Lecture 32

Question 1

What are metabolic pathways?

Answer 1

Metabolic pathways are arrays of enzyme catalyzed reactions that result in the synthesis of compounds that are vital to the life of the organism

Question 2

What are two types of metabolic pathways?

Answer 2

Catabolic and Anabolic pathways

Question 3

What are 3 major characteristics of a catabolic pathway?

Answer 3

1) Breakdown of a complex substance into simple substances 2) Mostly oxidative reactions 3) Reactions result in a release of energy

Question 4

What are 3 major characteristics of an anabolic pathway?

Answer 4

1) Formation of a complex substance from simple substances 2) Mostly reductive reactions 3) Reactions require energy

Question 5

What are 4 processes of carbohydrate metabolism that occur in the liver?

Answer 5

1) Glycogenesis 2) Glycogenolysis 3) Glycolysis 4) Gluconeogenesis

Question 6

What mainly occurs in Glycogenesis?

Answer 6

Glucose is converted to glycogen for storage (generating glycogen from glucose)

Question 7

What mainly occurs in Glycogenolysis?

Answer 7

Glycogen is broken down (oxidized) to glucose for use (lysing glycogen to form glucose)

Question 8

What mainly occurs in Glycolysis?

Answer 8

Glucose is converted to pyruvate (lysis of glucose)

Question 9

What mainly happens in Gluconeogenesis?

Answer 9

Formation of glucose from non-glucose precursor molecules (generating glucose)

Question 10

What is the most important process to obtain energy for any other life processes?

Answer 10

Glycolysis

Question 11

What can glycolysis be used for?

Answer 11

1) Muscle contraction 2) Nerve stimulation 3) Ion channel transport 4) Any other process that requires ATP

Question 12

What can pyruvate be broken down into and when does this occur?

Answer 12

During states of hunger or starvation, Pyruvate (by product of glycolysis) can be broken down into alanine + serine (amino acids that can be used by the body)

Question 13

How many steps occur in the glycolysis pathway?

Answer 13

9

Question 14

What is the first step of glycolysis?

Answer 14

1) Glucose –> Glucose-6-phosphate 2) 1 ATP required for phosphorylation 3) 1st of 3 irreversible reactions 4) Hexokinase is the enzyme that catalyzes this reaction (allosteric modulation) 5) Glucokinase (allosteric modulation) can also catalyze this reaction, but only in the liver when you overeat (Glucokinase has a higher Km through the process of gluconeogenesis and can handle more substrate to catalyze at once)

Question 15

What is the second step of glycolysis?

Answer 15

1) Glucose-6-phosphate –> Fructose-6-phosphate 2) No ATP required 3) Phosphoglucose isomerase is the enzyme that catalyzes this reaction

Question 16

What is the third step of glycolysis?

Answer 16

1) Fructose-6-phosphate –> Fructose-1,6-bisphosphate 2) 1 ATP required for phosphorylation 3) 2nd of 3 irreversible reactions 4) Phosphofructo kinase is the enzyme that catalyzes this reaction (allosteric modulation)

Question 17

What are substances that allosterically regulate the conversion of Fructose-6-phosphate –> Fructose-1,6-bisphosphate?

Answer 17

This reaction is allosterically regulated by: a) ATP inhibition (negative feedback) b) Citrate inhibition (negative feedback) c) AMP activation (positive feedback) d) Fructose-2,6-bisphosphate activation (positive feedback)

Question 18

What is the fourth step of glycolysis?

Answer 18

1) Fructose-1,6-bisphosphate –> Dihydroxyacetone phosphate (DHAP) + Glyceraldehyde-3-phosphate 2) No ATP required 3) Fructose bisphosphate aldose is the enzyme that catalyzes this reaction 4) A triose phosphate isomerase is used to catalyze the conversion between Dihydroxyacetone phosphate (DHAP) and Glyceraldehyde-3-phosphate a) Glyceraldehyde-3-phosphate is used for the continuation of glycolysis, while DHAP can be used to form triglycerides

Question 19

What is the fifth step of glycolysis?

Answer 19

1) Glyceraldehyde-3-phosphate –> 1,3-Bisphosphoglycerate 2) No ATP required 3) Glyceraldehyde-3-phosphate dehydrogenase is the enzyme that catalyzes this reaction 4) Glyceraldehyde-3-phosphate is phosphorylated by the reduction of NAD –> NADH; this causes the oxidation of glyceraldehyde-3-phosphate to form 1,3-Bisphophoglycerate (NAD+ + Pi –> NADH + H+)

Question 20

What is the sixth step of glycolysis?

Answer 20

1) 1,3-Bisphosphoglycerate –> 3-Phosphoglycerate 2) No ATP required 3) Phosphoglycerate kinase is the enzyme that catalyzes this reaction 4) ADP is phosphorylated to produce ATP (first release of free energy)

Question 21

What is the seventh step of glycolysis?

Answer 21

1) 3-Phosphoglycerate –> 2-Phosphoglycerate 2) No ATP required 3) Phophoglycerate mutase is the enzyme that catalyzes this reaction

Question 22

What is the eighth step of glycolysis?

Answer 22

1) 2-Phosphoglycerate –> Phosphoenol pyruvate (PEP) 2) No ATP required 3) Enolase is the enzyme that catalyzes this reaction 4) H2O is released from this reaction

Question 23

What is the ninth and final step of glycolysis?

Answer 23

1) Phosphoenol pyruvate (PEP) –> Pyruvate 2) No ATP required 3) Pyruvate kinase is the enzyme that catalyzes this reaction 4) ADP is phosphorylated to produce ATP (second release of free energy) 5) 3rd of 3 irreversible reactions

Question 24

What step in glycolysis is temporarily inhibited by anaerobic conditions and why?

Answer 24

1) The fifth step of glycolysis in the conversion of Glyceraldehyde-3-phosphate to 1,3-Bisphosphoglycerate requires phosphorylation from the reduction of NAD+ + Pi–> NADH + H+ 2) In the absence of oxygen, the electron transport chain can no longer oxidize NADH to reform NAD+

Question 25

What is alternative pathway under anaerobic conditions that allows glycolysis to continue the production of pyruvate?

Answer 25

Under anaerobic conditions, pyruvate can be converted to lactic acid by oxidizing NADH to NAD+ (dehydrogenase does this). In doing so, NAD+ is now available for use in step 5 of glycolysis