How Cells Harvest
Chemical Energy
ATP Is Universal Energy Source

Photosynthesizers get
energy from the sun

Consumers get energy
from plants or other
organisms

ENERGY is ALWAYS
converted to the chemical
bond energy of ATP

Photosynthesis and
Respiration are LINKED
Photosynthesis

Overall reaction:
6 CO2 + 12 H2O  C6 H12O6 + 6 O2 + 6 H2O
Often shown as
6 CO2 + 6 H2O  C6 H12O6 + 6 O2
Photosynthesis Overview
Sunlight
12 H2O
6 CO2
ATP
Light Dependent
Reactions
ADP + P
NADPH
Light-Independent
Reactions
NADP+
6 O2
Reactions occur in grana of
the thylakoid membrane
system
Glucose-P + 6 H2O
Reactions occur in stroma
Overview of Cellular Respiration
 Glucose
+ 6 O2  6 CO2 + 6 H2O
30 - 32 ATP
The overall reaction is exergonic.
The energy given off is used to make ATP.
O2
Breathing
CO2
Lungs
CO2
Bloodstream
O2
Muscle cells carrying out
Cellular Respiration
Glucose  6 O2
6 CO2  6 H2O  30-32 ATP
•Breathing and cellular respiration are
closely related:
Cellular Respiration and ATP
 Cellular
respiration releases the energy
stored in glucose in a series of steps
 The energy released is stored as ATP and
released as heat


Aerobic respiration is ~34% efficient
Meaning… 34% of the energy stored in the
glucose is captured and stored as ATP
How Cells Make ATP

ATP is made in two ways during cellular
respiration:
1. Substrate level phosphorylation


Glycolysis
Citric acid cycle (Krebs cycle)
2. Oxidative phosphorylation

Electrons transport system and chemiosmosis
Substrate-level
phosphorylation
ENZYME
ATP is made in an enzyme
in a coupled reaction.
Substrate gives energy
and phosphate group (Pi)
to ADP and makes ATP.
Substrate
Product
Fig. 9.7
 Oxidative


phosphorylation
Electron carriers (NADH and FADH2) deliver
electrons to the Electron Transport Chain (ETC) on
the inner membrane of the mitochondria
Electrons are passed from membrane protein to
protein.
• Each transfer releases energy and pumps H+ out of the
matrix

Energy is used to create a chemical gradient
• Gradient is used to drive ATP synthesis by the enzyme
ATP synthase
Overview of Cellular Respiration
Carbohydrate Metabolism
 The
first pathway of carbohydrate
metabolism is called glycolysis.


Glucose is the starting material for glycolysis.
Glycolysis reactions occur in the cytoplasm.
Glycolysis
 Step
#1: Glucose is converted to glucose6-phosphate in a phosphorylation reaction


Reaction is endergonic
Reaction requires an input of ATP
 Step
#2: A rearrangement reaction occurs
to make fructose-6-phosphate
Glycolysis
 Step
#3: Another phosphorylation reaction
occurs to made fructose-1,6-diphosphate


Reaction is endergonic
Reaction requires an input of ATP
 Step
#4: Fructose-1,6-diphosphate is
broken in to 2 three carbon compounds
Glycolysis
5
more steps occur and 2 pyruvate are
made

These steps release energy and electrons.
• Energy released is used to make ATP by substrate
level phosphorylation
• Electrons are attached to the electron carrier NAD+
to form 2 NADH

The NADH deliver electrons and H+ to the electron
transport system
More on NADH
 Synthesis
of NADH (simplified version):
NAD+ + 2 e + H+  NADH

