BCH 361 - EXAM 3 QUESTIONS
WITH REVISED AND UPDATED
ANSWERS
Non-covalent inhibitors: - Answer-PDH is regulated mostly by energy charge. Molecules
signaling high energy such as ATP, acetyl CoA and NADH inhibit PDH (either through
allosteric regulation or by activating PDH kinase). Pyruvate and ADP, which are present
at high concentrations when energy charge is low, activates the enzyme by inhibiting
PDH kinase. CA2+ and insulin are activators of the PDH phosphatase, resulting in
activation of PDH.
PDH complex reaction step 1: - Answer-E1 decarboxylates pyruvate and attaches the
remaining two carbons to TPP, forming hydromethyl-TPP. TPP's ability to form carbo-
anion is crucial to this step.
PDH complex reaction step 2: - Answer-The lipoamide arm of E2 swings onto E1,
where the two-carbon fragment is transferred to lipoamide by the formation of a
thioester bond, producing acetyllipoamide.
PDH complex reaction step 3: - Answer-The acetyllipoamide is returned to E2, and the
lipoamide transfers the acetyl group to CoA, forming acetyl CoA.
PDH complex reaction step 4: - Answer-Finally, the reduced lipoamide arm translocates
to the active site of E3, where it reduced FAD to FADH2, which in turn transfers electron
to NAD+, producing NADH, the final electron acceptor.
In each citric acid cycle:
___ NADH.
___ FADH2.
___ ATP/GTP.
___ CO2. - Answer-3 NADH.
1 FADH2.
1 ATP/GTP.
2 CO2.
Goal of citric acid cycle: - Answer-to harvest the high-energy electrons from acetyl CoA
by oxidizing the carbons to CO2.
While PDH can be used to regulate CAC, _____ ____ and _____ ______ are the major
regulatory points in CAC itself. - Answer-Isocitrate dehydrogenase, alpha-ketoglutarate
dehydrogenase.
, CAC is controlled by energy charge: - Answer-both enzymes (Isocitrate dehydrogenase
& alpha-ketoglutarate dehydrogenase) are inhibited by ATP and NADH while ADP can
also activate isocitrate dehydrogenase.
Anapleurotic reaction: - Answer-"Replenish reactions". (Conversion of pyruvate to
oxaloacetate is a major anapleurotic reaction)
The amount of CAC intermediates cannot be increased through acetyl CoA. They are
replenished... - Answer-directly by converted other molecules (such as pyruvates and
amino acids) to CAC intermediates.
Although animals cannot generate glucose from acetyl CoA, plants and micro-
organisms can produce glucose using acetyl-CoA through the ______ cycle. - Answer-
glyoxylate
The glyoxylate cycle is almost identical to the CAC with the exception of ______ extra
enzymes. - Answer-two.
A redox reaction in which electrons from the _____ agent is transferred to the ______
agent. - Answer-Reducing, oxidizing.
The reducing agent is always ____ in a redox reaction. - Answer-Oxidized.
The oxidizing agent is always ____ in a redox reaction. - Answer-Reduced.
A molecules affinity for electrons is described by its _____ _______ ______. - Answer-
Standard reduction potential.
_______ reduction potential means the molecule has a higher affinity for electrons, this
is a good _____ agent. - Answer-Higher, oxidizing.
ETC is responsible for... - Answer-established the proton concentration gradient across
the inner mitochondrial membrane.
ETC is made up of _____ protein complexes which are all embedded in the inner
______ _______. - Answer-Four. Mitochondrial membrane.
Each ETC complex contains a number of permanently attached prosthetic electron
carriers. These include: - Answer-FMN, heme, FeS clusters.
Mobile electron carriers for the ETC: - Answer-Ubiquinone (coenzyme Q) and
cytochrome C.
