GLYCOLYSIS &
GLUCONEOGENESIS
GLUCONEOGENES
CHEM1829 Biological Chemistry for Optometry Students,
T3 2023
Dr Gee Chong Ling
on behalf of Dr Lana C. Ly
g.ling@unsw.edu.au
School of Biotechnology & Biomolecular Sciences
Image source: stickpng.com/img/food/sugar-cubes/three-sugar-cubes-on-a-spoon
GLYCOLYSIS & GLUCONEOGENESIS:
LECTURE OVERVIEW
Dietary Carbohydrates
Glucose Metabolism Overview
The Glycolytic Pathway (Glycolysis)
Gluconeogenesis
Diabetes
LEARNING OUTCOMES (LOs)
1.
2.
3.
4.
5.
6.
7.
8.
9.
LO#
Slides that directly
address LOs are
annotated with this
List and describe different types of dietary carbohydrates.
Describe the main function and properties of glycolysis.
Describe different modes of carbohydrate transport into cells.
Explain the two major phases of glycolysis.
Describe the stoichiometry of glycolysis.
Describe the major control mechanism of glycolysis.
Describe the main function and properties of gluconeogenesis.
List the main precursors for glucose synthesis in the liver.
List and describe the three enzymatic steps of glycolysis that are bypassed in
gluconeogenesis.
10.Explain the energy requirements of gluconeogenesis.
11.Explain the reciprocal regulation of glycolysis and gluconeogenesis.
12.Explain the relationship between blood [glucose] and cataract formation in diabetes patients.
DIETARY CARBOHYDRATES
Carbohydrate – A sugar (monosaccharide) or one of its dimers (disaccharides) or
polymers (polysaccharides) that consist of carbon, hydrogen and oxygen atoms
LO1
LO1
DIETARY CARBOHYDRATES
Carbohydrate – A sugar (monosaccharide) or one of its dimers (disaccharides) or
polymers (polysaccharides) that consist of carbon, hydrogen and oxygen atoms
• MONOSACCHARIDES
E.g. glucose
Images created using Biorender.com
LO1
DIETARY CARBOHYDRATES
Carbohydrate – A sugar (monosaccharide) or one of its dimers (disaccharides) or
polymers (polysaccharides) that consist of carbon, hydrogen and oxygen atoms
• MONOSACCHARIDES
E.g. glucose
• DISACCHARIDES E.g. maltose
Two monosaccharides joined by a glycosidic bond/linkage
Glucose
Glucose
Maltose
Images created using Biorender.com
LO1
DIETARY CARBOHYDRATES
Carbohydrate – A sugar (monosaccharide) or one of its dimers (disaccharides) or
polymers (polysaccharides) that consist of carbon, hydrogen and oxygen atoms
• MONOSACCHARIDES
E.g. glucose
• DISACCHARIDES E.g. maltose
Two monosaccharides joined by a glycosidic bond/linkage
Glucose
Glucose
Maltose
• POLYSACCHARIDES E.g. cellulose, starch (grains & vegetables), glycogen
Polymers with hundreds to thousands of monosaccharides joined by glycosidic bonds
Images created using Biorender.com
LO1
CARBOHYDRATES
Plants
(structural component)
Plants
(storage carbohydrate)
Animals
(storage carbohydrate)
no
Amylose – no
Amylopectin – yes
yes
Image source: byjus.com
LO1
CARBOHYDRATES
Plants
(structural component)
Plants
(storage carbohydrate)
Animals
(storage carbohydrate)
no
Amylose – no
Amylopectin – yes
yes
Image source: byjus.com
LO1
CARBOHYDRATES
Plants
(structural component)
Plants
(storage carbohydrate)
Animals
(storage carbohydrate)
no
Amylose – no
Amylopectin – yes
yes
Image source: byjus.com
GLUCOSE
METABOLISM
OVERVIEW
Glycolysis
Gluconeogenesis
Pratt & Cornely, Essential
Biochemistry (2004)
LO2
GLYCOLYSIS
Glycolysis is a series of ten enzyme-catalysed steps in which a 6-carbon glucose molecule is
broken down into two 3-carbon pyruvate molecules
GLYCOLYSIS
‘sweet’
To loosen/
divide/cut apart
6-carbon glucose
glycolysis
Two 3-carbon
pyruvate molecules
LO2
GLYCOLYSIS
Glycolysis is a series of ten enzyme-catalysed steps in which a 6-carbon glucose molecule is
broken down into two 3-carbon pyruvate molecules
GLYCOLYSIS
‘sweet’
6-carbon glucose
glycolysis
To loosen/
divide/cut apart
