Chapter 9.5.1 (Exam 2) Metabolic Pathways Flashcards
Metabolic Pathways Are Interrelated and Regulated
How are polysaccharides catabolized to be used in metabolic pathways?
Polysaccharides are hydrolyzed to glucose → enters glycolysis
How are polypeptides catabolized to be used in metabolic pathways?
Proteins are hydrolyzed to amino acids, → glycolysis or citric acid cycle
How are lipids catabolized to be used in metabolic pathways?
Lipids are broken down to:
glycerol → DHAP → glycolysis
fatty acids → acetyl CoA → citric acid cycle
How is the catabolism of lipids, polypeptides, and polysaccharides reversed?
Anabolic interconversions
Which anabolic interconversion forms glucose?
Gluconeogenesis: citric acid cycle and glycolysis intermediates are reduced to form glucose
Which anabolic interconversion forms lipids?
Acetyl CoA can be used to form fatty acids
Which anabolic interconversions form nucleic acid components?
Citric acid cycle intermediates can be used to synthesize nucleic acid components:
α-ketoglutarate → purines
Oxaloacetate → pyrimidines
How do cells “decide” which pathways to use?
Levels of substances in the metabolic pool are quite constant
Organisms regulate enzymes to maintain balance between catabolism and anabolism
What is the main control point in glycolysis?
The main control point in glycolysis is the enzyme phosphofructokinase (PFK) (step 3), which is inhibited by ATP
How does the PFK enzyme control glycolysis?
In fermentation, PFK operates at a high rate to produce ATP
If O2 is present, more ATP is produced, which inhibits the enzyme and slows glycolysis
What is the main control point of the citric acid cycle?
The main control point in the citric acid cycle is isocitrate dehydrogenase (step 3)
How does isocitrate dehydrogenase control the citric acid cycle?
By detecting NADH and ATP; if too much of either accumulates, the citric acid cycle shuts down
