Transcript Cellular Respiration

Chapter 7
Cellular Respiration
Mighty Mitochondria
http://www.ageofautism.com/2008/04/dr-blaylock-on.html
Vocabulary Pretest Section 1
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Cellular Respiration
Pyruvic Acid
NADH
Anaerobic
Aerobic Respiration
Glycolysis
NAD+
Fermentation
Lactic Acid Fermentation
Alcoholic Fermentation
Kilocalorie
A. Does not require oxygen
B. Anaerobic breakdown of glucose
into pyruvic acid
C. Breakdown of carbohydrates
in the absence of oxygen
D. Occurs in muscle cells during
periods of strenuous exercise
E. A unit of energy equal to 1000 calories
F. Occurs when yeast breakdown sugar
G. Results in large amounts of ATP
(uses oxygen)
H. An electron carrier
I. The reduced form of NAD+
J. Three carbon compound produced
by glycolysis
K. The process by which cells obtain energy
from carbohydrates
Answer Key
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Cellular Respiration
Pyruvic Acid
NADH
Anaerobic
Aerobic Respiration
Glycolysis
NAD+
Fermentation
Lactic Acid Fermentation
Alcoholic Fermentation
Kilocalorie
K
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I
A
G
B
H
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D
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Cellular Respiration
• Cellular Respiration —the process by which cells
get energy from carbohydrates; oxygen combines
with glucose to form water and carbon dioxide
C6H12O6 + 6O2
6CO2 + 6H2O + energy (ATP)
• The equation is a simple summary of a very
complex process.
• The overall purpose is to convert food into energy
by breaking down organic fuel molecules.
• When oxygen is present during this process it is
called aerobic respiration ( which is the most
efficient).
• If no oxygen is present it is called anaerobic
respiration (which is much less efficient).
• Both types (aerobic and anaerobic) start with a
process called glycolysis.
Glycolysis
• Glycolysis —first stage of cellular respiration.
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Glycolysis means “glucose splitting”
Occurs in the cytosol
No oxygen is needed
Glucose molecules are broken down into two
3-carbon molecules of pyruvic acid
Pyruvic acid is then used in the Krebs Cycle (which is
the second stage of aerobic respiration)
Specific enzymes are needed
2 molecules of ATP are produced
2 molecules of NADH (an electron carrier molecule)
are produced
4 stages of Glycolysis
1. 2 phosphates are added to glucose. They are
released from 2 molecules of ATP (changing it to
ADP).
2. The glucose molecule (with its 2 phosphates) is
then split into 2 molecules of G3P
(glyceraldehyde 3-phosphate)
2 G3P molecules
G3P
G3P
3. Each G3P gets oxidized by adding another phosphate
group. Also, electrons and hydrogen atoms are
removed from the 3C molecule. They are added to
2 molecules of NAD+ (nicotinamide adenine
dinucleotide) to create 2 NADH and 2 H+. These
will go to the electron transport chain later on.
4. The phosphate groups are now removed from
each molecule creating 2 molecules of pyruvic
acid (3C). The phosphates are added to 4
molecules of ADP producing 4 ATP molecules.
G3P
G3P
http://science.halleyhosting.com/sci/ibbio/cellenergy/resp/respirnotes/glycolysis2.htm
Summary of Glycolysis
• Basically:
▫ One glucose (6C) is broken into two molecules of
pyruvic acid (3C)
▫ If oxygen is available, the pyruvic acid will move into
the mitochondria and aerobic respiration will begin.
▫ 4 ATP molecules are produced. Two are used to
break apart the next glucose molecule and keep
glycolysis going.
▫ This leaves a net yield of 2 ATP molecules for
use by the cell.
▫ Two NAD+ are converted into 2 NADH and 2H+.
These go to Electron Transport.
Efficiency of Glycolysis
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Measured in kilocalories (kcal)
One kilocalorie equals 1,000 calories (cal)
Complete oxidation of glucose releases 686 kcal
Production of ATP absorbs 7 kcal
2ATP are produced from every glucose molecule broken
down by glycolysis
• The efficiency is therefore calculated by the following
formula:
Efficiency of
glycolysis
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Energy required to make ATP
Energy released by oxidation of glucose
2 x 7 kcal
686 kcal
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100% = 2%
Section 2 Vocabulary Pretest
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Mitochondrial matrix
Acetyl CoA
Krebs Cycle
Oxaloacetic Acid
Citric Acid
FAD
A. Biochemical pathway that
generates ATP
B. 6 carbon compound used in
the Krebs cycle
C. Electron acceptor: Flavin
adenine dinucleotide
D. The space inside the inner
membrane of a mitochondrion
E. 2 carbon compound made
from pyruvic acid
F. 4 carbon compound used in
the Krebs cycle
Answer Key
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Mitochondrial matrix
Acetyl CoA
Krebs Cycle
Oxaloacetic Acid
Citric Acid
FAD
D
E
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F
B
C
Aerobic Respiration
• In most cells, the pyruvic acid produced in
glycolysis enters the pathway of aerobic
respiration.
