Chapter 12- Bioenergetic and Regulation of Metabolism Flashcards
what does the brain rely on for metabolism
only glucose
what type of system is a biological system?
open system, b/c they can exchange both energy and matter with the environment.
energy exchanged in form of mechanical work or heat.
matter exchanged through food consumption and elimination, as well as respiration.
biochemical studies
typically done on cellular or subcelluar level, which is considered a closed system b/c there is no exchange of energy with the environment.
- in a closed system change in internal energy can only come from work or heat (change U = Q - W)…. so in this system only heat applies.
internal energy
sum of all different interactions b/w and w/i atoms in a system
ex: vibration, rotation, linear motion, and stored chemicals
bioenergetics
describes energy states in biological systems.
ex: changes in free energy.
Gibbs free energy equation
chgG = chgH -T chgS
-G = spontaneous \+G = nonspontaneous
modified standard state (G*’)
necessary change in pH for biochemical reactions.
pH - 7 (usually concentration of 1, so pH of 0)
T - 25*C
p - 1 atm
most energy-rich nutrient
fats (9 kcal/g of energy), preferred for long-term energy storage.
carbs, proteins, and ketones only have about 4 kcal/g
*same physical space but more energy in it.
2 processes in which ATP is formed
- substrate-level phosphorylation
2. oxidative phosphorylation
why is it good that ATP is a midlevel
b/c when an ATP is used it provides G*’ = 30 kJ/mol of energy no matter what the reaction needs. so it may lose energy if the reaction only requires 10 kJ/mol.
if it were any larger it would waste too much.
*numbers are actually negative when releasing energy
highest to lowest G*’ energy provided
(MOST NEGATIVE CAUSE RELEASES MOST ENERGY)
cAMP, Creatine phosphate, ATP, Glucose 6-phosphate, AMP (adenosine monophosphate)
(MOST POSITIVE CAUSE RELEASES LEAST ENERGY)
what is ATP typically used for
to fuel energetically unfavorable reactions or to activate or inactivate other molecules
ATP hydrolysis vs. ATP cleavage
hydrolysis: usually part of coupled reactions, like with Na/K pump
cleavage: transfer of phosphate group to another molecule-aka. phosphoryl group transfers-, typically (in)activates a target molecule
if chgG is negative and E (electromotive force) is positive then…
the oxidation-reduction reaction is spontaneous
high-energy electron carriers in cytoplasm
NADH, NADPH, FADH2, ubiquinone, cytochromes, and glutathione
flavin mononucleotide (FMN)
membrane-bound electron carriers embedded within the inner mitochondrial membrane. this one is bound to complex I of the electron transport chain and can also act as a soluble electron carrier
flavoproteins
contain modified vitamin B12 (riboflavin). They are nucleic acid derivatives (FAD or FMN).
they are in the mitochondria or chloroplasts as electron carriers. also used as cofactors for enzymes in oxidation of fatty acids, decarboxylation of pyruvate, and reduction of glutathione.
key difference between chemistry and biochemistry?
chemistry- equilibrium states are desired
biochemistry- equilibrium states are NOT desired (homeostasis is desired instead)
homeostasis
physiological tendency toward a relatively stable state that is maintained and adjusted, often with expenditure of energy
postprandial state
aka. absorptive or well-fed state. occurs shortly after eating and lasts for 3 to 4 hours after eating. greater anabolism and fuel storage. nutrients flood from the gut to the liver via the heptaic portal vein.
insulin release due to high blood glucose levels.
anabolism
synthesis of biomolecules
catabolism
breakdown of biomolecules for energy
3 major target tissues for insulin
promotes glucose entry into all of these.
- liver - promotes glycogen synthesis
- muscle- promotes glycogen synthesis and protein synthesis
- adipose tissue- promotes triacylglycerol synthesis
what happens after the glycogen stores are filled?
liver converts excess glucose to fatty acids and triacylglycerols
tissues that are insensitive to insulin
- nervous tissue- gets energy from oxidizing glucose to CO2 and water
- red blood cells- can only use glucose anaerobically cause they lack mitochondria
- intestinal mucosa
- kidney tubules
- B-cells of the pancreas
postabsorptive state and counterregulatory hormones
aka. fasting state. release of amino acids from skeletal muscle and fatty acids from adipose tissue are both stimulated by the decrease in insulin and by an increase in levels of epinephrine.
counterregulatory hormones have opposite effect of insulin:
- glucagon
- cortisol
- epinephrine
- norepinephrine
- growth hormone
hepatic
relating to the liver
prolonged fasting
aka. starvation. levels of glucagon and epinephrine are markedly elevated. rapid degeneration of glycogen stores in the liver. both gluconeogenesis and lypolysis are occurring rapidly.
peptide hormones
typically water-soluble. able to rapidly adjust metabolic processes of cells via second messenger cascades. (ex: insulin)
amino acid-derivative hormones
typically fat-soluble. enact longer-range effects by exerting regulatory actions at the transcriptional level.
insulin
peptide hormone secreted by the B-cells of the pancreatic islets of Langerhans. key player in uptake and storage of glucose.
how does insulin increase glycogen synthesis in the liver?
increasing the activity of glucokinase and glycogen synthase, while decreasing the activity of enzymes that promote glycogen breakdown (glycogen phosphorylase and glucose-6-phosphatase)
what does insulin increase and decrease?
