Biology: Oxidative Phosphorylation and Electron Transport Chain

Oxidative Phosphorylation and Electron Transport Chain

• Oxidative phosphorylation uses energy from moving electrons to create a proton gradient, which drives ATP production.
• The process involves three main steps: electron transport chain, electron movement, and energy transfer.

Electron Transport Chain

• Electrons transfer energy to pumps, creating a proton gradient used to produce ATP.
• Complexes involved in electron transport are located in the inner mitochondrial membrane.
• These complexes take electrons from molecules that come from food.

Creating a Gradient

• Pumping protons out creates a high concentration of protons outside the inner membrane compared to inside.
• This creates a proton gradient.

ATP Production

• A proton gradient powers ATP synthase, allowing protons to flow back into the mitochondria.
• This process produces ATP.

Water Formation

• At the end of the electron transport chain, electrons combine with oxygen and protons to form water.

Process

• The process uses energy from oxidizing NADH and FADH2 to pump protons into a space, creating a gradient.
• This gradient powers the production of ATP as protons flow into the mitochondria.

ATP Production from Glucose

• Cells produce ATP from glucose in three main stages: glycolysis, citric acid cycle, and oxidative phosphorylation.

Glycolysis

• One glucose molecule is broken down into two pyruvate molecules, producing a net gain of 2 ATP.

Citric Acid Cycle

• Each pyruvate is broken down in a cycle that must turn twice for each glucose molecule.
• Two cycles produce 2 ATP directly and create NADH + FADH2.

Oxidative Phosphorylation

• NADH + FADH2 are used in electron transport chains, producing up to 34 ATP.

Dehydrogenation

• Dehydrogenation changes the -OH group on the beta carbon into a C=O double bond, making it more reactive.

Acetyl-transfer

• Acetyl-transfer breaks fatty acid chains into smaller pieces, creating acetyl-CoA, and produces energy in the citric acid cycle.

Fatty Acid Synthesis

• Fatty acid synthesis occurs in the cytosol, involving the conversion of acetyl-CoA into a 3-carbon molecule called malonyl-CoA.
• More acetyl groups are added to build a longer fatty acid chain.

Fatty Acid Breakdown

• Fatty acids are attached to CoA, forming acetyl-CoA, and are broken down into smaller pieces, each with 2 carbon atoms, to produce energy.

Difference Between Acetyl-CoA and Acyl-CoA

• Acyl-CoA has a longer carbon chain and is involved in the metabolism of fatty acids.
• Acetyl-CoA contains two carbon acetyls and is central in energy production, entering the citric acid cycle to generate energy.

4 Steps in Total

• Dehydrogenation removes hydrogen atoms from a specific place in a molecule, transferring them to FAD+ and forming a double bond between neighboring carbon atoms.
• Hydration adds water to the double bond, changing it to a single bond and attaching a hydroxyl group to the beta carbon.

Breakdown of Amino Acids

• Amino acids are recycled, and their carbon skeletons can be used as intermediates in the TCA cycle.
• Amino groups are converted into carbamoyl phosphate for the urea cycle, while the remaining carbon part becomes an alpha-keto acid.

Amino Acid Degradation and Nitrogen Excretion

• Amino group from an amino acid is converted into carbamoyl phosphate for the urea cycle.
• The remaining carbon part becomes an alpha-keto acid, which can be used for energy or glucose production.

Urea Cycle

• Amino group is added to alpha-ketoglutarate to make glutamate, and then removed from glutamate to regenerate alpha-ketoglutarate.
• Urea cycle starts by using amino groups and energy to make carbamoyl-phosphate.

Urea Cycle Steps

• Ornithine reacts with carbamoyl phosphate to make citrulline.
• Citrulline exits mitochondria and combines with aspartate to form arginosuccinate.
• Arginosuccinate undergoes a reaction to produce arginine and release fumarate.
• Arginine breaks down to regenerate ornithine, completing the urea cycle.

Key Points

• One amino group in the cycle comes from amino acids that have been transported into mitochondria.
• Other amino groups come from aspartate, derived from oxaloacetate in the TCA cycle.

Krebs Cycle

• Glucogenic amino acids provide carbon skeletons that go into the TCA cycle to make energy or glucose.
• Ketogenic amino acids are used in processes that lead to the production of ketone bodies or fats for energy.