Chapter 3- Fuel for Muscle and Exercise Metabolism Flashcards
1
Q
what provides energy for muscle contraction?
A
the breakdown of ATP into inorganic phosphate and ADP
2
Q
what are type I fibers ?
A
slow-acting, more myoglobin therefore more capacity for oxidative metabolism
3
Q
what are type II fibers
A
fast-acting, fewer mitochondria and capillary supply, fatigue rapidly
4
Q
what are the three things contained in skeletal muscle
A
75% water
20% protein (myosin, actin, tropomyosin)
5% salts and substances
5
Q
the hydrolysis of ATP yields how many kJ? kcal ?
A
31 kJ or 7 kcal
6
Q
what is the formula of ATP hydrolysis ?
A
ATP + H2O=> ADP+ Pi + H+
7
Q
what are the three mechanisms involved in resynthesis of ATP
A
PCr hydrolysis
glycolysis
TCA cycle
8
Q
what is the resting concentration of ATP in muscle? what does this imply
A
4-5 mmol/kg ww muscle (only enough energy for a few seconds)
9
Q
when does PCr hydrolysis begin ? what is its purpose
A
at immediate onset of contraction to buffer ADP accumulation after you use up the initial quantity of ATP in muscle. this prevents rapid acidification of the muscle and therefore premature fatigue
10
Q
how much is [PCr] in sarcoplasm compared to ATP
A
3-4x
11
Q
why can’t we rely only on PCr hydrolysis ?
A
rate of PCr hydrolysis declines after only a few seconds of maximal force contraction
12
Q
where does PCr hydrolysis occur
A
the sarcoplasm
13
Q
how does glucose uptake from blood happen? with help from what ?
A
GLUT4 transporter
14
Q
what occurs to prevent the loss of glucose from the cell after it passes through the transporter in the muscle ?
A
an irreversible phosphorylation catalyzed by hexokinase.
glucose + ATP => ADP+ glucose-6-phosphate
15
Q
why is the transformation of glucose into glucose-6-phosphate irreversible in the muscle and not the liver?
A
because skeletal muscles lack the enzyme glucose-6-phosphatase, but the liver does not
16
Q
how does one control the production of glucose-6-phosphate in the skeletal muscle ?
A
by negative feedback on hexokinase
17
Q
how does one break down muscle glycogen in order to utilize it ? (formula)
A
glycogen phosphorylase breaks off glucose molecule from glycogen
glycogen + Pi => glucose-1-phosphate + glycogen shorter by one glucose
then, glucose-1-phosphate has the Pi placed on a different carbon to become glucose-6-phosphate with phosphoglucomutase
18
Q
what is the amount of ATP used in glycogen breakdown ?
A
none
you use an inorganic phosphate to bind to glucose so no ATP needed
19
Q
what does phosphoglucomutase do
A
in glycogen breakdown, glucose-1-phosphate has the Pi placed on a different carbon to become glucose-6-phosphate
20
Q
what are the two sources for glycolysis
A
glucose and glycogen
21
Q
what is the main step between glucose/glycogen and pyruvate in glycolysis ?
A
fructose-1,6-bisphosphate is cleaved by aldolase into 2 glyceraldehyde-3-phosphate
22
Q
when pyruvate is produced, what are the two pathways for it ?
A
either it becomes lactate or acetyl CoA
23
Q
how does pyruvate become lactate
A
with lactate dehydrogenase
pyruvate+ NADH => lactate+ NAD+
24
Q
how does pyruvate become acetyl coA
A
with pyruvate dehydrogenase
pyruvate+ CoA + NAD+ => Acetyl CoA + NADH
25
in glycolysis from glucose, what is the total ATP produced ? the net ATP produced ?
total ATP = 4 (2 from each glyceraldehyde-3-phosphate)
| net = 4-2 = 2
26
in glycolysis from glycogen, what is the total ATP produced ? the net ATP produced ?
total ATP = 4
| net= 4-1 = 3
27
what happens if glycolysis is too fast?
availability of NAD+ (necessary cofactor) becomes the limiting factor, and the reaction is limited at the 2 3C chain split (stays at glyceraldehyde 3-phosphate)
28
how can one regenerate the NAD+ in muscle ?
reduction of pyruvate to lactate
29
when does lactate formation occur ?
always, it's just that it accumulates in heavy exercise
30
how does the body deal with lactic acid accumulation ?
lactate brought to liver and converted back to glucose in the Cori Cycle
31
what does the Cori Cycle do
lactate brought to liver and converted back to glucose
32
what is the main goal of the Cori Cycle
gluconeogenesis
33
in resting state, how many ATP and lactate are needed in the Cori Cycle to produce 1 glucose ?
