Mitocondrias y Glucólisis

• These notes cover the topics of mitochondria and glycolysis.

Mitochondria

• Mitochondria are organelles with a double membrane.
• They evolved from aerobic bacteria.
• They exhibit variable shapes, generally kidney-shaped.
• They are responsible for oxygen utilization in metabolism.
• Mitochondria account for 15-20% of cellular volume.
• They can be spherical, kidney-shaped, spiral, or branching networks.
• Main parts include outer and inner mitochondrial membranes, intermembrane space, cristae, and matrix.

Outer Mitochondrial Membrane (OMM or MME)

• Its protein-to-lipid ratio is 1:1.
• It is permeable to ions, metabolites, and organic molecules.
• Permeability is due to porins that form pores of about 2 nm in diameter.
• It is also permeable to polypeptides up to 5 kDa via TOM (translocases of the outer membrane).
• It performs enzymatic functions like fatty acid synthesis, heme synthesis, and adrenaline and hormone degradation.

Inner Mitochondrial Membrane (IMM or MMI)

• Its protein-to-lipid ratio is 3:1.
• It is less permeable and contains lipids like cardiolipin and ubiquinone.
• It has numerous folds called cristae.
• It contains translocases (TIM), G3PDH (shuttle), antiporters (ANT), and symporters.

Intermembrane Space

• It contains cytochrome C and proteins for apoptosis.
• Its pH is approximately 7.

Mitochondrial Matrix

• It contains mitochondrial DNA, tRNA, and rRNA.
• The pH is approximately 8.
• It contains complexes of pyruvate, Krebs cycle enzymes, fatty acid oxidation enzymes, and amino acid transferases.
• Mitochondria possess about a thousand different proteins, with 99% imported from the cytosol and 1% locally synthesized.

Mitochondrial Growth and Fission

• Mitochondria can increase in size through lipid and protein import, local protein synthesis, and mtDNA replication.
• Mitochondria can also fuse, creating networks.

Mitochondrial Fission

• After reaching a certain size, mitochondria can divide, increasing their number.
• This process involves the endoplasmic reticulum (ER) and cytosolic proteins called Drp1 (dynamin-related proteins), which are GTPases.

Mitochondrial Functions

• They perform oxidative degradation of nutrients to generate ATP (cellular respiration).
  • This includes carbohydrates, fats, and proteins.
• They perform interconversion between amino acids and ketoacids, including synthesis of non-essential amino acids.
• They act as a storage for Ca2+ ions.
• They synthesize istereoid hormones.
• They participate in autophagy and apoptosis.
• They synthesize heme groups.

Oxidative Degradation of Glucose (GIC)

• It occurs in 4 steps: glycolysis, oxidative decarboxylation of pyruvate, Krebs cycle (TCA), and oxidative phosphorylation.
• Glycolysis occurs in the cytosol, while the rest of the steps occur in the mitochondria.

Glycolysis

• It transforms one glucose molecule into two pyruvate molecules.
• Key enzymes in glycolysis include hexokinase, isomerase, phosphofructokinase, aldolase, isomerase, dehydrogenase, phosphoglycerate kinase, isomerase, enolase, and pyruvate kinase.
• Kinases transfer phosphate groups.
• Dehydrogenases perform redox reactions with coenzymes.

Glycolysis Balance

• Two pyruvate molecules can enter the mitochondria for further degradation or degrade in the cytosol via fermentation.
• Two ATP are generated, with a gross production of 4 ATP and a net gain of 2 ATP.
• Two NADH molecules are generated, which can be exchanged for ATP.