Wk 2 - bioenergetics, exercise metabolism and hormonal responses to exercise Flashcards
What are bioenergetics?
-Bioenergetics -> Flow and exchange of energy within a living system. Conversion of foodstuffs (fats, proteins, carbohydrates) into usable energy for cell work. ‘Chemical -> mechanical’.
What is metabolism?
-Metabolism -> Sum of all chemical reactions that occur in the body.
* Anabolic reactions – synthesis of molecules e.g. glucose being stores as glycogen
* Catabolic reactions – breakdown of molecules e.g. glycogen being broken down into glucose
What are cellular chemical reactions?
-Cellular chemical reactions -> Energy cannot be created or destroyed only transformed from one form to another (1st law of thermodynamics). Endergonic = requires energy to be added to the reactants. Exergonic = releases energy.
-Cellular chemical reactions: coupled reactions -> Liberation of energy in an exergonic reaction drives an endergonic reaction.
What are oxidation-reduction reactions?
-Oxidation-reduction reactions -> Are always coupled reactions. Oxidation = removing an electron. Reduction = addition of an electron. Nicotinamide adenine dinucleotide (NAD) and Flavin adenine dinucleotide (FAD) play an important role in the transfer of electrons, acting as ‘carrier molecules’ during bioenergetic reactions.
Describe enzymes: catalysts for reactions:
-Enzymes: catalysts for reactions -> Enzymes are proteins that lower the energy of activation and accelerate chemical reactions. Increased rate of product formation. Enzymes are not consumed or changed by the reaction they are involved in.
How do enzymes lower the energy of activation?
- Kinase – add a phosphate group
- Dehydrogenases – remove hydrogen atoms
- Oxidases – catalyse oxidation-reduction reactions involving oxygen
- Isomerases – rearrangement of the structure of molecules
How does the cellular environment influence enzyme activity?
-> Temperature and pH level. pH level – Heavy exercise increases lactate threshold. Increased H+ results in a lowered pH. Lowered pH ATP production and muscular fatigue.
Describe ATP
-Adenosine triphosphate (ATP) -> High energy phosphate molecule. Synthesis: ADP + Pi = ATP. Breakdown: ATP -> (ATPase) -> ADP + Pi + Energy. ‘Universal energy donor’. Only small amounts of ATP in intramuscular stores (enough <2s of all-out exercise).
Describe bioenergetics: metabolic pathways activated to form ATP:
- Anaerobic pathways (substrate-level phosphorylation) – Do not involve oxygen and there is PC breakdown and glycolysis (degradation of glucose)
- Aerobic pathways – Required oxygen, oxidative phosphorylation, dependent on respiratory and cardiovascular systems to deliver adequate O2.
Describe anaerobic ATP production: ATP-PC system and glycolysis
- ATP-PC system -> Most rapid (milliseconds) and simplest (one-enzyme reaction) method of producing ATP by phosphocreatine breakdown. Although PC can be reformed with recovery, limited capacity to provide prolonged energy e.g. depleted after 10-15secs all out activity.
- Glycolysis -> Increase in the by-products of ATP breakdown activates energy influx through reactions of the glycolytic pathway. Anaerobic glycolytic capacity is threefold higher (~30-90s) than the ATP-PC system. Besides ATP, produces: 2 NADH, and 2 pyruvate or 2 lactate.
What is the net gain of glycolysis dependent on the starting point?
-> Glycolysis occurs in 2 phases. Net gain of glucose is the substrate 2 ATP. Net gain of glycogen is the substrate 3 ATP.
Describe electron carrier molecules and how it is achieved:
-Electron carrier molecules -> For chemical reactions in glycolysis to continue, adequate amounts of NAD+ must be available to accept H+. Therefore NAD+ needs to be rapidly reformed from NADH. This is achieved as follows:
1. If sufficient O2 is available, H+ can be ‘shuttled’ into the mitochondria for ATP generation (aerobic)
2. In the absence of O2, pyruvate can accept the hydrogens to form lactate (anaerobic) (catalysed via lactate dehydrogenase)
+Lacate formation allows the recycling of NAD+ so that glycolysis can continue without O2.
Describe the Krebs cycle and endurance exercise below VO2 max:
Endurance exercise below VO2 mx allows time to mobilize substrates from energy stores. In this instance, aerobic ATP generation dominates and results from cooperation between (and the ETC):
* Citric acid cycle -> (Krebs cycle) Completes oxidation (electron removal) of acetyl CoA (formed from fuels fats, CHO, proteins) to provide electrons for the electron transport chain.
1. Glycolysis generates 2 molecules of pyruvate
2. Pyruvic acid (3-C) enters the mitochondria and is converted to acetyl-CoA (2-C), losing a carbon (generating CO2)
3. Acetyl-CoA combines with oxaloacetate (4-C) to form citrate (6-C)
4. Series of reactions to generate oxaloacetate (generating 2 CO2 molecules)
5. Each turn of the cycle, 1 ATP molecule is synthesized from guanosine triphosphate (GTP: high-energy compound) with the release of high-energy electrons (3 NADH and 1 FADH2)
Describe the electron transport chain:
- Electrons removed from NADH and FADH are passed along a series of carriers (cytochromes) coupled with the pumping of H+ into the intermembrane space
- Increased concentration of H+ ions in the intermembrane space
- Results in electrochemical gradient
- ATP produced as H+ ions diffuse back across the membrane
+At the end of the ETC, O2 accepts the electrons that are passed along and combines with hydrogen to form H20 (chemiosmotic hypothesis). Without O2 available to accept these electrons, oxidative phosphorylation is not possible.
