Biochemistry - Muscle Metabolism

Front 1

What fuel sources can muscles use for energy?

Back 1

glucose (from blood), glucose (from glycogen), free fatty acids (ncludes acetate from ethanol), ketone bodies, lactate (from muscle or RBCs) and amino acids (particularly branch-chain AAs)

Front 2

What pathways are active in muscle cells?

Back 2

- Glycolysis
- Glycogenolysis and glycogenesis (some)
- TCA cycle (most)
- Beta oxidation (most)
- Electron transport chain (most)

Front 3

What pathways are not active in muscle cells?

Back 3

- Fatty acid synthesis
- Gluconeogenesis (liver & kidney)
- Pentose Phosphate Pathway
- Ketone body synthesis (liver)

Front 4

What provides the immediate source of energy for muscle contraction but is not a good energy store since many reactions are allosterically inhibited or activated by it?

Back 4

ATP

Front 5

The amount of ATP stored in muscle can sustain contraction for how long?

Back 5

1.2 seconds

Front 6

___________ (a phosphogen) acts as a store of high energy phosphate and is able to regenerate ATP from ADP

Back 6

Phosphocreatine

Front 7

ADP + P-creatine <------->

Back 7

ATP + creatine

Front 8

ADP + P-creatine <-------> ATP
+ creatine (what enzyme?)

Back 8

creatine phosphokinase

Front 9

The amount of phosphocreatine in muscle can sustain contraction for how long?

Back 9

approximately 9 seconds

Front 10

What happens during the resting phase?

Back 10

Phosphocreatine stores are regenerated from ATP by reversal of the reaction catalyzed by creatine phosphokinase

Front 11

How many high energy bonds present in ATP is normally available when muscles contract to produce ADP?

Back 11

Two high energy bonds

Front 12

___________ catalyzes a reaction whereby the other high energy bond left in the ADP can also be used

Back 12

adenylate kinase

Front 13

ADP + ADP <-------> ATP + AMP
(what enzyme?)

Back 13

adenylate kinase

Front 14

Muscle cells contain what enzyme even though there is no gluconeogenesis?

Back 14

PFK-2

Front 15

The cardiac isozyme of PFK-2 is phosphorylated by a cascade initiated by __________

Back 15

insulin

Front 16

Under anaerobic condiions, what is produced that has a negative allosteric effect of PFK-1?

Back 16

H+ ions

Front 17

During strenuous exercise, what accumulates that signals a need for ATP?

Back 17

AMP

Front 18

AMP allosterically activates what enzyme?

Back 18

PFK-1

Front 19

AMP stimulates __________ and also stimulates ___________

Back 19

glycolysis, glycogenolysis

Front 20

What is the importance of Anaerobic Glycolysis?

Back 20

- Onset of exercise. Takes more than a minute for the blood supply of exercising muscle to increase due to vasodilation and increased cardiac output
- Provision of energy in type IIB (white fibers). Have high glycolytic, low aerobic capacity. Low leverls of hexokinase. Little circulating blood glucose used, uses glucose from glycogen
- When need for ATP exceeds the capacity of aerobic ATP producing systems, e.g. during extreme exercise, fight or flight

Front 21

What is produced during anaerobic exercise and can be used by resting skeletal muscle or by the heart?

Back 21

Lactate

Front 22

What molecule can be transported to the liver to be converted back to glucose as part of the Cori Cycle?

Back 22

Lactate

Front 23

Producation of what decreases with the duration of moderate long term exercise?

Back 23

Lactate

Front 24

__________ muscle fibers have a higher concentration of glycolytic enzymes to compensate for low efficiency.

Back 24

Type IIB

Front 25

What molecule in Type IIB muscle fibers is used 12x faster than Type I fibers?

Back 25

Glucose-6-P

Front 26

How long does it take for glycogen stores to be exhausted during strenuous anaerobic exercise?

Back 26

2 minutes

Front 27

What is muscle fatigue believed to be due to?

Back 27

lowering of the cellular pH from 7.0 to approximately 6.4

Front 28

How does AMP stimulate glycolysis?

Back 28

By stimulating PFK-1

Front 29

How does AMP stimulate glycogenolysis?

Back 29

By stimulating glycogen phosphorylase b (only in muscle)

Front 30

An increase in the intracellular _____ derived from the sarcoplasmic reticulum stimulates glycogen phoshporylase kinase?

Back 30

Ca2+

Front 31

During the fight or flight response, __________ is released and stimulated the cAMP mediated cascade in muscle cells.

Back 31

Epinephrine

Front 32

True or False. Muscle cells do not synthesize FAs.

Back 32

True. They use FAs from the blood

Front 33

What enzyme synthesizes malonyl-CoA?

Back 33

Acetyl-CoA carboxylase

Front 34

_____________ inhibits transport of FAs into mitochondria and hence beta-oxidation, via its negative effect on _____________

Back 34

Malonyl-CoA, carnitine palmitoyl transferase I (CPT-1)

Front 35

Muslce cells also contain the enzyme ______________, which converts malonyl-CoA to acetyl-CoA thus removing the inhibition on beta oxidation

Back 35

malonyl-CoA decarboxylase

Front 36

What enzyme phosphorylates Acetyl-CoA carboxylase?

Back 36

AMP-activated protein kinase (AMP-PK) ---> malonyle-CoA levels decrease,, increasing beta oxidation and ATP production

Front 37

What enzyme phosphorylates malonyl-CoA decarboxylase?

Back 37

AMP-activated protein kinase (AMP-PK) ---> removes inhibition from beta oxidation

Front 38

What determines muscle cells' choice of fuel?

Back 38

Depends on the nutrition state and the availability of particular fuels

Front 39

What source of fuel do muscle cells mainly use during prolonged exercise or starvation?

Back 39

Fatty acids. Blood glucose levels fall, as does insulin level - skeletal and cardiac muscle cells normally require insulin for glucose uptake so FA usage favored

Front 40

During extreme exercise, how do muscles get glucose for energy?

Back 40

AMP acting via the AMP-activated protein kinase (AMP-PK) can mobilize GLUT4 transporters to the sarcolemma overcoming insulin dependence for glucose uptake

Front 41

As exercise proceeds, muscle begins to oxidize FAs. What enzyme becomes active?

Back 41

hormone sensitive lipase

Front 42

As FAs are oxidized, the concentration of _________ and _______ in mitochondria increases.

Back 42

acetyl-CoA, NADH ---> inhibits Pyruvate Dehydrogenase (PDH)

Front 43

What inhibits Pyruvate Dehydrogenase as a result of FA oxidation?

Back 43

acetyl-CoA and NADH. This decreases the lfow of carbon units from glucose into the TCA cycle which saves glucose for other tissues

Front 44

How is glucose conserved for other tissues during exercise?

Back 44

Fatty acid oxidation increases the concentration of acetyl-CoA and NADH which decreases the flow of carbon units from glucose into the TCA cycle (PDH inhibited)