Lecture 1 Flashcards by Jessica Kaufman

Energy currency

ATP

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ATP production ___ during exercise

increases

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ATP has:
1.
2.
3.
energy systems

Immediate
Short term
Long-term

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Anaerobic metabolism

does NOT requite oxygen for the release of energy from fuels

ATP-CP system
* 2. Glycolysis (glucose → pyruvate)*

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Sources of muscle glucose for glycolytic metabolism

blood glucose from exogenous source
glycogen (from muscle)
blood glucose from liver glycogen
⇣ All go to: glycolytic sequence (ADP + Pi → ATP)
1. Pyruvic acid in slow glycolysis
2. Lactic acid in fast glycolysis

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Energy release from carbs

Glucose: 36ATP

Avg carbohydrate = 4.2kcal/gm

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Energy release from fats

146 ATP

trigylcerides: 457 ATP

average lipid 9.4kcal/gm

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Energy release from proteins

average protein = 5.65 kcal/gm

in the body: 4.6kcal/gm (due to loss of H+ by urea)

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Glycolysis occurs in the:

cytosol

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Hexokinase & glycolysis

Hexokinase traps glucose in the cell by adding a phosphate group

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Phosphofructokinase (PFK)

Rate-limiting enzyme for glycolysis which is under regulatory control

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Glycolysis generates ATP very (fast/slow) without a requirement for ___ - but limited amounts are produced ( __ ATP per glucose)

Fast

no requirement for O2

limited amount - 2ATP/glucose

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Glycolysis is an extremely important source of ATP especially at the ___ of exercise & when exercise is: __

or when:

onset of exercise (first 90s)
intense exercise
at maximal levels of exercise when demand for O2 outstrips deliver to the muscle cell

Example: exercise in patients with chronic CV or respiratory diseases

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Small amounts of lactic acid are formed ___ in tissues and red blood cells

continuously

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Accumulation of lactate in the blood means that production >> ___

production>>utilization by other tissues

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Lactate can be metabolized by other cells for:

-energy (liver, heart, muscle)

or used for gluconeogenesis in the liver

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Accumulation of blood lactate is associated with

significant levels of anerobic metabolism

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formation of lactic acid (diagram)

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Aerobic Metabolism

Requires oxygen for the release of energy from fuels

Krebs cycle oxidizes carb, fat, & protein breakdown products - liberate electrons (H+)*
O2 drives oxidative phosphorylation - the production of ATP from electrons*

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Krebs Cycle is part of ___ metabolism

aerobic

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Krebs cycle is the intersection of:

carbohydrate, fat, and protein catabolism

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(Krebs Cycle) carbohydrates, fats, and some amino acids provide:

acetyl-CoA

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(Krebs Cycle) proteins provide mostly

pyruvate (and other Krebs cycle intermediates)

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Krebs cycle produces

FADH and NADH → used by electron transport chain to produce ATP

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Metabolic Mill

describes the Krebs cycle as the convergence point for a carbohydrate, fat, and protein catabolism

Lipids burn in a:

carbohydrate flame -*pyruvate supplies oxaloacetate (an acceptor for Acetyl-CoA)*

If the rate of glycolysis is too slow for the amount of lipid breakdown =

build-up of excessive Acetyl-CoA and FFA build up in the plasma → ketone body formation by the liver (diabetic ketoacidosis)

Acetyl-CoA is the ___ to the Krebs Cycle

entry point

Amino acids can enter the krebs cycle at __ points

several

Excess glucose can be stored as

fat

excess protein can be stored as (and also used as)

1. fat 2. Protein can be used to by the liver to make glucose (gluconeogenesis)

Excess fat & glucose

excess fat cannot be used to make glucose

Excess fat & the liver

in the liver, the glycerol derived from the breakdown of triglycerides can be used as the backbone for synthesis of glucose. *ONLY PROVIDES A SMALL AMOUNT OF GLUCOSE*

Carbohydrate (CHO) functions in the body

1. Fuel for CNS and red blood cells 2. Energy source during activity 3. Helps preserve tissue protein 4. Serve as a primer for fat metabolism

Most of the time, CNS uses __ for energy exclusively

glucose

Under chronic low carbohydrate conditions, like ketoacidosis or starvation (hypoglycemia), the CNS can adapt over time and metabolize ___ for energy.

ketones

symptoms of hypoglycemia

weakness hunger dizziness *profound hypoglycemia can cause unconsiousness and irreversible brain damage*

Relationship between glycogen stores and fatigue

Pre-exercise muscle glycogen depletion impairs vigorous exercise capacity

Moderately Heavy Exercise (70% VO2 Max): note reliance on blood glucose and glycogen stores decline

