Glucose Utilization

Glucose Utilization

PATHWAYS: 4 W’sWhat = Net ReactionWhy = Purpose(s) of Pathway

Where = Organism/Tissue/Organelle

When = Regulation of Pathway

Glucose

AcetylCoA

Pyruvate

NADH/FADH2

KrebsCycle

C6

C4

C5

C4

ATP

Glycolysis

Bridging Rx.

Oxidative PhosphorylationADP

O2

NAD+/FAD

Metabolic Mainstreet

GLUCOSE + 2ADP + 2NAD+

2PYRUVATE + 2ATP + 2NADH

GLYCOLYSIS: Net Reaction (What)

10 Enzymes

Glucose gets oxidized - NAD+ gets reducedTwo ADP molecules get phosphorylated

Glycolysis is a a) catabolic b) anabolic pathway?

Do bacteria have a glycolysis pathway? a) yes b) no c) only anaerobic bacteria

1. Generate ATP a. immediate (2 “anaerobic” ATP) b. future - more ATP from pyruvate & NADH

GLYCOLYSIS: Purpose (Why)

2. Provide intermediates/pyruvate for synthesis reactions

Where?All Organisms: bacteria, plants, animalsAll Cell Types: liver, muscle, neurons, adipose, etc.

Cytoplasm

Low Energy Charge phosphofructokinase (-) ATP

(+) F2,6-BP hexokinase (-) G-6-P pyruvate kinase (-) ATP

When?

HO

OH

OOH

OH

OH

OH

O

OH

HO

OH

OH

a - Glucose b - Fructose

CH2 – OH |CH – OH |CH2 – OH glycerol

CHO | CH – OH | CH2 – OHglyceraldehyde

COO-

| CH – OH | CH2 – OH glycerate

COO-

|CH – OH |CH2 – O - PO3

2-

Name this molecule.

a) Glycerol phosphate b) Glyceraldehyde 3 phosphate c) 3 – phosphoglycerate d) 1 - phosphoglycerate

COO-

| C=O | CH3 pyruvate

COO-

| C-OH || CH2 enol pyruvate

CH2 - OH | C=O | CH2 - OH Dihydroxy acetone

GLYCOLYSIS

Glucose

Glucose-6-Phosphate

Fructose-6-Phosphate

Fructose 1,6 Bisphosphate

DHAP + Glyceraldehyde-3-P

Glyceraldehyde-3-P

Pyruvate

PEP

2-Phosphoglycerate

3-Phosphoglycerate

1,3-BPG

2 ATP → 2 ADP

C6 → 2C3

2 NAD+ reduced → 2 NADH 4 ADP → 4 ATP

Glucose in

2 pyruvate out

Glycolysis: The Preparatory Phase

Glycolysis: The Payoff Phase

GLUCOSE + 2ADP + 2NAD+

2PYRUVATE + 2ATP + 2NADH

GLYCOLYSIS: Net Reaction (What)

10 Enzymes

Glucose gets oxidized - NAD+ gets reducedTwo ADP molecules get phosphorylated

What is the limiting reagent for glycolysis?a) Glucose b) ADP c) NAD+

fuel in

SH2 NADH ATP

S NAD+ ADP

work output

Glucose

AcetylCoA

Pyruvate

NADH/FADH2

KrebsCycle

C6

C4

C5

C4

ATP

Glycolysis

Bridging Rx.

OP

ADP O2

Metabolic MainstreetNAD+

NADH

Lactate

Aerobic~ 36 ATP

How do you supplyNAD+ to glycolysisWhen a lack of O2

Prevents OP!

GLUCOSE + 2ADP + 2NAD+

2PYRUVATE + 2ATP + 2NADH

GLYCOLYSIS: Anaerobic

10 Enzymes

COO-

|NAD+ + H - C - OH | CH3

COO-

| C = O + NADH | CH3

Muscle

Liver

Lactate

Lactate Dehydrogenase (LDH)

GLYCOLYSIS : Side Reactions

Glucose

Glucose-6-Phosphate Glycogen R-5-P/Glucose Fructose-6-Phosphate 2,3 BPG Fructose 1,6 Bisphosphate

