Energy Metabolism Flashcards
(105 cards)
1
Q
What is a kilocalorie (kCal)?
A
- A measure of heat that expresses a food’s energy value
- 1 kCal = quantity of energy needed to raise the temperature of 1 kg of water 1 degree C
2
Q
Energy Value of the Macronutrients
A
- Carbohydrate = 4 kCal/g
- Fat = 9 kCal/g
- Protein = 4 kCal/g
3
Q
Bioenergetics
A
The flow and exchange of energy within a living system
4
Q
Oxidation Reaction
A
Reactions that:
- Involve electron loss (always)
- Transfer oxygen, hydrogen atoms, or electrons
5
Q
Reduction Reaction
A
Reactions that involve electron gain (always)
6
Q
Reducing Agent
A
Substance that donates or loses electrons as it oxidizes
7
Q
Oxidizing Agent
A
Substance that gains electrons as it is reduced
8
Q
ATP
A
- Food macronutrients provide major sources of potential energy but do not transfer directly to biologic work
- The PE within ATP powers all of the cell’s energy-requiring processes
- Represents the cell’s energy currency
9
Q
ATP Composition
A
Adenosine linked to 3 phosphates
10
Q
ATP Hydrolyzation
A
- ADP forms when ATP joins with water
- Reaction catalyzed by ATPase
11
Q
Locations of ATP Production in the Cell
A
- Mitochondria
- Cytosol
12
Q
The Cell’s Major Energy-Transforming Activities
A
- Extract PE from food and conserve it within ATP bonds
- Extract and transfer the chemical energy in ATP to power biologic work
13
Q
ATP Supply
A
- Cells contain only a small quantity of ATP (80-100 g)
- Has to be continually resynthesized
14
Q
Primary Means of ATP Production
A
- ATP-PCr
- Glycolysis
- Oxidative phosphorylation
15
Q
Phosphocreatine
A
- Some energy for ATP resynthesis comes from anaerobic splitting of a phosphate from PCr
- Cells store ~4-6x more PCr than ATP
- Reaches its max energy yield in about 10 seconds
- Reaction catalyzed by phosphocreatine kinase (PCK)
16
Q
Function of ATP-PCr System
A
High intensity exercise of short duration
17
Q
Glycolysis
A
- Breakdown of glucose
- Occurs in the cytosol of the cell
18
Q
Glucose
A
Blood sugar (CHO)
19
Q
Glycogen
A
- Storage form of glucose
- Chain of glucose molecules
- Synthesized by glycogen synthase
- Some stored in muscle and liver
20
Q
Glycogenesis
A
Formation of glycogen
21
Q
Glycogenolysis
A
Breakdown of glycogen
22
Q
Glyconeogenesis
A
Formation of “new” glucose from other substances, such as protein and fat
23
Q
Forms of Carbohydrate Breakdown
A
- Aerobic glycolysis
- Anaerobic glycolysis
24
Q
Aerobic Glycolysis
A
- Pyruvate becomes the end product
- Slow Process
25
Anaerobic Glycolysis
- Results in lactate formation
| - Rapid process
26
Enzymes for Glycolysis
- Hexokinase
- Phosphofructokinase
- Pyruvate kinase
27
Hexokinase
- Phosphorylates glucose
| - Makes glucose-6-phosphate
28
Phosphofructokinase
- Phosphorylates glucose-6-phosphate
| - Makes fructose-1,6-biphosphate
29
Pyruvate Kinase
- Responsible for ADP + P --> ATP at the end of glycolysis
| - Makes pyruvate for Kreb Cycle
30
Glycolysis is Regulated by
- Concentrations of the enzymes
- Levels of the substrate fructose-1,6-biphosphate
- Oxygen
31
Products of Glycolysis (per glucose)
- ATP --> 2 from glucose
- ATP --> 3 from glycogen
- NADH --> 2
- Pyruvate --> 2
32
Intermediate Step
- Pyruvate is converted into Acetyl CoA (aerobic)
| - Pyruvate is converted into Lactate (anaerobic)
33
Pyruvate Dehydrogenase
- Oxidizes pyruvate
- Removes a carbon to make CO2
- Reduces NAD+ to make NADH
- Adds CoA to the 2-carbon molecule to make Acetyl CoA
34
Products of the Intermediate Step (per glucose)
NADH --> 2
35
Energy Metabolism Regulation
Compounds that either inhibit or activate enzymes in the oxidative pathways modulate regulatory control of glycolysis and the citric acid cycle
36
Enzyme Inhibitors
- ATP
| - NADH
37
Enzyme Activators
- ADP
| - NAD+
38
What has the greatest effect on the rate limiting enzymes for energy metabolism?
