Download Biology 123 SI-Dr. Raut`s Class Session 10

Biology 123 SI-Dr. Raut’s Class
Session 10 - 2/18/2015
* I will not be covering glycolysis again. However, at the beginning of the session I will ask for
questions, so feel free to ask about any aspects that are confusing.
1. How does the pyruvate that gets produced by glycolysis get to the citric acid cycle? What is
this step called? Draw it out.
First of all, pyruvate is in the cytoplasm and needs to be moved into the mitochondria. Since
pyruvate has a negative charge, the mitochondria’s membrane does not want to let it through,
and a transport protein must be used. This transport protein requires one ATP and is therefore
active transport. It is important to remember that if oxygen is not present, pyruvate will never
enter the mitochondria. After entering into the mitochondria, pyruvate goes through an
intermediate step. This intermediate step occurs between glycolysis and the citric acid cycle and
uses a multienzyme complex. During this step, CO2 is released by decarboxylation, NADH is
made by oxidizing the remaining two carbon fragment, and Coenzyme A is added onto the two
carbon fragment creating Acetyl CoA.
2. What do you produce in this step?
For each pyruvate, one CO2, one NADH, and one Acetyl CoA are produced.
*all the products will be multiplied by two if discussing them per glucose.
3. Where does the oxaloacetate come from in the citric acid cycle?
Oxaloacetate is from the previous turn of the citric acid cycle. At the completion of each turn of
the citric acid cycle, oxaloacetate is regenerated to be available for the next cycle.
4. Draw the citric acid cycle. Be sure to show all intermediates and by products. Understand
what is happening at each step.
*You do not have to know about the enzymes, since they are not in the book. This is just the best
picture I could find. Page 171 is a better picture to study.
5. What is produced by the citric acid cycle?
For one Acetyl CoA, two CO2, two NADH, one FADH2, and one GTP/ATP are produced.
*Multiply all products by two if discussing them per glucose.
6. Where does the citric acid cycle take place?
The citric acid cycle takes place inside the matrix of the mitochondria.
7. What is the difference in substrate level phosphorylation and oxidative phosphorylation?
Substrate level phosphorylation directly produces ATP in glycolysis and the citric acid cycle.
Involves an enzyme (kinase) moving a phosphate group off of a phosphorylated organic
molecule and onto ADP creating ATP. Oxidative phosphorylation creates ATP using the electron
transport chain and chemiosmosis.
8. What are the two components of oxidative phosphorylation?
The two components of oxidative phosphorylation are the electron transport chain and
chemiosomosis.
9. What is the electron transport chain made out of?
The electron transport chain is made out of four protein complexes. These complexes may have
prosthetic groups which are nonprotein components that are essential to the enzyme. Ubiquinone
is hydrophobic electron carrier (not a protein) that does not reside within a complex and instead
hinges complex one, two, and three together. Most of the electron carriers between ubiquinone
and oxygen are cytochromes which are proteins with a heme group which consists of an iron
atom that accepts and donates electrons. Oxygen is the final electron acceptor.
10. Describe how the electron transport chain works.
The electron carriers in the electron transport chain are set up in order of increasing
electronegativity, with oxygen, the most electronegative, at the end. Electrons are transported
from NADH to the first molecule of the electron transport chain in complex one. From there the
electrons flow down the electron transport chain. Every time the electrons move to a molecule,
that particular molecule is reduced. When the electrons move on to the next molecule, the first
molecule is oxidized. Therefore the electron transport chain is a series of redox reaction, with
oxygen getting oxidized at the end. When the electrons combine with ½ O2, two hydrogen atoms
join ½ O2 to make metabolic water.
11. Where is the electron transport chain located?
The electron transport chain is embedded into the inner membrane of the mitochondria.
12. Describe the process of chemiosmosis. Drawing a rough sketch may be helpful.
During certain reactions throughout the electron transport chain, H+ is taken up and then released
into the intermembrane space. This causes there to be a higher concentration of H+ in the
intermembrane space than in the matrix of the mitochondria. This builds up a proton motive
force. ATP synthase is a transport protein that lines the inner membrane. ATP synthase will
allow protons to come through and into the matrix, but as the protons come through they cause a
rotor on the protein to spin, which causes the internal rod of the protein to spin, which in turn
activates catalytic sites in the catalytic knob which produce ATP from ADP and inorganic
phosphate.
13. How many molecules of CO2 are generated for each molecule of acetyl CoA introduced into
the citric acid cycle?
a. 1
b. 2
c. 3
d. 4
e. 6
14. In the chemiosmotic mechanism,
a. ATP production is linked to the proton gradient established by the electron transport chain.
b. the difference in pH between the intermembrane space and the cytosol drives the formation of
ATP.
c. the flow of H+ through ATP synthases rotates a rotor and rod, driving the hydrolysis of ATP
d. the energy by the reduction and subsequent oxidation of electron carriers transfers a phosphate
to ADP.
e. the production of water in the mitochondrial matrix by the reduction of oxygen leads to a net
flow of water out of a mitochondrion.