Aerobic Carbohydrate Metabolism

Question 1

In the cellular respiration, this cycle follows glycolysis, being the next step in energy production

Answer 1

Kreb’s cycle!

AKA the tricarboxylic acid (TCA) cyle or the citric acid cycle

the TCA cycle is at the crossroads of many metabolic pathways in the body. Also, it generates some ATP directly via GTP, but it more importantly generates several electron carrying molecules that feed into the ETC to generate huge amounts of ATP

Question 2

Where does the citric acid cycle take place in aerobic prokaryotes?

Answer 2

the cytosol

Question 3

Where does the citric acid cycle take place?

Answer 3

The mitochondrial matrix

Question 4

What is one of the end products of aerobic glycolysis that enters the citrcic acid cycle, but must be converted into acetyl-Coa via oxidative carboxylation?

Answer 4

Pyruvate

Question 5

For every molecule of pyruvate that is decarboxylated by pyruvate dehydrogenase, how many molecules of NADH and CO2 are generated?

Answer 5

1 NADH and 1 CO2

this takes place in the mitochondria in the PDC

PDC = pyruvate dehydrogenase complex

Question 6

Describe the PDC structure and function

Answer 6

The pyruvate dehydrogenase complex (PDC) is called a complex because it is composed of multiple mplecules. It is made up of 3 distinct enzymes, but the most important one is pyruvate dehydrogenase. It also requires the action of 5 coenzymes thiamine phyrophosphate TPP, FAD, NAD+, CoA and lipoate (note, the first 4 coenzymes are B vitamin derived). The purpose of this complex is to convert pyruvate into acetyl-CoA

Question 7

What is the main entry-point/kickstarter of the Kreb’s cycle?

Answer 7

acetyl-CoA

Question 8

When acetyl-CoA joins with oxaloacetate at the begining of the Kreb’s cycle, whaty six-carbon molecule is formed?

Answer 8

Citrate

oxaloacetate + acteyl-CoA → citrate = Step 1 of Kreb’s Cycle

Citrate then undergoes a series of redox and decarboxylation reactions to generate. The final product is pxolacetate, which joins with acetyl-CoA to restart the Kreb’s cycle process again

Question 9

The mnenonic for the Kreb’s Cycle intermediates is: Can I Keep Selling Sex For Money, Officer? What are the intermediates?

Answer 9

Citrate
Isocitrate
Oxoglutarate (aka α-Ketoglutaric acid)
Succinyl-CoA
Succinate
Fumarate
Malate
Oxaloacetate (oxaloacetic acid)

Question 10

What is the 3rd intermediate in the Kreb’s cycle – oxoglutarate – also called?

Answer 10

α-Ketoglutaric acid

Question 11

What are the net products of the Kreb’s per one turn?

hint: there’s 4

Answer 11

• 1 GTP (or ATP)
• 3 NADH
• 2 FADH2
• 2 CO2

per glucose, it would be double the amount of each product

Question 12

How many turns of the TCA cycle are there per glucose?

Answer 12

2 turns of the TCA cycle per glucose

Question 13

true or false

Intermediates of the TCA are precursors for other metabolic pocesses

Answer 13

True.

The TCA is the metabolic crossroads of the body

byproduts of other processes (lipids, proteins) can also center the TCA cycle

Question 14

What are the irreversible steps of the Kreb’s cycle?

Answer 14

Step 1, Step 3
Step 4

This means that these steps are so highly exergonic that they cannot effectively be reversed

Question 15

Summarize step 1 of the Kreb’s cycle

Answer 15

acetyl-CoA (2C) → oxaloacetate (4C) → citrate (6C)

Catylyzed by citrate synthase
Irreversible

Question 16

Summarize step 3 of the Kreb’s cycle

Answer 16

isocitrate (6C) → α-Ketoglutaric acid

Catylyzed by isocitrate dehydrogenase
This is the first time in the TCA where we lose 1 carbon; the decarboxylation of isocitrate results in 1 CO2. This step also produces a NADH. It is rate-limiting and irreversible

Question 17

Summarize step 4 of the Kreb’s cycle

Answer 17

α-Ketoglutaric acid (5C) → succinyl-CoA (4C)

this is catylyzed by α-Ketoglutarate dehydrogenase and involves the release of 1 CO2. Like step 3, this step involves the loss of a carbon from the skeleton of what was once citrate, produces 1 NADH, and is irreversible

Question 18

What are the two electron carriers involved in the ETC?

Answer 18

uniquinone (Q) often written as CoQ and cytochrome c

Question 19

uniquinone (Q) is also called…

Answer 19

CoQ

Question 20

ATP synthase is fueled by…

Answer 20

a proton gradient

this is key to the ETC

Question 21

____ attaches a phosphate group to ADP to form ATP

Answer 21

ATP synthase

this process is fueled by a proton gradient

Question 22

How do ATP and ADP regulate the citric acid cycle?

Answer 22

↑ATP, ↑ products of TCA cycle = ↓ TCA activity
↑ ADP (showing that cell needs energy) = ↑ TCA cycle
thus ↑ ADP = ↑ ETC/oxidative phosphorylation

Question 23

What clinical condition is a classic example in which the ETC function is impaired?

Answer 23

cyanide poisoning

when you see cyanide on MCAT, think ETC

Question 25

What does a high ADP:ATP ratio imply?

Answer 25

The cell needs more energy

↑ ADP = ADP that this needs to be converted to ATP

Question 26

The series of spontaneous electron transfer reactions in the ETC can be modeled after what concept (that is also tested on the MCAT?)

Answer 26

Galvanic cells