2 lactate and 6 ATP
34
where is the Cori Cycle taking place ? why
the liver because lactate can only go to pyruvate and therefore glucose in the liver
35
what does TCA cycle stand for
tricarboxylic acid cycle (Krebs)
36
what are the two main sources of energy for the TCA cycle
fats and carbs
37
where does the TCA cycle occur ?
in the mitochondrion
38
where does glycolysis occur ?
cytoplasm/sarcoplasm
39
how does a pyruvate get into the TCA cycle ?
it has to first go to the mitochondrion from the cytoplasm
40
what are the two nutrients needed in enzymatic reactions ?
NADH and FADH2
41
what and where is the electron transport chain
creates a proton gradient across inner membrane and mitochondrial matrix
42
what does oxygen do in the ETC
removes electrons from the chain
43
how much ATP is made from ETC ?
38 ATP
44
after how long is glycogen depleted in exercise ?
1-2 h
45
what determines the sustainability of an exercise ?
glycogen stores
46
what is the enzyme responsible for lipolysis
| ?
hormone-sensitive lipase
47
what are the 5 hormones that stimulate HSL ?
```
epinephrine
norepinephrine
glucagon
cortisol
growth hormone
```
48
what inhibits HSL ?
insulin
49
what does HSL do ?
breaks down triacylglycerol into glycerol and 3 FA which go into the blood
50
break down the source of the 38 ATP from the complete oxidation of one glucose molecule
from glycolysis:
2 + 6 (from NADH)
from TCA:
24 (from NADH) + 4 (from FADH2) + 2 (from GTP)
therefore 38 in total
51
how do fatty acids enter the mitochondria ?
< or = to 12 carbons without membrane transporter
| > or = to 14 carbons with membrane transporter
52
why does insulin inhibit HSL ?
bc it promotes TG synthesis
53
during prolonged moderate exercise, what is the rate of lipolysis and the rate of entry of FA into circulation like ?
adipose tissue blood flow increases
54
during intense exercise, what is the rate of lipolysis and the rate of entry of FA into circulation like ?
SNS vasoconstriction causes fall in adipose tissue blood flow, meaning accumulation of FA in adipose tissue
55
the concentration of what limits fat mobilization during intense exercise
lactate because a high amount promotes re-esterification (more TG) and therefore limits entry of FA into bloodstream
56
what happens to glycerol once it's in the circulation ?
taken up by liver or converted into glucose
57
what happens to FA once they are in circulation ?
loosely bounded with albumin for the most part
58
what is uptake of FA by muscle related to directly ?
the plasma FA concentration
59
how do long chain (= or > 14 carbon) FFA get into the mitochondria for oxidation ?
via the carnitine shuttle
60
what is the carnitine shuttle ?
two forms of carnitine-acyl-transferase in the mitochondrial membrane of the muscle. CAT-I outside membrane, CAT-II on inner surface.
FFA becomes FA-CoA or acyl-CoA with acyl-CoA synthetase
then, at the outer membrane, acyl-CoA releases its CoA and binds to carnitine (fatty acyl-carnitine + free CoA) which transports it across membrane in carnitine transporter.. then in the mitochondrion, carnitine is removed and fatty acyl-CoA is reformed
61
what is the main rate-limiting step in utilization of FFA for energy ?
carnitine shuttle
62
beta-oxidation cleaves how many carbons at a time? what does this imply for the beta oxidation of a 16 carbon FA ?
2 carbons at a time
| for a 16C- cleave 7 times
63
what is CAT I (carnitine acyl-transferase) inhibited by ?
malonyl CoA
64
what does malonyl CoA do ?
promote TG formation in cell and therefore inhibits CAT I
65
what does beta-oxidation achieve ?
breakdown of carbons in order to create acetyl CoA to be used in TCA
66
what are ketones ?
by-products of incomplete fat catabolism
67
what are 3 examples of ketones ?
acetone
acetoacetate
beta or 3-hydroxybutyrate
68
what do ketones consist of
2 acetyl CoA form acetoacetate which then can transform reversibly or irreversibly into other ketones
69
what ketone reaction is irreversible
acetoacetate to acetone
70
what is ketosis ?
elevated concentration of ketone bodies (>3mg/dL)
71
what is ketoacidosis ?
concentration of ketones > 90 mg/dL
| overwhelms normal compensatory mechanisms
72
in a type I diabetic, what will be the concentration of ketones ?
90 mg/dL
73
in a healthy person, what will be the concentration of ketones ?