Cellular ADP concentrations
39
When is the Lactic Acid System used?
- Used to phosphorylate ADP during intense, short-duration exercise
- Used in max exercise that usually lasts for 60-180 seconds before rapid and large accumulations of blood lactate occurs
40
Where does the energy for the Lactic Acid System come from?
- Comes from stored muscle glycogen breakdown via anaerobic glycolysis
- Results in lactate formation
41
Blood Lactate Threshold
- Occurs when the muscle cells can neither meet the energy demand of exercise aerobically nor oxidize lactate at its rate of formation
- Occurs at a higher percentage of VO2 max for trained vs untrained individuals
42
Kreb's Cycle
- Step that follows glycolysis in aerobic metabolism
- Takes Acetyl CoA through the cycle to produce ATP, NADH, and FADH2
- Takes place in the mitochondrial matrix
43
Enzymes of Kreb's Cycle
- Citrate Synthase
| - Succinate Dehydrogenase
44
Citrate Synthase
- Catalyzes first reaction of Kreb's Cycle
- If citrate synthase concentration goes up, oxidative capacity goes up
- Anything else???
45
Succinate Dehydrogenase
-
46
Products of the Kreb's Cycle
- ATP --> 1 ATP x 2 = 2 ATP
- NADH --> 3 NADH x 2 = 6 NADH
- FADH2 --> 1 FADH2 x 2 = 2 FADH2
47
Oxidative Phosphorylation
Oxidation
- NADH and FADH2 transfer electrons to ETC
- Final acceptor of electron is oxygen
Phosphorylation
- Energy generated by oxidation is used to resynthesized
48
Amount of ATP from NADH and FADH2
- 3 ATP from each NADH
| - 2 ATP from each FADH2
49
Electron Transport Chain
-
50
Respiratory Chain
-
51
Electron Transport
-
52
Fat Catabolism Energy Sources
- Triglycerides stored directly within the muscle fiber
- Circulating triglycerides in lipoprotein
- Circulating free fatty acids mobilized from triglycerides in adipose tissue
53
Lipolysis
Breakdown of triglycerides into glycerol and free fatty acids (FFAs)
54
Beta Oxidation
- Subsequential removal of 2-Carbon units by oxidation at the beta position
- Each round of B-oxidation produces 1 NADH, 1 FADH2, and 1 ACoA
- ACoA --> Kreb's Cycle
- NADH and FADH2 --> ETC
55
Lipase
- Enzyme that breaks down triglycerides
| - As enzyme concentration increases, fat oxidation increases
56
Types of Lipase
- Hormone Sensitive Lipase
| - ATGL Lipase
57
Fat Catabolism Process
1) Breakdown of triglycerides to FFAs
2) Transport of FFAs in the blood
3) Uptake of FFAs from blood to muscle
4) Preparation of FFAs for catabolism
5) Entry of activated FFA into muscle mitochondria
6) Breakdown of FFA to ACoA via B-oxidation and the production of NADH and FADH2
7) Coupled oxidation in citric acid cycle and ETC
58
Triglycerides
- Stored form of fat in muscle and adipose tissue
| - Breaks down into glycerol and fatty acids
59
Phospholipids
Not used as an energy source
60
Steroids
- Derived from cholesterol
| - Used for sex hormone
61
Protein
- Composed of amino acids
- Some can be converted to glucose in the liver via gluconeogenesis
- Can be converted to metabolic intermediates which contribute as a fuel in muscle
- Not a primary energy source during exercise
62
Lactate Threshold
- The point at which blood lactic acid rises systemically during incremental exercise
- Appears at ~50-60% VO2 max in untrained subjects
- Appears at ~65-80% VO2 max in trained subjects
- One of the best determinants of an athlete's pace in endurance events
63
Other names for lactate threshold
- Anaerobic threshold
- Onset of blood lactate accumulation (OBLA)
- Blood lactate levels reach 4 mmol/L
64
Factors related to lactate threshold
- Low tissue oxygen
- Reliance on glycolysis
- Activation of fast-twitch muscle fibers
- Reduced lactate removal
65
Rest-to-Exercise Transitions
- ATP production increases immediately