• Glycolysis is a “universal” catabolic pathway that is found in protozoans,
bacteria, fungi, algae, higher plants and higher animals
o Occurs in cells of ALL human tissues
Two 3-carbon
pyruvate molecules
LO2
GLYCOLYSIS
Glycolysis is a series of ten enzyme-catalysed steps in which a 6-carbon glucose molecule is
broken down into two 3-carbon pyruvate molecules
GLYCOLYSIS
‘sweet’
6-carbon glucose
glycolysis
To loosen/
divide/cut apart
• Glycolysis is a “universal” catabolic pathway that is found in protozoans,
bacteria, fungi, algae, higher plants and higher animals
o Occurs in cells of ALL human tissues
• Glucose breakdown via glycolysis is the ONLY major route for ATP
production in red blood cells, brain, nervous tissue and the retina
o In exercising skeletal muscle, glucose breakdown via glycolysis is the
FASTEST route for ATP production
Two 3-carbon
pyruvate molecules
Image template from Biorender.com
CARBOHYDRATE TRANSPORT INTO CELLS VIA
TRANSPORTERS
Symports
The movement of two molecules in
the same direction through a cell
membrane via a protein channel
Transporter image created using Biorender.com
E.g. Na+/glucose symports transport glucose &
galactose from the small intestine into intestinal
mucosal cells
LO3
CARBOHYDRATE TRANSPORT INTO CELLS VIA
TRANSPORTERS
Symports
The movement of two molecules in
the same direction through a cell
membrane via a protein channel
Uniports
The movement of one molecule
through a cell membrane via a
protein channel
•
•
Transporter image created using Biorender.com
E.g. Na+/glucose symports transport glucose &
galactose from the small intestine into intestinal
mucosal cells
E.g. GLUT family of uniports facilitates uptake of
glucose & other monosaccharides from the blood
& small intestine into cells of various tissues
GLUT1 for the blood-brain/retinal barrier
GLUT4 for glucose into adipose tissue, heart and skeletal muscle
LO3
CARBOHYDRATE TRANSPORT INTO CELLS VIA
TRANSPORTERS
Symports
The movement of two molecules in
the same direction through a cell
membrane via a protein channel
Uniports
The movement of one molecule
through a cell membrane via a
protein channel
•
•
LO3
E.g. Na+/glucose symports transport glucose &
galactose from the small intestine into intestinal
mucosal cells
E.g. GLUT family of uniports facilitates uptake of
glucose & other monosaccharides from the blood
& small intestine into cells of various tissues
GLUT1 for the blood-brain/retinal barrier
GLUT4 for glucose into adipose tissue, heart and skeletal muscle
Insulin increases vesicle
fusion so that GLUT4 is
translocated to the
plasma membrane
which increases the rate
of glucose uptake
Transporter image created using Biorender.com
Pratt & Cornely, Essential Biochemistry (2004)
1
Energy
Investment
Phase
THE GLYCOLYTIC
PATHWAY
Glycolysis occurs in the cytosol of cells
The ten reactions of glycolysis can be
divided into two phases:
Phase I:
2
Energy
Payoff
Phase
Energy Investment (Reactions 1-5)
Phase II:
Energy Payoff (Reactions 6-10)
LO4
THE GLYCOLYTIC PATHWAY – PHASE I
Energy
Investment
Phase
LO4
THE GLYCOLYTIC PATHWAY – PHASE I
Energy
Investment
Phase
LO4
THE GLYCOLYTIC PATHWAY – PHASE I
The major rate-limiting step
of the glycolytic pathway
Energy
Investment
Phase
LO4
THE GLYCOLYTIC PATHWAY – PHASE I
The major rate-limiting step
of the glycolytic pathway
Energy
Investment
Phase
LO4
THE GLYCOLYTIC PATHWAY – PHASE I
The major rate-limiting step
of the glycolytic pathway
Energy
Investment
Phase
LO4
LO4
THE GLYCOLYTIC PATHWAY – PHASE I
The major rate-limiting step
of the glycolytic pathway
Energy
Investment
Phase
Effective overall reaction is:
F-1,6-bisP
2 GAP
THE GLYCOLYTIC PATHWAY – PHASE II
LO4
In the energy payoff phase, there is
generation of:
• 2 NADH
• 2 H+
• 4 ATP  what would be the net
production of ATP from glycolysis?
