Biology for AP® Courses - Cellular Respiration

Definition: Cellular respiration is the set of metabolic processes that convert nutrients into energy (ATP) in cells.

Concept: This geothermal energy plant transforms thermal energy from deep in the ground into electrical energy, which can be easily used.
- Credit: Modification of work by the U.S. Department of Defense
- Licensing: OpenStax ancillary resource is © Rice University under a CC-BY 4.0 International license.

Stages of Oxidation/Reduction:
- Process: Electrons are lost from carbon as methane (CH₄) is oxidized to carbon dioxide (CO₂).
- This loss of electrons results in a loss of energy.
- Reduction Process: Electrons are gained during the reduction of carbon dioxide to methane, leading to:
- Gain in potential energy.
- Often accompanied by adding a proton (H⁺).
- Credit: Ryan, K., Rao, A., and Fletcher, S. Department of Biology, Texas A&M University.

NAD⁺ and NADH:
- Oxidized Form (NAD⁺): Shown on the left.
- Reduced Form (NADH): Shown on the right.
- Difference: The nitrogenous base in NADH contains one more hydrogen ion and two more electrons than in NAD⁺.

Structure: ATP (adenosine triphosphate) consists of three phosphate groups (00A…3655,2. 2, y3, 78,74, 74 -18, C0, C0.2. H2.2. B0.F1.F2,2.B2.B1.BB.A0.A1. CH4) that can be removed by hydrolysis to form ADP (adenosine diphosphate) or AMP (adenosine monophosphate).
Mechanism of Action:
- The negative charges on the phosphate groups repel each other, which requires energy to bond them together.
- Energy is released when these bonds break.

Phosphorylation:
- In reactions, the gamma (third) phosphate of ATP is attached to a protein.
- Substrate-level Phosphorylation: A phosphate group that is covalently attached to another molecule is transferred to ADP to form ATP.

Location in Cells:
- In eukaryotes: Takes place in mitochondria.
- In prokaryotes: Takes place in the plasma membrane.

First Half of Glycolysis: Involves the consumption of two ATP molecules in the phosphorylation of glucose, splitting it into two three-carbon molecules.
Second Half of Glycolysis:
- Involves phosphorylation without ATP investment (step 6).
- Produces:
- Two NADH
- Four ATP molecules per glucose.

Process Overview:
- The acetyl group from acetyl CoA attaches to a four-carbon oxaloacetate molecule to form a six-carbon citrate molecule.
- Citrate is oxidized through a series of steps, releasing two carbon dioxide molecules for each acetyl group entering the cycle.
- Outputs per Cycle:
- Three NAD⁺ molecules are reduced to NADH.
- One FAD molecule is reduced to FADH₂.
- One ATP or GTP produced by substrate-level phosphorylation.
Cycle Continuity: The cycle runs continuously in the presence of sufficient reactants because the final product is also the first reactant.

Definition: A series of electron transporters embedded in the inner mitochondrial membrane that shuttle electrons from NADH and FADH₂ to molecular oxygen.
Mechanism: Protons are pumped from the mitochondrial matrix to the intermembrane space, and oxygen is reduced to form water.

Function: ATP synthase is a complex molecular machine that uses a proton (H⁺) gradient to form ATP from ADP and inorganic phosphate (Pi).

Fermentation: In grape juice fermentation into wine, carbon dioxide (CO₂) is produced as a byproduct. Fermentation tanks have valves to release pressure from CO₂.
Implications: Fermentation allows certain organisms to generate ATP in the absence of oxygen.

Carbon Skeletons from Amino Acids: Derive from proteins and can enter the citric acid cycle.
Glycogen Hydrolysis: Glycogen from the liver and muscles is hydrolyzed into glucose-1-phosphate and can feed into the catabolic pathways for carbohydrates.

GLUT4: A glucose transporter stored in vesicles. Upon insulin binding to a receptor in the plasma membrane, GLUT4-containing vesicles fuse with the plasma membrane, allowing glucose transport into the cell.
Regulation of Glycolysis: The glycolysis pathway is primarily regulated at the three key enzymatic steps (steps 1, 2, and 7), which involve the hydrolysis of ATP.