Glycolysis Flashcards
Glycolysis Overview
-common in prokaryotic and eukaryotic
Glycolysis-oxidation of glucose to 2 pyruvate
Common in prokaryotic and eukaryotic cells and occurs in:
1)Cytosol
anaerobic/aerobic conditions
-Anaerobic- fermentation produces lactate and Ethanol
-Aerobic- occurs in mitochondria
2) ALL TISSUES
1st step of glycolysis
- Enzyme used
- reaction type form Enzyme
- Cofactor
- Free Energy
- reversible or irreversible
Glucose-> Glucose 6-Phosphate REGULATED Enzyme-Hexokinase -transfer of phosphate, which traps glucose in cell because no transporters exist that can transport phosphorylated glucose (or other carbohydrates phosphorylated) -activates/ destabilizes glucose
Cofactor:
-ATP complexed with Divalent cation (Mg2+ or Mn2+)
Free Energy
Exergonic (-G)
Irreversible
Hexokinases
Binding of glucose causes conformation change in hexokinase- Cleft closes
- active site around glucose becomes more non polar which favors donation of gamma phosphate from ATP
- excludes water from Active site which prevents hydrolysis of gamma phosphate of ATP by water
EX: Induced Fit
Substrate induced cleft is a general feature of kinases
Step 2 of Glycolysis
- Enzyme used
- reaction type form Enzyme
- Helper molecules
- Free Energy
- reversible or irreversible
Glucose 6-Phosphate -> Fructose 6-Phosphate
Enzyme- Phosphoglucose or Phosphohexose Isomerase
-isomerization- conversion of aldose C-1 to ketose C-2
-NO helper molecules
-Exergonic
-Reversible
NO REgulation
Step 3 of Glycolysis
- Enzyme used
- reaction type form Enzyme
- Helper molecules
- Free Energy
- reversible or irreversible
Fructose 6-Phosphate -> Fructose 1,6-Bisphosphate
Enzyme: Phosphofructose Kinase-1 (PFK-1)
-MOST IMPORTANT CONTROL POINT OF METABOLISM
-Phosphoryl transfer from gamma phosphate of ATP to C-1
-NO helper molecules
-Exergonic
-irreversible
REGULATED
PFK-2
Phosphofructose Kinase-2
Synthesis of Fructose 2,6 Bisphosphate
-activates glycolysis
-inactivates gluconeogensis
Hormonal Control:
1) well fed-after carb rich meal stimulated by high insulin/low glucagon
2) Starvation- inhibited by low insulin/high glucagon so glycolysis is inhibited; gluconeogenesis stimulated
Adenylate Kinase
Salvages ATP from 2 ADP molecules
-primary reason why AMP represents the low energy charge
Step 4 of Glycolysis
- Enzyme used
- reaction type form Enzyme
- Helper molecules
- Free Energy
- reversible or irreversible
Fructose 1,6-Bisphosphate -> Glyceraldehyde 3-Phosphate + Dihydroxyacetone phosphate Enzyme-Aldolase A -aldol cleavage -No helper molecules -Exergonic -reversible
Triose Phosphate Isomerase
- reaction type form Enzyme
- Helper molecules
- Free Energy
- reversible or irreversible
Dihydroxyacetone -> Glyceraldehyde 3-phosphate
- isomerization
- NO HELPER MOLECULES
- Endergonic
- Reversible
@ equilibrium 96% of products will be dihydroxyacetone phosphate and 4% will be glyceraldehyde 3-phosphate
Step 5 of Glycolysis
- Enzyme used
- reaction type form Enzyme
- Helper molecules
- Free Energy
- reversible or irreversible
Glyceraldehyde 3-phosphate-> 1,3-bisphosphoglycerate
Enzyme-Phosphoglyceraldehye Dehydrogenase (Glyceralde 3-Phophate Dehydrogenase)
-phosphorylation couples to oxidation of aldehyde to carboxylic acid
-Coenyze-NAD+
-Exergonic
-Reversible
Step 6 of Glycolysis
- Enzyme used
- reaction type form Enzyme
- Helper molecules
- Free Energy
- reversible or irreversible
1,3-Bisphosphoglycerate -> 3-phosphoglycerate
3-Bisphosphoglycerate Kinase
-phosphoryl transfer from 1,3-BPG to ADP to produce ATP
**SUBSTRATE LEVEL PHOSPHORYLATION
-NO helper molecules
-Endergonic
-Reversible-UNUSUAL for kinases
Step 7 of Glycolysis
- Enzyme used
- reaction type form Enzyme
- Helper molecules
- Free Energy
- reversible or irreversible
