Lecture 17: Delivery of Fuel to the Mitochondria

Question 1

What are the 4 allosteric inhibitors of the TCA?

Answer 1

1. NADH
2. Succinyl-CoA
3. Citrate
4. ATP

Question 2

What are the 4 allosteric activators of the TCA?

Answer 2

1. AMP/ADP
2. CoA
3. NAD+
4. Ca2+

Question 3

Why does calcium stimulate the TCA?

Answer 3

Because internal concentration have been used by muscle contraction, so extracellular calcium is needed = starved state

Question 4

What are the 3 exergonic steps of the TCA = the steps that are regulated?

Answer 4

1, 3, and 4

Question 5

Why does NADH produced by glycolysis need to be transported to mitosol?

Answer 5

To be used by ETC

Question 6

What are the 2 shuttles to transport NADH to mitosol?

Answer 6

1. Malate-aspartate shuttle

2. Glycerol-3-phosphate shuttle

Question 7

Describe the 6 steps of the malate-aspartate shuttle of NADH inside the mitosol.

Answer 7

1. IMS: malate dehydrogenase reduces oxaloacetate to malate using NADH
2. Malate crosses mito inner membrane via the malate-alpha-ketoglutarate transporter (antiporter)
3. malate dehydrogenase oxidizes malate to oxaloacetate using NAD+ and making NADH
4. Matrix: aspartate amino transferase converts oxaloacetate to aspartate (using amino group from glutamate to make alpha-ketoglutarate)
5. Aspartate crosses mito inner membrane via the glutamate-aspartate transporter (antiporter)
6. IMS: aspartate amino transferase converts aspartate to oxaloacetate (giving amino group back to alpha ketoglutarate to form glumatame)

Question 8

ΔG°’ of oxaloacetate to malate?

Answer 8

Large negative (opposite of the other way around)

Question 9

How does the concentration of oxaloacetate in the matrix compare to that in the IMS

Answer 9

Low in mitosol

High in IMS

Question 10

In what 3 tissues is the malate-aspartate shuttle used?

Answer 10

1. Liver
2. Kidney
3. Heart

Question 11

What is a downside of the malate-aspartate shuttle?

Answer 11

Too slow

Question 12

Describe the steps of the glycerol-3-phosphate shuttle.

Answer 12

1. IMS: glycerol-3-phosphate dehydrogenase coverts DHAP to glycerol-3-phosphate using NADH
2. H2 is transferred from glycerol-3-phosphate to FAD forming FADH2 and DHAP (complex II of ETC)
3. H2 is transferred from FADH2 to Q

Question 13

Why does 1 NADH either produce 1.5 or 2.5 ATPs?

Answer 13

1.5 if using glycerol-3-phosphate shuttle because bypassing Complex I so lack of 4 H+ being pumped out of matrix

Question 14

What is a downside of the glycerol-3-phosphate shuttle?

Answer 14

Only produces 1.5 ATP per NADH instead of 2.5

Question 15

How many ATP per glucose if the malate-aspartate shuttle for glycolysis NADH is used?

Answer 15

32

Question 16

How many ATP per glucose if the glycerol-3-phosphate shuttle for glycolysis NADH is used?

Answer 16

30

Question 17

How are fats (triacylglycerides) transported from the small intestine to target cells? 6 steps

Answer 17

1. Bile salts emulsify FAs so that they can access the more aqueous environment
2. Pancreas secretes lipases to degrade TAGs into FAs and glycerol
3. Mucosa takes up FAs + glycerol, re-esterifies them into TAGs, and packages them into chylomicrons
4. Chylomicrons travel through blood and lymph and bind to target tissues
5. Lipoprotein lipase activated by apoC-II to hydrolyze TAGs into FAs and glycerol for absorption
6. TAGs are reformed

Question 18

Can TAGs cross cellular or mucosal membranes?

Answer 18

NOPE

Question 19

What are chylomycrons? What 4 types of molecules in them? Which one responsible for triggering TAG/cholesterol uptake?

