Bioenergetics & Regulation of Metabolism Flashcards
Open Systems
- systems that can exchange both energy and matter with the environment
- biological systems are often considered this
Closed Systems
- systems that do not exchange matter with the environment
- cellular or subcellular systems are this
- change in internal energy can come only in the form of work or heat
Internal Energy
- the sum of all the different interactions between and within atoms in a system
- includes: vibration, rotation, linear motion, stored chemical energies
Bioenergetics
- used to describe energy states in biological systems
- ATP plays a crucial role in transferring energy from energy-releasing catabolic processes to energy-requiring anabolic processes
GIbbs Free Energy
- ΔG
- determines whether or not a chemical reaction is favorable and will occur
Enthalpy
- ΔH
- measures overall change in heat of a system during a reaction
Entropy
- ΔS
- measures the degree of disorder or energy dispersion in a system
- units: J/K
At constant ____ and ____, enthalpy and thermodynamic heat exchange (Q) are equal
pressure and volume
GIbbs Free Energy Equation
ΔG = ΔH - TΔS
What does a -ΔG indicate?
- spontaneous reaction that proceeds in the forward direction
- has a net loss of energy
What does a +ΔG indicate?
- nonspontaneous reactions that would be spontaneous if they proceeded in the reverse direction
- has a net gain of energy
What happens when ΔG approaches zero?
occurs when the reaction proceeds to equilibrium and there is no net change in concentration of reactants or products
Standard Free Energy (ΔG°)
- the energy change that occurs at standard concentrations of 1M, pressure of 1 atm, and temperature of 25°C
- equation: ΔG = ΔG° + RT ln(Q)
List the following in order of highest to lowest energy when combusted: proteins, carbs, ketones, fats
fats > carbs = proteins = ketones
ATP
- major energy currency in body
- formed from substrate-level phosphorylation as well as oxidative phosphorylation
- mid-level energy carrier – because it can’t get back the ‘leftover’ free energy after a reaction
- used to fuel energetically unfavorable reactions, or to activate or inactivate other molecules
- mostly produced by mitochondrial ATP Synthase
- consumed through hydrolysis or the transfer of a phosphate group to another molecule
How much energy does ATP provided under normal physiological conditions?
30 kJ/mol
Adenosine Diphosphate (ADP)
produced when one phosphate group is removed from ATP
Adenosine Monophosphate (AMP)
produced when two phosphate groups are removed from ATP
Why is ATP such a good energy carrier?
its high-energy phosphate bonds and presence of a significant charge
What are some characteristics of a long-term storage molecule?
energy density and stable, nonrepulsive bonds, primarily seen in lipids
ATP Cleavage
transfer of a high-energy phosphate group from ATP to another molecule
How do you determine the free energy of a phosphoryl group transfer to another biological molecule?
use Hess’s Law to calculate the difference in free energy between the reactants and products
How does coupling with ATP Hydrolysis alter the energies of a reaction?
ATP hydrolysis yields about 30 kJ/mol of energy which can be harnessed to drive other reactions forward; this may allow a nonspontaneous reaction to occur or increase the rate of a spontaneous reaction
How do you determine the number of electrons being transferred?
half-reactions
-divide oxidation-reduction reactions into their half-reaction components
What molecules in the cytoplasm act as high-energy electron carriers?
NADH, NADPH, FADH2, UQ, cytochrome, glutathione
Flavoproteins
- nucleic acid derivatives that contain a modified vitamin B2 (or riboflavin)
- generally either Flavin Adenine Dinucleotide (FAD) or Flavin Mononucleotide (FMN)
- present in the mitochondria and chloroplasts as electron carriers
- also involved in modification of other B Vitamins to active forms
- function as coenzymes for enzymes in the oxidation of fatty acids, the decarboxylation of pyruvate, and reduction of glutathione
Homeostasis
physiological tendency toward a relatively stable state that is maintained and adjusted, often with the expenditure of energy
Anabolism
synthesis of biomolecules when there is sufficient energy
Catabolism
breakdown of biomolecules for energy
Postprandial (Absorptive) State
- well-fed state
- occurs shortly after eating
- marked by greater anabolism and fuel storage
- lasts 3-5 hours after eating a meal
- in the liver: glucose is stored as glycogen (glycogenesis) or converted to triacylglycerols and fatty acids that are converted into VLDL for exportation into blood because liver can’t store triglycerides
- in adipose tissue: glucose is turned into triglycerides and stored as fat, VLDL from liver are turned into fatty acids then stored as fat
- in muscle: glucose is converted to glycogen (glycogenesis), or is converted to pyruvate to convert to ATP so muscle has reusable energy, amino acids stored as protein
- in the brain: glucose from blood is converted to pyruvate and undergoes cellular respiration to produce ATP
What is the only fatty acid the body can synthesize on its own?