3-phosphoglycerate -> 2-phosphoglycerate
Enzyme- Phosphoglyceromutase (Phosphoglycerate Mutase)
-phosphoryl shift from C-3 to C-2
-NO helper molecules
-Endergonic
-Reversible
Step 8 of Glycolysis
- Enzyme used
- reaction type form Enzyme
- Helper molecules
- Free Energy
- reversible or irreversible
2-phosphoglycerate -> Phosphoenolpyruvate Enzyme-Enolase -dehydration reaction -NO helper molecules -Exergonic -Reversible
Step 9 of Glycolysis
- Enzyme used
- reaction type form Enzyme
- Helper molecules
- Free Energy
- reversible or irreversible
Phosphoenolpyruvate -> Pyruvate Enzyme-Pyruvate Kinase -phosphoryl transfer from PEP to ADP to produce ATP SUBSTRATE LEVEL PHOSPHORYLATION -NO helper molcules -endergonic -Reversible
3 Fates of pyruvate after Glycolysis
FERMENTATION:Anaerobic Conditions-occurs in cytoplasm
1) Lactic Acid (Higher eukaryotes)
2) Ethanol (microorganisms)
Pyruvate Oxidation:Aerobic Conditions-matrix of mitochondria
Pyruvate-> Ethanol
- Enzyme used
- reaction type form Enzyme
- Helper molecules
- Free Energy
- reversible or irreversible
FERMENATION-ANAEROBIC-CYTOPLASM 1) Pyruvate-> Acetaldehyde Enzyme-Pyruvate Decarboxylase -decarboxylation -coenzymes-Thiamine pyrophosphate derivative of B2 -Exergonic -reversible
2) Acetaldehyde-> Ethanol Enzyme: Alcohol Dehydrogenase -oxidation reaction -Cofactor-Zn2+ -Coenzyme-NADH *REGENERATES NAD+
Pyruvate-> Lactate
FERMENATION-ANAEROBIC-CYTOPLASM Enzyme: Lactate Dehydrogenase -oxidation reaction -Coenzyme-NADH REGENERTAES NAD+
-end product of glycolysis in RBC, lens and cornea of eye, kidney medulla, testes, leukocytes
Exercising: Pyruvate
Exercise: Muscles produce lactate
- formation of lactate reduces pH potentially leading to cramps
- lactate diffuses into blood and can be used to make glucose in liver
Heart gathers lactate from blood and converts to pyruvate
Rossmann Folds
NAD+ binding domains are similar in all dehydrogenase
- Glyceraldehyde 3-phosphoglycerate dehydrogenase
- lactate dehydrogenase
- Alcohol dehydrogenase
Composed of:
- 4 Alpha helixes
- 6 parallel beta strands
Resting Muscles: Regulation
In resting muscles, Glycolysis is INHIBITED By High Energy Charge (DONT NEED ATP for muscle contraction)
1) High energy Charge (high ATP, Low AMP), ATP binds to allosteric sites on PFK-1 and Pyruvate Kinase inhibiting these enzymes
2) Inhibition of PFK-1 and Pyruvate Kinase leads to increase in Glucose 6-Phosphate which binds to allosteric site on Hexokinase and inhibits its activity
Contracting Muscles: Regulation
In Contracting Muscles, Glycolysis is stimulated by LOW ENERGY CHARGE (NEED MORE ATP)
1) contracting muscles quickly utilize existing ATP (converting it to ADP and AMP) reducing the energy charge of surrounding tissue (Low ATP, High AMP)
- AMP displaces ATP from allosteric site of PFK-1 stimulating it
- as PFK-1 is activated Glucose 6-Phosphate is consumed reducing its concentration
- As Fructose 1,6-Bisphosphate is formed if FEEDS FORWARD and stimulates Pyruvate Kinase
Hexokinase Regulation
-Allosterically and Hormonal
Allosterically regulated:
-Glucose 6-Phosphate
Hormonal:
- Insulin Signals an increase of glucose in the blood from the fed State and stimulates Hexokinase
- Glucagon signal a low conc of blood glucose and inhibits hexokinase
PFK-1 Regulation:
-Allosterically and hormonal
Allosterically regulated by ENERGY CHARGE (ATP:AMP)
-stimulated by Fructose 2,6-Bisphosphate and AMP (LOW ENERGY CHARGE-Not enough ATP)
Inhibited by ATP (HIGH ENERGY CHARGE-To much ATP), Citrate, and H+
Hormonal:
- Insulin signals an increase of glucose in blood from the fed state and stimulates PFK-1
- Glucagona signals a low concentration of blood glucose in the fasting state and inhibits PFK-1
Pyruvate Kinase Regulation:
-Allosterically and Hormonal
Allosterically regulated by ENERGY CHARGE:
- Stimulated by Fructose 1,6-Bisphosphate by feedforward stimulation
- Inhibited by ATP (HIGH ENERGY CHARGE) and alanine
IN THE LIVER:
-Glucagon signals low blood glucose and stimulates cAMP protein kinase activity to phosphorylate PK inactivating it
Hormonal
- Insulin signals an increase of glucose in blood from the fed state and stimulates PK
- Glucagon signals a low concentration of blood glucose in the fasting state and inhibits PK
Regulation of Glycolysis in Various Tissues
In muscle, glycolysis is used to produce ATP to power contraction:
-Primary Control is ENERGY CHARGE (ATP:AMP)
In Liver, glycolysis is involved in:
- maintenance of blood glucose levels
- synthesizes glycogen to store glucose when glucose concentrations are high
- generates intermediates for biosynthesis
Liver: Glycolysis Regulation
1) Glucokinase an isozyme of hexokinase
- low affinity (larger Km) for glucose->allows brand and muscles to have first call on glucose
2) PFK
- ATP allosterically inhibits PKA (HIGH ENERGY CHARGE); binding of ATP lowers PFK’s affinity for fructose 6-phosphate
- Fermentation does not usually occur in the liver so H+ DOES NOT AFFECT the liver isozyme PFK
- Citrate amplifies the inhibition of ATP on PFK, and high concentration of Citrate signals high concentration of intermediates for biosynthesis
Fructose 2,6 Bisphosphate STIMULATES PFK-1 Activity!
3) Pyruvate Kinase- 2 primary isoforms
- M form=Muscles
- L form=liver
- isoforms differ in susceptibility to phosphorylation
a) phosphorylated form=off
b) dephosphorylated form=on
Other Carbohydrates through Glycolysis
Fructose and Galactose (usually from lactose) are converted to glucose for catabolism
Fructose Metabolism in Glycolysis
Fructose 1-Phosphate IN LIVER: (4th step of glycolysis)
1) Fructose-> Fructose 1-Phosphate catalyzed by fructokinase at the expense of ATP-> ADP
2) Fructose 1-Phosphate-> Dihydroxyacetone Phosphate + Glyceraldehyde catalyzed by Fructose 1-Phosphate Aldolase
3) Glyceraldehyde-> Glyceraldehyde 3-Phosphate catalyzed by Triose Kinase at the expense of ATP-> ADP
OTHER TISSUE:
-Fructose-> Fructose 6-Phosphate by hexokinase (1st step of glycolysis) at the expense of ATP-ADP
Hexokinase VS Glucokinase
Hexokinase:
- Low Km=High affinity for Glucose
- Km<0.1 mM
- permits efficient metabolism of glucose
Glucokinase (HexokinaseD or Type IV)
- senses glucose levels in adult kidney and liver
- High Km=low affinity for glucose
Pyruvate Kinase Deficiency in RBC
PK deficiency causes change of shape in RBC’s due to insufficient energy production resulting in hemolytic anemia
Glucose Transport
1) Sodium Monosaccharide cotransport system
- transports glucose “against” concentration gradient
- sodium concentration gradient requires energy via sodium/potassium ATPase pumps
2) Sodium independent facilitated diffusion (transport) of glucose “down” its concentration gradient across the plasma membrane
- 14 isoforms of Glucose transports (GLUT)
3) Normal serum glucose level=4mM-8mM
4) Km is substrate conc at 1/2Vmax
GLUT
- 14 different isoforms
- single polypeptide of 500 amino acids
- 12 transmembrane alpha helixe structure
- tissue specific pattern of expression
Glycolysis in Cancer Cells
In cancer cells, glycolysis often functions anaerobically (fermentation), even in the presence of oxygen
- called anaerobic glycolysis or WARBURG effect
- medicine capitalizes on this when testing for cancer
Galactitol
Causes Cataract:
- the increased galactose concentration in the blood caused by galactosemia, leads to an increase concentration in some tissues
- ex; eyes lack the ability to metabolize thus it is converted to galactitol which causes cateracts
