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Biology 2112 Exam 3 Study Guide
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Biology 2112 Exam 3 Study Guide
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STUDY GUIDE - EXAMINATION 3Lecture 16 - Glycolysis
1.
a. What is an oxidation-reduction reaction? (Pg. 166, 1st column, 1st paragraph)
- In an oxidation-reduction (redox) reaction, the loss of electrons from one substance is
called oxidation, and the addition of electrons to another substance is known as
reduction.
b. In the oxidation-reduction reaction shown below, which reaction component is the
reducing agent and which is the oxidizing agent?
C6H12O6 + 6 O2 -------> 6 CO2 + 6 H2O + Energy (ATP + heat)
- Reducing agent oxidizing agent
2.
a. How is the formation of a polar covalent bond an example of an oxidation-reduction
reaction? (Pg. 166, paragraph 3, sentence 1 and Figure 9.3)
- Not all redox reactions involve the complete transfer of electrons from one substance to
another; some change the degree of electron sharing in covalent bonds.
b. How does the potential energy in an electron relate to its association with an
electronegative atom? (Pg. 166, paragraph 5)
- An electron loses potential energy when it shifts from a less electronegative atom
towards a more electronegative one
3.
a. What are the roles of dehydrogenase and the coenzyme nicotinamide adenine
dinucleotide (NAD+) in catabolic pathways? (Pg. 167, paragraphs 2-3)
- Enzymes called dehydrogenases remove a pair of hydrogen atoms from glucose and
other organic molecules in food, thereby oxidizing it. The dehydrogenase delivers the 2
electrons along with one proton to its coenzyme, NAD+, forming NADH. The other
proton is released into the surrounding solution.
4.
a. Energy from electrons carried by NADH (and FADH2) is harvested through a controlled
release as they travel toward an electronegative oxygen atom. How does the controlled
release of energy occur? (Pg. 168, paragraph 2 sentences 1-4 and Fig. 9.5b)
- Electron transfer from NADH to oxygen is an exergonic reaction with a free energy
change of -53 kcal/mol (-222 kJ/mol). Instead of this energy being released and wasted
in one explosive step, electrons cascade down the chain from one carrier molecule to
the next in a series of redox reactions, losing a small amount of energy with each step
until they finally reach oxygen, the terminal electron acceptor, which has a great affinity
for electrons. Each “downhill” carrier is more electronegative than, and thus capable of
oxidizing its “uphill” neighbor, with oxygen at the bottom of the chain. Therefore, the
electrons transferred from glucose to NAD+ which is thus reduced to NADH, fall down an
, energy gradient in the electron transport chain to a far more stable location in the
electronegative oxygen atom.
5.
a. Define substrate-level phosphorylation. (One sentence, Pg. 169, Fig. 9.7)
- When an enzyme transfers a phosphate group from a substrate molecule to ADP rather
than adding an inorganic phosphate to ADP as in oxidative phosphorylation.
6.
a. How does the energy investment phase of glycolysis differ from the energy pay-off
phase? (Describe the products of glycolysis in your answer.) (Pg. 170, Fig. 9.8)
- During the investment phase, the cell actually spends ATP. During the payoff phase, ATP
is produced and NAD+ is reduced to NADH. The net energy yield from glycolysis per
glucose molecule is 2 ATP plus 2 NADH
b. What is the fate of the final product of glycolysis? (Pg. 171, 2nd paragraph, and Fig.
9.10)
- Upon entering the mitochondria via active transport pyruvate is first converted to a
compound called acetyl coenzyme A (acetyl CoA). The acetyl group enters the citric acid
cycle.
7.
a. What is the donor of the H+ ion donated to NAD+ when pyruvate enters the
mitochondrial matrix? (Lecture notes and Slide 15)
- Thiamine pyrophosphate (TPP) – Vitamin B1 – coenzyme of pyruvate dehydrogenase.
