Glycolysis learning outcomes
• Be able to state the 3 stages of respiration (E)
• Be able to describe an overview of the stages
of glycolysis (C)
• Be able to describe in detail (e.g. name of an
enzyme, why a process occurs) the process of
glycolysis (A)
Respiration
Things to cover:
• What is ATP and why is it important?
• What is the structure of ATP?
• What are co-enzymes, what is their role?
• What happens in:
–Glycolysis
Starter Quiz
• Overall reaction for aerobic respiration
• Definition of respiration
– The release of chemical potential energy from organic
molecules
• Two uses of the energy released by respiration
• What does ATP stand for?
– Adenosine triphosphate
Starter Quiz
1. Why does each cell require the structures associated
with respiration?
1. ATP cannot cross the plasma membrane
2. 2 advantages of ATP over direct energy transfer from
glucose
1. Idea of packaging of energy
3. Why is all the chemical energy released during
respiration not transferred to ATP
1. Lost as heat
4. How much energy is released through the
condensation of ATP  ADPAMP
1. 75.4KJmol-1
The structure of ATP
Adenosine triphosphate
-ATP is a phosphorylated
nucleotide (similar to the
structure of DNA and RNA)
(ATP cant leave the cell where it
is made)
Why ATP acts as an energy store...
-When 1 phosphate group is
removed from each molecule in
one mole of ATP, 30.5 kJ of
energy’s released
ATPase
-This is a hydrolysis reaction
(requires water), and is
catalysed by enzymes called
ATPases
Energy released
(30.5KJ mol-1)
Water
ADP
Pi
The energy released from hydrolysis of ATP
adenosine
diphosphate
adenosine
monophosphate
ATP is useful as an
energy carrier
(currency) because it
cycles.
It also “packages” the
energy released from
respiration into useful
amounts.
• Respiration provides the energy
required for the condensation
reaction that converts ADP 
ATP
• i.e. For each 30.5KJ mol-1 of
energy that is released by
hydrolysis of ATP the same
energy must also be input from
respiration to reform the ATP.
•The energy for condensation
reaction comes from the
chemical energy stored in
Glucose.
How it all fits together
Glucose (high stored chemical potential energy )
ADP
ATP
Hydrolysis
Condensation
Respiration
ATP
Energy
Transferred
ADP
Carbon Dioxide + Water
(low stored chemical potential energy )
5 questions
1.What is respiration?
2.Give three uses of respiration?
3.What are the three main components from ATP?
4.How much energy is released from hydrolysis of
ATP?
5.Why do cells require ATP?
4 main processes in aerobic
respiration
1. Glycolysis
2. Link Reaction
3. Krebs Cycle
4. Oxidative Phosphorylation
Key players you need to know the
structure of in respiration
• Glucose
• ADP / ATP
• Co-enzymes: NAD, FAD, Co-enzyme A
The primary
substrate for
respiration is
glucose
(C6H12O6)
Other substrates can
be used. We will talk
about these later!
Enzymes in Respiration
• Respiration releases chemical potential energy from
the substrate through a series of reactions.
• Each stage of respiration is catalysed by a specific
enzyme
• Reactions in respiration are examples of Oxidation
and Reduction reactions.
– Oxidation: loss of electrons (loss of hydrogen).
– Reduction: gain of electrons (gain of hydrogen).
Co-enzymes
• Enzymes needed to assist other enzymes in a
reduction or oxidation reaction (because they can
pick up and lose hydrogen atoms)
• Co-enzymes used in respiration:
– NAD Nicotinamide Adenine Dinucleotide
– CoA Coenzyme A
– FAD Flavine Adenine Dinucleotide
• Co-enzymes that have been reduced are used in the
final stage of respiration (oxidative phosphorylation)
which produces a lot of ATP.
Co-enzymes how they work – NAD as an example
Substrate
H
NAD
NAD
Hydrogen atom lost
Hydrogen atom
accepted by co-enzyme
Oxidised Substrate
NADH
Reduced NAD
Co-enzyme is oxidised
NADH
H
Hydrogen is removed.
