2 \space Pyruvate This process is an example of catabolism.
• The splitting of glucose into pyruvate happens in the cytoplasm.
• Free energy is ATP - the glucose broken into pyruvate produces ATP and gives reduced electron carriers called NADH.

Pyruvate Oxidation

• The door to the mitochondria is opened with pyruvate oxidation.
• The pyruvate enters the mitochondria where energy is produced.
• The pyruvate loses one carbon, now it has been oxidized into acetyl CoA.
• Enzymes: Proteins to help catalyze a chemical reaction.
• Coenzymes: Helpers to enzymes. Example: Vitamins that help enzyme reaction.

Citric Acid Cycle

• Acetyl CoA - This is a ticket to the next energy ride.
• It jumps into this spinning cycle, a spinning cycle. With every spin, products are created:
• 2 ATPs
• NADH and FADH2. (Electron Carriers)
• Carbon Dioxide

Oxidative Phosphorylation

• NADH and FADH2, these "energy delivery trucks" drop off elections off at Electron Transport Chain (ETC)
• Hot potato, machine pass along the electrons from "energy delivery trucks", they pump protons (H+) across the wall, builds pressure and then Chemomyosis.
• Chemo Osmosis: Gradient is being established when moving protons(H+) from high to low concentrations.
• When the protons reach a space of lower concentration, the moving protons spin a machine call ATP synthase, which is like a tiny windmill, making a ton of ATP.
• Finally, oxygen comes in, grabs the used electrons and Hydrgon and forms water.