• This pathway produces nearly 20 times as
much ATP as is produced by glycolysis alone and
is therefore the most efficient.
• Oxygen must be available for this to happen.
• There are two major stages: The Krebs Cycle
and the Electron Transport Chain
Intermediate Step
• Aerobic Respiration takes
place in the mitochondria
of the cell.
• Before the Krebs Cycle can
begin, each of the two pyruvic
acid molecules must be
converted.
• The pyruvic acid enters the
mitochondrial matrix
(space inside the inner
membrane of the
mitochondria)
• It reacts with a molecule
called coenzyme A to form
Acetyl Coenzyme A
(acetyl CoA)
http://www.methuen.k12.ma.us/mnmelan/Respiration%20L2.htm
• Notice that acetyl CoA only has 2
carbon atoms.
• The lost carbon atom is released in a
molecule of CO2
• Also, this reaction reduces a molecule
of NAD+ to NADH + H+
• This happens to both molecules of
pyruvic acid
• Therefore, the end result is:
▫ 2 molecules of Acetyl CoA for the
Krebs cycle
▫ 2 molecules of CO2 to be released
▫ 2 molecules of NADH for electron
transport.
http://www.methuen.k12.ma.us/mnmelan/Respiration%20L2.htm
The Krebs Cycle
• The Krebs Cycle (named for Hans Krebs) is a
biochemical pathway that breaks down acetyl CoA.
• Two turns of the Krebs Cycle produce:
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2 ATP molecules
4 CO2 molecules
6 NADH molecule
2 FADH2 molecules
5 Steps of the Krebs Cycle
1. Acetyl CoA (2 carbon compound) combines
with Oxaloacetic acid (4 carbon compound) to
produce Citric Acid (6 carbon compound).
This regenerates and releases CoA.
2. Citric acid releases a CO2 molecule and is
oxidized by losing a hydrogen atom. This forms
a new 5 carbon compound. The hydrogen atom is
transferred to NAD+, reducing it to NADH.
3. The 5 carbon compound now releases a CO2
molecule and a hydrogen atom. This creates a 4
carbon compound and the hydrogen atom is
again added to NAD+, reducing it to NADH. A
molecule of ATP is also synthesized from ADP.
4. The 4 carbon compound releases a hydrogen
atom which is used to reduce FAD (Flavin
Adenine Dinucleotide) to FADH2. (FAD, like
NAD+ also accepts electrons during redox
reactions.
5. The 4 carbon compound now releases a
hydrogen atom to regenerate oxaloacetic acid,
which can be used to start the Krebs cycle over
again. The hydrogen atom released again
reduces NAD+ to NADH.
http://www.methuen.k12.ma.us/mnmelan/Respiration%20L2.htm
Review of the Gylcolysis and the Krebs
Cycle
• In Glycolysis, one glucose molecule produces two
pyruvic acid molecules, which can then form two
molecules of Acetyl CoA.
• Both of the Acetyl CoA molecules enter the Krebs
Cycle creating two turns of the cycle.
• This produces 6 NADH, 2 FADH2, 2 ATP and 4
CO2 molecules (waste product that diffuses out of
the cell).
• The 6 NADH and 2 FADH2 molecules drive the
next stage of aerobic respiration—the Electron
Transport Chain.
Electron Transport Chain
• The Electron Transport Chain, linked with
chemiosmosis makes up the second stage of
aerobic respiration.
▫ Electrons are transferred from one molecule to
another by several electron carrying molecules
located in the membrane of the mitochondria.
▫ All steps occur in the cristae (inner membrane)
▫ Follow the steps in the diagram:
http://www.methuen.k12.ma.us/mnmelan/Respiration%20L2.htm
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ATP is produced when NADH and FADH2 release hydrogen atoms (this
regenrates NAD+ and FAD, which return to the Krebs Cycle to be reused) Each
hydrogen atom gives up electrons and hydrogen ions (H+)
The electrons released are at a high energy level and move down the chain. They
lose energy as they move from molecule to molecule.