8.
a. List four vitamins that play a direct role in glycolysis and the citric acid cycle. (Lecture
notes and Slides 14 – 15)
- Vitamin B5, Vitamin B1, lipoyllysine
Lecture 17 - The citric acid cycle and oxidative phosphorylation
1.
a. Where does the citric acid cycle occur? (Lecture notes)
- Mitochondrion.
b. What are all of the products of the citric acid cycle and how are they used? (Pg. 173, Fig.
9.12; Pg. 172, second column, paragraph 3)
- 3 NAD+ are reduced to NADH. FAD accepts 2 electrons and 2 protons to become
FADH2. In many animal tissue cells, a GTP molecule is produced by substrate level
phosphorylation. The GTP may be used to make an ATP molecule or to directly power
work in a cell. Each glucose gives rise to two molecules of acetyl CoA that enter the
cycle. The total yield from per glucose from the citric acid cycle turns out to be 6 NADH,
2 FADH2, and 2 ATP.
2.
a. Describe the oxidation-reduction that the components of the electron transport chain
undergo as electrons are accepted and donated. Include in your answer the direction of
, electronegativity as well as the separate roles of the components of the electron
transport chain including flavin mononucleotide, the Fe-S group, ubiquinone, and the
cytochromes. (Pg. 173, paragraphs 1-3)
- The ETC is a collection of molecules embedded in the inner membrane of the
mitochondria in eukaryotic cells. Most components of the chain are proteins which exist
in multiprotein complexes. Tightly bound to the proteins are prosthetic groups –
nonprotein components such as cofactors and coenzymes essential for the catalytic
functions of certain enzymes. During electron transport, carriers alternate between
reduced and oxidized states as they accept and then donate electrons. A component
becomes reduced when it accepts electrons from its uphill neighbor which has a lower
affinity for electrons (less electronegative). It returns to its oxidized form as it passes
electrons to its downhill more electronegative neighbor. Electrons acquired from glucose
by NAD+ during glycolysis and the citric acid cycle are transferred from NADH to the first
molecule of the ETC in complex 1. This molecule is a Flavoprotein due to its prosthetic
group called a Flavin mononucleotide. The Flavoprotein returns to its oxidized form as it
passes electrons to Fe-S (an iron-sulfur protein). Fe-S then passes electrons to a
compound called ubiquinone. Ubiquinone is a small hydrophobic molecule and is not a
protein. It is individually mobile rather than residing in a particular complex. Most of the
remaining electron carriers between ubiquinone and oxygen are proteins called
cytochromes. Their prosthetic group is called a heme group and has an iron atom that
accepts and donates electrons. The last cytochrome passes the electrons to oxygen
which also picks up a pair of hydrogen ions (protons) from the aqueous solution
neutralizing the -2 charge of the added electrons and forming water.
3.
a. How is electron transport related to ATP synthesis? Include the terms proton-motive
force and chemiosmosis in your answer. (Pg. 177, paragraph 1, sentences 5-7 and
paragraph 2, sentences 1-2 and Fig. 9.15)
- Establishing the H+ gradient is a major function of the ETC. The chain is an energy
converter that uses the exergonic Flow of electrons from NADH and FADH2 to pump H+
across the membrane from the mitochondrial matrix to the intermembrane space. H+ has
a tendency to move back across the membrane diffusing down its gradient. ATP
synthases are the only sites that provide a route through the membrane for H+. The
passage of H+ through ATP synthase uses the exergonic Flow of H+ to drive
phosphorylation of ADP. Thus, energy stored in an H + gradient across a membrane
couples the redox reactions of the ETC to ATP synthesis. At certain steps along the
chain, electron transfers cause H+ to be taken up and released into the surrounding
solution. In eukaryotic cells, the electron carriers are spatially arranged in the inner
mitochondrial matrix and deposited in the intermembrane space. The H+ gradient that
results is referred to as a proton-move force, emphasizing the capacity of the gradient to
perform work. The force drives H+ back across the membrane through the channels
provided by ATP synthases. Chemiosmosis is an energy-coupling mechanism that uses
energy stored in the form of an H+ gradient across a membrane to drive cellular work.
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