Unit 4: Chapter 19

Question 1

Each acetyl CoA enters citric acid cycle to become oxidized and loses _____ as ____

Answer 1

2 carbon; 2 CO2

Question 2

First stage of Citric Acid cycle

Answer 2

• 2 carbons are introduced into the cycle by condensation of an acetyl group with a 4 carbon compound, oxaloacetate to produce 6 carbon compound of citrate
• Citrate undergoes 2 oxidative decarboxylations to releas 2 CO2

Question 3

Second stage of citric acid cycle

Answer 3

Oxaloacetate regenerated

Question 4

Both stages of citric acid cycle generate

Answer 4

High energy electrons that are used to power the synthesis of ATP in oxidative phosphorylation

Question 5

Cellular Respiration

Answer 5

Glucose –> 2 pyruvate (glycolysis) –> CO2 + 2 acetyl CoA (when O2 available in mitochondria –> lose CO2 (citric acid cycle)

REMINDER: acetyl CoA can be made from glucose, fatty acids, and amino acids

Question 6

Citric acid cycle produces NADH and FADH2 which is important:

Answer 6

• Have the power to generate ATP in later stages up to 9 ATP
• NADH = 2.5 ATP
• FADH2 = 1.5 ATP

Question 7

True or False: Acetyl CoA is just produced by just glucose

Answer 7

False: Acetyl CoA can be produced from glucose, fatty acids, and amino acids

Question 8

Where is location of Acetyl CoA formation/ pyruvate dehydrogenase complex?

Answer 8

Mitochondrial Matrix

Question 9

Where is location of citric acid cycle?

Answer 9

Mitochondrial Matrix

Question 10

Where is location of electron transport chian, proton pump, and ATP synthesis?

Answer 10

Intermembrane mitochondria

Question 11

Electron Transport Chain

Answer 11

Membrane protein embedded in the inner mitochondria membrnae

Question 12

Step 1 of Citric Acid Cycle

Answer 12

• Citrate synthase catalyzes condensation of oxaloacetate (4 carbon) and acetyl CoA (2 carbon) to form citryl CoA intermediate (thioester bond)
• Citryl CoA is cleaved with water to make citrate (6 carbon) and releases CoA
• Irreversible reaction
• Very negative ΔG°’

Question 13

Why is step 1 of citric acid cyle irreversible reaction?

Answer 13

Due to thioester bond in acetyl CoA which is very high energy bond to drive reaction

Question 14

Synthase

Answer 14

enzyme that catalyzes synthetic reaction in which two units are joined usually without the direct participation of ATP or other NTP

Question 15

Citrate Synthase

Answer 15

• Catalyzes step 1 of citric acid cycle
• Exhibits induced fit
• Binds to oxaloacetate and conformational change occurs for formation of binding site for acetyl CoA

Question 16

Formation of reaction intermediate in step 1 ______ causes a structural change that completes active site formation

Answer 16

Citryl CoA

Question 17

Aconitase

Answer 17

• Catalyzes formation of isocitrate from citrate
• Switches H and OH location in order for clevage to occur and CO2 to be removed
• Tertiary alcohol to secondary alcohol
• Shuts down citric acid cycle and cellular respiration –> role as pesticide

Question 18

Step 2 of citric acid cycle

Answer 18

• Aconitase catalyzes isomerization of citrate to isocitrate
• location of H and OH switch

Question 19

Aconitase is inhibited by

Answer 19

metabolite of fluroacetate which acts as suicide/ irreversible inhibitor

Question 20

Fluroacetate

Answer 20

Suicide/ irreversible inhibitor
Found in floweering plants
When ingested, turns into fluroacetyl COA which reacts with citrate to form flurocitrate

Question 21

What enzyme shuts down citric acid cycle and cellular respiration and acts as pesticide?

Answer 21

Aconitase

Question 22

What enzyme switches H and OH position?

Answer 22

Aconitase

Question 23

Step 3 of citric acid cycle

Answer 23

• Isocitrate dehydrogenase catalyzes oxidative decarboxylation of isocitrate to form alpha ketoglutarate and captures high energy electron as NADH
• Isocitrate (6 carbon) oxidized to oxalosuccinate intermediate (6 carbon) and decarboxylated to alpha ketoglutarate and releases CO2 (5 carbon)
• First oxidative decarboxlation (CO2 released)

Question 24

Acetyl CoA introduced 2 carbon unit but 2 carbon will not release as CO2 the ____ but _____

Answer 24

first time; second time

Question 25

Step 4 of Citric Acid Cycle

Answer 25

- Alpha ketoglutarate dehydrogenase complex catalyzes the synthesis of succinyl CoA from alpha keto glutarate and generates NADH - Second oxidative phosphorylation (releases CO2)

Question 26

Alpha ketoglutarate dehydrogenase complex in step 4 of citric acid cycle is structurally and mechanically similiar to

Answer 26

pyruvate dehydrogenase complex

Question 27

In first time of citric acid cycle, the 2 carbon that are released are from where?