The lost energy is used to pump the hydrogen ions from the matrix to the other
side of the membrane.
A concentration gradient of hydrogen ions across the membrane is created.
H+ are pumped back in by ATP synthase embedded in the membrane.
ATP is made from ADP and phosphates.
Oxygen is the final electron acceptor and also accepts H+ ions to make water.
Efficiency of Cellular Respiration
• Through Aerobic Cellular Respiration, a
maximum of 38 ATP molecules can be
produced from one glucose molecule.
▫ 2 from Glycolysis
▫ 2 from Krebs cycle
▫ 32-34 from the Electron Transport Chain
• To see how we get 38, follow
along….
▫ 2 ATPs directly from
glycolysis
▫ 2ATPs directly from
Krebs cycle
▫ Each NADH can generate
3ATPs from electron
transport (30 total)
▫ Each FADH2 can generate
2ATPs from electron
transport (4 total)
http://www.methuen.k12.ma.us/mnmelan/Respiration%20L2.htm
• The actual number of ATP molecules generated through
Aerobic Respiration varies from cell to cell. (36-38)
• Most eukaryotic cells produce only 36 molecules per
glucose molecule because the active transport of NADH
through a cell membrane uses up some ATP.
• When 38 ATP molecules are generated the efficiency is
calculated as follows:
Efficiency of
Cellular Respiration
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Energy required to make ATP
Energy released by oxidation of glucose
38 x 7 kcal
686 kcal
x 100%
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= 39%
This is 20 times more efficient than glycolysis alone !!
Anaerobic Respiration
• If no oxygen is present, the Krebs Cycle and
Electron Transport Chain are not utilized.
• The cell must have a way to keep glycolysis going.
• Glycolysis would stop without a cellular process that
recycles NAD+ and NADH.
• Without such a process, glycolysis would quickly use
up all the NAD+ in the cell.
• Glycolysis and ATP production would stop and the
cell would die.
• Fermentation to the rescue 
Fermentation
• Fermentation is the chemical pathway that
recycles NAD+ in the absence of oxygen. It keeps
glycolysis going. No additional ATP is made.
Therefore, you still have the 2% efficiency rate
for energy release.
• Two types of fermentation:
▫ Lactic Acid Fermentation
▫ Alcoholic Fermentation
Lactic Acid Fermentation
• Pyruvic acid is converted by a specific enzyme into
lactic acid.
• Two hydrogen atoms from NADH and H+ are transferred
to pyruvic acid to form the lactic acid molecule.
• NADH is oxidized to NAD+ and reused to keep glycolysis
going.
http://www.methuen.k12.ma.us/mnmelan/Respiration%20L2.htm
• Lactic acid fermentation
occurs in foods such as
yogurt and cheese as well
as certain animal cells.
• Occurs mostly in muscle
cells during hard exercise.
▫ Muscle cells use up oxygen
too fast and switch from
aerobic to anaerobic
respiration.
▫ Lactic acid builds up
reducing the cells ability to
contract. This causes
fatigue, pain and cramps.
http://www.burnthefatchallenge.com/wp/wpcontent/uploads/2011/01/treadmill-300x300.gif
Slow down!!! Allow the lactic
acid time to diffuse back into the
blood stream and to the liver
where it is converted back into
pyruvic acid.
Alcoholic Fermentation
• Converts pyruvic acid to carbon dioxide and ethyl
alcohol.
• NAD+ is recycled in the same manner as before.
http://www.methuen.k12.ma.us/mnmelan/Respiration%20L2.htm
• Bakers use the alcoholic
fermentation of yeast to
make bread.
• CO2 is produced and
trapped in the dough,
causing it to rise.
• When the dough is
baked, yeast cells die
and the alcohol
evaporates.
You can’t get drunk from eating
bread !!!
Click to reveal
COMPARING PHOTOSYNTHESIS AND CELLULAR RESPIRATION
PHOTOSYNTHESIS
RESPIRATION
FUNCTION
Production of Glucose
Oxidation of Glucose
LOCATION
chloroplasts
mitochondria
REACTANTS
6CO2 + 6H2O
C6H12O6 + 6O2
PRODUCTS
C6H12O6 + 6O2
6CO2 + 6H2O
EQUATION
light
6CO2 + 6H2O
C6H12O6 + 6O2
C6H12O6 + 6O2
6CO2 + 6H2O +ATP