<3 mg/dL
74
when would a ketogenic diet be suggested ?
pediatric epilepsy
75
what 2 normal compensatory mechanisms do we have for ketosis ?
bicarbonate buffering
and respiratory compensation
76
usually, proteins contribute to how much of energy provision ?
5%
77
when do proteins contribute more to energy ?
starvation or depletion of glycogen stores
78
what are the two things that happen before a protein can be oxidized ?
transamination (removal of NH2 group, transfer it to a ketoacid to form a different amino acid)
deamination (formation of ammonia)
remaining molecule can enter TCA
79
how many amino acids can be oxidized to significant amounts ?
6
80
what are the 6 amino acids that can be oxidized to significant amounts ?
```
leucine
isoleucine
valine
asparagine
aspartate
glutamate
```
81
how is energy extracted from protein amino acids ?
after it is digested and absorbed into liver, it can be synthesized into proteins or released into blood for cellular uptake
82
if there is excess protein consumption, what happens ?
used for energy, and the extra is converted into fatty acids for storage as TG
83
why is it untrue that more protein= more muscle ?
because extra protein will turn into TG in storage
84
what are the two kinds of amino acids in terms of structure ?
glucogenic and ketogenic
85
give 5 examples of glucogenic a.a
```
alanine
glycine
serine
cysteine
tryptophan
```
86
give 2 examples of ketogenic a.a
lysine, leucine
87
what happens to the carbon skeletons of glucogenic a.a ?
turn into pyruvate, which will then either go to gluconeogenesis in the liver or become acetyl coA and to into TCA
88
what happens to the carbon skeletons of ketogenic a.a ?
turn into acetyl coA and then either become FFA, ketones, or go into TCA
89
in the process of deamination in the liver, what happens to the NH3 (ammonia) ?
becomes urea and excreted by kidneys in urine
90
what is gluconeogenesis ?
formation of glucose from non carb sources such as protein
91
how do CHO intake impact protein metabolism
low CHO = high protein metabolism
92
at 60% VO2max what is one's main source of energy at the onset of workout ?
ATP and PCr
93
at 60% VO2max what is one's main source of energy at 5-10 s of workout ?
glycolysis
94
at 60% VO2max what is one's main source of energy after a few minutes ?
glycogen stores
95
at 60% VO2max what is one's main source of energy at 30 min ?
glycogen but starting to metabolize fat
96
at 60% VO2max what is one's main source of energy at 45 min ?
glycogen and fat
97
how much glycogen is stored in liver and muscle and blood
liver: 100g
muscle: 300g
blood: 0.9g/L or 5 mmol/L
98
where is fat stored ?
in white adipose tissue and also intramuscularly
99
where is fat found in muscle ?
dispersed along muscle fibers, close to mitochondria within fibers
100
what supports the view that intramuscular fat could be a good source of energy during prolonged exercise ?
decrease of intramuscular triglyceride post-exercise
101
which fibers contain more intramuscular triglyceride ?
type I
102
which nutrient is the best at energy storage ?
fat
103
what is the drawback to fat as fuel ?
slow, takes more time to tap into it as source of fuel
104
1g fat, carb, protein= ? kcal
1 g fat= 9 kcal
1 g carb = 4 kcal
1 g protein = 4 kcal
105
why are carbs not as efficient in storage ?
1g carb stored with 3g water, less efficient and can be overloaded with water
106
how much exercise time can blood, muscle, and liver CHO provide ?
2 hrs
107
how much exercise time can fat provide ?
>80 hrs but you need to know how to utilize it
108
how much exercise time can protein provide ?
30 hours but rarely used (only in dire situations)
109
what is the limitation to fat as fuel in high intensity exercise ?
can't maintain exercise at an intensity higher than 60% VO2max
110
what are 4 intramuscular factors that regulate mobilization of fuels
ATP/ADP
Pi
AMP
Ca2+
111
how does ATP regulate fuel mobilization
decline in ATP cellular concentration means parallel increases in ADP and AMP, directly stimulate anaerobic and oxidative resynthesis
112
what is the rate-limiting step in glycolysis ?
conversion of fructose-6-phosphate to fructose-1,6-diphosphate by phosphofructokinase (PFK)
113
what is the rate-limiting step in glycogen breakdown to prepare for glycolysis ?
glycogen phosphorylase concentration who converts glycogen to glucose-1-phosphate
114
what is the rate-limiting step in carb oxidation
from pyruvate to acetyl coA by pyruvate dehydrogenase
115
what is the rate limiting step in the TCA cycle ?
citrate synthase concentration
116
what controls glycogen phosphorylase in the rate-limiting step of glycogen breakdown
glycogen breaking down to glucose-1-phosphate
+ AMP, Pi, Ca2+, epinephrine
- ATP
117
what controls phosphofructokinase in the rate-limiting step of glycolysis
fructose-6-phosphate going to fructose-1,6-diphosphate
+ ADP, AMP, Pi, NH4+
- ATP, H+
118
what controls pyruvate dehydrogenase in rate limiting step of carb oxydation
pyruvate goes to acetyl coa
+ Ca2+, ADP, CoA, NAD+
- ATP, NADH
119
what controls citrate synthase in rate limiting step of TCA ?
