Glycolysis Flashcards
1
Q
What are the four glucose transporters?
A
- GLUT1
- GLUT2
- GLUT3
- GLUT4
2
Q
GLUT2
A
- low-affinity transported in hepatocytes (liver cells) and pancreatic cells (specifically on the beta-islet cells)
- capture excess glucose for storage
- high Km
- can’t be saturated under normal physiological conditions
- not responsive to insulin but serves as glucose sensor to cause release of insulin in pancreatic beta-cells
3
Q
GLUT4
A
- present in adipose and muscle tissue
- Km is low and close to normal glucose levels in blood so the transporter is saturated when blood glucose levels are slightly elevated compared to normal
- transport rate increases when insulin level increases
4
Q
What is the role glucose plays in adipose tissue?
A
glucose is required to form DHAP which is converted to glycerol phosphate to store incoming fatty acids as triacylglycerols
5
Q
Glycolysis
A
- carried out by all cells in their cytoplasm
- the only energy-yielding pathway for red blood cells
- does not require presence of oxygen
- converts glucose molecule into 2 pyruvate molecules, releasing energy captured in two substrate-level phosphorylations and one oxidation reaction
- 2 NADH from glycolysis typically leads to 3 ATP, giving this process a total of 5 ATP produced
6
Q
What monosaccharides can enter glycolysis pathway?
A
- glucose
- galactose
- fructose
7
Q
List the enzymes used in glycolysis in order (10)
A
- Hexokinase (or if in liver/pancreas then Glucokinase)
- Phosphoglucose Isomerase
- Phosphofructose Kinase
- Fructose Bisphosphate Aldose
(5. Triose Phosphate Isomerase) - Glyceraldehyde 3-Phosphate Dehydrogenase
- Phosphoglycerate Kinase
- Phosphoglycerate Mutase
- Enolase
- Pyruvate Kinase
8
Q
Which enzymes are irreversible?
A
- How Glycolysis Pushes Forward the Process: Kinases*
- Hexokinase
- Glucokinase
- PFK-1
- Pyruvate Kinase
9
Q
Hexokinase
A
- phosphorylates glucose to form glucose 6-phosphate
- requires ATP input
- “traps” glucose in cell
- inhibitor: glucose 6-phosphate
- activator: AMP/ADP
- irreversible
- low Km [reaches max velocity at low concentrations of glucose]
10
Q
Glucokinase
A
- phosphorylates glucose to form glucose 6-phosphate
- requires ATP input
- “traps” glucose in cell
- only found in liver cells and pancreatic beta-islet cells
- irreversible
- high Km [low affinity for glucose so requires high concentrations of glucose to achieve Vmax]
- responsive to insulin in liver
- induced by insulin
11
Q
Phosphofructokinase-1 (PFK-1)
A
- allosteric enzyme that regulates the pace of glycolysis
- rate-limiting enzyme
- phosphorylates fructose 6-phosphate to fructose 1,6-bisphosphate
- requires ATP input
- irreversible
- inhibitors: ATP, citrate, glucagon
- activators: AMP, fructose 2,6-bisphosphate, insulin
12
Q
Phosphofructokinase-2 (PFK-2)
A
- produces the fructose 2,6-bisphosphate that activates PFK-1
- mostly found in liver
- allows cells to over-ride inhibition caused by ATP so glycolysis can continue
- inhibitors: glucagon
- activators: insulin `
13
Q
Glyceraldehyde-3-Phosphate Dehydrogenase
A
- dehydrogenates glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate
- during this reaction, NAD+ is reduced to NADH (oxidation) which is coupled to the phosphorylation of the substrate to form the 1,3-bisphosphoglycerate product
- reversible rxn
14
Q
3-Phosphoglycerate Kinase
A
- substrate level phosphorylation – transfers phosphate group from 1,3-bisphosphoglycerate to ADP, forming ATP and 3-phosphoglycerate
- step produces 2 ATP/ glucose
- reversible rxn that does not depend on oxygen so is only source of ATP in ANAEROBIC tissue
15
Q
Pyruvate Kinase
A
- final enzyme in AEROBIC glycolysis
- catalyzes substrate-level phosphorylation of ADP using substrate phosphoenolpyruvate (PEP)
- activated by fructose 1,6 bisphosphate from PFK-1 rxn (this is example of feed-forward activation because product of earlier reaction stimulates a later rxn)
- activators: fructose 1,6 bisphosphate, AMP/ADP
- inhibitors: ATP, acetyl-CoA, Alanine