Is NAD+ oxidized or reduced in this reaction?
Glycolysis
Energy requiring steps:
2 ATP invested
Energy releasing steps:
2 NADH formed
4 ATP formed
Net yield is 2 ATP and 2 NADH
Does NOT require O2
Occurs in the cytoplasm
Glycolysis Summary
 Where
it occurs:
 First substrate: (starting “material”)
 End product:
 Also made:


net gain of ____ ATP (why net?, how made?)
_____ NADH (made from?)
Glycolysis Summary
Where it occurs: Cytoplasm
First Substrate: Glucose (6C)
End product: 2 Pyruvate (3C)
Glycolysis Summary
Also made


net gain of 2 ATP made by substratelevel phosphorylation
• Pathway requires an input of 2 ATP
to start and makes a total of 4 ATP
2 NADH – each made from NAD+ ,2e
and H+
Energy Releasing Pathways
•
What happens to the products of
glycolysis depends upon cell conditions.
 Aerobic conditions
• Preparatory step and Citric Acid/Krebs
cycle
• Electron transport chain
 Anaerobic conditions
• Fermentation
GLYCOLYSIS
OR
ANAEROBIC
Conditions
No oxygen present
Net gain of 2 ATP
AEROBIC
RESPIRATION
Oxygen present
Net gain of 30-32 ATP
GLYCOLYSIS
OR
AEROBIC
RESPIRATION
ANAEROBIC
• Fermentation occurs
• Type depends upon cell type
• Reactions occur in cytoplasm
•
•
•
•
Preparatory step
Krebs Cycle
Electron Transport Chain
Reactions occur in
mitochondria
Pathways of Aerobic Respiration
Glycolysis
1.
followed by Pyruvate oxidation
Citric Acid cycle
2.

3.
Also called Krebs Cycle
Electron Transport Chain (ETC) and
Chemiosmosis
Aerobic Conditions
 The
first reaction that occurs after
glycolysis is pyruvate oxidation


Also called the Preparatory Step
This reaction occurs as the pyruvate
enter the matrix of the mitochondria
Pyruvate Oxidation


As the pyruvate enter the mitochondria
each has a carbon removed and coenzyme A added
Produced in the Prep. Step
• 2 NADH (go to ETC)
• 2 CO2 (diffuse out of mitochondria and cell)
Pyruvate Oxidation
Cytoplasm
------------------------------
Matrix of the
mitochondria
------------------------------
Aerobic Respiration

For each glucose metabolized the
Preparatory Step makes
• 2 NADH - go to ETC
• 2 CO2 - diffuse out of mitochondria and cell
• 2 Acetyl Co-A - enter into Citric acid cycle
*aka – Krebs cycle
Pyruvate Oxidation Summary
 Where
and when it occurs:
 Substrate:
 End Product:
 Also made:


___________
___________
Pyruvate Oxidation Summary
Where and when it occurs: Occurs as
pyruvate enter mitochondria, occurs under
aerobic conditions
Substrate: 2 Pyruvate (3C)
End Product: 2 Acetyl-CoA (2C)
Also made:


2 CO2
2 NADH
Citric Acid Cycle = Krebs Cycle


Step 1: Each Acetyl-CoA (2C) joins with
an oxaloacetate (4C) to form a citrate
(6C)
Rest of the citric acid cycle reactions
occur
• Last reaction produces another
oxaloacetate (4C) which joins with the
next available acetyl-co A…….
• ATP, NADH, FADH2, and CO2 are
made in these reactions….see board
CoA
Acetyl CoA
CoA
2 carbons enter cycle
Oxaloacetate
Citrate
NADH
 H
CO2
NAD
CITRIC ACID CYCLE
leaves
cycle
NAD
Malate
NADH
ADP
FADH2

P
ATP
Alpha-ketoglutarate
FAD
CO2
Succinate
NADH
 H
NAD
leaves
cycle
 H
 In
the Krebs cycle, the metabolism of
2 pyruvates made from a single
glucose produces:




2 ATP - by substrate-level phosphorylation
6 NADH - go to ETC
2 FADH2 - go to ETC
4 CO2 - diffuse out of mitochondria and cell
Citric Acid Cycle Summary
 Where
it occurs:
 Starting substrates:
 Last product of pathway:
 Also made (in total for 2 acetyl-CoA entering)
____
____
____
____
CO2
ATP (method made by?)
NADH
FADH2
Citric Acid Cycle Summary

