Unit 3: Glycolysis

how glucose is used in the body

• storage as starch, glycogen

• oxidation via glycolysis to pyruvate

• oxidation via pentose phosphate pathway to ribose-5-phosphate for nucleic acids

• synthesis of structural polysaccharides (cell walls)

energy investment phase requires

2 ATP

net products of glycolysis

• 2 pyruvate

• 2 H2O

• 2 ATP

• 2 NADH

in glycolysis, the oxidation of the carbons in glucose is coupled with

ATP hydrolysis (exergonic)

net rxn for glycolysis

glucose + 2NAD+ + 2ADP + 2 Pi —> 2 pyruvate + 2 NADH + 2 ATP + 2 H+ + 2 H2O

preparatory phase of glycolysis

glucose is made into a symmetrical molecule which is then cleaves to eventually become 2 pyruvate later

payoff phase of glycolysis

2 G3P become 2 pyruvate and 2 ATP are net gained

STEP 1 glycolysis

hexokinase phosphorylates the C6 of glucose, turning it into glucose-6-phosphate using ATP

• exergonic/favorable rxn

• glucose-6-phosphate is an allosteric inhibitor of hexokinase

glucokinase

an unusual hexokinase

glucokinase 4 is aka hexokinase 4

• is only active in glucose rich environments to convert glucose to glucose-6-phosphate

glucose-6-phosphate is produced from

blood glucose

glucose-6-phosphate is an allosteric inhibitor of

hexokinase

why is step 1 of glycolysis so important?

since it allows glucose to stay inside of the cell, since glucose-6-phosphate cannot easily leave the cell

• if it was not phsophorylated and was just normal glucose, it would want to leave the cell due to its EC gradient via GLUT-4

hexokinase is normally

active

• maintains the conc of glucose inside the cell

glucokinase 4

aka hexokinase 4

• only active in glucose rich environments to convert glucose to glucose-6-phosphate

• is the predominant hexokinase in the liver and keeps blood glu low by storing it as glycogen

• this is the only hexokinase NOT allosterically regulated via negative feedback by glucose-6-phosphate

  • so it allows more glu to be brought it and stored as glycogen

hexokinases are generally ______ by glucose-6-P

allosterically inhibited

diff fates of glucose-6-P

• can become glycogen or glucoronate (for carb synthesis)

Km of hexokinase vs hexokinase 4

• glucokinase 4 has a Km for glucose of 10 mM

• hexokinase has Km for glucose of 0.1 mM

• so glucokinase works better in glucose rich environments to bind and convert glucose