Chapter 8 - Metabolic Pathways Flashcards
What is the most common enzyme that makes use of glucose when it enters the cell?
hexokinase
What is a kinase?
an enzyme that involves the transfer of a terminal phosphate group of an ATP unit to some other compound
In glycolysis, what happens to glucose (Step 1)?
Step 1 (first investment step): glucose is converted to glucose-6-phosphate with the help of hexokinase which transfers a phosphate from ATP to the C6 position.

What is the significance of phophorylating glucose once it is inside the cell?
Adding a negative charge from the phosphate group traps glucose in the cell. It cannot pass through the cell membrane.
In glycolysis, what happens to glucose-6-phosphate?
Step 2: glucose-6-phosphate is isomerized into fructose-6-phosphate by the enzyme phosphoglucose isomerase.
*enediol intermediate

In glycolysis, what happens to fructose-6-phosphate?
Step 3 (second investment step): fructose-6-phosphate is converted to fructose-1,6-diphosphate by a transferase, phosphofructokinase, which transfers a phosphate from ATP to the C1 position.

In glycolysis, what happens to fructose-1,6-diphosphate?
Step 4: fructose-1,6-diphosphate is cleaved by a lyase, aldolase between C3 and C4 to form dihydroxyacetonephosphate (DHAP) and glyceraldehyde 3-phosphate (G3P).
*Reverse aldol condensation

In glycolysis, what happens to dihydroxyacetonephosphate (DHAP)?
Step 5: dihydroxyacetonephosphate (DHAP) is isomerized into glyceraldehyde-3-phosphate (G3P) by triose phosphate isomerase.

Describe Phase I of glycolysis (final products, what has been used)
Glucose is converted into two triose phosphates (G3P). There has been no oxidation/reduction. 2 ATP have been used.
In glycolysis, what happens to glyceraldehyde-3-phosphate (G3P)?
Step 6: glyceraldehyde-3-phosphate (G3P) is converted to 1,3-diphosphoglycerate (1,3-DPG) by glyceraldehyde-3-phosphate dehydrogenase, which uses NAD+ to oxidize the C1 position and adds a phosphate from Pi.

In glycolysis, what happens to 1,3-diphosphoglycerate?
Step 7: 1,3-diphosphoglycerate is converted to 3-phosphoglycerate by phosphoglycerate kinase, which transfers a phosphate to ADP to form ATP.

In glycolysis, what happens to 3-phosphoglycerate?
Step 8: 3-phosphoglycerate is converted to 2-phosphoglycerate by phosphoglyceromutase, which exchanges the current phosphate for a phosphate on the enzyme.

In glycolysis, what happens to 2-phosphoglycerate? What is a side reaction?
Step 9: 2-phosphoglycerate is converted to phosphoenolpyruvate (PEP) by enolase.
*2-phosphoglycerate can also be converted to 2,3-bisphosphoglycerate (2,3-BPG) by 2,3-BPG phosphatase.

In glycolysis, what happens to phosphoenolpyruvate (PEP)?
Step 10: phosphoenolpyruvate (PEP) is converted to pyruvate by pyruvate kinase, which transfers a phosphate group to ADP to form ATP.

In which ways can NAD+/FAD be regenerated after glycolysis?
Anaerobic conditions: pyruvate can be converted to lactate by lactace dehydrogenase, which uses NADH to reduce pyruvate, forming NAD+.
Yeasts (alcoholic fermentation): pyruvate can be converted to acetaldehyde by the lyase, pyruvate decarboxylase and then to ethanol by alcohol dehydrogenase, which uses NADH to reduce acetaldehyde, forming NAD+.
*Aerobic conditions: pyruvate is oxidized to carbon dioxide through the Krebs cycle, producing more NADH and FADH2. Those lost electrons are eventually shuttled to oxygen on the electron transport chain, regenerating NAD+ and FAD.
What is the most important regulatory step in glycolysis? What are 3 examples of inhibition at this step?
Regulation is important at step 3. Phosphofructokinase is inhibited by high levels of ATP, H+ (from formation of lactate), and citrate (Krebs cycle). These signifiy that glucose is being used well, and shouldn’t be wasted.
What hydrolytic enzymes break down disaccharides in the small intestine?
maltase, sucrase, and lactase (sometimes)
How can monosaccharides other than glucose be used for glycolysis?
They must be converted to an intermediate in the glycolytic pathway.
Where does glycolysis occur in the cell?
cytosol
Where does the Krebs/citric acid cycle occur in the cell?
mitochondrial matrix
What is the first major reaction pyruvate undergoes in its journey to the Krebs cycle?
Pyruvate is decarboxylated by a pyruvate dehydrogenase complex (3 enzymes) to form acetyl-coenzyme A and carbon dioxide. This step is accompanied by NAD+ which reduces to NADH.
How is acetyl coenzyme A introduced to the Krebs cycle?
It is undergoes an aldol condensation and hydrolysis with oxaloacetic acid to form citrate and releases coenzyme A. The lyase, citrate synthetase carries out this reaction.

What is the unique functional group in acetyl-coenzyme A and succinyl-coenzyme A?
They have a high energy thioester bond.

What is a lyase?
an enzyme that catalyzes the breaking of bonds by means other than hydrolysis and oxidation, often forming a new double bond or ring structure