Where it occurs: matrix of mitochondria
 Starting substrates: acetyl-CoA, oxaloacetate
 Last product of pathway: oxaloacetate
 Also made (in total for 2 acetyl-CoA)
4 CO2
2 ATP (by substrate level phophorylation)
6 NADH
2 FADH2
Electron Transport Chain
(ETC)
 ETC
occurs at electron carriers (proteins)
located on the inner membrane of the
mitochondria

Electrons from NADH and FADH2 are passed
from one electron carrier to the next.
• Transfers are called red-ox reactions
• Each transfer releases energy
ETC
 Some
of the electron carriers are also
proton (H+) pumps
• Use the energy released by the red-ox
reactions (e transfer reactions) to pump H+
out of the matrix.
H
H
H
Protein
complex
Intermembrane
space
Inner
mitochondrial
membrane
Mitochondrial
matrix
H
Electron
carrier
H
H
ATP
synthase
FAD
NAD
NADH
H
H
FADH2
Electron
flow
H
H
1
2
O2 2
H
H
H
Electron Transport Chain
ADP
H2O
 P
ATP
H
Chemiosmosis
ETC
 NADH
and FADH2 each transfer 2e and
H+ to a specific ETS protein


Notice -- they do NOT start with the same
ETC protein
In the process are the NADH and
FADH2 oxidized or reduced?
H
H
H
Protein
complex
Intermembrane
space
Inner
mitochondrial
membrane
H
Electron
carrier
H
1
2
O2
ATP
synthase
 2 H
H
Mitochondrial
matrix
H
H
FAD
NAD
NADH
H
H
FADH2
Electron
flow
H
H
Electron Transport Chain
H2O
ADP
 P
ATP
H
Chemiosmosis
ETC
 H+ from
the matrix follow the electrons into
proton pumps
 At each proton pump the H+ are pumped
out of the matrix into the intermembrane
space

This creates an electrical & chemical gradient
• Form of _________ energy
ETC
 Electron
transfers stop when the last ETC
protein transfers the 2e to oxygen which:


Joins with H+ to form water
The last electron acceptor is oxygen and
water forms. (know this)
Chemiosmosis and ATP Synthesis
 ….back
to the H+ ions pumped into the
intermembrane space

The potential energy of H+ gradient is
drive ATP synthesis at the enzyme ATP
synthase
ETC and ATP Synthesis
 The
enzyme ATP synthase is embedded
in the inner membrane of the mitochondria
flow of H+ through this enzyme
releases energy and this energy is used to
make ATP .
 The
Chemiosmosis and ATP Synthesis
 This


method of making ATP is called
Oxidative phosphorylation
Also referred to as chemiosmosis
Chemiosmosis and ATP Synthesis
 The



more H+ pumped out of the matrix
The steeper the gradient
the more potential energy
the more ATP that can be made by ATP
synthase
ETC and ATP Synthesis
 Each
NADH made in the mitochondria
results in enough H+ being pumped out of
the matrix to make 2.5 ATP.
FADH2 results in enough H+ being
pumped out of the matrix to make 1.5
ATP.
 Each
NADH from Glycolysis
 The
NADH made in glycolysis must enter
the matrix in order to deliver their electrons
to the ETC
 How
they “enter” the mitochondria
depends upon the cell type.
NADH from Glycolysis
 In
most cells the 2 NADH made in
glycolysis pass their electrons and H+ to
FAD in the matrix making:

2 FADH2 -- take the electrons and H+ to the
ETC where a total of ____ ATP are made
NADH from Glycolysis
 In
liver, heart, and kidney cells the 2
NADH made in the cytoplasm pass their
electrons and H+ to NAD+ in the matrix
making:

2 NADH -- which take the electrons and H+ to
the ETC where a total of ____ ATP are made
or 2 NADH
ATP Synthesis Summary
 Glycolysis


____ ATP (net) (method?)
____ NADH  ____ ATP (most cells)
 Preparatory


step
____ ATP
_____ NADH  ____ ATP (method?)
ATP Synthesis Summary
 Krebs
Cycle
____ ATP (method?)
____ NADH  ____ ATP (method?)
____ FADH2  ____ ATP (method?)
NADH and FADH2 Summary
Glycolysis  2 NADH
• Made in the cytoplasm
• How they enter the mitochondria depends upon
the type of cell
Preparatory Step  2 NADH
Kreb’s Cycle  6 NADH and 2 FADH2
Fermentation
 Under
anaerobic conditions the products
of glycolysis enter fermentation reactions.