Complex I: - Answer-Electrons from NADH are used to reduce ubiquinone (Q) to
ubiquinol (QH2). In the process, protons are directly transferred from matrix into the
WITH REVISED AND UPDATED
ANSWERS
Non-covalent inhibitors: - Answer-PDH is regulated mostly by energy charge. Molecules
signaling high energy such as ATP, acetyl CoA and NADH inhibit PDH (either through
allosteric regulation or by activating PDH kinase). Pyruvate and ADP, which are present
at high concentrations when energy charge is low, activates the enzyme by inhibiting
PDH kinase. CA2+ and insulin are activators of the PDH phosphatase, resulting in
activation of PDH.
PDH complex reaction step 1: - Answer-E1 decarboxylates pyruvate and attaches the
remaining two carbons to TPP, forming hydromethyl-TPP. TPP's ability to form carbo-
anion is crucial to this step.
PDH complex reaction step 2: - Answer-The lipoamide arm of E2 swings onto E1,
where the two-carbon fragment is transferred to lipoamide by the formation of a
thioester bond, producing acetyllipoamide.
PDH complex reaction step 3: - Answer-The acetyllipoamide is returned to E2, and the
lipoamide transfers the acetyl group to CoA, forming acetyl CoA.
PDH complex reaction step 4: - Answer-Finally, the reduced lipoamide arm translocates
to the active site of E3, where it reduced FAD to FADH2, which in turn transfers electron
to NAD+, producing NADH, the final electron acceptor.
In each citric acid cycle:
___ NADH.
___ FADH2.
___ ATP/GTP.
___ CO2. - Answer-3 NADH.
1 FADH2.
1 ATP/GTP.
2 CO2.
Goal of citric acid cycle: - Answer-to harvest the high-energy electrons from acetyl CoA
by oxidizing the carbons to CO2.
While PDH can be used to regulate CAC, _____ ____ and _____ ______ are the major
regulatory points in CAC itself. - Answer-Isocitrate dehydrogenase, alpha-ketoglutarate
dehydrogenase.
, CAC is controlled by energy charge: - Answer-both enzymes (Isocitrate dehydrogenase
& alpha-ketoglutarate dehydrogenase) are inhibited by ATP and NADH while ADP can
also activate isocitrate dehydrogenase.
Anapleurotic reaction: - Answer-"Replenish reactions". (Conversion of pyruvate to
oxaloacetate is a major anapleurotic reaction)
The amount of CAC intermediates cannot be increased through acetyl CoA. They are
replenished... - Answer-directly by converted other molecules (such as pyruvates and
amino acids) to CAC intermediates.
Although animals cannot generate glucose from acetyl CoA, plants and micro-
organisms can produce glucose using acetyl-CoA through the ______ cycle. - Answer-
glyoxylate
The glyoxylate cycle is almost identical to the CAC with the exception of ______ extra
enzymes. - Answer-two.
A redox reaction in which electrons from the _____ agent is transferred to the ______
agent. - Answer-Reducing, oxidizing.
The reducing agent is always ____ in a redox reaction. - Answer-Oxidized.
The oxidizing agent is always ____ in a redox reaction. - Answer-Reduced.
A molecules affinity for electrons is described by its _____ _______ ______. - Answer-
Standard reduction potential.
_______ reduction potential means the molecule has a higher affinity for electrons, this
is a good _____ agent. - Answer-Higher, oxidizing.
ETC is responsible for... - Answer-established the proton concentration gradient across
the inner mitochondrial membrane.
ETC is made up of _____ protein complexes which are all embedded in the inner
______ _______. - Answer-Four. Mitochondrial membrane.
Each ETC complex contains a number of permanently attached prosthetic electron
carriers. These include: - Answer-FMN, heme, FeS clusters.
Mobile electron carriers for the ETC: - Answer-Ubiquinone (coenzyme Q) and
cytochrome C.
Complex I: - Answer-Electrons from NADH are used to reduce ubiquinone (Q) to
ubiquinol (QH2). In the process, protons are directly transferred from matrix into the