+ Interactions between metabolic fuels -> Beta oxidation: process of oxidizing fatty acids to Acetyl-CoA
What is the aerobic ATP tally per glucose molecule? + draw the glucose molecule
-Efficiency of respiration (energy contained in ATP produced/ total potential energy in a glucose molecule)
-In addition to substrate-level phosphorylation (4 ATP), 10 NADH and 2 FADH are shuttled into the mitochondria: total = 32 ATP molecules -> total = 38 ATP molecules. Total ATP is variable as NADH is used as a reducing agent in other processes and the proton gradient is used in transporting other substances through the inner membrane into the matrix.
What is feedback inhibition and what are the rate limiting enzymes?
-Biochemical pathways are regulated by very precise control systems (feedback inhibition)
-Rate limiting enzymes:
1. Are found early in a metabolic pathway
2. Activity is regulated by modulators
What are the metabolic responses to exercise: influence of duration and intensity
- Short-term, high intensity exercise (<5 secs) – ATP produced via ATP-PC
- Intense exercise > 5 secs – shift to ATP production via glycolysis
- Events lasting > 45 secs – ATP production through ATP-PC, glycolysis and aerobic systems. 50% anaerobic/ 50% aerobic at 2 mins.
- Prolonged exercise (> 10 mins) – ATP production primarily from aerobic metabolism.
Summarise cellular respiration in 3 points
-Muscle cells store limited amounts of ATP, given exercise requires a constant supply of ATP to provide energy needed for contraction, metabolic pathways must exist in the cell that are capable of rapidly producing ATP
-Short bouts of exercise, the contribution of aerobically produced ATP is small because of the time required to complete the many reactions involved in the citric acid cycle and the ETC
-The shorter the duration of all-out activity, the greater the contribution of anaerobic energy production; conversely, the longer the duration, the greater the contribution of aerobic energy production
Describe 4 processes how blood glucose is maintained during exercise:
-Blood glucose homeostasis during exercise -> Plasma glucose when fasting or during exercise maintained through 4 processes:
* Mobilization of glucose from liver glycogen stores
* Mobilization of FFA from adipose tissue – spares blood glucose
* Gluconeogenesis from amino acids, lactic acid, and glycerol
* Blocking the entry of glucose into cells – forces use of FFA as a fuel
+Controlled by hormones -> Permissive or slow-acting (thyroxine, cortisol and growth hormone) and fast-acting (epinephrine, norepinephrine, insulin and glucagon)
What are permissive and slow-acting hormones?
-> Act in a permissive manner to allow other hormones to exert their full effect
Describe thyroid hormones:
-> Influences the number of receptors on the surface of a cell for other hormones to interact with. The affinity of the receptor for the hormone.
* Triiodothyronine (T3) enhances effect of epinephrine to mobilize free fatty acids from adipose tissues (little effect without T3)
* No real change in thyroid hormones during exercise
* Hypothyroid state interferes with the ability of other hormones to mobilize fuel for exercise (linked to overall metabolic rate)
Describe growth hormone:
- Growth hormone -> Essential for growth of all tissues – increases amino acid uptake and protein synthesis. Spares plasma glucose – Reduces the use of plasma glucose, increases gluconeogenesis and mobilizes fatty acids from adipose tissue.
* Growth hormone and performance -> GH increases protein synthesis in muscle and long bone growth. High dose: more adverse effects from benefits. No evidence from GH promotes strength gains. Difficult to detect suage by athletes. Questionable benefits as anti-ageing therapy.
* Changes in GH during exercise -> Net effect of GH is to preserve plasma glucose concentrations – Increases gluconeogenesis in liver and blocks glucose entry to adipose cell to favour fat mobilisation. Increase in plasma GH with increases intensity.
Describe cortisol:
- Cortisol -> Steroid hormone derived from cholesterol and secreted from the adrenal cortex.
* Stimulated by -> Stress, via Adrenocorticotropic hormone (ACTH) and exercise
* Contributes to the maintenance of plasma glucose by a variety of mechanisms
* Considerations -> 1. Diurnal variation: Concentrations peak in the am and drop throughout the day. 2. Events other than exercise e.g. emotional arousal
* Increases proportional to an increase in exercise intensity -> The direct effect of cortisol is mediated through the slow process of DNA transcription and translation to protein synthesis. Therefore, changes in cortisol may be related to repair of exercise-induced tissue damage rather than the mobilization of fuel per se.
Describe catecholamines:
- Catecholamines -> Secreted from the adrenal medulla:
- Epinephrine (E ) (80%) and norepinephrine (NE) – Fast-acting hormones, part of fight or flight responses. Bind to adrenergic responses (alpha and beta). Effects depend on hormone used and receptor type).
* Fast-acting hormones -> Catecholamines.
* Return Plasma E and NE increase during exercise -> Related to increased HR and BP during exercise e.g. sympathetic activation
* Endurance training causes a rapid decrease in catecholamine responses to a fixed intensity exercise bout
* Catecholamine responses to supramaximal exercise -> Trained individuals have a greater capacity (~35% higher) to increase catecholamines compared to untrained individuals. Regular stimulation of the SNS increases capacity to respond to extreme challenges e.g. supramaximal exercise.
* Glycogen depletion -> Glycogenolysis is related to exercise intensity. High-intensity exercise results in greater and more rapid glycogen depletion.
* Role of plasma epinephrine -> Plasma epinephrine is a powerful simulator of glycogenolysis. High-intensity exercise results in greater increases in plasma epinephrine.