- Oxygen uptake increases rapidly
- Reaches steady state within 1-4 minutes
- After steady state is reached, ATP requirements are met through aerobic ATP production
- Initial ATP production through anaerobic pathways
- Incurs oxygen deficit
66
VO2 Max
- When oxygen consumption plateaus or increases only slightly with additional increases in exercise intensity
- Provides a quantitative measure of aperson's capacity for aerobic ATP synthesis
67
Other names for VO2 Max
- Maximal oxygen uptake
- Maximal oxygen consumption
- Maximal aerobic power
- Aerobic capacity
68
Oxygen Deficit
- Difference between total oxygen consumed during exercise and the total that would have been consumed had steady-state oxygen uptake been achieved at the start of exercise
- Represents immediate anaerobic energy usage until aerobic pathways can meet energy demands
69
Oxygen Deficit for Trained Subjects
- Trained subjects have a lower oxygen deficit
- They have better-developed aerobic bioenergetic capacity due to cardiovascular or muscular adaptation
- Results in lesser lactic acid production
70
Effect of Training on Oxygen Deficit
- Training reduces oxygen deficit
| - Slope of the graph is steeper
71
Other terms for oxygen deficit
- Oxygen debt
| - Excess post-exercise oxygen consumption (EPOC)
72
Rapid Portion of O2 Debt
- Resynthesis of stored PC
| - Replenishing muscle and blood O2 stores
73
Slow Portion of O2 Debt
- Elevated heart rate and breathing = increased energy need
- Elevated body temperature = increased metabolic rate
- Elevated epinephrine and norepinephrine = increased metabolic rate
- Conversion of lactic acid to glucose (gluconeogenesis)
74
Factors Contributed to Increased EPOC
- Resynthesis of PC in muscle
- Lactate conversion to glucose
- Restoration of muscle and blood oxygen stores
- Elevated body temperature
- Post-exercise elevation of HR and breathing
- Elevated hormones
75
Muscle Fiber Types
- Fast-twitch (type II)
| - Slow-twitch (type I)
76
Fast-Twitch Muscle
- Rapid contraction speed and high capacity for anaerobic ATP production in glycolysis
- Highly active in change-of-pace and stop-and-go activities
- Type IIa --> high aerobic capacity
- Type IIb
77
Slow-Twitch Muscle
- Generates energy through aerobic pathways
- Slower contraction speed than fast-twitch
- Active in continuous activities requiring steady-state aerobic energy transfer
78
Methods for Measuring Energy Cost of Exercise
- Direct Calorimetry
| - Indirect Calorimetry
79
Direct Calorimetry
- Measures the body's heat production to calculate energy expenditure
- Considerable theoretical implications, but limited practical implications, especially for sports
80
Indirect Calorimetry
Calculates energy expenditure from RER of CO2 and O2
81
Types of Indirect Calorimetry
- Closed-Circuit
| - Open-Circuit
82
Advantages of Indirect Calorimetry
- Simpler and less expensive
| - Yields results comparable to direct measurement in the human calorimeter
83
Closed-Circuit Spirometry
- Simple method and is able to directly measure O2 consumption
- Limited practical applications
84
Procedure for Closed-Circuit Spirometry
- Subject breathes 100% O2 from prefilled spirometer
- It is a closed system because the subject rebreathes only the gas in the spirometer
- A canister of potassium hydroxide is placed in the breathing circuit absorbs CO2 in the exhaled air
- A drum attached to the spirometer revolves at a known speed to record O2 consumed from changes in the system's total volume
85
Problems with Closed-Circuit Spirometry
- Becomes problematic during exercise
- Subject must remain close to the bulky equipment
- Circuit offers considerable resistance to accommodate the large breathing volumes during exercise
