Ch. 19 Energy Balance/Metabolism (Day 1) Flashcards
What is energy?
Capacity to do work
Types:
–chemical, transport, mechanical
What are the 2 major users of energy that our cells have?
Maintain ion gradients
–e.g. Na+/K+ pump
Maintenance (e.g. turnover) and repair
–e.g. protein synthesis
What are all the users of energy that our cells have?
Maintain ion gradients
–e.g. Na+/K+ pump
Maintenance (e.g. turnover) and repair
–e.g. protein synthesis
Movement (muscle contraction)
Reproduction
Lactation
Thermogenesis
What is metabolism?
Overall energy economy in a cell or organism
What is metabolic rate (MR)?
Sum total of all energy-obtaining and energy-consuming processes
Catabolism
Breakdown of macromolecules (fuels) to obtain usable energy –> ATP
big molecules –> small molecules + ATP
Anabolism
Use of energy (ATP) to produce new macromolecules
small molecules + ATP –> big molecules
Energy balance
Energy stored + energy intake minus energy expenditure
Energy expenditure: work + heat
Energy balance is a ____ ____ in which energy demand is balanced with energy supply.
Steady state
The turnover rate of the ATP cycle is equivalent to ____ ____.
Metabolic Rate
Flux through ATP demand pathways is ____ by flux through ATP supply pathways.
balanced
Catabolism in Anaerobic Organisms…
final common pathway whereby the chemical energy in fuel molecules is conserved as ATP is called RESPIRATION
Respiration is a process of slow, controlled ____, and we gain energy at various stages along the way.
Combustion (oxidation)
All the macronutrients feed into a final, common pathway in ____. (Catabolism or Anabolism)?
Catabolism
____ is the basic metabolic fuel.
Glucose
The TCA Cycle is the rotary engine of ____.
Metabolism
Energy content of food
Direct calorimetry
1 Calorie = 1,000 calories = 1 kcal = 4.184 kJ
Amount of heat needed to raise temperature of 1 liter of water by 1ºC = 1 Calorie
Yields “gross” energy of food
Includes combustion of indigestible components
–e.g. fiber, so energy content of some foods wasn’t accurate
Gross Energy Content
Adjusted for indigestible components and for any other relevant losses, then this modified value is used on food labels
W.O. Atwater, USDA (1900)
obtained gross energy values from various foods, applied corrections for digestibility, energy losses in urine; published series of tables of foodstuff energy contents
Several variations on Atwater’s general system, but his basic approach remains basis for current food labeling policies, despite some significant problems
What are the energy contents of the following metabolic fuels: CHO, PRO, and fat?
CHO: 4kcal (16.7kJ)/g
PRO: 4kcal (16.7kJ)/g
Fat: 9kcal (37.7kJ)/g
Under normal, well-fed conditions, protein is NOT used for energy, but is preferentially used for ____ ____.
Protein synthesis.
However, this can change under certain conditions, e.g. fasting, starvation, prolonged exercise
Energy Expenditure: Indirect Calorimetry
Since combustion (oxidation) of fuels to provide energy, and the use of that derived energy requires OXYGEN, then the rate of OXYGEN CONSUMPTION can be used to measure metabolic rate
1 liter O2 consumed per 4.5-5.0 kcal released from metabolized food
Metabolic rate (kcal/day) = liter O2 consumed/day * 4.8 kcal/L O2
Basal Metabolic Rate (BMR)
Minimal rate for maintaining life, aka SMR (12 hours post absorptive state, resting)
What influences metabolic rate?
Age: as age increases, MR decreases
Sex: female MR = 0.9 * male MR
Lean muscle mass (LMM): as LMM increases, MR increases
Activity level: as physical activity increases, MR increases
Diet: eating meal increases MR via thermic effect of food (aka “heat increment, HI”) - heat loss due to processes of uptake/assimilation/processing of nutrients - varies w/ nutrient - protein has highest HI
Hormones: thyroid hormones, epinephrine, norepinephrine
Genetic factors: poorly characterized
Metabolism: Recap
Overall biochemical processes mediating disposition of macronutrients (PRO, CHO, fat)
Oxidation for energy vs. biosynthesis vs. storage
Catabolism: large molecules –> small molecules –> ATP generation
Anabolism: small molecules + ATP –> large molecules
Fed (absorptive) state
Anabolic, fuels from food – oxidation –> ATP and storage
Fasted (post absorptive) state
Catabolic, body stores – oxidation –> ATP
How is energy stored in the body?
CHO: glycogen in liver and muscle via glycogenesis - reverse process is glycogenolysis
Fat: triglycerides in adipose
Under normal conditions, what determines whether metabolism goes in the direction of anabolism vs. catabolism?
