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Providing Energy for Muscle
direct phosphorylation, aerobic metabolism, anaerobic metabolism
54
Anatomy
Undergraduate 2
03/08/2014

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Term
What are the 3 main pathways for supplying energy to muscle fibers? Which is reversible?
Definition
Direct phosphorylation of creatine phosphate (rev.)
Aerobic metabolism
Anaerobic metabolism
Term
What are some bodily functions that require ATP?
Definition
G actin -> F Actin
contractile process
pumping Ca to initiate muscle relaxation
Maintaining Na/K ion gradients
Term
True or False

The ATP in resting muscle is sufficient for sustaining numerous twitches
Definition
False

only 1-2 seconds worth can be supported by ATP in resting muscle
Term
What is the immediate source of energy for the conversion of ADP to ATP?
Definition
creatine phosphate (phosphocreatine)
Term
What enzyme recycles ATP?
Definition
creatine kinase
Term
In resting muscles, how much phosphocreatine is present in comparison to ATP?
Definition
2x as much
Term
Where does the reaction involving creatine kinase take place?
Definition
sarcoplasm
Term
How is creatinine removed from the body?
Definition
excreted in the urine
Term
Describe the cycle of muscle contraction using ATP & the enzymatic action of creatine kinase
Definition
1. Glucose converted to ATP
2. ATP fuels muscle contraction
3. ATP converted into ADP + Pi
4. Creatine kinase transferrs P from phosphocreatine to ADP to from ATP
5. Creatine product is converted to creatinine
6. Creatinine is excreted via the urine
Term
Where does creatine get rephosphorylated?
Definition
in the mitochondrial membrane
Term
Can phosphocreatine be depleted?
Definition
yes
Term
How many ATP are produced by the direct phosphorylation of creatine phosphate?
Definition
1 ATP
Term
What is the primary means of producing ATP?
Definition
aerobic metabolism
Term
Which macronutrients can be used to synthesized ATP? Which specific molecules?
Definition
CHO, proteins, lipids

glucose, pyruvate, free fatty acids, amino acids
Term
True or False

ATP synthesis can also occur via degradation products of CHO, lipids & proteins
Definition
true
Term
What are the major substrates for aerobic ATP synthesis in the fed state? Fasted state?
Definition
Fed: glucose
Fasted: free fatty acids from breakdown of TG's
glycogen
Term
When is glycogen used as a backup substrate for aerobic metabolism?
Definition
when glucose & free fatty acids are not broken down fast enough to meet the demands of the contracting muscle
Term
What happens to 'excess' glucose?
Definition
it is stored in the liver as glycogen
Term
After glucose has been absorbed from the GIT, where does it go?
Definition
to the liver, where it is stored as glycogen for future use

to the muscle where it is used for ATP synthesis
Term
How much glycogen is stored in the muscle?
Definition
1% of muscle weight, enough for a few thousand twitches
Term
Where is glycogen found in the muscle?
Definition
at the I bands
Term
What is the process for the initial breakdown of glycogen?
Definition
glycogen -> glucose-1-phosphate
Term
What process in aerobic metabolism does not require oxygen?
Definition
glycolysis
Term
What form of metabolism is used for long term, slow muscle contraction?
Definition
aerobic metabolism
Term
How many ATP are generated from a single glucose molecule?
Definition
36-38
Term
Where does glycolysis occur in the muscle fiber?
Definition
sarcoplasm
Term
What are the products of glycolysis?
Definition
2 moles of pyruvate
CO2
H2O
4 NADH
2 ATP (from glucose) or 3 ATP (from glycogen)
Term
Where does the TCA cycle occur in the muscle fiber?
Definition
in the mitochondria
Term
What reaction occurs in the TCA cycle?
Definition
pyruvate is convered into acetyla CoA, NADH & FADH2 are produced
Term
Where does oxidative phosphorylation occur?
Definition
in the mitochondria of muscle fibers
Term
Why is aerobic metabolism more efficient than anaerobic?
Definition
anaerobic metabolism is limited to the generation of ATP in glycolysis
Term
What is lost with anaerobic metabolism?
Definition
ability to combine H+ with O2 to produce H2O, releasing energy
Term
How much faster is anaerobic glycolysis vs aerobic?
Definition
2.5X
Term
What enzyme is active in anaerobic glycolysis?
Definition
lactate dehydrogenase
Term
What happens to the H+ ions in anaerobic metabolism?
Definition
they cannot be removed fast enough so they accumulate in the muscle, LDH adds them to pyruvate to produce lactic acid
Term
What are the two isoforms of LDH?
Definition
LDH-1: aerobic metabolism
LDH-5: anaerobic metabolism
Term
What inhibits the action of LDH-1?
Definition
pyruvic acid & lactic acid
Term
Which isoform of LDH is typical for skeletal muscles?
Definition
LDH-5
Term
What is the fate of the lactic acid produced during anaerobic metabolism?
Definition
transported to liver: converted to glucose
transported to heart: used as energy source
Term
What is the limiting factor for a runner in a sprint?
Definition
oxygen
Term
What is the effect of high levels of lactic acid in the muscle?
Definition
-muscle pH decreases
-glycolysis decreases
-ATP synthesis decreases
-muscle fatigues & stops contracting
Term
Why do muscles fatigue & stop contracting when lactic acid levels are high?
Definition
low pH & lack of energy available in the form of ATP
Term
What is the role of lactic acid in the conversion of muscle to meat?
Definition
no circulatory system to transport lactic acid so it remains in the muscle
Term
When are aerobic metabolism & creatine phosphate able to meet the energy requirements of muscle?
Definition
-if the muscle is working slowly & has adequate O2
Term
What is glycogenolysis?
Definition
the breakdown of glycogen into glucose & glucose-1-phosphate
Term
Is glycogenolysis used in aerobic or anaerobic metabolim?
Definition
can be used in either
Term
What hormones affect glycogenolysis & why?
Definition
adrenalin & epinephrine
-response to an external stressor causes them to be released, stimulates breakdown of glycogen
Term
Where does glycogenolysis occur?
Definition
in the liver (glucose enters blood) & in muscle tissue (glucose is metabolized)
Term
Describe the initiation process of glycogenolysis
Definition
1. fight/flight causes adrenaline or epinephrine to be released
2. adenylate kinase is activated
3. a series of steps produces an active phosphorylase enzyme
4. phosphorylase enzyme breaks down glycogen
Term
What else is produced besides chemical energy during nutrient metabolism?
Definition
heat
Term
What happens if excess heat cannot be removed from the body?
Definition
hyperthermia
Term
What are the energy substrate & product(s) of phosphorylation of creatine phosphate?
Definition
S: creatine phosphate
P: 1 ATP
Term
What are the energy substrate & product(s) of anaerobic metabolism?
Definition
S: glucose
P: 2 ATP, 2 lactic acid
Term
What are the energy substrate & product(s) of aerobic metabolism?
Definition
S: glucose, pyruvate, amino acids
P:36 ATP, CO2, H2O
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