Download 19 Oxidative Phosphorylation-Electron Transport A

19 Oxidative Phosphorylation-Electron Transport
A/P Biology Pages 172-182
Name: ________________________ Date: _______________ Period: __________
If we take a look at the over-all picture of Glycolysis- we can see that this process
that requires no oxygen, releases a few high energy products (ATP/NADH/pyruvate):
When we look at the over-all picture of the Krebs cycle we see more high energy
products being produced:
The object is to capture as much energy as possible (as ATP) from these high energy
products.
Electron Transport is a construct of a
series of proteins embedded in the
mitochondrial membrane. The
mitochondrion looks like this in a simplistic
picture:
Page 2 (Cont. #19)
The key is looking at this rather complex organelle up close-at the level of the “matrix”
and the “inter-membrane space”.
Embedded in the “inner
membrane” are a number of protein
complexes that are used to step down the
energy provided by either NADH or
FADH2. What is meant by this “stepdown” is the relative energy from the
proton/electron donor (NADH/FADH2)
and the final acceptor of those protons
and electrons, oxygen.
The diagram to the left is merely
to show the step-down of
the amount of energy the
electrons have allowing
the protons to be expelled
from the matrix and
shunted to the “inter
membrane” space. The
“*” denotes when the
electron loses enough
energy to couple the
movement of a proton
from the matrix to the
inter-membrane space.
The final acceptor of the
“formally” excited
electron is oxygen. A
constant supply of
oxygen (by breathing) is
necessary for each and
every cell to allow the
diffusion of oxygen into
the cell and then into the
mitochondria for THIS
specific purpose! If we deprive the cell of oxygen- the electron transport backs up and
halts the production of ATP for each and EVERY mitochondria. This shuts them down.
You can guess that the cell will run out of ATP molecules and shut down as well.
Page 3 (Cont. #19 A/P Biology)
Another view of the relationship of the Krebs Cycle and the electron transport chain
embedded in the “inner-membrane” (see diagram of mitochondria, page 2 of this
handout) of the mitochondria looks like this:
Let us take a closer look
at an artists rendering of
just a small part of this
electron transport:
1.) NADH binds to the
first enzyme complex
called NADH-Q
reductase (also called
“complex 1”) One proton
is pumped out. (see H+)
2.) The electrons are then
transferred to Coenzyme
Q (also called
Ubiquinone). This is
often referred to as
“Complex 2”. One proton is pumped out.
Page 4 (Cont. #19 A/P Biology)
3.) Electrons are transferred from Coenzyme Q to Cytochrome “bc” complex also known
as “Complex 3”.
4.) Electrons are then transferred to Cytochrome “C” which is a peripheral membrane
protein (i.e. it sits on top of the inner membrane on the inter-membrane space side. This
protein is somewhat famous because it is relative easy to study AND because the primary
structure of the protein is “Highly Conserved” throughout many different organisms.
That means that the amino acid sequence in a rat’s mitochondria is strikingly similar to
that found in a human’s mitochondria and mitochondria found in single-celled
eukaryotes.
5.) Cytochrome C transfers its electrons to the Cytochrome oxidase complex (also called
“Complex 4”). The electrons are passed to the matrix where OXYGEN accepts the
electrons and one proton is pumped out.
The pumping of the protons across the membrane establishes a “Proton Gradient” across
the inner membrane. The energy stored in the proton gradient is used to drive the ATP
synthesis reaction as the protons flow back to the matrix through Complex 5 (ATP
synthetases- there are more than one- in fact there are hundreds per mitochondria).
You can see animation of the Glycolytic cycle, Krebs Cycle, and electron transport
pumping synthesis in action by going to: You tube and searching for Glycolysis or
Krebs or Electron Transport and watching/listening to the videos presented!
To summarize the complete oxidative respiration:
Without the presence of oxygen, there can be no receptor for the electrons within the
mitochondrial matrix and the electron transport chain will rapidly shut down. Without a
constant supply of ATP there are NO cells that can sustain function (that is remain
organized in the process of using ATP)! FADH2 does not create as many ATP molecules
Page 5 (Cont. #19 A/P Biology)
compared to NADH because it contributes its hydrogen and electrons at a slightly lower
energy level (to Coenzyme Q (CoQ … see picture pg. 2) than NADH. The proton will
then be donated to Cyctochrome b/c will then follow the same route of electron transport
and proton pumping as NADH. That means there is one less proton being pumped out of
the matrix and into Inter membrane space when FADH2 donates the proton. That equates
to one less ATP molecule being made.
