Download 2. Pyruvate Oxidation

Cellular Respiration:
Harvesting Chemical Energy

Aerobic metabolism
(oxygen is present)


When enough oxygen reaches
cells to support energy needs
Anaerobic metabolism
(oxygen is not present)

When the demand for oxygen
outstrips the body’s ability to
deliver it
Sunlight
energy
Ecosystem
Photosynthesis
(in chloroplasts)
Glucose
Oxygen
Carbon dioxide
Water
Cellular respiration
(in mitochondria)
for cellular work
Heat energy
Cellular Respiration



is the step-wise release of energy from
carbohydrates and other molecules
Energy from these reactions is used to synthesize
ATP molecules
This is an aerobic process—it requires oxygen
Don’t mix up Cellular Respiration and Respiratory
Breathing!

Cellular respiration and breathing are closely
related


Cellular respiration requires a cell to exchange
gases with its surroundings
Breathing exchanges these gases between the
blood and outside air
Breathing
Lungs
Muscle
cells
Cellular
respiration
Figure 6.4
The Overall Equation for Cellular Respiration

A common fuel molecule for cellular respiration
is glucose

Glucose
This is the overall equation for what happens
to glucose during cellular respiration
Oxygen
Carbon
dioxide
Water
Energy
Catabolic or anabolic?
The Role of Oxygen in Cellular Respiration

During cellular respiration, hydrogen and its
bonding electrons change partners


Hydrogen and its electrons go from sugar to
oxygen, forming water
Why?
 Oxygen is much more electronegative than
carbon (it’s a good tief of electrons!)
The Reactions We’ll See

1.
2.
3.
4.
5.
There are several types of reactions that we will
encounter along the way.
REDOX – Electrons being taken from one and added
to another.
Phosphorylation/Dephosphorylation – The
adding/removal of a phosphate group (PO4).
Carboxylation/Decarboxylation – The
adding/removal of a carbon.
Hydration/Dehydration - The adding/removal of a
water molecule (H2O).
Isomerization – Making a molecule into its isomer –
same parts, different arrangement.
Review

The loss of electrons (or hydrogen) during a
redox reaction is called ________________

The acceptance of electrons during a redox
reaction is called _____________
LEO
GER
Oxidation
[Glucose loses electrons (and hydrogens)]
Glucose
Oxygen
Carbon
dioxide
Water
Reduction
[Oxygen gains electrons (and hydrogens)]
Breakdown of Cellular Respiration
Four main parts (reactions):
1. Glycolysis (splitting of sugar)
 cytosol, just outside of mitochondria.
2. Pyruvate Oxidation
 migration from cytosol to matrix.
Breakdown of Cellular Respiration
3. Krebs Cycle (Citric Acid Cycle)
 mitochondrial matrix
4. Electron Transport Chain (ETC) and Oxidative
Phosphorylation
 Also called Chemiosmosis
 inner mitochondrial membrane
Goals of Cellular Respiration

To break the bonds between the six carbon atoms in
glucose (this creates 6 molecules of carbon dioxide)

To move hydrogen atom electrons from glucose to oxygen
to form 6 molecules of water

While the various reactions take place, free energy is
released from the bonds as they break; thus the cell works
to trap as much of the released free energy in the form of
ATP
A Road Map for Cellular Respiration
Cytosol
Mitochondrion
High-energy
electrons
carried
mainly by
NADH
High-energy
electrons
carried
by NADH
Glycolysis
Glucose
2
Pyruvic
acid
Krebs
Cycle
Electron
Transport
Substrate-Level Phosphorylation

ATP is formed
directly when an
enzyme transfers
a phosphate
group from a
substrate to ADP
Oxidative Phosphorylation

Different from substrate-level phosphorylation

ATP is formed INDIRECTLY via other redox
reactions (i.e. NAD+ and FADH)
Oxidative Phosphorylation NAD+ and FAD
•Oxidation-reduction reactions use NAD+ or FADH
(nicotinamide adenine dinucleotide, flavin
adenine dinucleotide) which are coenzymes
(A molecule that binds to an enzyme and is essential for its
activity, but
is not permanently
alteredNAD+
by the accepts
reaction). two
•When
a metabolite
is oxidized,
NAD+ electrons
and FAD can
be used
over andion
over(H+)
again.
plus
a hydrogen
andThey
NADH
are likeresults,
trucks that
carry and
deliver
where
its
leaving
a free
H+ energy
ion in the
cell
needed.
- NAD+ is reduced to NADH
•Conversely, NADH can also reduce a metabolite
by giving up electrons
- NADH is oxidized to NAD+
Oxidative Phosphorylation NAD+ and FAD
Did you Know?

NAD+ is a derivative of vitamin B3 (also known
as niacin or niacinamide)
An Overview
Glycolysis = ‘Sugar-breaking’
Where?
• Occurs in the cytoplasm
What?
• It is the breakdown of glucose
Start with: glucose
End with: two pyruvate molecules.
• Glycolysis is universally found in all organisms.
• Glycolysis does not require oxygen (anaerobic).
The Wonderful World of the Mitochondria
2. Pyruvate Oxidation

Occurs when Oxygen is present
(aerobic)

Mitochondrial
2 Pyruvate (3C) molecules are
Matrix
transported through the mitochondria
membrane to the matrix and is converted
to 2 Acetyl CoA (2C) molecules
Cytosol
2 CO2
C
C
C
Matrix
C-C
2 Pyruvate
2 NAD+
2NADH
2 Acetyl CoA
Pyruvate Oxidation
•This stage connects glycolysis to the Krebs
cycle
•Pyruvate is converted to acetyl CoA and CO2 is
released
•During this oxidation reaction, NAD+ is
converted to NADH + H+
•This reaction occurs twice per glucose
molecule
Review: Cellular Respiration
Glycolysis
Glucose
Pyruvate
Pyruvate Oxidation
Pyruvate
Acetyl-CoA
Acetyl-CoA
ATP
Krebs Cycle
Pyruvate Oxidation
Cytoplasm
Mitochondrion Matrix
O
O
O
C
Pyruvate Transport
C
O Protein
H
C
H
H
Krebs Cycle
Redox
Reaction
O
O
C
Pyruvate
C
Decarboxylase
Acetic Acid
H Group
C
H
CoA
H
C
O
Acetyl-CoA
H C
H
H
H
H
NAD+
S
Reduced
NADH + H+
S
CoA
Summary of Pyruvate Oxidation





Pyruvate oxidation occurs twice to use one
molecule of glucose
One molecule of NADH produced
One molecule of CO2 is released
The product of pyruvate oxidation is acetylCoA
In cellular respiration, acetyl-CoA enters
Krebs Cycle to eventually produce molecules
of ATP