Glycolysis Flashcards
Enzyme for Glucose –> Glucose-6-P
Hexokinase
Enzyme for G6P –> Fructose-6-P
Phosphoglucose isomerase
Bis vs Di
Bis is Phosphate on two different carbons, while bi is on the same carbon
What is an inositol?
6 carbon ring with 6 OH groups
Enzyme for F6P –> Fructose-1,6-Bisphosphate
Phosphofructokinase
Enzyme for Fructose-1,6-bisphosphate –> Dihydroxyacetone P or Glyceraldehyde-3-P and interconversion for DHP to G-3-P
Aldolase and Triose-P isomerase
Enzyme for G-3-P –> 1,3-BPG
Glyceraldehyde-3-P dehydrogenase
Enzyme for 1,3-BPG –> 3-P-Glycerate
Phosphoglycerate kinase
Enzyme for 3-P-Glycerate –> 2-P-Glycerate
P-Glycerate mutase
Enzyme for 2-P-Glycerate –> Phosphoenolpyrvuate
Enolase
Enzyme for Phosphoenolpyruvate –> Pyruvate
Pyruvate Kinase
Which enzymes in glycolysis are capable of interconversion and which reactions do they catalyze?
Phsophoglucose isomerase
Triose-P-Isomerase
Phosphoglycerate mutase
Enolase
Which enzymes use ATP to catalyze their reaction?
Hexokinase
Phosphofructokinase
Which enzymes use ADP to catalyze their reaction?
Phosphoglycerate kinase
Pyruvate Kinase
Which enzymes convert NAD+Pi to NADH in their reaction
Glyceraldehyde-3-P dehydrogenase
What are the 3 rate-limiting steps and their enzymes in glycolysis
1) Glucose –> G-6-P, Hexokinase
2) F-6-P –> F-1,6-Bis, Phosphofructokinase
3) Phosphoenolpyruvate –> Pyruvate, Pyruvate Kinase
What is Iodoacetate and how does it function?
A non-specific inhibitor of G-3-P dehydrogenase, preventing oxidation of NAD
How is NADH reoxidized back to NAD for use in Glycolysis?
In aerobic conditions:
- NADH -> shuttles -> ETC -> O2
In anaerobic conditions:
- NADH+pyruvate -> NAD+lactate (via lactate dehydrogenase)
Fate of pyruvate
Anaerobic conditions:
- Pyruvate+NADH -> lactate+NAD
- via Lactate dehydrogenase
Aerobic conditions:
- Pyruvate -> Acetyl-CoA -> TCA or FAs
- via pyruvate dehydrogenase
Fate of pyruvate in yeast
Pyruvate -> acetaldehyde
acetaldehyde -> EtOH
- via EtOH dehydrogenase and oxidation of NADH to NAD
Why does Glucokinase have a high Km?
Acts as glucose sensor. In liver, ensures that it only functions when hepatocyte glucose is elevated (meal). Also regulates insulin release from pancreatic ß-cells
Which reactions in glycolysis consume ATP?
Glucose to G6P
F6P to F6BisP
Why is anaerobic glycolysis important?
Allows for the production of ATP in cells that lack mitochondria (RBC and parts of eye) or cells in hypoxia
2 ways Glucose is transported into the cell
1) Facilitate diffusion
2) Countertransport with Na+
What type of transporters are used in facilitated diffusion of glucose?
Tissue-specific GLUT1-14 uniporters
What type of transporters are used in counter transport of glucose and what creates the gradient?
- SGLT transporters found in the intestinal epithelium
- Na+ gradient out of the cell created by Na+/K+ ATPase
GLUT for liver
GLUT-2
GLUT for brain
GLUT-1
GLUT for muscle and adipose tissue
GLUT-4, requires insulin
How is PFK-1 activated?
non-covalent allosteric activation by AMP, ADP and F-2,6-BP (important in liver)
How is PFK-1 inhibited?
Elevated ATP and Citrate
- ATP is a substrate, but if it becomes too high, it starts binding to the allosteric site
What inhibits Hexokinase?
