Cellular respiration: Process by which cells obtain energy from organic molecules.
Primary goal: create energy intermediates such as ATP and NADH.
Aerobic respiration: Uses oxygen; consumes $$O2andreleases$$ and releases $$CO2$$.
Glucose (C6H12O6) is broken down into carbon dioxide and water.
$$C6H{12}O6 + 6O2 \rightarrow 6CO2 + 6H2O$$
Glycolysis
Glucose (6-carbon molecule) is broken down into two pyruvate molecules (3-carbon).
Occurs in the cytosol.
Net production of 2 ATP and 2 NADH.
Pyruvate Breakdown
Pyruvate is transported into the mitochondria.
Oxidized to form two acetyl groups, releasing two CO2$$CO_2$$ molecules.
Produces 2 NADH.
Citric Acid Cycle
Acetyl groups are oxidized, releasing four CO2$$CO_2$$ molecules.
Produces 2 ATP, 6 NADH, and 2 FADH2.
Oxidative Phosphorylation
NADH and FADH2 are oxidized via the electron transport chain, creating an H+ gradient.
The H+ gradient is used to produce approximately 30-34 ATP.
Occurs in the cytosol; does not require oxygen.
Evolutionarily ancient; nearly identical in all species.
Three phases:
Energy investment: 2 ATP are hydrolyzed.
Cleavage: Glucose is broken into two 3-carbon molecules (glyceraldehyde-3-phosphate).
Energy liberation: Produces 2 NADH and 4 ATP (net gain of 2 ATP).
Substrate-level phosphorylation: Phosphate group is transferred from an enzyme-bound substrate to ADP.
Net products: two pyruvates, two ATP (net), two NADH.
Pyruvate enters the mitochondrial matrix in eukaryotic cells.
Pyruvate dehydrogenase complex oxidizes pyruvate, releasing one CO2$$CO_2$$ molecule per pyruvate.
Forms acetyl CoA and one NADH per pyruvate.
Occurs in the mitochondrial matrix.
Acetyl group from acetyl CoA combines with oxaloacetate (4-carbon) to form citrate (6-carbon).
For each acetyl group:
Two CO2$$CO_2$$ molecules are released.
One ATP (originally GTP) is produced.
Three NADH are produced.
One FADH2 is produced.
Oxaloacetate is regenerated.
Two components:
Electron Transport Chain (ETC).
ATP Synthase.
High-energy electrons from NADH and FADH2 are transferred to the ETC.
Electrons release energy as they move along the chain, creating an H+ electrochemical gradient.
ATP synthase uses the energy in the H+ gradient to synthesize ATP.
Located in the inner mitochondrial membrane.
NADH and FADH2 are oxidized, and electrons enter the chain.
Electrons are passed along protein complexes and organic molecules (e.g., ubiquinone).
Energy released is used to pump H+ ions across the inner membrane, forming a gradient.
Oxygen accepts electrons at the end of the chain, forming water.
H+ ions flow through ATP synthase, releasing energy.
Energy is used to covalently attach a phosphate group to ADP, forming ATP.
Chemiosmosis: ATP synthesis driven by the movement of ions across a membrane.
ATP Yield:
Glycolysis: 2 ATP
Citric Acid Cycle: 2 ATP
Oxidative Phosphorylation: 30-34 ATP
The enzyme has transmembrane and extramembrane parts, including a ring of c subunits
H+ ions in the intermembrane space enter a half channel and bind to a c subunit, then rotate around the ring until reaching another half channel that releases H+ into the matrix
The gamma subunit rotates, which is attached to the c-subunits, as well
The rotation causes conformational changes in the beta subunits, which make up the location where ATP is synthesized, generating three phases: 1) binding of ADP and inorganic phosphate, 2) using induced fit to create ATP, which is now tightly bound, and 3) a release of the ATP
The various beta subunits are in different phases at the same time
Besides glucose, other molecules (carbohydrates, proteins, fats) can be used for energy.
These molecules enter glycolysis or the citric acid cycle at various points.
Cellular Respiration Vocabulary