Glycolysis Flashcards
Glycolysis
- break down glucose and provide energy by ATP
- ANAEROBIC PATHWAY
- end product is pyruvate
- happens in the cytosol
The fate of pyruvavte in humans depends on
- whether or not an adequate supply of oxygen is available
- whether mitochondria are present
Aerobic glycolysis
- in cells with oxygen and mitochondria
- pyruvate is final end product
- NADH from glycolysis is oxidized to NAD+ and oxygen is the final electron acceptor
- NAD+ IS REQUIRED FOR GLYCOLYSIS TO PROCEED
- pyruvate will continue to TCA cycle
Anaerobic glycolysis
- lack mitochondria or oxygen
- pyruvate is the final electron acceptor
- pyruvate is converted lactate
- allows for the regeneration of NAD+
- no TCA cycle
- pyruvate to lactic acid is the final step
Transport of glucose into cell
-glucose cant diffuse into the cell because it is hydrophyllic and cant get through the lipid bi layer of the membrane
Glucose transporter (GLUT)
- GLUT proteins span the membrane
- ATP independent (passive transport)
- glucose binds and changes shape so it can pass through the membrane
- moves from more concentrated to less concentrated
GLUT 1
in most tissues, abundant in brain and RBC
-basal uptake of glucose
GLUT 2
liver, pancreatic beta cells
-glucose uptake and release by the liver
GLUT 3
in most tissues, abundant in brain and RBC
-basal uptake of glucose
GLUT 4
Skeletal muscle and adipose tissue
- insulin stimulated glucose uptake stimulated by exercise
- ON THE PLASMA MEMBRANE ALL THE TIME
GLUT 5
- tissue specific
- specific regulation
- specificity for substrate
SGLT system
- transport glucose against its concentration gradient by co-transporting Na+ down its gradient.
- active transport
- epithelial cells of intestines, renal tubes,choroid plexus
What are the two stages of glycolysis
- energy investment phase(1)
- energy generation phase (2)
Name the two coupled reactions with the hydrolysis of ATP
Step 1- phosphorylation of glucose to glucose 6-phosphate
Step 3- phosphorylation of fructose 6-phosphate
Name the two coupled reactions by substrate level phosphorylation
Step 7- Synthesis of 3-phosphoglycerate producing ATP
Step 10- Formation of pyruvate and production of ATP
What are the three irreversible reactions
- Step 3-phosphorylation of fructose 6-phosphate (inhibited by citrate and ATP)(activated by high AMP levels)
- Step 1- phosphorylation of glucose to glucose 6-phosphate (Hexokinase regulated by negative feedback of glucose 6-phosphate)
- Step 10-formation of pyruvate and production of ATP(regulated by glucagon-inactivates kinase and insulin-activates kinase)
What is the rate limiting step?
Step 3: Phosphorylation of fructose 6-phosphate
- PFK-1 regulation
- too high ATP and citrate inhibit reaction
- low AMP activate reaction
- positive regulation from PFK-2
SGLT System
- Active transport of glucose against it’s gradient
- requires energy supplied by Na or K ATPase that pumps Na outside the cell to create the gradient
- in intestines, renal tubules, choroid plexus
NET OUTCOME OF GLYCOLYSIS
Glucose—->2 pyruvate
2ADP———>2 ATP
2 NAD+———->2 NADH
anaerobic- NADH cannot be converted to ATP
Aerobic-NADH CAN be converted to ATP(net yield 8 ATP)
What are the two steps for NADH stuff
Step 6: oxidation of glyceraldehyde 3-phosphate
NAD+—–>NADH
Step 10b- Pyruvate to lactate (only for anaerobic)
NADH——>NAD+
After step 10
aerobic-ETC, pyruvate converted to acetyl coA and create even more energy
Anaerobic- reduce to lactate(reversible) to generate NAD+
RBC
- need glycolysis because they have no mitochondria and rely on it for energy (ATP)
- without it, hemolytic anemia and cell death
Consequences of lactate build up
- normal in exercising muscle and RBC
- too much lowers pH and causes cramping
- can lower intracellular pH to denature enzymes and cause cell death (MI, pulmonary embolism, hemorrhage)
- lactic acidosis(lower pH of blood)
Alternative fates of pyruvate
- pyruvate—->acetyl coA: TCA cycle, irreversible, important for cardiac muscle
- pyruvate—>oxaloacetate: can replinish TCA cycle intermediates, can be used for gluconeogenesis
- pyruvate—->ethanol: not in humans
- Pyruvate—-> lactate
