11- Glycolysis 2

• Which steps in the payoff phase are irreversible?

  Step 7 and Step 10
• Why do we double up after step 5?

  We are acting on the two molecules of GADP produced
• Describe Step 6


  Catalysed by Glyceraldehyde-3-phosphate dehydrogenase, GADP is phosphorylated to 1,3-bisphosphoglycerate by an inorganic phosphate, reducing NAD+ in the process
• Describe Step 7


  A phosphate group is transferred to ADP, releasing 3-phosphoglycerate and ATP, catalysed by phoshoglycerate kinase
• Describe Step 8


  The phosphate group is moved from C3 to C2 to form 2-phosphoglycerate, catalysed by phosphoglyceromutase
• Describe step 9


  Enolase catalyses the transformation of 2-phosphoglycerate to phosphoenolpyruvate. The presence of the double bond makes the molecule more unstable
• Describe step 10


  Pyruvate kinase transforms Phosphoenolpyruvate to pyruvate, and the phosphate group is transferred to ADP to form ATP
• What is the net gain of glycolysis?

  2 ATP
• What are the potential fates of Pyruvate?

  - Complete oxidation to CO2 in the Krebs cycle

  - Conversion to lactate in anaerobic conditions
• Describe anaerobic respiration


  In anaerobic conditions, the cell must produce all of its ATP via glycolysis, but in step 6, NAD+ is consumed, so NADH must be re-oxidised to NAD+
• What is the conversion of Pyruvate to lactate catalysed by?

  Lactate Dehydrogenase
• Give an example of how another substrate might enter the Krebs cycle via glycolysis

  - Glycerol may be converted to Glycerol-3-phosphate then Dihydroxyphosphate and enter glycolysis
• What is the gibbs free energy of the conversion of glucose to pyruvate?

  -147kJmol (exergonic)
• What is the gibbs free energy of the conversion of ADP to ATP

  +30kJmol (endergonic) (x2 ATP =60)
• What is the gibbs free energy for glycolysis as a whole ?

  -87kJmol, still an exergonic reaction despite being coupled to an energy requiring reaction
• Which steps of glycolysis are exergonic/favoured reactions?

  - Step 1 (Hydrolysis of ATP)

  - Step 3 (Hydrolysis of ATP)

  - Step 7 (Production of ATP)

  - Step 10 (Production of ATP)
• Why are many of the steps of glycolysis easily reversed?


  The free energy change of each individual reaction is not great
• What are the 3 regulated irreversible steps?

  - step 1, Hexokinase

  - step 3, phosphofructokinase

  - Step 10 , pyruvate kinase
• Which molecules allosterically inhibit PFK?

  ATP, NADH, Citrate, Long-chain fatty acids, H+
• Why do these inhibit PFK?

  ATP and NADH are indicative of a high energy state, citrate and fatty acids are indicators of alternate energy sources
• Which molecules allosterically activate PFK?

  AMP, Fructose, 2,6-bisphosphate
• How does ATP regulate phosphofructokinase?

  It binds at a spec ion regulatory site and lowers the activity
• Describe the regulation of Fructose 2,6-bisphosphate

  -Fructose 2,6 bisphosphate is formed as an offshoot step from fructose-6-phosphate

  - It increases the affinity of PFK for F6P and decreases the inhibitory effect of ATP

  - An abundance of F6P leads to more F26BP and this in turn stimulates PFK
• What is this known as?

  Feed forward stimulation
• What enzyme converts fructose-6-phosphate to fructose-2,6-bisphosphate?

  phosphofructokinase-2, PFK2
• Describe the regulation of PFK in the muscle

  - Primary control is ratio of ATP:AMP

  - AMP reverses inhibitory action of ATP

  - Periods of intense exercise lead to lactic acid, the inhibition of PFK by H+ protects the muscle from acid damage
• Describe the regulation of PFK in the liver

  - ATP regulation is important

  - low pH is not a regulator as the liver does not produce lactic acid

  - Inhibition by citrate enhances ATP effect

  - F-2,6-BP a key regulator, as F-6-P rises with blood glucose
• What is Hexokinase inhibited by?

  Glucose-6-Phosphate
• What are the functions of this inhibition?

  - Ensures that if the cell has sufficient G6P, phosphorylation of glucose will decrease

  - Glucose in blood becomes available for glucokinase, which is not inhibited by G6P