So where does the oxygen come from for the electrons and the protons to combine
with to make water? All organisms (heterotrophs and autotrophs alike) MUST take in
oxygen so that it can be the receptor for the electron in the electron transport IF the
organism HAS mitochondrion! Bacteria and yeast still require a little oxygen to allow
NADH to be oxidized to replenish the necessary high energy compound (NAD+) to allow
glucose to be broken down to pyruvate (see overall picture of Glycolysis – handout #17note NAD+ is necessary to transform glyceraldehydes-3-phosphate to 1,3-bisphosphoglycerate)! Carefully scan the diagram and follow the production of NADH and
then the production of NAD+ after pyruvate is made!
The take-home message here is not to have you memorize these steps, rather
understand the basic flow of high energy compounds as they are produced and degraded,
what “waste products” are formed and how much energy (ATP) is produced over-all.
The act of cellular respiration answers two key questions about life:
1.) Why is it necessary we breathe in OXYGEN? …to accept the electron in the
electron transport chain, and that electron transport chain powers the production
of ATP that runs nearly all reactions that require energy in the cell.
2.) Why is carbon dioxide a waste product and why do we make so much of it?
…you lose all of the carbons of glucose during the breakdown of pyruvate to
acetyl-CoA and acetyl-CoA through the Krebs cycle!
So you see there is a certain conservation of atoms here. Oxygen is taken in and
transformed into water. Sugar is taken in and is released as carbon dioxide and ATP (of
course a lot of heat is lost in this process…but it is the cost of living).
A recent article in Popular Science Magazine (Feb. 2009) entitled “Freezing the
Heart to Save Lives” brings the dynamics of oxygen as a required molecule not only for
its position to accept the final electron in the electron transport chain, but also its toxicity
if the cell is without oxygen for a while. If we examine what happens to a heart attack
patient or a victim of drowning, we see that by some means oxygen does not flow to
individual cells. All the electron transport chains still run at full tilt transferring electrons
to Cytochrome A in every single mitochondrion in every cell of the body! Rescuers or
doctors try to revive the drowning victim or the heart attack patient. What happens? As
soon as oxygen becomes available, every single Cytochrome A molecule tries to release
all of their electrons to a relatively few oxygen molecules creating “free radicals”
(oxygen molecules with extra electrons). As stated in the article, “When oxygen flow
returns, the mitochondria start producing free radicals; other cellular ion levels also go
awry. The injured cells start dying, and in response, the immune system releases
chemicals (sic: interleukins- cell signals to attract more immune response cells) that
worsen the effect. The problem is most pronounced in the heart and the brain, which use
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more oxygen that other organs.” In other words while trying to save someone who has
stopped breathing- you naturally try to restore oxygen to all the cells. If too much time
goes by, the back up in the electron transport chain becomes over-whelming. How are
doctors trying to solve this problem? They cool the body because, “…the mitochondria
and the immune system are not as active at low temperatures.” There is still a lot of
research that needs to be worked out for a standard procedures and reasonable outcomes
for heart attack victims or victims of drowning. The gist of the argument lies in the
absolute requirement for oxygen to accept electrons – and realizing what might happen to
the cell if it is starved of that oxygen for a period of time. Cooling the body (rapidly)
MAY (and seems to) help because it might prevent the build up of electrons in the
electron transport chain. However, the risks of hypothermia to the body as a whole must
be considered as well.
Two more key questions are:
1.) What happens to the water that is produced? and
2.) What happens to the carbon dioxide that is produced as waste?
We will answer these questions as part of the next handouts discussing photosynthesis!
After reading the required text and this handout…answer the following questions here
and on your scan-tron.
