7.4 The Citric Acid Cycle

Question 1

the citric acid cycle is the stage in cellular respiration in which:

Answer 1

fuel molecules are completely oxidized

Question 2

Describe the outcomes of the citric acid cycle:

Answer 2

the acetyl group of acetyl-CoA is completely oxidized to carbon dioxide, the chemical energy is transferred to ATP by substrate-level phosphorylation and to the reduced electron carriers NADH and FADH2

Question 3

by producing NADH and FADH2, the citric acid cycle is able to supply electrons to the:

Answer 3

electron transport chain, leading to the production of much more energy in the form of ATP

Question 4

the citric acid cycle takes place in the:

Answer 4

mitochondrial matrix

Question 5

the citric acid cycle is composed of:

Answer 5

8 reactions

Question 6

the starting molecule is:

Answer 6

oxaloacetate and is regenerated at the end

Question 7

in the first reaction, the 2-carbon acetyl group of acetyl-CoA is transferred to:

Answer 7

a 4-carbon molecule of oxaloacetate to form the 6-carbon molecule citric acid

Question 8

the last reaction in the citric acid cycle regenerates a molecule of:

Answer 8

oxaloacetate, joining to a new acetyl group and allowing the cycle to continue

Question 9

the citric acid cycle results in the complete oxidation of:

Answer 9

the acetyl group of acetyl-CoA

Question 10

how many carbons are eliminated during the cycle?

Answer 10

2 carbons that are released as carbon dioxide

Question 11

which reaction is the source of carbon dioxide released during cellular respiration?

Answer 11

the citric acid cycle

Question 12

the oxidation reactions that produce carbon dioxide are coupled with:

Answer 12

the reduction of the electron carrier NAD+ to NADH

Question 13

how many reduced electron carriers does the citric acid cycle produce?

Answer 13

3 NADH, 1 FADH2 per turn of the cycle

Question 14

one of the reactions in the citric acid cycle uses substrate-level phosphorylation to generate a molecule of:

Answer 14

GTP

Question 15

GTP can transfer:

Answer 15

its terminal phosphate to transform ADP to form ATP

Question 16

what is the only substrate-level phosphorylation reaction in the citric acid cycle?

Answer 16

the production of GTP

Question 17

what are the overall products produced from a single molecule of glucose into two molecules of acetyl-CoA?

Answer 17

2 molecules of ATP, 6 molecules of NADH, 2 molecules of FADH2

Question 18

some bacteria run the citric acid cycle in reverse? how does this process work then?

Answer 18

carbon dioxide is incorporated into organic molecules, requires energy such as sunlight or chemical reactions

Question 19

the intermediates generated step by step in the citric acid cycle provide:

Answer 19

the building blocks for synthesizing the cell’s key biomolecules

Question 20

pyruvate is the starting point for the synthesis of:

Answer 20

sugars and the amino acid alanine

Question 21

acetate is the starting point for the synthesis of:

Answer 21

lipids

Question 22

oxaloacetates is modified to form:

Answer 22

different amino acids and pyrimidine bases

Question 23

what suggests that the citric acid cycle evolved early?

Answer 23

because the centrality of the citric acid cycle to both the synthesis of biomolecules and to meeting the energy requirements of cells suggested it appeared in the first cells to feature metabolism