• 2 H2O
Energy
Payoff
Phase
THE GLYCOLYTIC PATHWAY – PHASE II
LO4
In the energy payoff phase, there is
generation of:
• 2 NADH
• 2 H+
• 4 ATP  what would be the net
production of ATP from glycolysis?
• 2 H2O
Energy
Payoff
Phase
THE GLYCOLYTIC PATHWAY – PHASE II
LO4
In the energy payoff phase, there is
generation of:
• 2 NADH
• 2 H+
• 4 ATP  what would be the net
production of ATP from glycolysis?
• 2 H2O
Energy
Payoff
Phase
THE GLYCOLYTIC PATHWAY – PHASE II
LO4
In the energy payoff phase, there is
generation of:
• 2 NADH
• 2 H+
• 4 ATP  what would be the net
production of ATP from glycolysis?
• 2 H2O
Energy
Payoff
Phase
THE GLYCOLYTIC PATHWAY – PHASE II
LO4
In the energy payoff phase, there is
generation of:
• 2 NADH
• 2 H+
• 4 ATP  what would be the net
production of ATP from glycolysis?
• 2 H2O
Energy
Payoff
Phase
STOICHIOMETRY OF GLYCOLYSIS
Glucose + 2 ADP
+ 2 NAD+ + 2 Pi
2 Pyruvate + 2 ATP
+ 2 NADH + 2 H+ + 2 H2O
Image created using Biorender.com
LO5
LO6
CONTROL OF GLYCOLYSIS
The major mechanism of control is by
feedback regulation of allosteric enzymes,
such as phosphofructokinase
Phosphofructokinase catalyses the third step
of the glycolytic pathway
•
Inhibited by:
o Citrate
o ATP
•
Stimulated by:
o AMP
o Fructose-2,6-biphosphate
Image created using Biorender.com
FATES OF GLYCOLYTIC PRODUCTS
What happens to the major products of glycolysis –
pyruvate, ATP & NADH?
ATP is utilised in energy-requiring cellular processes
But how is pyruvate used?
How is NADH re-oxidised?
More from next lecture on
TCA Cycle & Oxidative Phosphorylation 
WHAT IS GLUCONEOGENESIS?
WHERE DOES IT OCCUR?
gluconeogenesis
‘sweet’
New
Creation / generation
Gluconeogenesis is the synthesis of glucose from
non-carbohydrate precursors
•
When dietary sources of glucose are not available
and when the liver has exhausted its supply of
glycogen, glucose is synthesised via
gluconeogenesis
•
Gluconeogenesis is a UNIVERSAL pathway –
present in plants, animals, fungi & microorganisms
LO7
LO8
WHAT IS GLUCONEOGENESIS?
WHERE DOES IT OCCUR?
gluconeogenesis
‘sweet’
New
Creation / generation
Gluconeogenesis is the synthesis of glucose from
non-carbohydrate precursors
•
•
When dietary sources of glucose are not available
and when the liver has exhausted its supply of
glycogen, glucose is synthesised via
gluconeogenesis
Gluconeogenesis is a UNIVERSAL pathway –
present in plants, animals, fungi & microorganisms
LO7
LO8
Gluconeogenesis occurs
primarily in the liver and, to a
lesser extent, in the kidneys
In the liver, the important precursors for
glucose synthesis are:
pyruvate
lactate
glycerol
OTHER NON-CARBOHYDRATE PRECURSORS
• Other non-carbohydrate precursors of gluconeogenesis
include:
o TCA Cycle intermediates
o Carbon skeletons of most amino acids
LO8
The TCA Cycle will
be discussed in
your next lecture!
