Unit C:
Section 7.1-7.2
Cellular Respiration Releases
Energy from Organic Compounds
Overview of Cellular Respiration
• Cellular respiration releases energy by oxidizing glucose
into carbon dioxide, which means that electrons are
removed from glucose, releasing energy and producing
carbon dioxide and water.
• Cellular Respiration occurs in the cytoplasm and the
mitochondria in plant cells.
• Cellular respiration begins with a process called
glycolysis or “the splitting of sugars.”
• Following glycolysis, cellular respiration can be carried
out in both aerobic (with oxygen) and anaerobic
conditions (without oxygen).
Glycolysis
• Glycolysis is an anaerobic process, which
means that it can proceed without oxygen.
• It occurs in the cytoplasm, just outside the
mitochondria.
• The role of glycolysis is to split glucose
into two, three carbon compounds called
pyruvate.
Glycolysis
• Glycolysis begins with a single glucose
molecule.
• 2 ATP molecules are used to break down
the glucose molecule into two intermediate
3 carbon compounds.
• From the two intermediate 3 carbon compounds,
a series of reactions occur to produce two
identical 3 carbon compounds called pyruvate.
• During the conversion from the intermediate
molecules to pyruvate, 4 ATP’s and 2 NADH’s
are produced.
• Later the NADH’s are used to convert FAD into
FADH2 (flavin adenine dinucleotide), another
high energy molecule.
Final Products of Glycolysis
• 2 ATP’s ( 4 produced – 2 used = 2)
• 2 FADH2
• 2 pyruvate
The 3 Fates of Pyruvate
•
Once pyruvate is produced, it can
proceed in 3 different ways, depending
on the presence or absence of oxygen.
1) The Kreb’s Cycle (aerobic)
2) Lactate Fermentation (anaerobic)
3) Ethanol Fermentation (anaerobic)
Prep for
The Kreb’s Cycle
• When sufficient oxygen is present in the cell, pyruvate is
transported into the matrix of the mitochondria in
preparation for the Kreb’s Cycle.
• Before pyruvate can enter The Kreb’s Cycle it must
undergo one reaction.
• A molecule called Coenzyme A (Co A) reacts with
pyruvate (3C) to produce acetyl coenzyme A (2 C) and
carbon dioxide (1C).
• During this process one molecule of NAD+ is reduced to
NADH.
The Kreb’s Cycle
(Aerobic Cellular Respiration)
Step 1:
• Acetyl CoA (2C) combines with a 4C starting
compound to produce a 6C compound.
Step 2:
• The 6C compound donates an electron to NAD+,
reducing it to NADH.
• This produces a 5C molecule and a free
molecule of CO2 .
Step 3:
• This 5C molecule donates another
electron to NAD+, reducing it to NADH as
well as adds a phosphate to ADP to form
ATP.
• This produces a 4C compound and
another free molecule ofCO2 .
Step 4:
• The 4C compound reduces FAD to
FADH2 and NAD+ to NADH.
• This recreates the 4C starting molecule for
the Kreb’s cycle, so the process can
continue.
Final Products for
The Kreb’s Cycle
(including preparation)
•
•
•
•
4 NADH
1 FADH2
1 ATP
2 CO2
x2=
8 NADH
2 FADH2
2 ATP
4 CO2
** Because glucose breaks into 2 pyruvate
molecules, the Kreb’s cycle must happen
twice to fully break down glucose.
The Electron Transport System and
Chemiosmosis
• The NADH and FADH2 molecules
produced during aerobic cellular
respiration, transport hydrogen ions and
their accompanying electrons to an
electron transport system.
• Just like in photosynthesis the electrons
are passed down the chain, losing energy
with each transfer.
• The energy released is used for pumping
hydrogen ions out of the inner matrix into
the intermembrane space of the
mitochondria.
• The hydrogen ions re-enter the inner
matrix through ATP synthase, which uses
the energy in the concentration gradient to
bind a phosphate group to ADP, forming
ATP. This process is called chemiosmosis
just like in photosynthesis
• The final step on the electron transport
system passes the electron to a oxygen
atom.
• The oxygen accepts the electrons and
hydrogen ions to form water.
Overall Production of ATP
1 NADH = 3 ATPS
1 FADH2 = 2 ATPS
Glycolysis = 2 ATP
2 FADH2
 2 ATP
 4 ATP
Prep for Kreb’s = 2 NADH  6 ATP
(2 pyruvates)
Kreb’s Cycle = 6 NADH
(2 cycles per one
2 FADH2
glucose molecule)
2 ATP
 18 ATP
 4 ATP
 2 ATP
= 36 ATP