Mitochondria Structure and Function

Study Notes

Mitochondria are the powerhouses of the cell, responsible for ATP production
Outer membrane allows small molecules to pass through via porins
Inner membrane contains proteins for oxidative phosphorylation, including ATP synthase, electron transport proteins, and transport proteins
Intermembrane space lies between the inner and outer membranes, continuous with the lumen of the cristae
Matrix is the central compartment within the inner membrane, containing mitochondrial DNA (mtDNA)

Circular DNA, resembling bacterial DNA, located in the matrix
Codes for proteins essential for mitochondrial function (e.g., Tim, electron transport proteins), ribosomes, and transfer RNAs (tRNA)
Most mitochondrial proteins are coded by nuclear DNA, synthesized in the cytosol, and transported into the mitochondria

Mitochondria exist as a tubular and branched network, constantly changing
Fusion merges two mitochondria into one, promoting homogeneity within the cell
Fission fragments damaged or mutated mitochondrial parts, which are removed by autophagy, or separates them for cell division and transport

ATP (adenosine triphosphate) is the cellular energy currency composed of adenine, ribose, and three phosphate groups
ATP is primarily generated by aerobic respiration in mitochondria, with minimal amounts produced by glycolysis
Glucose breakdown is central to both catabolic (breaking down) and anabolic (building up) pathways
Glucose is broken down into pyruvate during glycolysis
Pyruvate is converted to acetyl CoA, which fuels the citric acid cycle
Other molecules like fats, proteins, and carbohydrates can also be broken down to feed into this pathway
Glucose can be stored as glycogen (in animals) or starch (in plants)
Glycolysis provides substrates for nucleotide synthesis, while acetyl CoA can be used to make fatty acids and phospholipids

Glycolysis: Occurs in the cytosol, producing a small amount of ATP and NADH, and breaking down glucose into two pyruvate molecules
Citric Acid Cycle (Krebs Cycle): Takes place in the mitochondrial matrix, producing NADH, FADH2, and some ATP from the breakdown of two pyruvates
Electron Transport Chain: Embedded in the inner mitochondrial membrane, uses NADH and FADH2 to generate a proton-motive force – an electrochemical gradient of H+ across the inner membrane into the intermembrane space
ATP Synthesis: Utilizes the ATP synthase enzyme and the proton-motive force to phosphorylate ADP to ATP by allowing protons to flow back into the matrix