Palmitate
What are the 3 target tissues for insulin?
- liver
- muscle
- adipose tissue
What two types of cells are insensitive to insulin?
- nervous tissue
- red blood cells
What hormones oppose the actions of insulin?
- all considered counterregulatory hormones*
- glucagon
- cortisol
- epinephrine
- norepinephrine
- growth hormone
Postabsorptive (Fasting) State
- occurs when you haven’t eaten in awhile
- body needs to break down stored energy and use it
- greatest decrease in insulin levels during this state
- glycogenolysis begins almost immediately
- gluconeogenesis takes about 12 hours to occur
- in the liver: glycogen broken down to glucose and transferred to blood, amino acids are taken up and converted to ketoacids that are directly used to make glucose, some ketoacids still broken down into acetyl-CoA to produce ATP, glycerol and fatty acids are converted into glucose, fatty acids broken down to form ketones
- in adipose tissue: triglycerides broken down into glycerol and fatty acids then transferred to liver to make more glucose
- in muscle: protein broken down into amino acids then transferred to liver to make more glucose, glycogen converted to glucose which is then broken into acetyl-CoA and creates ATP, if no oxygen then muscle converts glucose to lactate for ATP production
- in the brain: glucose converted to pyruvate and goes through cellular respiration to make ATP, ketones from liver used here for energy
Prolonged Fasting (Starvation)
- elevated levels of glucagon and epinephrine
- rapid degradation of glycogen stores in liver
- gluconeogenic activity continues in liver and plays important role in maintaining blood glucose levels
- after 24hrs gluconeogenesis is main source of glucose for body
- rapid lipolysis resulting in excess acetyl-CoA that is used in synthesis of ketone bodies
- muscle utilizes fatty acids as its major fuel source
- brain derives majority of energy from ketones
What cells are least adaptable to different energy stores?
cells that rely solely on anaerobic respiration, specifically red blood cells
Insulin
- involved in regulation of metabolism
- peptide hormone
- most important controller of its secretion: plasma glucose levels
- secreted by beta-cells of the pancreatic islets of Langerhans
- acts through second messenger cascades
- promotes glucose uptake by adipose tissue and muslce, glucose utilization in muscle cells, and macromolecule storage (glycogenesis, lipogenesis)
In what tissues is glucose uptake not affected by insulin?
- nervous tissue
- kidney tubules
- intestinal mucosa
- red blood cells
- beta cells of the pancreas
Insulin increases (3):
- glucose and triacylglycerol uptake by fat cells
- lipoprotein lipase activity, which clears VLDL and chylomicrons from blood
- triacylglycerol synthesis (lipogenesis) in adipose tissue and the liver from acetyl-CoA
Insulin decreases (2):
- triacylglycerol breakdown (lipolysis) in adipose tissue
- formation of ketone bodies by the liver
Glucagon
- involved in regulation of metabolism
- peptide hormone
- secreted by alpha cells of the pancreatic islets of Langerhans
- most important promoter of its secretion: low plasma glucose
- primary target: hepatocyte (liver cells)
- acts through second messenger cascades
- increases blood glucose levels
Main effects of Glucagon (4):
- increased liver glycogenolysis (activates glycogen phosphorylase and inactivates glycogen synthase)
- increased liver gluconeogenesis (promotes conversion of pyruvate to PEP)
- increased liver ketogenesis and decreased lipogenesis
- increased lipolysis in liver (activates hormone-sensitive lipase)
What metabolic processes are stimulated by Glucagon?
- protein catabolism
- ureagenesis
- ketogenesis
- gluconeogenesis
- glycogenolysis
- lipolysis
What metabolic processes are stimulated by Insulin?
- glyconeogenesis
- lipid synthesis
- protein synthesis
- glycolysis
Glucocorticoids
- involved in regulation of metabolism
- produced in adrenal cortex
- responsible for part of stress response
- includes cortisol, which is a steroid hormone so enacts longer-range effects at the transcriptional level
How does cortisol increase blood glucose levels?