+ ADP, NAD+
| - ATP, NADH
120
which hormone is anabolic ?
insulin
121
which hormones are catabolic ?
all those we've learned except insulin
122
glucagon: how is it stimulated and what does it do
stimulated by fall in blood glucose
| stimulates gluconeogenesis and liver glycogen breakdown
123
epinephrine: how is it stimulated and what does it do
stimulated by stress and fall in blood glucose
| stimulates glycogen breakdown and lipolysis
124
norepinephrine: how is it stimulated and what does it do
stimulated by stress, fall in blood glucose and BP
| stimulates glycogen breakdown and lipolysis
125
cortisol: how is it stimulated and what does it do
stimulated by stress, ACTH, interleukin-6
| stimulates protein breakdown, lipolysis, gluconeogenesis
126
growth hormone: how is it stimulated and what does it do
stimulated by stress
| stimulates lipolysis
127
interleukin-6: how is it stimulated and what does it do
stimulated by Ca2+ and decreased glycogen
| stimulates glycogen breakdown, cortisol secretion, lipolysis
128
insulin : how is it stimulated and what does it do
stimulated by rise in blood glucose and amino acid
stimulates uptake of blood glucose and amino acids
inhibits lipolysis and protein breakdown
129
why does Ca2+ cause positive feedback for energy ?
stimulates GLUT4 translocation and therefore glucose uptake
130
in exercise, what is enhanced in order for cells to take in glucose ?
GLUT4
131
how is insulin enhanced in exercise ?
it's not
132
what promotes GLUT4 translocation
Ca2+ increase due to exercise
133
what mostly promotes GLUT4 at rest ? in exercise
at rest: insulin
| in exercise : Ca2+
134
how does epinephrine and glucagon act upon a cell to activate HSL ?
bind to membrane, release adenylate cyclase and enzyme cascade, covalent activation leads to hormone activation
135
what role does cortisol have in lipolysis ?
increases effectiveness of catecholamines
136
if you stop exercising, does lipolysis stop right away
no
137
what is fatigue ?
inability to maintain work at a given force/power output
138
what will the rates of anaerobic ATP resynthesis be like from PCr hydrolysis over time ?
at first, strong
| then, declines abruptly until there is almost none at 20-30s
139
what will the rates of anaerobic ATP resynthesis be like from glycolysis over time ?
slowly increase until a drop at 20-30s
140
in a graph with x=time and y=g glycogen/kg muscle, how will the slope vary with varying %VO2max
at 120%VO2max, extremely sharp drop in slope
then less and less sharp drop
30% VO2max depletion much slower, since there is also fat oxidation that supplies energy
141
in a graph with x=time and y=g glycogen/kg muscle, what are the two things we can look at with varying %VO2max
the slope of decline in glycogen and also the duration of the exercise
30%Vo2max able to last longer and with less of a decline in glycogen bc there is also fat utilization
142
why is there a drop in plasma FA at 30 min of exercise ?
fatty acid oxidation takes time, usually starts at 30 min after prolonged exercise, therefore will use up plasma FA until lipolysis comes through at 30 min
143
when does peak uptake of glucose occur regardless of exercise intensity ?
90 min
144
how can one increase the utilization of glucose depending on the intensity of the workout ?
increase intensity and you'll uptake more glucose
145
as duration of exercise increases, which fuel utilization will increase the most ?
fat
146
as duration of exercise increases, which fuel utilization will decrease the most ?
muscle glycogen
147
what is a way of replenishing glycogen stores ?
sports drinks
148
in resting post-absorptive state, glucose release is enough only for what ?
CHO demands of CNS
149
energy going to CNS in post absorptive state is what%
70% CHO from liver glycogen
| 30% from gluconeogenesis
150
in exercise, rate of hepatic glucose release related to what
exercise intensity (contribute to 90% CHO)
151
in trained athletes, how will hormone concentrations change during exercise ?
they will have an attenuated response
152
what will happen to intramuscular triglyceride content in trained athletes ?
increase concentration due to better fat utilization
153
how will rate of lactate accumulation change in trained athletes ?
decrease
154
how will rate of muscle glycogen and glucose change in trained athletes ?
decrease
