Untitled Quiz

Mitochondria Basics

• Most ATP production occurs in mitochondria.
• Mitochondria have two membranes (inner and outer) and two compartments (matrix and intermembrane space).
• The inner mitochondrial membrane contains the electron transport system, ATP synthase (F1F0-ATPase), and transporters for metabolites.
• The inner membrane is highly folded into cristae, increasing the surface area for energy production.
• The matrix contains enzymes for the citric acid cycle, beta-oxidation, and mitochondrial DNA, ribosomes, and replication enzymes.
• The outer membrane contains porins, allowing free passage of molecules smaller than 1000 daltons.

Redox Potential and Electron Transport

• Redox potential describes the energetic favorability of electron reduction, indicating the strength of a molecule as an electron donor.
• Electron transport in mitochondria involves a series of redox reactions, with electrons moving from NADH and FADH2 to oxygen.
• The electron transport chain pumps protons across the inner mitochondrial membrane, creating a proton gradient.

ATP Synthesis

• The proton gradient drives ATP synthesis by ATP synthase (F1F0-ATPase).
• ATP synthase uses the energy from the proton gradient to phosphorylate ADP to ATP.
• The electron transport chain pumps 12 H+ per NADH and 8 H+ per FADH2, contributing to the proton gradient.

ATP Yield per Glucose

• One matrix NADH yields 12 H+ and 3 ATP.
• One cytosolic NADH (60% efficient) yields ~7.2 H+ and 1.8 ATP.
• One FADH2 yields 8 H+ and 2 ATP.
• The complete oxidation of glucose generates approximately 35.5 ATP molecules, representing 38.3% efficiency in converting energy from glucose to ATP.

ATP Synthase Reversibility

• ATP synthase can also hydrolyze ATP to generate a proton gradient, reversing the ATP synthesis process.
• This property highlights ATP synthase's role as a reversible enzyme, allowing for a bidirectional energy flow.

Mitochondrial Genome

• Mitochondria possess their own DNA, a circular molecule of 16.6 kilobase pairs.
• The mitochondrial genome encodes some mitochondrial proteins, such as 7 out of 42 subunits of complex I.
• Most mitochondrial proteins are encoded in the nuclear genome, with human mitochondria containing 37 genes, including 13 protein-coding genes.

Mitochondria Division

• The division of mitochondria is controlled by dynamin-related protein-1 (Drp1), which pinches off the membrane by hydrolyzing GTP.

Control of Mitochondria

• Mitochondria function semi-independently within the cytoplasm.
• Their number, localization, and function are regulated by cellular demand.
• They exhibit tissue-specific functions, such as steroid synthesis in adrenal cells and heme biosynthesis in bone marrow.

Protein Import

• Most mitochondrial proteins are translated by cytosolic ribosomes and imported after translation.
• A 20 to 55 amino acid sequence (presequence) at the N-terminal end of the protein acts as a signal for import into different compartments.
• The presequence is recognized by outer membrane translocator (TOM) and inner membrane translocator (TIM) complexes.
• ATP hydrolysis by Hsp70 helps to unfold and import proteins.
• Different pathways are engaged for inner membrane proteins, outer membrane proteins, and intermembrane space proteins.

Lipid Delivery

• Mitochondria depend on the endoplasmic reticulum (ER) for membrane lipid delivery, as they lack the capacity to synthesize their own lipids.
• Specialized proteins facilitate the transfer of lipids from ER to mitochondria.