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Questions and Answers
What process is employed for the transport of NADH across the mitochondrial membranes?
What is the primary role of NADH in the cellular respiration process described?
What is the general energy yield associated with the conversion process involving NADH in the malate-aspartate shuttle?
In the context of redox potential, what does a higher redox potential indicate?
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What role does NADH dehydrogenase play in the electron transport chain?
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What is the primary function of mitochondria?
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How many H+ ions are associated with one molecule of NADH?
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Which of the following is a component of the inner mitochondrial membrane?
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What is the role of porin in the outer mitochondrial membrane?
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What is the ATP yield from one cytosolic NADH?
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Which of the following represents the total ATP produced per glucose molecule?
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What structural feature increases the surface area of the inner mitochondrial membrane?
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What is the function of the H+ gradient in mitochondria aside from ATP synthesis?
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Which of the following is NOT found in the mitochondrial matrix?
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What structure allows for the flexibility and movement of the inner mitochondrial membrane?
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What occurs during ATP hydrolysis by F1 ATPase?
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Which of the following statements about the mitochondrial genome is accurate?
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Which metabolite can freely pass through the outer mitochondrial membrane due to its size?
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What efficiency percentage is associated with the energy conversion process in mitochondria?
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What assists in pulling the protein into the mitochondrial matrix during import?
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Where is the electron transport system located in mitochondria?
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Which of the following is true regarding ATP synthase?
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Which proteins are responsible for the import of multi-pass transmembrane proteins into mitochondria?
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How are inner membrane proteins encoded by the mitochondrial genome transferred?
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What is required for the transport of proteins to the outer membrane or intermembrane space of mitochondria?
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What is the source of lipid delivery from the endoplasmic reticulum (ER) to mitochondria?
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What role does dynamin-related protein-1 (Drp1) play in mitochondrial function?
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How are the majority of mitochondrial proteins synthesized?
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What function does the N-terminal presequence of mitochondrial proteins serve?
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Which structure is responsible for recognizing the signal sequence of mitochondrial proteins during import?
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Which of the following is NOT a destination for mitochondrial proteins after import?
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What is the role of cytosolic Hsp70 in mitochondrial protein import?
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Which tissue-specific function is associated with mitochondria?
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What characterizes mitochondria in relation to vesicular traffic?
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Study Notes
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.
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