_____ 1.) Look at the picture on page 1 of this handout. How many NET ATPs are
produced by glycolysis?
a.) 1 b.) 2 c.) 3 d.) 4 e.) 6
_____ 2.) How many oxygen molecules are required to allow the cell to undergo
glycolysis?
a.) Zero b.) Two c.) Four d.) Six e.) Eight or more
_____ 3.) Each molecule of glucose that undergoes glycolysis produces how many
pyruvate molecules?
a.) 1 b.) 2 c.) 3 d.) 4 e.) 6
_____ 4.) Other than pyruvate and ATP, what other “high energy product” is produced
by glycolysis?
a.) water b.) glucose c.) sucrose d.) deoxyribose e.) NADH
_____ 5.) When pyruvate (a three carbon molecule) enters the mitochondria, what is
really happening (for our purposes) is that two pyruvate are entering the mitochondriai.e. to account for all SIX carbon of glucose. One carbon dioxide molecule is removed
from pyruvate as it enters through the mitochondrial membrane (lost as CO2).The Krebs
cycle removes two more carbons as CO2. How many turns of the Krebs cycle are needed
to release all 6 carbons from glucose?
a.) 1 b.) 2 c.) 3 d.) 4 e.) 6
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_____ 6.) Speculated why there are so many “cristae” in the mitochondrial membrane?
a.) there has to be “canals” that move products from place to place, just like
endoplasmic reticulum
b.) the electron transport chain complex is embedded in the inner membrane and the
more surface area of that membrane the more electron transport can be undertaken
c.) the “cristae” give the mitochondria its unique “look” so we can tell the difference
between it and other organelles
d.) the mitochondria has no “cristae”, rather several organelles are found inside the
mitochondria
e.) none of the above are correct
_____ 7.) To create ATP, the extra protons (and electrons) MUST be accepted by WHAT
molecule to produce water?
a.) water b.) sulfur c.) phosphorous d.) oxygen e.) glucose
_____ 8.) What “DRIVES” the production of ATP as a result of the electron transport?
a.) the proton gradient from the inter-membrane to the matrix- using ATP synthase
b.) the water production
c.) the carbon dioxide production
d.) the NADH production
e.) the glucose production
_____ 9.) Theoretically, EACH NADH produces three ATP and EACH FADH2 produces
2 ATP molecules. Glucose is broken down using the glyocolytic cycle and the Krebs
cycle. NADH/FADH2 is oxidized via the electron transport chain. Go back through Both
diagrams and determine how many NET ATP molecules should be produced during the
breakdown of one molecule of glucose (remember, two molecules of ATP are used up at
the beginning of glycolysis!).
a.) 30 ATP b.) 32 ATP c.) 34 ATP d.) 36 ATP e.) 40 ATP
_____ 10.) Look at the over-all reaction on page 4 of this handout. Where is water
produced as a product?
a.) When glucose is broken down
b.) When pyruvate is broken down to acetyl-CoA
c.) At the end of the electron transport chain
d.) All of the above are correct
_____ 11.) According to the first picture on page three, where does the Krebs Cycle take
place?
a.) in the cytoplasm
b.) in the inter-membrane space of the mitochondria
c.) in the inter-membrane of the mitochondria
d.) in the matrix of the mitochondria
e.) outside of the cell altogether
Page 8 (Cont. #19 AP Biology)
_____ 12.) Why is it you can’t deprive yourself of oxygen for more than a few minutes?
a.) oxygen is needed to initially breakdown glucose in the cytoplasm
b.) oxygen is needed to breakdown pyruvate to acetyl-CoA
c.) oxygen is needed to allow acetyl-CoA to enter the Krebs cycle
d.) oxygen is needed during the Krebs cycle
e.) oxygen is needed at the end of the electron transport chain
_____ 13.) Cytochrome “C” is a “surface” protein found on the outer portion of the innermembrane of the mitochondria. The actual amino acid sequence is highly conserved.