- increased delivery of amino acids
- increased lipolysis
- inhibits glucose in uptake in muscle, lymphoid, and fat tissue
- increases gluconeogenesis
- increases activity of counterregulatory hormones (glucagon, epinephrine, etc)
Catecholamines
- involved in regulation of metabolism
- secreted by the adrenal medulla
- includes epinephrine and norepinephrine
- increases activity of liver and muscle phosphorylase, thus promoting glycogenolysis
- act on adipose tissue to increase lipolysis by increasing activity of hormone-sensitive lipase
Thyroid Hormones
- involved in regulation of metabolism
- activity is largely permissive – levels are kept more or less constant
- increase basal metabolic rate (increased O2 consumption and heat production)
- primary effects in lipid and carbohydrate metabolism
- accelerate cholesterol clearance from the plasma and increase rate of glucose absorption from small intestine
What fuel is utilized in the Liver in the well-fed state? Fasting?
- well-fed: glucose, amino acids
- fasting: fatty acids
What fuel is utilized in the Resting Skeletal Muscle in the well-fed state? Fasting?
- well-fed: glucose
- fasting: fatty acids, ketones
What fuel is utilized in Cardiac Muscle in the well-fed state? Fasting?
- well-fed: fatty acids
- fasting: fatty acids, ketones
What fuel is utilized in Adipose Tissue in the well-fed state? Fasting?
- well-fed: glucose
- fasting: fatty acids
What fuel is utilized in the Brain in the well-fed state? Fasting?
- well-fed: glucose
- fasting: glucose (ketones in prolonged fast)
What fuel is utilized in Red Blood Cells in the well-fed state? Fasting?
- well-fed: glucose
- fasting: glucose
What are the two main roles of the liver in fuel metabolism?
- maintain a constant level of blood glucose under a range of conditions
- synthesize ketones when excess fatty acids are being oxidized
What happens in the liver after a meal, in a well-fed state?
- insulin increase stimulates glycogen synthesis and fatty acid synthesis in liver
- fatty acids are converted to triacylglycerols and released into the blood as VLDL
- liver derives most of its energy from the oxidation of excess amino acids
What happens in the liver between meals or during prolonged fasts?
- liver releases glucose into blood
- glucagon stimulates glycogen degradation and gluconeogenesis
What happens in adipose tissue after a meal, in a well-fed state?
- insulin stimulates glucose uptake and triggers fatty acid release from VLDL and chylomicrons
- lipoprotein lipase (enzyme found in capillary bed of adipose tissue) releases fatty acids which are then taken up by adipose tissues and re-esterified to triacylglycerols for storage
What happens in adipose tissue during the fasting state?
- decreased levels of insulin
- increased epinephrine activates hormone-sensitive lipase in fat cells, allowing fatty acids to be released into blood
What happens in resting muscle in a well-fed state?
- insulin promotes glucose uptake
- restoration of glycogen stores
- use of amino acids for protein synthesis
- excess glucose and amino acids can be oxidized for energy
What happens in resting muscle in the fasting state?
- use of fatty acids derived from free fatty acids in the bloodstream
- use of ketone bodies if fasting state is prolonged
Active Muscle Metabolism
- short-lived source of energy (2-7 seconds) comes from creatine phosphate – transfers a phosphate group to ADP to form ATP
- short bursts of high-intensity exercise is supported by anaerobic glycolysis
- during moderate exercise oxidation of glucose and fatty acids occurs
Cardiac Muscle Metabolism
unlike any other tissue, this tissue prefers fatty acids as their major fuel, even in the well-fed state
What happens in the brain during hypoglycemic conditions?
hypothalamic centers in brain sense a fall in blood glucose, and release glucagon and epinephrine
What fuel can’t cross the blood-brain barrier, and therefore can’t be used as an energy course for the brain?
fatty acids
What is the energy source of the brain between meals?
blood glucose supplied by hepatic glycogenolysis or gluconeogenesis
What organ consumes the greatest amount of glucose relative to its percentage of body mass?
brain
What hormones and substrates in the blood can be used as indicators of metabolic function?
- glucose
- thyroid hormones
- thyroid-stimulating hormone
- insulin
- glucagon
- oxygen
- carbon dioxide
Respirometry
allows accurate measurement of the respiratory quotient
Respiratory Quotient
RQ = CO2 produced / O2 consumed
Calorimeters
measure basal metabolic rate based on heat exchange with the environment
Ghrelin
- hormone secreted by the stomach in response to signals of an impending meal
- its release can be signaled by sight, sound, taste, and smell
- increases appetite and stimulates secretion of Orexin
Orexin
- hormone that further increases appetite
- involved in alertness and sleep-wake cycle
- release can also be triggered by hypoglycemia
LEptin
- hormone secreted by fat cells that decreases appetite by suppressing orexin production
- genetic variations in this have been linked to obesity
Body Mass Index Equation
BMI = mass (kg) / height^2 (m)
What is the normal range for BMI?
18.5-25
What BMI is considered obese?
30 and over