*Glucose as an energy source during activity* Glycogen in liver and muscle can be broken down into

glucose

*Glucose as an energy source during activity* Muscle glycogen stores can be depleted after:

several hours → causing fatigue

*Glucose as an energy source during activity* Blood glucose is also taken up by ___ which increases with __ intensity

active muscle *uptake increases with exercise intensity*

*Glucose as an energy source during activity* As muscle glycogen stores decline there is an increasing reliance on ___ as the source of carbohydrate

blood glucose

Carbohydrate supplementation during prolonged exercise can ___ fatigue

delay * Carb intake is 1g/min or drinking 240mL (8oz) of a 5% carbohydrate solution every 15 mins* * Absorption from GI tract = limiting factor → igestion should take place early in the prolonged exercise (within first 90 mins) so carbohydrates are available during the latter stages of exercise*

“Hitting the wall”

Correlation between low levels of muscle glycogen and fatigue

**_Relationship between glycogen stores and fatigue_**

1. muscle glycogen plays a role as a primer for lipid metabolism 2. rate of energy production is slower from lipids than from glycolysis 3. *RESULT: slow ATP production and increasing cellular acidosis -→ promote fatigue*

Role of lipids in the body

1. Energy source and storage 2. Protection of Vital Organs (padding) 3. Thermal insulation (subcutaneous fat) 1. protective during prolonged cold exposure 2. Hinders thermoregulation during heat stress 4. Vitamin carrier and hunger supressor

Fatty acids are stored as ____ in ___ and to a limited extent in \_\_\_

stored as: trigylcerides in: adipocytes and limited extent in muscle cells

fatty acids are liberated from triglycerides and enter ____ in \_\_\_\_

enter: beta-oxidation in: mitochondria

Beta-oxidation produces ___ for electron transport chain and ____ for Krebs Cycle

H+ for electron transport chain and acetyl CoA for Krebs Cycle

At rest, lipids provide \_\_\_% of energy

50-90%

the proportion of energy supplied by lipids increases with

duration of exercise

proportion of energy suppled by lipid also depends on

intensity of exerucse

At ___ to ___ intensity, the greatest % of energy requirements during steady state exercise is derived from lipids

light to moderate (60-70% VO2 Max) *At very heavy exercise intensities (e.g. \>80% VO2 max) lipid oxidation drops off considerably → extra demand for ATP with heavy intensity is supplied by glucose*

**_\*\*\*With higher intensity exercises, a reduction in the % of energy derived from fat doesn't necessarily mean that the amount of fat burned goes down as well_**

*Lipids as an energy source after training* Training adaptations increase the ability to use ___ as an energy source especially those mobilized from

increase the ability to use fat as an energy source; especially those mobilized from muscle trigylceride stores

*Lipids as an energy source after training* Absolute rates of fat oxidation during submax exercise are higher after

aerobic exercise training

*Lipids as an energy source after training* Factors that contribute to increased endurance after exercise training

1. Conserving limited glycogen stores 2. enhanced lipid oxidation

Sources of proteins

plasma, muscle, visceral tissue

At rest \_\_% of energy is supplied by protein catabolism

2-5%

Certain amino acids can be used for:

1. Gluconeogenesis 2. Energy source (Krebs Cycle) 3. Fat synthesis (they can be a source of acetyl-CoA, the building block for fat)

Proteins produce ___ (as well as other Kreb Cycle intermediates)

Acetyl-CoA

Protein and ATP during exercise

protein is not a major source of ATP during exercise in a well-nourished individual

branched chain amino acids & ATP during exercise

branch chain amino acids can be oxidized by skeletal muscle and thus can supply ATP

Lack of CHO or lipid for metabolism results in a large increase in

protein catabolism

protein use for energy greatly increases when subjects exercise in a ____ state.

glycogen-depleted

the liver can produce glucose from precursors released from active muscle: (2 precursors)

1. lactic acid 2. alanine

Alanine is converted to glucose in the \_\_\_\_ supplies plasma glucose to \_\_\_\_\_\_

1. converted to glucose in the liver 2. Supplies plasma glucose to muscle

**_\*\*Alanine is an important source for gluconeogenesis in_**

long-term (hours) endurance exercise *up to 45% of liver glucose release is due to alanine*

Estimate \_\_\_% of total energy requirement for prolonged exercise is supplied by alanine-glucose cycle

10-15%

Maximal absolute rates of fat oxidation occur over a wide range of light to moderate exercise ## Footnote **_\*\*Fat max 55 to 72% VO2 max, corresponses to ___ HR Max_**

68-79%

**\*\*_% of energy derived from fat decreases as exercise intensity \_\_\__**

increases