Ch 23 Bio Exam 4

Question 1

• citrate synthase catalyzes the condensation of an acetyl group (2C) from acetyl CoA with oxaloacetate (4C) to yield citrate (6C) and coenzyme A.
• the energy to form citrate is provided by the hydrolysis of the high-energy thioester bond in acetyl CoA.

Answer 1

• reaction 1 of the citric acid cycle

Question 2

• citrate rearranges to isocitrate, a secondary alcohol.
• aconitase catalyzes the dehydration of citrate (tertiary alcohol) to yield cis-aconitate, followed by a hydration that forms isocitrate.

Answer 2

• reaction 2 of the citric acid cycle

Question 3

• One carbon is removed by converting a carboxylate group (COO−) to CO2.
• The dehydrogenase removes hydrogen ions and electrons, used to reduce NAD+ to NADH and H+.

Answer 3

• reaction 3, isocitrate undergoes decarboxylation by isocitrate dehydrogenase

citric acid cycle

Question 4

Where is NADH produce in the CAC?

Answer 4

• Reaction 3
• Reaction 4
• Reaction 8

Question 5

• α-ketoglutarate (5C) undergoes decarboxylation to yield (4C) succinyl CoA.
• oxidation of the thiol group (—SH) in HS—CoA provides hydrogen that is transferred to NAD+ to form a second molecule of NADH and H+.

Answer 5

• reaction 4, catalyzed by α-ketoglutarate dehydrogenase

Citric acid cycle

Question 6

• hydrolysis of the thioester bond in succinyl CoA yields succinate and HS—CoA.
• energy from hydrolysis is transferred to the condensation of phosphate and GDP forming GTP, a high-energy compound similar to ATP.

Answer 6

• reaction 5, catalyzed by succinyl CoA synthetase

citric acid cycle

Question 7

• succinate is oxidized to fumarate, a compound with a C = C bond.
• 2H lost from succinate are used to reduce the coenzyme FAD to FADH2.

Answer 7

• reaction 6, catalyzed by succinate dehydrogenase

citric acid cycle

Question 8

• catalyzed by fumarase, water is added to the double bond of fumarate to yield malate, a secondary alcohol.

Answer 8

• reaction 7 hydration

citric acid cycle

Question 9

• the hydroxyl group in malate is oxidized to a carbonyl group, yielding oxaloacetate.
• oxidation provides hydrogen ions and electrons for the reduction of NAD+ to NADH and H+.

Answer 9

• reaction 8, catalyzed by malate dehydrogenase

Question 10

Where is FADH produced in the CAC?

Answer 10

• Reaction 6

Question 11

Where is ATP created in the CAC?

Answer 11

• Reaction 5

Question 12

• an acetyl group bonds with oxaloacetate to form citrate.
• two decarboxylations remove two carbons as two CO2.
• four oxidations provide hydrogen for three NADHs and one FADH2.
  a direct phosphorylation forms GTP (ATP).

Answer 12

• Citric acid cycle

Question 13

When does the reaction rate for the citric acid cycle increase and decrease?

Answer 13

• increases when low levels of ATP activate isocitrate dehydrogenase.
• decreases when high levels of ATP or NADH inhibit citrate synthase (first step in cycle).

Question 14

• hydrogen ions and electrons from NADH and FADH2 are passed from one electron acceptor or carrier to the next until they combine with oxygen to form H2O.
• energy released during electron transport is used to synthesize ATP from ADP and Pi during oxidative phosphorylation.

Answer 14

• electron transport or the respiratory chain

Question 15

______ carries electrons from complexes I and II to complex III.

Answer 15

• CoQH2

Question 16

For every two electrons that pass from NADH to CoQ, _____ are pumped across the mitochondrial membrane, producing a charge separation on opposite sides of the membrane.

Answer 16

• 4H+

Question 17

Complex II consists of the enzyme ____ from the citric acid cycle.

Answer 17

• succinate dehydrogenase

Question 18

In complex II,

CoQ obtains hydrogen and electrons directly from _____. This produces CoQH2 and regenerates the oxidized coenzyme FAD, which becomes available to oxidize more substrates.

Answer 18

• FADH2

Question 19

Energy is coupled with the production of ATP in a process called ________. In 1978, Peter Mitchell theorized about a chemiosmotic model, which
links the energy from electron transport to a hydrogen ion gradient that drives the synthesis of ATP.

• allows complexes I, III, and IV to act as hydrogen ion pumps, producing a hydrogen ion gradient.
• equalizes pH and electrical charge between the matrix and intermembrane space that occurs when H+ must return to the matrix.

Answer 19

• oxidative phosphorylation

Question 20

How is the electron transport chain regulated?

Answer 20

Electron transport

• is regulated by the availability of ADP, Pi, oxygen (O2), and NADH.
• decreases with low levels of any of these compounds and decreases the formation of ATP.

When a cell is active and ATP is consumed rapidly, the elevated levels of ADP will activate the synthesis of ATP.

The activity of electron transport is strongly dependent on the availability of ADP for ATP synthesis.

Question 21

In the Electron transport chain, what is the final electron acceptor?

Answer 21

• Oxygen creating water

Question 22

The hydrogen ions and electrons from NADH can be moved into and out of the mitochondria by a transporter, _______.

______ catalyzes the reaction of oxaloacetate and NADH to yield _____ and NAD+.

Answer 22

• the malate–aspartate shuttle
• malate dehydrogenase
• Malate

Question 23

The oxidation to ______ provides hydrogen ions and electrons that are used to reduce NAD+ to NADH, which can now enter electron transport to synthesize ATP.

Answer 23

• oxaloacetate

Question 24

A transporter binds the malate and carries it across the membrane into the matrix, where _____ oxidizes malate back to oxaloacetate.

Answer 24

• malate dehydrogenase