INCREASES
- glucose and triglyceride uptake by fat cells
- lipoprotein lipase activity, which clears VLDL and chylomicrons from the blood
- triacylglycerol synthesis (lipogenesis) in adipose tissue and the liver from acetyl-CoA
DECREASES
- triacylglycerol breakdown (lipolysis) in adipose tissue
- formation of ketone bodies by the liver
most important controller of insulin
plasma glucose. insulin secretion is directly proportional.
how does glucose promote insulin secretion
must enter B-cell but also be metabolized, increasing intracellular ATP concentration–this then promotes exocytosis of insulin through several ion and voltage-gated channels.
glucagon
peptide hormone secreted by the a-cells of the pancreatic islets of Langerhans. acts through secondary messengers. typically released after a meal rich in proteins.
- increases liver glycogenolysis and gluconeogenesis
- increased liver ketogenesis and decreased lipogenesis
- increased lipolysis in the liver
hypoglycemia
low plasma glucose. most important physiological promoter of glucagon secretion
hyperglycemia
elevated plasma glucose. most important inhibitor of glucagon secretion.
glucocorticoids
come from adrenal cortex. are responsible for part of stress response. rapidly metabolizes glucose. (ex: cortisol)
-implicated in stress-related weight gain b/c they increase glucose levels, which causes insulin secretion.
cortisol
type of glucocorticoid that elevates blood glucose levels and inhibiting glucose uptake in most tissues. stimulates glucose release in liver. enhances activity of glucagon, epinephrine, and other catecholamines.
adrenal cortex
adrenal medulla
cortex- produces steriods (glucocorticoids, mineralocorticoids, and sex hormones)
medulla- produces catecholamines
catecholamines
secreted by the adrenal medulla and include epinephrine and norepinephrine (aka adrenaline and noradrenaline). increase activity of liver. act on adipose tissue to increase lipolysis by increasing activity of the hormone-sensitive lipase.
thyroid hormone
largely permissive activity, levels are typically left constant. increase basal metabolic rate w/ increased O2 consumption and heart production when they are secreted. primary effects in lipid and carbohydrate metabolism. accelerate cholesterol clearance from splasma and increase rate of glucose absorption from small intestine.
2 important thyroid hormones
- Thyroxine (T4)- increases metabolic rate, which occurs after latency of 3 hours but can last for 3 days
- Triiodothyronine (T3)- produces a more rapid increase in metabolic rate but has a shorter duration of activity.
T4 is like a precursor to T3.
major sites of metabolic activity in the body
liver skeletal muscle cardiac muscle brain adipocytes
2 major roles of the liver in fuel metabolism
maintains a constant level of blood glucose under a wide range of conditions
and to synthesize ketones when excess fatty acids are being oxidized
what does insulin released after a meal do to adipose tissue
stimulates glucose uptake, triggers fatty acid release from VLDLs and chylomicrons.
Major fuels of skeletal muscle
Glucose and fatty acids
Creatine phosphate
Transfers phosphate to ADP to form ATP. Very short lived source of energy (2-7 seconds)
Cardiac muscle preferred source of energy
Fatty acids (even in well-fed state)
Brain facts
2% total body weight
15% cardiac output
Uses 20% total O2
Consumes 25% of total glucose
*fatty acids can’t cross BBB
What are the primary factors that determine body mass
Water, carbohydrates, proteins, lipids (not nucleic acids)
Respirometry and RQ
respirometry- allows accurate measurement of the respiratory quotient (RQ)- can be measured experimentally or calculated as RQ = (CO2 produced/ O2 consumed) for the complete combustion of a given fuel source.
lipid RQ- 0.7
amino acid RQ- 0.8 to 0.9
carbohydrate RQ- 1
what is basal metabolic rate and how is it measured?
measured using calorimeters based on heat exchange with environment. can be estimated based on age, weight, height, and gender.
basic factors that determine body mass
water, carbohydrates, protein, and lipids (not nucleic acids).
3 hormones that control hunger and satiety
- ghrelin
- orexin
- leptin
Ghrelin
secreted by stomach in response to signals of impending meal (sight, sound, taste, and smell)
increases appetite and stimulates secretion of orexin
Orexin
stimulated by ghrelin. further increases appetite. involved in alertness and the sleep-wake cycle. hypoglycemia also triggers its release.
Leptin
hormone secreted by fat cells that decreases appetite by supressing orexin production.
genetic variations in leptin and its receptors have been implicated in obesity.