Image created using Biorender.com
OTHER NON-CARBOHYDRATE PRECURSORS
• Other non-carbohydrate precursors of gluconeogenesis
include:
o TCA Cycle intermediates
o Carbon skeletons of most amino acids
Firstly, ALL of these precursors
must be converted to the 4-carbon
compound, oxaloacetate
LO8
The TCA Cycle will
be discussed in
your next lecture!
oxaloacetate
Image created using Biorender.com
LO8
OTHER NON-CARBOHYDRATE PRECURSORS
• Other non-carbohydrate precursors of gluconeogenesis
include:
o TCA Cycle intermediates
o Carbon skeletons of most amino acids
Firstly, ALL of these precursors
must be converted to the 4-carbon
compound, oxaloacetate
The TCA Cycle will
be discussed in
your next lecture!
oxaloacetate
• The ONLY amino acids in animals that cannot be converted to
oxaloacetate and act as precursors are leucine and lysine
because their breakdown yields only acetyl-CoA
• Similarly, fatty acids cannot act as glucose precursors in animals because most are completely
degraded to acetyl-CoA
Image created using Biorender.com
LO9
Three of the ten reactions in
glycolysis are thermodynamically
irreversible
These three reactions are specifically
bypassed in gluconeogenesis while
the remaining seven reactions can be
used in reverse
Bypass II
Glycolysis (catabolism)
Gluconeogenesis is the sometimes
called “reverse glycolysis”, BUT…
Gluconeogenesis (anabolism)
IS GLUCONEOGENESIS
THE REVERSE OF
GLYCOLYSIS?
Bypass III
Bypass I
BYPASS I: PYRUVATE  PHOSPHOENOLPYRUVATE (PEP)
LO9
Bypass I
Image source: Essential Biochemistry, Pratt & Cornely, John Wiley & Sons Inc.
Bypass II
Glycolysis (catabolism)
Gluconeogenesis (anabolism)
Bypass III
Bypass I
BYPASS II: FRUCTOSE-1,6-BISPHOSPHATE
 FRUCTOSE-6-PHOSPHATE
LO9
Bypass II
Image source: Essential Biochemistry, Pratt & Cornely, John Wiley & Sons Inc.
BYPASS III: GLUCOSE-6-PHOSPHATE  GLUCOSE
LO9
Bypass III
Image source: Essential Biochemistry, Pratt & Cornely, John Wiley & Sons Inc.
GLUCONEOGENESIS SUMMARY
LO10
The net reaction beginning with pyruvate is:
2 pyruvate + 4 ATP + 2 GTP
+ 2 NADH + 2 H+ + 6 H2O
glucose + 2 NAD+  4 ADP
+ 2 GDP + 6 Pi
GLUCONEOGENESIS
•
Gluconeogenesis is energetically expensive!
•
Producing 1 glucose molecule from 2 pyruvate molecules consumes 6 ATP
To avoid the potential waste of metabolic free energy, gluconeogenic cells
(mainly liver) carefully regulate the opposing pathways of glycolysis &
gluconeogenesis according to the cell’s energy needs
Image source: thenounproject.com/browse/icons/term/expensive/?iconspage=1
CONTROL OF GLUCONEOGENESIS
LO11
Fructose-2,6-bisphosphate is a potent allosteric ACTIVATOR of phosphofructokinase (PFK)
(glycolysis) and a potent INHIBITOR of fructose bisphosphatase (FBPase) (gluconeogenesis)
This mode of regulation is efficient because a single compound can
control flux through two opposing pathways in a reciprocal manner
Image adapted from Essential Biochemistry, Pratt & Cornely, John Wiley & Sons Inc.
DIABETES
• Insulin decreases blood
[glucose] when
concentrations are high
(after a meal) by activating
glucose transport into cells
via GLUT4 transporters
• Glucagon increases blood
[glucose] when
concentrations are low by
stimulating the liver to
release glucose into the
blood (from glycogen
stores and/or
gluconeogenesis)
Image template by Biorender.com
Diabetes mellitus – a disorder marked by an inability to maintain
glucose homeostasis by either failure to produce insulin, or reduced
responsiveness of target cells to insulin
LO12
DIABETES & THE EYE
Glucose transport into cells of the eye is NOT insulin-dependent
•
In diabetes, cells in the eye are constantly exposed to elevated intracellular [glucose]
•
This can lead to the production of sorbitol via aldose reductase
Sorbitol accumulation causes osmotic imbalances which can lead to
cataract formation and possibly contribute to diabetic retinopathy
LO12
READING
Biochemistry
Berg, Tymoczko, & Stryer
7th-9th Editions
Chapter 16: Glycolysis & Gluconeogenesis
Biochemistry: A Short Course
Tymoczko, Berg & Stryer
2nd Edition
Chapters 16 & 17
Special thank you to Lana Ly and Anne Galea for slide material contributions!