G6P
What inhibits Glucokinase?
F6P, activates Glucokinase Inhibitory Protein and causes sequestration of Glucokinase
What does Citrate indicate in relation to PFK-1?
Citrate indicates alternative source of fuel is available and high level of acetyl-CoA in mitochondria. Since it can’t get into the cytosol, it is turned into citrate, so a rise in citrate concentration signals that there is energy, so it inhibits glycolysis
If the PFK2/FBPase2 complex is phosphorylated, what does that mean?
Inhibition of Glycolysis
Glucagon activates PKA which phosphorylates the kinase (PFK2). This leads to activation of the phosphatase (F26BPase) which de-phosphorylates F26BP, turning it back into F6P, inhibiting the function of PFK-1 and stopping glycolysis.
If the PFK2/FBPase2 complex is de-phosphorylated, what does that mean?
Activation of Glycolysis
Insulin triggers de-phosphorylation of the kinase (PFK2), leading to the phosphorylation of F6P, creating F26BP, which activates PFK-1.
MODY2
inhibitory mutation of Glucokinase
- not enough uptake of glucose
PHHI
Activating mutation of Glucokinase
- too much Insulin
GLUT4 deficiency in muscle
Found in DM2 and non diabetic offspring, may contribute to development of diabetes
Aldolase B deficiency
Deficiency in Fructolysis pathway, leads to loss of cellular ATP as it is tied up in F1P
What is different about the Fructose pathway vs Glycolysis?
It bypasses the early checkpoints and skips straight to Aldolase step
Fructose -> F1P -> DHAP/Glyceraldehye -> Gald3P
How does fructose increase glucose usage?
F1P inhibits the binding of GKRP to Glucokinase
What effect does PFK2/F26BPase have on Glucokinase?
Binds Glucokinase and keeps it in the cytoplasm
What is Galactosemia?
Accumulation of Galactose due to a galactokinase deficiency which leads to galactitol accumulation, which can lead to cataracts
Galactose trapping
Deficiency in galactose 1-P uridyl transferase results in buildup of G1P and trapping of phosphate in this form
What does Adenylate Kinase do and what is its significance
Adenylate Kinase interconverts 2 ADP <-> AMP+ATP
- AMP is an extremely sensitive indicator of [ATP] change
How is PFK2/F26BPase regulated in muscle?
The concentration of F6P.
High [F6P] = PFK2 activity
Low [F6P] = F26BPase activity
Inhibition of Pyruvate Kinase
1) ATP
2) Alanine: Inhibits PK to prevent PEP from being converted back to Pyruvate, after being converted to OAA in gluconeogenesis
3) Phosphorylation via PKA: low glucose in liver = glucagon = activation of PKA = phosphorylation of PK = inhibition of glycolysis/activation of gluconeogenesis
Activation of Pyruvate Kinase
High concentrations of F16BP
Produced by PFK1, so feedforward regulation
How does Fructose feed into Glycolysis?
Fructose is converted into Fructose-1-P by Fructokinase
Fructose-1-P is converted into Glyceraldehyde and DHAP by Aldolase B
Glyceraldehyde is converted into G3P by Triose Kinase
DHAP is converted into G3P by triose phosphate isomerase
ATP->ADP by Fructokinase and Triose Kinase
What does an Aldolase B deficiency result in?
Lose of cellular ATP, as all the phosphate will be tied up in F1P
Glucokinase Inhibitory Protein (aka GKRP)
Found in the liver, binds glucokinase and keeps it in the nucleus
- inhibited by F1P, stimulating glucokinase activity
How does Fructose increase glucose usage
F1P binds Glucokinase inhibitory protein, and releases Glucokinase from the cytoplasm
Galactosemia
Accumulation of Galactitol because of Galactose pathway deficiency, which accumulates and causes cataracts
Treated by avoiding lactose and galactose
PKM2
Fetal form of Pyruvate Kinase, present in some cancer cells
Inhibition causes purposeful buildup of glycolytic intermediates, so they can eb diverted to synthesize more cell constituents