Feeding determines anabolism
Fasting determines catabolism
What determines fed vs fasted state?
Blood glucose levels
Ratio of insulin:glucagon (counter-regulatory hormones)
Decreased blood glucose levels = fasting
Increased blood glucose levels = fed
In regards to metabolism, what is periphery?
Everything except the liver
Why is glucose so important?
Major metabolic fuel for all tissues, obligatory fuel for RBC’s, renal medulla, and under non-starvation conditions, the brain
–glucose is only fuel that supports anabolic metabolism
Sole fuel for muscle contraction “fight or flight” conditions
Provides anapldrotic precursors for TCA cycle
–an anapleurotic reaction is one which feeds intermediates into TCA cycle
Provides carbon skeletons for synthesis of nonessential AA’s
–20AA’s: 8 essential (come from diet only), 12 made in body
Provides carbon precursors for triglycerides (TG) components (glycerol and fatty acids)
What is glucose used for?
Precursor for DNA and RNA
AA’s
Fatty acids (FA) (storage)
Glycogen (storage)
ATP production
Fate of fuels: Fed State (HIGH INSULIN, low glucagon)
CHO:
- 1) increased glucose uptake by cells from blood
- 2) increased glucose utilization for ATP production
- 3) increased glycogenesis in liver, muscle (storage as glycogen)
- 4) increased lipogenesis in liver (conversion of glucose to FA)
Fat: FA + glycerol –> TG storage in adipose
PRO: AA’s used strictly for protein synthesis (P.S.); any excess not used for P.S. are deaminated and carbon skeletons are used for energy production or fat synthesis
Fate of fuels: Fasted State (low insulin, HIGH GLUCAGON)
CHO:
- 1) decreased glucose uptake by cells from blood
- 2) decreased glucose utilization for ATP production
- 3) decreased glycogenesis in liver, muscle (i.e. decreased glycogen storage)
- 4) decreased lipogenesis, increased lipolysis (liver)
- 5) increased glycogenolysis in liver, muscle (i.e. increased breakdown of glycogen stores)
- 6) increased gluconeogenesis
Fat: TG –> FA + glycerol in adipose, FA + glycerol –> liver
PRO: increased protein breakdown, AA carbon skeletons used for gluconeogenesis
Fed State
INSULIN:glucagon –> glucose utilization and storage as glycogen and fat
Fasted State
insulin:GLUCAGON –> breakdown of stored fat, glycogen, and production of new glucose
body protein –> AA –> ATP, glucose
One-way reaction between pyruvate and ____ ____ = no net carbon flux from fat –> glucose
Acetyl CoA
During fasting, where does carbon needed for gluconeogenesis come from if it can’t come from fat?
Body protein
Nitrogen Excretion: Urea Cycle
Protein: nitrogen disposal problem - NH3, NH4+ are toxic, require large volume of water for direct excretion (e.g. fish, amphibians)
Urea formation in liver - energetically costly, but avoids ammonia toxicity
AA’s stripped of ammonia, ammonia converted to less toxic formula –> excreted
What is needed to keep the TCA cycle going?
Glucose
If glucose insufficient, cycle slows up –> less ATP produced - this has implications for fat use during fasting/starvation
Oxaloacetic Acid (OAA)
Combines w/ Acetyl CoA for TCA cycle
Ketosis
Incomplete oxidation of FA - due to combination of low levels of incoming glucose + high levels of incoming FA
- No glucose coming in
- Breakdown of FA mobilized from adipose results in high levels of Acetyl CoA
- OAA diverted towards gluconeogenesis instead of combing w/ Acetyl CoA –> depletes TCA cycle of intermediates, so it slows down
Can the brain use ketosis for energy?
Yes, but under conditions such as starvation
Ketone Bodies: An Alternate Source of Energy for the Brain
Prolonged high systemic levels of them can be detrimental
At high plasma levels, kidney unable to completely reabsorb k.b. –> net energy loss to body
k.b.’s are organic –> metabolic acidosis
kidney can acidify urine to only pH of 4.5-5.0 (pK of k.b.), thus only about 50% of excreted k.b. are in acid form –> the remainder must be accompanied by a cation, e.g. Na+/K+ –> ionic depletion
Energy Stores
Ready reserve: phosphocreatine and ATP
–lasts for seconds
Long-term: CHO, PRO, and fat
- -glycogen, protein, triacylglycerol
- -lasts minutes to months
What are the priorities during fasting/starvation?
1) maintain blood glucose
2) conserve body protein
- -no storage depot for protein b/c we use it
The majority of our energy reserve is stored as?
Fat
About 200x more energy stored as fat than CHO
Energy stored as fat
> 5:1 compared w/ protein
> 160:1 compared w/ CHO