- CO2 removal lags behind its production rate during intense exercise
86
Open-CIrcuit Spirometry
Provides a relatively simple, practical way to measure O2 consumption and infer energy expenditure
87
Procedure for Open-Circuit Spirometry
- Subject inhales ambient air with a constant composition (20.93% O2, 0.03% CO2, 79.04% nitrogen)
- Changes in O2 and CO2 %'s in expired air compared with the % in inspired ambient air indirectly reflect the ongoing process of energy metabolism
88
Doubly Labeled Water Technique
- Provides a safe way to estimate total daily energy expenditure in free-living conditions without the normal constraints imposed by laboratory
- Expensive and needs sophisticated measurement equipment
89
Doubly Labeled Water Technique Procedure
- Subject consumes water with a known concentration of stable isotopes of hydrogen and O2
- Labeled hydrogen leaves the body in sweat, urine, and pulmonary water vapor
- Labeled oxygen leaves as both water and CO2
- Differences between elimination rates of isotopes relative to the body's normal levels estimate total CO2 production
- O2 consumption is estimated from CO2 production and an assumed RQ value of 0.85
90
Effectiveness of Doubly Labeled Water Technique
- Within 3-5% compared to directly measured energy expenditure in controlled settings
- Provides an ideal way to assess total energy expenditure over prolonged periods including bed rest and extreme activities
- Drawbacks include the cost of the water and expense incurred in spectrometric analysis of both isotopes
91
Respiratory Exchange Ratio
- Ratio between CO2 released (VCO2) and oxygen consumed (VO2)
- RER = VCO2/VO2
- RER = 0.7 = 100% fat utilization
- RER = 1.00 = 100% carb utilization
92
Sources of fat during exercise
- Intramuscular triglycerides
| - Plasma FFA
93
Intramuscular Triglycerides
Primary source of fat during higher intensity exercise
94
Plasma FFA
- From adipose tissue lipolysis
(triglycerides --> glycerol + FFA)
- FFA converted to acetyl-CoA and enters Krebs cycle
- Primary source of fat during low-intensity exercise
- Becomes more important as muscle triglyceride levels decline in long-duration exercise
95
What happens to FOx in obese populations
Obese populations have a decreased ability to oxidize fat
96
Metabolic Flexibility
- The capacity for the organism to adapt fuel oxidation to fuel availability
- Especially evident during a fasting state
97
Metabolism
Involves all of the chemical reactions of biomolecules within the body that encompass synthesis and breakdown
98
Total daily energy expenditure factors
- Resting metabolic rate (60-75%)
- Thermogenic effect of food consumed (10%)
- Energy expended during physical activity and recovery (15-30%)
99
Metabolic Rate
Rate at which the body expends energy at rest and during exercise
100
Basal Metabolic Rate
- Minimum energy required for essential physiological function
- Between 1200 and 2400 kCal
101
Resting Metabolic Rate
- Minimum energy required for normal daily activity
| - Between 1800 and 300 kCal
102
Factors affecting BMR
- Fat-Free mass up = BMR up
- Body surface area up = BMR up
- Age up = BMR down
- Body temperature = BMR up
- Stress up = BMR up
- Thyroxine and epinephrine up = BMR up
103
Physical Activity and Metabolism
- Most profound effect on metabolism
- Each 1 pound gain in FFM increases RMR by 7-10 kCal daily
- Offsets the decrease in RMR that usually accompanies aging
104
Thermic Effect of Food
- Food consumption increases energy metabolism, maxing out within an hour of a meal
- Overweight people often have a blunted thermic response to eating that contributes to excess body fat
105
Metabolic Equivalent (MET)
- Energy/O2 requirement when at rest
| - 1 MET = 3.5 mL x kg^-1 x min^-1