The hydrogen atom is used
to generate ATP
•When a co-enzyme takes on a Hydrogen atom it is
“reduced”
•When it deposits a Hydrogen it is oxidised
•Co-enzymes are continuously cycled
NAD
•
•
•
•
Derived from vitamin B
Dinucelotide
Nicotinamide is the hydrogen acceptor
NAD (oxidised); NADH = reduced
Used in
• Glycolysis
• Link reaction
• Krebs cycle
• (also anaerobic respiration – lactate pathways)
Do not confuse with NADP
Coenzyme A (CoA)
• Derived from vitamin B
• Used in the link reaction to transfer products
of glycolysis into the mitochondria
• Carries Ethanoate groups created through
oxidation during the link reaction onto the
krebs cycle
FAD
• Derived from vitamin B2
• Made from Adenine Ribose and 2 phosphate
groups
• FAD  FADH
• Used in the Krebs cycle
Respiration – Part 1
Glycolysis
Respiration: Glycolysis
•Takes place in the cytoplasm
•Does not require oxygen
•Glucose is split into two molecules of
Pyruvate (a 3 carbon sugar)
•2 parts: energy investment phase, energy
pay off phase
Respiration: Glycolysis – outcomes
•Net gain of 2 ATP
• 2 reduced NAD (NADH)
•(2 molecules of pyruvate)
Ledger
Step 1:
Enzyme: Hexokinase
ATP : -1
(ADP: +1)
CH2OH
P
O
P
P
ADP
ATP
Glucose-6-phosphate
Glucose
•Glucose enters the cell
•The enzyme hexokinase transfers a phosphate from ATP to the glucose.
•The charge on the Phosphorylation has two affects:
1. phosphate group prevents the glucose from leaving the cell because the
plasma membrane is impermeable to ions
2. Makes the glucose more chemically reactive
Glycolysis steps
Glucose (6 Carbon)
ATP
ADP
Glucose-6-phosphate
(6 carbon)
Fructose-6-phosphate
(6 carbon)
ATP
ADP
Hexose1,6-bisphosphate
(6 carbon)
2 x Oxidased
NAD
2 x ADP + Pi
2 x Triose Phosphate (3 carbon)
2 x Reduced
NAD
2 x ATP
2x intermediate compounds (3 carbon)
2 x ADP + Pi
2x
2x Pyruvate (3 carbon)
ATP
Steps 1-4: Energy investment phase
• ATP is hydrolysed; exogonic reaction
• 2 ATP converted to ADP
• The stored energy in ATP is needed to
destabilise and activate the substrate molecule
by phosphorylation of the substrate.
• Therefore some ATP is needed in order to
generate ATP
Glycolysis step 1: Phosphorylation
Glucose (6 Carbon)
•ATP is hydrolysed.
•Energy released is used
to attach Pi to the Glucose
at Carbon number 6
ATP
•Destabilises glucose
ADP
•Prevents from leaving the
cell
Glucose-6-phosphate
(6 carbon)
Glycolysis step 2: Phosphorylation
Glucose-6-phosphate
(6 carbon)
• Configuration of the
molecule changes to
form a 5 carbon ring
•Requires an isomerase
enzyme
Fructose-1-phosphate
(6 carbon)
Ledger
Step 2:
Enzyme: Phosphoglucoisomerase
CH2O
C
H
P
O
H
CH2O
H
C
C
HO OH
ATP : -1
(ADP: +1)
H
C
C
H
OH
P
CH2OH
O
OH
Fructose-6-phosphate
Glucose-6-phosphate
•The enzyme rearranges the atoms in glucose-6-phosphate to form its isomer,
fructose-6-phosphate.
• The structure of fructose-6-phosphate can be represented like this
Glycolysis step 3: Phosphorylation
Fructose-1-phosphate
(6 carbon)
ATP
ADP
Another ATP is hydrolysed
and the Pi released attaches
to the fructose at carbon
number 6.
Hexose1,6-bisphosphate
(6 carbon)
Ledger
Step 3:
Enzyme: Phosphofructokinase
CH2O
P
ATP : -2
-1
(ADP: +2)
+1)
CH2O H
O
P
P
P
ADP
ATP
Fructose-6-phosphate
Fructose-1,
6-bisphosphate
•The enzyme transfers a phosphate group from ATP to the sugar
• With phosphate groups on each end the sugar is now ready to split in half
• Note: 2 molecules of ATP have been invested so far in the process
Glycolysis step 4: Splitting hexose
Hexose1,6-bisphospahe
(6 carbon)
The hexose sugar is split into
two 3 carbon sugars
(for the rest of the process we
only follow one of the sugar
molecules)
Triose phosphate
(3 carbon)
Triose phosphate
(3 carbon)
Step 4:
Enzyme: Aldolase / Isomerase
Ledger
ATP : -2
(ADP: +2)
•The enzyme cleaves the Fructose-1,6-bisphosphate into two 3 carbon sugars:
• glyceraldehyde-3-phosphate
• dihydroacetone phosphate
• Both sugars are isomers of each other
• Isomerase catalyses the reversible conversion between the two isomers
Steps 5 -6: Energy payback
• Condensation reactions convert ADP to ATP. These reactions are
endogonic. Energy is transferred from the substrate to the ATP
molecule.