Which statement(s) is(are) reasonable to make?
a.) the three dimensional structure of the protein is conserved
b.) the structure/shape of the molecule MUST remain conserved to accept the
electron
c.) the structure/shape of the molecule MUST remain conserved to pass along the
electron
d.) all of the above are correct
_____ 14.) Look at the first diagram on page 3 of this handout. Protons (H+) are pumped
from the matrix to the inter-membrane space of the mitochondria. What provides the
driving force that pushes the protons into the inter-membrane space?
a.) the movement of water into the matrix
b.) the movement of water out of the matrix
c.) the movement of electrons from a high energy compound to a lower energy
compound
d.) the movement of NAD from a high energy compound to a lower energy
compound
e.) none of the above explains how the protons are pumped out
_____ 15.) What force causes the production of ATP from ADP plus inorganic phosphate
in the inter membrane of the mitochondria?
a.) protons moving from the inter-membrane space to the matrix through ATP
synthetase
b.) protons moving from the inter-membrane space to the outside of the mitochondria
c.) protons moving from the matrix to the inter-membrane space
d.) light hitting the mitochondria
e.) all of the above contribute to the production of ATP
Answer the following questions on this sheet only!
_____ 16.) What is substrate level phosphorylation?
a.) the generation of ATP by the direct transfer of a phosphate group to ATP from
another phosphorylated molecule using and enzyme
b.) the generation of ATP from inorganic phosphate and ADP using ATP synthetase
c.) the generation of glucose by reversing glycolysis (gluconeogenesis)
d.) it is the generation of NADH by oxidizing ATP
e.) none of the above are correct
Page 9 (Cont. Handout #19 AP Biology)
_____ 17.) Which macromolecule, a single molecule of glucose or a single molecule of a
long chain fatty acid produces more ATP molecules (pg. 179)…?
a.) glucose b.) fatty acid c.) they both produce the same amount of ATP molecules
_____ 18.) Speculate- what would you expect to happen to a muscle cell that is forced to
work harder with each and every work-out?
a.) more glycolytic enzyme complexes will be made
b.) more lactic acid will be produced
c.) more mitochondria will be produced
d.) all of the above are likely
_____ 19.) Speculate- what would you expect to happen to a muscle cell that over time
has fewer demands on it?
a.) less glycolytic enzyme complexes would be produced
b.) less lactic acid would be produced
c.) less mitochondria would be produced
d.) all of the above are likely
______ 20.) Would you ever expect there to be a “regulation” (that is adding more or less
electron transport chains) to the mitochondrial membranes based on energy demands?
(Pick the BEST answer!)
a.) yes, because if there is increased energy demands then the cell needs to produce
more electron transport chains to meet demand
b.) yes, there would be an increase in the number of electron transport complexes
limited by space available in the membrane
c.) no, extra electron transport chains would require too much energy to produce- that
is you would not get enough return to make it worthwhile for the mitochondria
d.) no, the extra electron transport chains might destabilize the membrane
Answer the following questions on this sheet only!
21.) According to the text, the complete oxidation of glucose yields 36 ATP which
equates to about 32% efficiency. Where does the rest of the energy go?
22.) Where is the electron transport complexes located in the mitochondria? Speculate as
to why this complex could NOT be located on the outer membrane of the mitochondria.
Page 10 (Cont. # 19 AP Biology)
23.) Speculate why just the electrons are moved through the complex proteins and not the
entire H+ molecule.
24.) Why does NADH create more ATP molecules than FADH2?
25.) Write out the NET equation for Cellular respiration and circle on the diagram on
Page 4 of this handout the “by-products” or waste produced by this process.
26.) Speculate why the mitochondria has the “cristae”
compared to the design shown to the right.
27.) Acetyl-CoA enters the Krebs cycle in what part of the Mitochondria? If we liken
the mitochondria to a simple one celled organism (it having its own DNA to make
proteins and enzymes), why doesn’t the mitochondria simply escape from the cell and
live on its own?
Date: ______________________________
Lesson Plan for Handout #19
AP Biology
Objective: TLWD ability to summarize the net production of ATP and NADH through
Glycolysis and Krebs, and explain how NADH is oxidized during electron transport to
create a electron transfer from high energy compounds to a low energy acceptor (1/2
oxygen) and the creation of a proton gradient that will drive the ATP synthetase reaction
to produce ATP when given handout #19.
Content: Glycolysis, Krebs, electron transport and final electron acceptors… translating
NADH to ATP.
Method: Power point, white board discussion
Homework: Handout #19