Module 04 - Glycolysis (Section 02) Flashcards
Where does Glycolysis occur?
in the cytoplasm of cells
What happens during Glycolysis?
conversion of one molecule of glucose into two molecules of pyruvate
Where is Glycolysis used? Why?
widespread - used in all cells where glucose is broken down to provide ATP and intermediates for other pathways
What does the Energy Investment Phase include?
- first 5 reactions
- 2 ATP used
What does the Energy Generation Phase include?
- final 5 reactions
- 2 NADH produced
- 4 ATP produced
What are the net products of Glycolysis?
- 2 pyruvate
- 2 ATP
- 2 NADH
When does the breakdown of glucose occur?
when the cell is in an energy poor state
What must the cell invest first to begin the breakdown of glucose?
- 2 ATP molecules
- regulate two enzymes in the process
What occurs during the first step of glycolysis?
- phosphate is transferred from ATP and added to glucose to form glucose 6-phosphate (G6P)
What is the phosphorylation of glucose reaction catalyzed by? Are they activated or inhibited?
- hexokinase in all cells except liver and pancreas
- glucokinase in liver and pancreas
- inhibited
Why is Hexokinase used for Glycolysis?
- has a low Km for glucose, allowing efficient phosphorylation and metabolism of glucose
- has low Vmax, preventing cells from consuming all their cellular phosphate to phosphorylate sugars
Why is Glucokinase used for Glycolysis?
- serves as glucose sensor for the liver and pancreas
- high Km, most active when glucose concentrations are high in the body
- high Vmax to allow the liver to quickly remove glucose from circulation after meal
What occurs during the third step of glycolysis?
- phosphate from ATP is transferred to fructose 6-P to form fructose 1,6-bisphosphate
What enzyme is used the catalyze the phosphorylation of fructose 6-P?
phosphofructokinase-1 (PFK-1)
What is PFK-1 activated by? (2)
- allosterically activated by AMP (indicates that cell is in energy poor state)
- activated by fructose 2,6-bisphosphate
What is PFK-1 inhibited by?
- its energy substrate ATP and citrate (indicates the cell is in energy rich state)
Summarize the energy investment phase of glycolysis.
- 1 molecules of glucose is oxidized to form 2 molecules of glyceraldehyde 3-phosphate
- step 1 and step 3 are the regulatory steps, each requiring the investment of1 molecule of ATP
Summarize the energy generation phase of glycolysis.
- begins with 2 molecules of glyceraldehyde 3-P, so all products are doubled from a single glucose molecule
- one regulatory step
- by the end, 2 NADH, 4 ATP, and 2 pyruvate are produced
What occurs during the sixth step of glycolysis?
- both molecules of glyceraldehyde 3-P are oxidized for form 1, 3-bisphosphoglycerate by glyceraldehyde 3-P dehydrogenase
- oxideizes the aldehyde and attaches a phosphate
- 1 NAD+ is reduced to NADH for each glyceraldehyde 3-P
What occurs during the seventh step of glycolysis?
- high energy phosphate is transferred from 1,3-bisphosphoglycerate to ADP forming 3-phosphoglycerate and ATP
What is the dephosphorylation of 1,3-bisphosphoglycerate catalyzed by?
phosphoglycerate kinase
How many ATP are produced during step 7 of glycolysis?
- 2 ATP
- at this point, the cell has paid off the ATP debt from the energy investment phase of glycolysis
What occurs during the tenth step of glycolysis?
- pyruvate kinase transfers a phosphate from phosphoenolpyruvate to ADP, forming 2 molecules of ATP and 2 molecules of pyruvate
- third irreversible regulatory step
What is pyruvate kinase activated by in step 10 of glycolysis? What does this do?
- the product of PFK-1, fructose 1,6-bisphosphate, in a feed-forward mechanism
- accelerates conversion of PEP to pyruvate and ATP, guaranteeing no buildup of glycolytic intermediates
What occurs during Aerobic Glycolysis?
- occurs when oxygen is readily available to the cell
- there is sufficient O2 present, therefore NADH produced by glycolysis is passed onto the ETC where it can be re-oxidized
- pyruvate is converted to acetyl-CoA for the TCA cycle
What occurs during Anaerobic Glycolysis?
- cells lack the O2 required by the ETC for it to function; must generate NAD+ through alternative pathway
- latase dehydrogenase reduces pyruvate to lactate and oxidized NADH to NAD+
How do hormone levels flactuate and regulate glycolysis in the well fed state?
- causes insulin levels in blood to rise
- insulin causes an increase in te levels of glucokinase, PFK, and PK by increasing their rates of synthesis
- increases the rate of glycolysis
How do hormone levels flactuate and regulate glycolysis in the fasting state?
- causes glucagon levels in blood to rise
- glucagon decreases the levels of glucokinase, PFK, and PK by decreasing their rates of synthesis
- decreases the rate of glycolysis
What are three types og pyruvate kinase defects?
- Changes in Km or Vmax for enzyme substrates or co-enzymes
- Alteration in enzyme gene expression or enzyme stability
- Abnormal response to the activator fructose 1,6-bisphosphate