Answer 19

Giant oil droplets containing TAGs, cholesterol, phospholipids, and apolipoproteins (triggers)

Question 20

What happens to the chylomicrons once they deliver TAGs to target cells? 3 steps

Answer 20

1. Liver collects them and repackages FAs and cholesterol in them into VLDLs (very low density lipoproteins)
2. VLDLs release their FAs to other tissues to become LDLs (with more cholesterol than FAs)
3. Liver collects LDLs

Question 21

Which are responsible for heart disease: VLDLs or LDLs?

Answer 21

LDLs

Question 22

What happens to the FAs when they are taken up by adipocytes?

Answer 22

They are stored as tryacylglycerides in lipid droplets encased in perilipin which shields them from surrounding water

Question 23

How do we break down the fat stored in adipocytes? 5 steps

Answer 23

1. Adrenaline is released in blood and triggers the release of cAMP
2. cAMP activates PKA
3. PKA phosphorylates perilipin which changes its conformation
4. PKA phosphorylates hormone sensitive lipase
5. HSP has access to TAGs and degrades them into FAs + glycerol

Question 24

How are FAs transported in the blood from adipocytes to target tissues?

Answer 24

Albumin

Question 25

What are the 2 possible fates of DHAP produced by glycolysis? When does each happen?

Answer 25

1. Conversion to glyceraldehyde 3-phosphate (GAP) to continue down glycolysis: need energy 2. Conversion to glycerol 3-phosphate to be used in TAG synthesis or in the glycerol-3-phosphate shuttle: well-fed

Question 26

What are the 2 ways to synthesize glycerol-3-phosphate for TAG synthesis? When is each used?

Answer 26

1. Glycerol kinase phosphorylates glycerol using ATP: when glucose is low 2. Glycerol 3-phosphate dehydrogenase converts DHAP to glycerol-3-phosphate: when glucose is high

Question 27

Which ONLY 2 tissues can synthesize tryacylglycerols when glucose is low? Why?

Answer 27

1. Liver 2. Kidney They have the glycerol kinase enzyme meaning that glycerol-3-phosphate can be made by glycerol phosphorylation (without DHAP)

Question 28

How are FAs attached to glycerol-3-phosphate to produce TAGs? 6 steps

Answer 28

1. Acyl-CoA synthetase attaches CoA-SH to FA to activate it using ATP (actually 2 steps) 2. Acyl transferase removes CoA-SH and attaches the FA to glycerol-3-phosphate 3. Steps 1 and 2 repeated to obtain phosphatidic acid 5. Phosphatidic acid phosphatase takes off phosphate group on glycerol 6. Steps 1 and 2 repeated to add the last FA

Question 29

How are FAs delivered to the mitosol for beta oxidation? 3 steps. For which FAs does this happen?

Answer 29

1. Carnitine-acyltransferase I attaches FA-CoAs to carnitine in cytosol 2. Transport to mitosol 3. Carnitine-acyltransferase II cleaves off carnitine FAs that have 14 Cs or more

Question 30

What is the role of malonyl-CoA?

Answer 30

It's the product of the first committed step of FA beta oxidation and inhibits CAT I from transporting more FAs in mitosol

Question 31

What % of FAs are made into TAGs during starvation?

Answer 31

75%

Question 32

How does the Atkins diet work?

Answer 32

Low of glucose = low glycerol-3-phosphate synthesis = low TAG synthesis in adipocytes

Question 33

What are the 2 uses for exporting aspartate out of the mitosol?

Answer 33

1. Exporting oxaloacetate (for use in the malate/asparte shuttle) 2. Exporting Nitrogen

Question 34

How does the esterification of FAs affect their hydrophobicity? Why?

Answer 34

Increase hydrophobicity because no more negative charge on carboxylic end of FA

Question 35

What are the 2 ways of synthesizing DHAP? Which one is fastest?

Answer 35

1. Glycolysis (fastest) | 2. AA degradation

Question 36

What does the rate of TAG synthesis in adipose tissue (aka fat storage) depend on?

Answer 36

The availability of DHAP

Question 37

What happens to FAs before they are sent to the mitosol via the carnitine shuttle? What 2 things drives this whole rxn forward?

Answer 37

Fatty-acyl CoA synthetase adds S-CoA to them: 1. Adds adenylate (adenosine + P) from ATP 2. Adds CoA-SH releasing AMP Driving RXN forward: 1. PPi is degraded by pyrophosphatase 2. AMP converted to ATP