Lipid Metabolism

Describe the reaction catalyzed by Acetyl CoA carboxylase and explain how phosphorylation affects the activity of the Acetyl CoA carboxylase.

In the first step, a carboxybiotin intermediate is formed at the expense of the hydrolysis of a molecule of ATP. The activated CO2 group is then transferred to acetyl CoA. Phosphorylation enhances the activity of the Acetyl CoA carboxylase. In a reaction catalyzed by Acetyl CoA carboxylase, ATP is hydrolyzed. Phosphorylation increases the amount of ATP present in the cell and with an increased ATP concentration, there will be increased hydrolysis.

Explain how acetyl-CoA carboxylase is regulated.

Insulin stimulates fatty acid synthesis by activating the carboxylase 1, whereas glucagon and epinephrine have the reverse effect Acetyl CoA carboxylase 1 responds to changes in its immediate environment, and is switched off by phosphorylation and activated by dephosphorylation.

Predict how increased NADH impacts flux through glycolysis, gluconeogenesis, the citric acid cycle, fatty acid oxidation, and fatty acid synthesis.

glycolysis -> Lower gluconeogenesis -> Higher citric acid cycle - >Lower fatty acid oxidation ->Lower fatty acid synthesis ->Higher

List the products of fatty acid oxidation.

Acetyl CoA NADH FADH2 H+

Explain how the acetyl CoA molecules, the raw material for Fatty acids synthesis, is transferred to the cytoplasm from mitochondria.

Acetyl CoA is transferred out of the mitochondria and into the cytoplasm in the form of citrate. In the mitochondrial matrix, Acetyl CoA is condensed with oxaloacetate.

Calculate the amount of ATP generated from a fatty acid of a particular length (e.g., C20) and compare this to the amount of ATP generated from glucose.

C20 + 9FAD + 9NAD+ + 9H2O + 9CoA ->10 acetyl CoA + 9FADH+ + 9NADH + 9H+

Explain how the products of ethanol metabolism can lead to liver disease and damage.

Fatty acid synthesis. Ethanol metabolism meets the bodies need for NADH and also signals that conditions are right for fatty acid synthesis. Consequently, triacylglycerol accumulates in the liver, leading to fatty liver disease.

Explain the three steps of fatty acid degradation and their subcellular localization.

First, the lipids must be mobilized. In this process of lipolysis, triacylglycerols are degraded to fatty acids and glycerol, which are released from the adipose tissue and transported to the energy- requiring tissues (Figure 27.1). Second, at these tissues, the fatty acids must be activated and transported into mitochondria for degradation. Third, the fatty acids are broken down in a step- by-step fashion into acetyl CoA, which is then processed in the citric acid cycle.

Describe the processes and locations of both the production and the catabolism of ketone bodies.

Ketogenesis occurs in the liver. Ketone bodies can be converted into Acetyl CoA, which then goes into the Citric Acid Cycle.

Explain how Type 2 diabetes can shift fuel usage from carbohydrates to fats and how this impacts the production of ketone bodies.

People with Type 2 diabetes are not producing insulin so excess glucose is not being converted into glycogen for later use. So when the blood sugar levels become low and there's no glycogen to be converted into glucose, the body releases fat cells. The fat cells are then broken down in the liver and turned into ketones, which are used as fuel, in replace of glucose.

Explain the three steps of fatty acid synthesis and their subcellular localization.

Step 1: Acetyl CoA is transferred from mitochondria to the cytoplasm. Acetyl CoA is transported in the form of citrate, which is cleaved to yield acetyl CoA and oxaloacetate. Step 2: Fatty acid synthesis begins in the cytoplasm with the activation of acetyl CoA, in a two-step reaction, to malonyl CoA. Step 3: The reaction intermediates are attached to an acyl carrier protein, which serves as the molecular foundation for the fatty acid being constructed. Fatty acid is synthesized, two carbon atoms at a time, in a five-step elongation cycle.