Lecture 9 - Energetics Flashcards
What is energetics?
- How animals convert glucose, lipids and proteins to energy
- Measuring what’s being utilized as an energy source in the body
Glycolysis
first step in breaking down glucose
Products of glycolysis
2 pyruvate, 2 ATP, and 2 NADH
Where does glycolysis occur?
cytosol
Do we put ATP into glycolysis?
Yes
Products of Kreb’s/TCA/CAC
- 1 ATP for each pyruvate
- 4 NADH
- 1 FADH2
Where does the Kreb cycle take place?
- mitochondria
Products of ETC
- each NADH provides 3 ATP
- each FADH2 provides 2 ATP
- glycolysis and TCA produce 10 NADH and 2 FADH2 per glucose molecule = 34 ATP total
Where does ETC take place?
In the membrane of mitochondria
How is acetate activated?
acetate + coenzyme A = acetyl coenzyme A
What does acetyl coenzyme A do?
- enters the Kreb’s cycle to yield 12 ATP/mole
- BUT 2 moles ATP required for activation of Acetate = net 10 ATP/acetate
How is propionate oxidized? Why?
- it is another SCFA that we can use to generate energy
- propionate to succinyl-CoA to malate to phosphoenolpyruvate to acetyl CoA
- acetyl CoA goes into the Kreb’s cycle
How many ATP do we get per propionate?
22 ATP - 4 ATP = 18 ATP/propionate
- about half the amount that we get from glucose
How are fatty acids metabolized?
Beta-oxidation
- FAs are just long chains of carbon and we now need to break them down into 2 carbon units
What happens at each step of beta-oxidation?
- we break off 2 carbon units and get 5 ATP and 1 Acetyl CoA
When palmitate undergoes beta-oxidation, how much ATP is generated?
131 ATP - 2 ATP = net 129 ATP/palmitate
How are non-esterified fatty acids aka FFA mobilized from adipose tissues?
- Hormone-sensitive lipase (HSL) simulates the release of NEFA
- NEFA bound to albumin circulates in the blood
- some are directly used by peripheral tissues and oxidized
- majority are taken up by the liver
Fat metabolism in the liver aka what does the liver do with FAs?
- re-esterified and stored as TG
- TG is incorporated into VLDL
- Beta-oxidation to make acetyl CoA
= complete oxidation (used as an energy course) or synthesize ketone bodies (pre-digestion of fatty acids)
Characteristics of ketone bodies
- water soluble (can go around the body similar to glucose and unlike FAs which are bound to albumen)
- decrease lipolysis rate
- normal fuel in muscles
How are ketone bodies utilized?
- incomplete beta-oxidation = end up with acetoacetate
- cannot be broken down in the liver so it’s sent out to other tissues in the form of ketone bodies where it can be broken down into Acetoacetyl CoA then 2 Acetyl CoA which enter the Kreb’s cycle
Ketosis
- generated in post absorptive state, particularly starvation from mobilized fatty acids
- results from liver’s limited capacity to oxidize fatty acids
What happens when ketone bodies decarboxylate?
They decarboxylate to acetone (volatile) and is detected in breath and urine
Where do glucogenic amino acids enter the Kreb’s cycle?
at many different points depending on their structure
Where do ketogenic amino acids enter the Kreb’s cycle?
- become acetoacetyl CoA or Acetyl CoA to enter the Kreb’s cycle
What do we use to determine how much energy we are getting out of a diet?
- bomb calorimetry
Why are we most interested in metabolizable energy?
- this is what the animal is actually getting out of the gross energy
- collect GE and DE to get ME
Direct calorimetry
- direct measurement of heat:
feed energy - fecal energy - urinary energy
Indirect calorimetry
- based on biochemical principles and known combustion values
- Glucose + O2 and Fat + O2; both yield CO2 and H2O but in different amounts
In regards to indirect calorimetry, by measuring CO2 vs O2 what do we get?
Respiratory Quotient
What happens if only Glucose is oxidized in the body?
- for every L of O2 we get 5 Kcal of energy
- RQ = 1
What happens if only Fat is oxidized in the body?
- for every L of O2 we get 4.71 Kcal of energy
- RQ = 0.70
What are the extremes of RQ?
0.7 to 1.0
How do we measure protein?
- by measuring how much nitrogen we have in the urine
- N in urine = utilization of aa as an energy source
How do we correct for protein oxidation
- end up with non-protein RQ which falls btw 0.7 and 1.0
- Co2 produced minus protein CO2 produced
- O2 consumed minus protein O2 consumed
What does total heat produced indicate?
Energy gained from metabolizing protein, CHO, and fat
What 3 data points do we need to begin total heat produced calculations?
- O2 consumed, L
- CO2 produced, L
- Urine N excreted, g