DHAP + Glyceraldehyde-3-P

Glyceraldehyde-3-P

Pyruvate

PEP

2-Phosphoglycerate

3-Phosphoglycerate

1,3-BPG Glycerol

GLYCOLYSIS: Regulation

Glucose (-) G-6-P 2nd

Glucose-6-Phosphate Glycogen

Fructose-6-Phosphate (-) ATP 1st

Fructose 1,6 Bisphosphate

DHAP + Glyceraldehyde-3-P

Glyceraldehyde-3-P

Pyruvate(-) ATP PEP

2-Phosphoglycerate

3-Phosphoglycerate

1,3-BPG

S PE

Metabolic Regulation

1. How Much Enzyme - Regulation of gene expression

2. Activity of Available EnzymeAllosteric EnzymesCovalent ModificationsProenzymes

Conditions in the cell (Goldilocks and the three Bears) a) Too much P – slow down pathway b) Too little P – speed up pathway c) [P] is just right – maintain steady state

Allosteric Enzymes R state (relaxed) – active: S → P T state (tense) – inactive (or less active): very little P formed

T ↔ R + S ↔ R + P

A negative regulator (-) will bind selectively to the less active form of an enzyme, shifting the conformational equilibrium toward this form and decreasing activity.

[T] increases and [R] decreases

T- ↔ (- regulator) + T ↔ R + S ↔ R + P

A positive regulator (+) will bind selectively to the more active form of an enzyme, shifting the conformational equilibrium toward this form and increasing activity. [T] decreases and [R] increases

T ↔ R + S ↔ R + P + (+ regulator) ↔ R+ + S

Glucose

AcetylCoA

Pyruvate

NADH/FADH2

KrebsCycle

C6

C4

C5

C4

ATP

Glycolysis

Bridging Rx.

OP

ADP O2

Metabolic MainstreetNAD+

NADH Aerobic~ 36 ATP

How do you supplyNAD+ to glycolysisWhen a lack of O2

Prevents OP!

Lactate

GLYCOLYSIS: Regulation

Glucose (-) G-6-P 2nd

Glucose-6-Phosphate Glycogen

Fructose-6-Phosphate (-) ATP 1st

Fructose 1,6 Bisphosphate

DHAP + Glyceraldehyde-3-P

Glyceraldehyde-3-P

Pyruvate(-) ATP PEP

2-Phosphoglycerate

3-Phosphoglycerate

1,3-BPG

1(-) G-6-P

3(-) ATP

Phosphofructokinase has distinct active and allosteric sitesATP is a negative allosteric regulator as well as a substrate.

Muscle (M4) - ↑ATP decreases PFK activity

[Glu]blood

Meal

Insulin

Glucagon

Fed

Fast early

late fast

Glycogen gone

6-12 hrs1-2 hrs

3 daysLong Term Fast

↑Liver Glycolysis

↓Liver Glycolysis

Liver Glycogenolysis provides glucose to blood/brain.

Liver Gluconeogenesis provides glucose to blood/brain.

Liver Glycolysis Regulation

Phosphofructokinase has distinct active and allosteric sitesATP is a negative allosteric regulator as well as a substrate.

Muscle (M4) - ↑ATP decreases PFK activity

Liver (L4)PhosphofructokinaseActivity in Glycolysis

Fixed [ATP]

↑[citrate] also enhances ATP (-) effect (signals sufficient building blocks)The liver runs glycolysis in the Fed state and blocks glycolysis in the Fasting State.This initially seems counterintuitive but …….

↑ATP decreases PFK activity↑ F-2,6-bP blocks ATP allosteric effect and ↑activityThe ↑F-2,6-bP is tied to insulin release (and high blood sugar)

Rat hepatocyte

Insulin & Fed state

GLUCONEOGENESIS ― What?

2Pyruvate + 4ATP + 2NADH 2GTP

Glucose + 4ADP + 2NAD+

2GDPto blood

Where? LiverWhy? To maintain blood [glucose] after glycogen is used upWhen? Fasting state – (particularly late fast) ↑ [acetylCoA] and glucagon

[Glu]blood

Meal

Insulin

Glucagon

Fed

Fast early

late fast

Glycogen gone

6-12 hrs1-2 hrs

3 daysLong Term Fast

Liver Gluconeogenesis provides glucose to blood/brain.

