Glycolysis Flashcards
Anabolic metabolic pathway
small molecules are assembled into large ones with the use of energy
Catabolic metabolic pathway
large molecules are broken down into small ones and energy is released
Glycolysis overview
series of reactions for the breakdown of glucose into 2 pyruvate under aerobic conditions or lactate under anaerobic conditions along with the production of a small amount of energy
2 main phases of glycolysis
preparatory phase (glucose-requiring phase) 1-5
payoff phase (energy-releasing phase) 6-10
glucose-requiring phase main events
2 ATP invested
hexose chain cleaved
produced 2TP
glucose is phosphorylated
energy-releasing phase main events
conversion of glyceraldehyde-3-phosphate to pyruvate
production of 1NADH and 2ATP
where does glycolysis occur
cytosol
Step 1 glycolysis: uptake and phosphorylation of glucose
phosphorylation of glucose to glucose-6-phosphate
irreversible reaction
catalysed by hexokinase that has a high affinity for glucose and is regulated by levels of glucose-6-phosphate
MG2+ is a cofactor
what enzyme catalyses the phosphorylation of glucose when glucose levels are high
glucokinase
present in liver and pancreatic cells
importance of phosphorylating glucose
produces a more reactive molecule
traps glucose inside the cell
step 2 glycolysis
glucose-6-phosphate is isomerised to fructose-6-phosphate, catalysed by phosphohexose isomerase
Mg2+ present
aldose-ketose isomerisation reaction
The glucopyranose ring of glucose-6-phosphate opens to form a linear structure. The enzyme then rearranges this structure into the furanose ring of fructose-6-phosphate. This ring-opening and closing facilitates the isomerization.
reversible, near equilibrium
step 3 glycolysis
fructose-6-phosphate phosphorylated to fructose 1,6-bisphosphate
catalysed by phosphofructokinase-1
irreversible, prevents reformation of glucose-6-phosphate
Mg2+
1ATP used
step 4 glycolysis
fructose-1,6-bisphosphate cleaved into two 3C compounds: glyceraldehyde-3-phosphate (GAP) and dihydroxyacetone phosphate (DHAP)
catalysed by aldolase
reversible
the 3C compounds are isomers but only GAP continues along the glycolytic pathway
step 5 glycolysis
DHAP converted to GAP
catalysed by triose-phosphate isomerase
reversible
step 6 glycolysis
GAP oxidised and phosphorylated to 1,3-bisphosphoglycerate, high energy electrons picked up by NAD+
catalysed by glyceraldehyde 3-phosphate dehydrogenase
NAD+ reduced to NADH and enters mitochondria (aerobic) (anaerobic, NADH is utilised by lactate dehydrogenase)
reversible
free phosphate (not from ATP?)
