Chapter 7:
Energy for
Cells
Cellular Respiration
ATP molecules are produced during cellular respiration with the help
of the mitochondria
Respiration is the reverse of photosynthesis
In photosynthesis, CO2 is reduced to make carbohydrate
In respiration, carbohydrate is oxidized along with O2 consumption and
CO2 and H2O are formed as by-products
Phases of Glucose Breakdown
Glycolysis: the breakdown of glucose to 2
molecules of pyruvate in the cytoplasm
2 ATP invested, 4 ATP and 1 NADH
produced
Preparatory reaction: pyruvate is broken
down to a 2-carbon acetyl group carried
by coenzyme A (CoA)
Occurs in the matrix of mitochondria
NADH and CO2 produced
Citric Acid Cycle: takes place in the
matrix of mitochondria
1 spin produces 3 NADH, 1 FADH2,
1 GTP and 2 CO2
ETC: NADH and FADH2 give up
electrons to the chain in the cristae of
mitochondria
This energy is used for the
production of ATP
O2 is the final electron acceptor and
H2O is produced
Glucose is broken down slowly so that
energy is not lost as heat
Coenzymes are nonprotein helpers that
assist in carrying out oxidation during
cellular respiration
Coenzymes NAD+ and FAD receive
hydrogen atoms and become NADH and
FADH2
Glycolysis
Glycolysis takes place within the cytoplasm
outside the mitochondria
Glucose, a C6 molecule, is broken down into 2
pyruvates, C3 molecules
2 steps:
In the energy-investment step, 2 ATPs are
used to activate the substrates
In the energy-harvesting step, substrates are
oxidized by the removal of hydrogen atoms
o
-
2 NADH and 4 ATP are produced
-
2 pyruvates are the end product of
glycolysis
-
If O2 is available, pyruvate will move into
the mitochondria
-
If no O2 is available, pyruvate is reduced
to lactate
What is the net gain of ATP for glycolysis?
Glycolysis
Inside the Mitochondria
Preparatory Reaction:
Occurs in the mitochondrial matrix
This reaction occurs 2X per glucose
Pyruvate is oxidized, CO2 is given off
NAD+  NADH
C2 acetyl group will attach to
coenzyme A (CoA) to form acetylCoA
Products: 2 CO2, 2 NADH, 2 acetylCoA
Citric Acid Cycle:
Occurs in the mitochondrial
matrix
Acetyl-CoA is joined to a C4
molecule to make a C6
citrate molecule
The acetyl group is oxidized
and the CO2 is given off
NAD+ and FAD accept
hydrogen atoms to make
NADH and FADH2
Substrate-level ATP synthesis
occurs resulting in
GTPATP
The cycle turns 2X
Inside the Mitochondria
Electron Transport Chain
The ETC is located in the cristae of the
mitochondria
The hydrogen atoms attached to NADH and
FADH2 consist of an electron (e-) and a
hydrogen ion (H+)
The ETC accepts only e- and not H+
A series of oxidation-reduction occurs as the
electron pairs are passed form carrier to carrier
Energy is released and captured for ATP
production
O2 is the final electron acceptor because it
attracts electrons more than the carriers of the
chain
O2 is combined with H+ to form H2O
Electrons from NADH make 3 ATP molecules,
electrons from FADH2 make 2 ATP
NAD+, FAD , and ADP are recycled
ATP synthase carried out ATP synthesis
in the inner mitochondrial membrane
(cristae of the membrane)
H+ gradient is created as a result of
oxidation/reduction
The flow of H+ through the ATP
synthase complex causes a
conformational change and the
synthase produces ATP
Energy Yield from Glucose
Metabolism
Per glucose:
•
•
•
•
•
Net gain of 2 ATP from
glycolysis
2 ATP from citric acid
cycle
10 NADH  30 ATP
2 FADH2  4 ATP
Total maximum number
of ATP is 38 ATP
Alternative Metabolic
Pathways
Proteins, Fats and Oils can
be used to make ATP
Glycerol is a carbohydrate
and can enter glycolysis
Fatty acids can be broken
down to acetyl groups and
enter the citric acid cycle
The hydrocarbon backbone
from an amino acid can
enter cellular respiration at
the pyruvate, acetyl-CoA, or
the citric acid cycle
Fermentation
When O2 is not available,
fermentation takes place
Fermentation is the anaerobic
breakdown of glucose and the
production of 2 ATP per glucose
Pyruvate formed by glycolysis accepts 2
hydrogen atoms and is reduced to
lactate
Why is this beneficial?
o
Fermentation is a way to produce ATP
when O2 is in limited supply
o
Although fermentation results in only 2
ATP, it still provides a quick burst of
ATP energy for short-term, strenuous
muscular activity
Microorganisms and
Fermentation
Bacteria use fermentation
to make organic acid,
alcohol, and CO2
Yeasts generate ethyl
alcohol and CO2
Yeasts are used to
ferment grapes for wine
production
The desired product is
ethyl alcohol