Gluconeogenesis

Glucose

AcetylCoA

Pyruvate

NADH/FADH2

KrebsCycle

C6

C4

C5

ATP

Glycolysis

Bridging Rx.

OP

ADP O2

NAD+/FAD

Metabolic Mainstreet

oxaloacetate

Gluconeogenesis - Bypass Enzymes

Glucose oxaloacetate Glucose-6-Phosphate

Fructose-6-Phosphate

Fructose 1,6 Bisphosphate

DHAP + Glyceraldehyde-3-P

Glyceraldehyde-3-P

Pyruvate

PEP

2-Phosphoglycerate

3-Phosphoglycerate

1,3-BPG

Pyruvate carboxylase

PEP carboxykinase

Fructose 1,6-bis phosphatase

Glucose 6-phosphatase (-) ATP

(-) ATP

(-) G-6-P

Gluconeogenesis - Bypass Enzymes

pyruvate + CO2 + ATP + H2O oxaloacetate + ADP,Pi + 2H+

oxaloacetate + GTP PEP + GDP + CO2

10. Pyruvate carboxylase & PEP carboxykinase (+) acetylCoA & (-) ADP

3. Fructose 1,6-bisphosphatase (-) fructose 2,6-bisphosphate (low fasting – high Fed) (-) AMP

fructose 1,6 bisphosphate + H2O fructose 6-phosphate + Pi

1. Glucose 6-phosphataseglucose 6-phosphate + H2O glucose + Pi

Where does Pyruvate come from?

Amino Acids

Pyruvate

Oxaloacetate

DHAP

Glucose

Glycerol

Lactate

Glucose

AcetylCoA

Pyruvate

NADH/FADH2

KrebsCycle

C6

C4

C5

ATP

Glycolysis

Bridging Rx.

OP

ADP O2

NAD+/FAD

Metabolic Mainstreet & fasting state

oxaloacetate

Protein

amino acids

Transamination & oxidative deamination

Fat

Fatty acids

Liver Regulation

Fructose-6-Phos

Fructose 1,6 Bisphos

PEP

Pyruvate oxaloacetate

(-) ADP(+) AcetylCoAPyruvate carboxylase

(-) ADPPEP carboxykinase(-) ATP

(-) Alanine(+) F-1,6 BPPyruvate kinase

(-) ATP(-) citrate(+) F-2,6 BP(+) AMPphosphofructokinase

(-) AMP (-) F-2,6 BP (+) citrateFructose 1,6-bisphosphatase

GlycolysisFed State

insulin GluconeogenesisFasting State

glucagon

Cori Cycle : Recycling Lactate

Muscle

Glucose

Lactate

Glucose

Lactate

Glycogen Glycogen

Liver

← LDH (Lactate Dehydrogenase) →

Glycolysis (all cells) & Gluconeogenesis (liver only)

Gluconeogeneis occurs in liver to provide glucose to blood during the fasting state.

It uses 4 separate enzymes to bypass all the ‘irreversible’ steps of glycolysis.Otherwise it shares the same enzymes with glycolysis.

The regulation of Gluconeogenesis and Glycolysis are coordinated and opposite.Glycolysis: on – Fed state with insulin and ↑F-2,6-bP, ↑AMP

off – Fasting state with ↑EC/ATP, ↑citrate Gluconeogeneis: on – Fasting State with glucagon, ↑acetylCoA/citrate

off – Fed state with insulin & ↑AMP/ADP, ↑F-2,6-bP

Glucose + 2NAD+ 2Pryruvate + 2NADH 2ADP → 2ATP

4ADP + 2GDP ← 4ATP + 2GTP

Today’s Topics: Cori Cycle & Gluconeogenesis reviewGlycogen Metabolism – Glycogenesis & GlycogenolysisPhosphorylase vs. Glycogen SynthaseHormones and Metabolic Regulation: Insulin vs. glucagonThe glucagon/epinephrine cascades

This pathway is negatively regulated by high ATP levels a) glycolysis b) gluconeogenesis c) both

This pathway is negatively regulated by high F-2,6-bP levels. a) glycolysis b) gluconeogenesis c) both

This pathway is negatively regulated (liver) during the fasting state. a) glycolysis b) gluconeogenesis c) both

Pentose Phosphate Pathway

To be covered with Fatty Acid Metabolism And ROS.