•4 molecules of ATP are formed (net gain of 2 ATP)
•Activation energy for the phosphorylation of ADP comes directly
from oxidation of the substrate.
•Hydrogen atoms are lost from the substrate – they are accepted by
the co-enzyme NAD which forms NADH (x2).
•(The NADH is used later in oxidative phosphorylation to generate
ATP)
Glycolysis step 5: Oxidation of triose phosphate
Remember this step happens
to each Triose molecule;
therefore:
Triose phospahte
(3 carbon)
ADP
ATP
NAD
NADH
Intermediate
3 carbon compound
•2 hydrogen atoms accepted
by NAD
• NAD is reduced producing 2
NADH
•2 ATP are formed by the
process of substrate level
phosphorylation. This is where
ATP is formed directly using
energy released from the
oxidation of the substrate.
Ledger
Step 5:
Enzyme: Triose phosphate dehydrogenase
CH2O
CHOH
ATP : -2
(ADP: +2)
NADH: +2
P
NAD
O P
•The enzyme catalyses
two steps
H
O
C
• first, the Glyceraldehyde-3-phosphate is oxidised by NAD.
Electrons and H+ are transferred to the NAD forming NADH.
• Results in production of 2 molecules of NADH
•The oxidation of the sugar is very exergonic
•The enzyme uses released energy to attach a phosphate group to
the sugar
• The phosphate ions come from the pool of inorganic phosphate
in the cytosol
Ledger
Step 5b:
Enzyme: Phosphoglycerokinase
ATP::-2
0
ATP
(ADP:+2)
0)
(ADP:
NADH: +2
P
CH2O
P
P
ADP
ATP
CHOH
O
C
O
P
3 - Phosphoglycerate
•The phosphate added in the previous step is transfered to ADP
• step 7 gives a gain of 2 molecules of ATP per molecule of glucose
that starts glycolysis
• The energy gained by the oxidation of sugar in step 6 has now
been released
Glycolysis step 6: Conversion to Pyruvate
Intermediate
3 carbon compound
ADP
ATP
Pyruvate
(3 carbon compound)
•2 ATP are formed;
substrate level
phosphorylation
• 4 steps each
catalysed by a specific
enzyme
• 2 molecules of
pyruvate are formed
Ledger
Step 6:
Enzyme: Phosphoglyceromutase
P
CH2O
ATP
ATP :: -2
0
(ADP:
(ADP:+2)
0)
NADH: +2
CHOH
O
C
O-
3 - Phosphoglycerate
2-Phosphoglycerate
•The enzyme relocates the remaining phosphate group
in preparation for the next step
Ledger
Step 6b:
Enzyme: Endolase
ATP
ATP :: -2
0
(ADP:
(ADP:+2)
0)
NADH: +2
CH2 OH
P
CHO
Water
O
C
O-
3 - Phosphoglycerate
2-Phosphoenolpyruvate
•The enzyme causes a double bond to form in the molecule by
extracting a molecule of water from each molecule of 2Phosphoglycerate. This arrangement makes the remaining
phosphate bond very unstable
Ledger
Step 6c:
Enzyme: Pyruvate Kinase
ATP
-2
ATP
ATP:::+2
0
(ADP:
(ADP:+2)
0)
NADH: +2
CH2
P
P
ADP
ATP
P
C O
O
C
O-
2-Phosphoenolpyruvate
Pyruvate
•The remaining phosphate group transfers to ADP
• A net gain in Glycolysis of 2 ATP per molecule of glucose
•Each molecule of glucose has produced 2 molecules of pyruvate
Glycolysis steps
Glucose (6 Carbon)
ATP
ADP
Glucose-6-phosphate
(6 carbon)
Fructose-6-phosphate
(6 carbon)
ATP
ADP
Hexose1,6-bisphosphate
(6 carbon)
2 x Oxidased
NAD
2 x ADP + Pi
2 x Triose Phosphate (3 carbon)
2 x Reduced
NAD
2 x ATP
2x intermediate compounds (3 carbon)
2 x ADP + Pi
2x
2x Pyruvate (3 carbon)
ATP