Answer 27

Oxaloacetate

Question 28

Alpha ketoglutarate dehydrogenase complex cofactors

Answer 28

TPP, Lipoic acid, FAD, coenzyme A, Mg2+

Question 29

Step 5 of Citric Acid Cycle

Answer 29

- Succinyl Coa synthetase catalyzes clevage of thioester linkage of Succinyl CoA and powers formation of ATP and forms succinate - Only step ATP generated - Only substrate level phosphorylation in cycle

Question 30

Suiccinyl CoA product of step 4 contains

Answer 30

thioester bond so compound has high phosphoryl transfer potential

Question 31

Substrate phosphorylation

Answer 31

High phosphoryl transfer potential compound donates phosphate to ADP for ATP formation

Question 32

What step of citric acid cycle is only step ATP generated and substrate level phosphorylation?

Answer 32

Step 5: Succinyl CoA to Succinate

Question 33

Reaction Mechanism of Succinyl CoA synthetase

Answer 33

- Histidine active site of Succinyl CoA synthetase performs nucleophillitic attack on Succinyl phosphate for succinate to be released - Hydrolysis of thioester bond to produce ATP

Question 34

What steps are invovled in regeneration of Oxaloacetate?

Answer 34

Steps 6, 7, 8

Question 35

_____ regenerates each citric acid cycle

Answer 35

Oxaloacetate (4 carbon)

Question 36

___ and ___ initiates another citric acid cycle

Answer 36

Oxaloacetate; acetyl CoA

Question 37

All enzymes in citric acid cycle are found in _____ but for sucinate dehydrogenase (step 6)

Answer 37

mitochondrial matrix

Question 38

All enzymes in citric acid cycle are found in mitochondrial matrix but for ___________

Answer 38

Succinate Dehydrogenase (step 6) embedded in innermitochondrial membrane

Question 38

Step 6 of citric acid cycle

Answer 38

- Catalyzed succinate dehydrogenase - Succinate oxidized to Furmate - FAD reduced to FADH2 - NOT IN MITOCHONDRIAL MATRIX, in innermitochondria membrane

Question 39

Step 7 of citric acid cycle

Answer 39

- Catalyzed by furamase - Furmate added water for double bond to form hydroxyl and hydrogen on maltate

Question 40

Step 8 of citric acid cycle

Answer 40

- Catalyzed by maltate dehydrogenase - Maltate oxidized to Oxaloacetate - NAD+ reduced to NADH - Fourth and final oxidation of cycle - Very positive ΔG°' - Very negative ΔG - Rxn pulls citrate synthetase reaction of the next step

Question 41

From glucose, what are the products of the citric acid cycle

Answer 41

6 NADH, 2 FADH2, 4 CO2, 2 ATP Products are doubled starting from glucose as we have 2 acetyl CoA

Question 42

Net reaction of Citric Acid Cycle with 1 acetyl CoA

Answer 42

1 acetyl CoA + 3 NAD+ + FADH + ADP + Pi + 2H20 --> 2CO2 + 3NADH + FADH2 + ATP + 2H+ + CoA

Question 43

Per pyruvate generates what and ATP equivalents

Answer 43

4 NADH = 10 ATP 1 FADH = 1.5 ATP 1 ATP Total 12.5 ATP per pyruvate

Question 44

How mcuh ATP is generates from glucose through acetyl CoA formation and citric acid cycle?

Answer 44

25 ATP

Question 45

What is key control point in citric acid cycle?

Answer 45

Isocitrate dehydrogenase and alpha ketoglutarate dehydrogenase

Question 46

Citric Acid Cycle must be reeplineshed because

Answer 46

Citric Acid cycle provides precursors for biosynthesis so replenishing reactions are needed (anaplerotic)

Question 47

Anaplerotic reactions refers to

Answer 47

Replening reactions

Question 48

Prominent anaplerotic reaction is catalyzed by ______ ________

Answer 48

pyruvate carboxylase

Question 49

Glyoxylate Cycle

Answer 49

- Similiar to citric acid cycle but bypass 2 decarboxylation steps, allowing synthesis of carbohydrates from fats - Not in humans - Succinate can be converted into oxaloacetate and into glucose since no carbon is loss - prominent in oil rich seeds

Question 50

Pyruvate carboxylase anaplerotic reaction

Answer 50

Increase in Acetyl CoA activated pyruvate carboxylase which activates oxaloacetate for repinish

Question 51

Key enzymes of glyoxylate cycle

Answer 51

Isocitrate lyase: catalyzes cleavage of isocitrate to glyoxylate and succinate Maltate synthase: catalyzes reaction of glyoxylate with acetyl CoA to produce maltate

Question 52

Reaction equation of glyoxylate cycle

Answer 52

2 acetyl CoA + NAD+ + 2H20 --> succinate + 2 COASH + NADH + 2H+ NO CO2 produced!! One extra oxaloacetate