All fermentation reactions occur in the
cytoplasm.
Fermentation
 The
purpose of all types of fermentation is
to regenerate NAD+ so that glycolysis can
continue.
Fermentation



Cell’s have a limited supply of NAD +
Under aerobic conditions the cell’s major
source of NAD+ is the first step of the ETC
Under anaerobic conditions the Krebs cycle
and ETC stop
• As a result NAD+ are no longer made in the
mitochondria.
Fermentation
 The
two most common forms of
fermentation are:


Lacate fermentation
Alcoholic fermentation
 Which
type of fermentation occurs
depends upon the organism.
Lactate Fermentation
 Lactate


fermentation occurs in:
Humans and all other animals
Many bacteria
Lactate Fermentation
2 Pyruvate* (3C)
2 NADH
2 NAD+  reused in glycolysis
2 Lactate* (3C)
* Also called: pyruvic acid and lactic acid
Lactate build up in the cell results in:
 Increased



blood supply to the area, which:
Blood brings oxygen
Blood “washes” out the lactate
Lactate is taken to the liver where it is
converted back to pyruvate (called the Cori
cycle)
• Too much lactate in the blood can cause acidosis
 Muscle
cramps if the lactate levels get too
high occurs - painful
Alcoholic Fermentation
 Alcoholic

fermentation occurs in:
Yeast (a fungus)
• used in making alcoholic beverages and “yeast”
breads

Many bacteria
• Including those used to make Swiss cheese
Alcoholic Fermentation
2 Pyruvate (3C)
__________
2 Acetaldehyde (2C)
2 NADH
2 NAD+ - reused in glycolysis
2 Ethanol (2C)
Alcoholic Fermentation
 Ethanol
(alcohol) builds up in the cell
 When it reaches too high a level it
denatures the cell’s proteins.


This results in cell death!
Wild yeasts die at 4% alcohol, wine making
yeasts die at 14% alcohol.
Alcoholic Fermentation
Reactions cannot be reversed.

Remember, the lactate fermentation reaction
is reversible
• Lactate can be converted back to pyruvate in the
liver, not in the cell it’s made in
 This
is the end of the slides needed.
 The slides that follow are slides that give
an overview of concepts related to the
ETC.
Electron Transfers and Energy
 Electron
transfer reactions are called
oxidation reduction reactions



Oxidation – loss of electron(s)
Reduction – gain of electron(s)
H+ often follow the electrons
Electron Transfers and Energy
 ALL
cells use the transfer of electrons and
H+ to capture some of the energy stored in
chemical bonds

Energy is temporarily stored in NADH and
FADH2
• The stored energy is then used to make ATP
Electron Transfers and Energy
 NAD+
 FAD


+ H + + 2 e  NADH
+ 2 H+ + 2 e  FADH2
Is the NAD+ oxidized or reduced in this
reaction?
In general the reduced molecule is of greater
energy due to the added energy of the
electrons
Electron Transfer Chains
 In
mitochondria and chloroplasts there are
electron transfer chains embedded in the
inner membranes


The passage of the electrons from electron
transfer protein to protein results in creation of
an electrochemical gradient
This gradient is a form of stored energy and
can be used to make ATP
Electron Transfer Chains
 In

mitochondria:
NADH and FADH2 give electrons and H+ to
specific proteins on the inner membrane of
the mitochondria
• this releases their stored energy

H + follow the electrons into the proteins
Electron Transfer Chains


Energy given off by the electron transfers is
used to pump H+ across the inner membrane
into the outer compartment
This creates a chemical/electrical gradient
• A form of potential energy
• An ATP-synthesizing enzyme uses this energy to
make ATP