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MC Biochem 2 > Glycolysis > Flashcards

Glycolysis Flashcards

1
Q

Glycolysis Overview

-common in prokaryotic and eukaryotic

A

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

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2
Q

1st step of glycolysis

  • Enzyme used
  • reaction type form Enzyme
  • Cofactor
  • Free Energy
  • reversible or irreversible
A 
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

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3
Q

Hexokinases

A

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

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4
Q

Step 2 of Glycolysis

  • Enzyme used
  • reaction type form Enzyme
  • Helper molecules
  • Free Energy
  • reversible or irreversible
A

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

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5
Q

Step 3 of Glycolysis

  • Enzyme used
  • reaction type form Enzyme
  • Helper molecules
  • Free Energy
  • reversible or irreversible
A

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

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6
Q

PFK-2

A

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

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7
Q

Adenylate Kinase

A

Salvages ATP from 2 ADP molecules

-primary reason why AMP represents the low energy charge

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8
Q

Step 4 of Glycolysis

  • Enzyme used
  • reaction type form Enzyme
  • Helper molecules
  • Free Energy
  • reversible or irreversible
A 
Fructose 1,6-Bisphosphate -> Glyceraldehyde 3-Phosphate + Dihydroxyacetone phosphate 
Enzyme-Aldolase A
-aldol cleavage
-No helper molecules
-Exergonic
-reversible
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9
Q

Triose Phosphate Isomerase

  • reaction type form Enzyme
  • Helper molecules
  • Free Energy
  • reversible or irreversible
A

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

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10
Q

Step 5 of Glycolysis

  • Enzyme used
  • reaction type form Enzyme
  • Helper molecules
  • Free Energy
  • reversible or irreversible
A

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

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11
Q

Step 6 of Glycolysis

  • Enzyme used
  • reaction type form Enzyme
  • Helper molecules
  • Free Energy
  • reversible or irreversible
A

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

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12
Q

Step 7 of Glycolysis

  • Enzyme used
  • reaction type form Enzyme
  • Helper molecules
  • Free Energy
  • reversible or irreversible
A

3-phosphoglycerate -> 2-phosphoglycerate
Enzyme- Phosphoglyceromutase (Phosphoglycerate Mutase)
-phosphoryl shift from C-3 to C-2
-NO helper molecules
-Endergonic
-Reversible

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13
Q

Step 8 of Glycolysis

  • Enzyme used
  • reaction type form Enzyme
  • Helper molecules
  • Free Energy
  • reversible or irreversible
A 
2-phosphoglycerate -> Phosphoenolpyruvate
Enzyme-Enolase
-dehydration reaction 
-NO helper molecules
-Exergonic
-Reversible
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14
Q

Step 9 of Glycolysis

  • Enzyme used
  • reaction type form Enzyme
  • Helper molecules
  • Free Energy
  • reversible or irreversible
A 
Phosphoenolpyruvate -> Pyruvate
Enzyme-Pyruvate Kinase
-phosphoryl transfer from PEP to ADP to produce ATP
SUBSTRATE LEVEL PHOSPHORYLATION
-NO helper molcules
-endergonic
-Reversible
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15
Q

3 Fates of pyruvate after Glycolysis

A

FERMENTATION:Anaerobic Conditions-occurs in cytoplasm

1) Lactic Acid (Higher eukaryotes)
2) Ethanol (microorganisms)

Pyruvate Oxidation:Aerobic Conditions-matrix of mitochondria

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16
Q

Pyruvate-> Ethanol

  • Enzyme used
  • reaction type form Enzyme
  • Helper molecules
  • Free Energy
  • reversible or irreversible
A 
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+
17
Q

Pyruvate-> Lactate

A 
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

18
Q

Exercising: Pyruvate

A

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

19
Q

Rossmann Folds

A

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
20
Q

Resting Muscles: Regulation

A

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

21
Q

Contracting Muscles: Regulation

A

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

22
Q

Hexokinase Regulation

-Allosterically and Hormonal

A

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
23
Q

PFK-1 Regulation:

-Allosterically and hormonal

A

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
24
Q

Pyruvate Kinase Regulation:

-Allosterically and Hormonal

A

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
25
Q

Regulation of Glycolysis in Various Tissues

A

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
26
Q

Liver: Glycolysis Regulation

A

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

27
Q

Other Carbohydrates through Glycolysis

A

Fructose and Galactose (usually from lactose) are converted to glucose for catabolism

28
Q

Fructose Metabolism in Glycolysis

A

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

29
Q

Hexokinase VS Glucokinase

A

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
30
Q

Pyruvate Kinase Deficiency in RBC

A

PK deficiency causes change of shape in RBC’s due to insufficient energy production resulting in hemolytic anemia

31
Q

Glucose Transport

A

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

32
Q

GLUT

A
  • 14 different isoforms
  • single polypeptide of 500 amino acids
  • 12 transmembrane alpha helixe structure
  • tissue specific pattern of expression
33
Q

Glycolysis in Cancer Cells

A

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
34
Q

Galactitol

A

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

MC Biochem 2 (31 decks)

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