Sunlight energy to chemical energy
Sunlight is the major energy
source for most life. This
energy drives the conversion
of atmospheric carbon dioxide
into organic molecules (sugar).
Cellular respiration is the
conversion of the chemical
energy in the sugars to heat or
kinetic energy.
Conservation of Energy
Can energy be lost?
NEVER,
it can only
be changed into
different
forms!!!
ENERGY IS ALWAYS CONSERVED.
Kinetic, potential energies translate into heat, chemical,
light energies.
Chemical Energy
“Burning of fuel”
Conversion of chemical energy found in food results in the
production of heat and kinetic energy.
This is cellular respiration.
Food is Chemical Energy
Calories get converted to kinetic energy or stored
Food calories get converted to fat calories if activity level
does not “burn” the chemical energy found in the food.
Some Activities Require Much More Energy
Photo ©: AFP/Joel Saget
ATP is the energy currency of the cell
Adenosine triphosphate (ATP) has a high energy bond at the last
phosphate. When this bond is broken a lot of energy is given
off.
ATP is recycled. When the high
energy bond is broken energy is
given off. To form the bond,
energy is harvested from food.
This is called energy coupling.
ATP works by transferring the high energy
phosphate to other molecules that use it for
work
There are three major
types of work done by
the high energy
phosphate of ATP.
In each case, the
phosphate is
transferred from one
molecule to the next
with the energy being
used to do work.
Burning of fuel requires oxygen
No matter what the activity level cells always need oxygen to
function. The more activity the more oxygen consumed.
There are three parts to energy metabolism
The molecules that we can get energy from
are diverse and enter the energy cycles in
different places
Acetyl CoA is a branch pt.
The food that is not needed
for energy gets converted to
a form of stored energy.
We call this FAT. It is
stored in special cells called
Adipocytes.
Each Macronutrient Enters the TCA Cycle
Carbohydrates – glycolysis then TCA then electron transport
Lipids – beta-oxidation into acetyl CoA then into TCA and
electron transport
CHO are required for complete oxidation
Amino acids – transamination reactions into TCA and then
electron transport
Carbohydrate Metabolism
Need to start with glucose (C6H12O6) or fructose (C6H12O6)
Glycolysis is the conversion of glucose into 2 pyruvic acids
generates:
two ATP
two high energy electron carriers NADH
NAD+  NADH
does not require oxygen (short term)
NADH + O2  NAD+ + H2O
if no oxygen (as in severely exercising muscles) then
pyruvic acid + NADH  lactic acid + NAD+
FEELTHE BURN
GLYCOLYSIS
Pyruvic acid prepared for entry into the Krebs
cycle by attaching CoEnzyme A. Loss of
carbon dioxide occurs
Carbohydrate Metabolism
Glycolysis – breaks monosaccharides down to pyruvic acid
aerobic  pyruvic acid goes to acetyl CoA
anaerobic  pyruvic acid goes to lactic acid (lactate)
TCA (Krebs Cycle) – acetyl CoA enters a cycle and combines
with OXALOACETATE. In the cycle high energy
electron carriers (NADH and FADH2) are produced
amino acids
Electron Transport – electrons are used to produce ATP
NADH and FADH2 are the sources of electrons
Pyruvic acid prepared for entry into the Krebs
cycle by attaching CoEnzyme A. Loss of
carbon dioxide occurs
The Krebs cycle is the site of entry for many
food molecules including fats, proteins, and
sugars
Acetyl CoA + Oxaloacetate  Citrate begins the cycle
without Oxaloacetate the cycle does not work
2 Acetyl CoAs/glucose
The electron transport chain is found in the
mitochondria membranes.
Each step in the electron transport chain moves H+’s up a
diffusion gradient. It is like pumping water up into a
reservoir. Eventually the potential energy of the H+’s is
released by flowing through ATP synthase. This makes
ATP.
GLUCONEOGENESIS is building glucose
from Krebs cycle intermediates
Occurs only in liver cells
makes glucose from OXALOACETATE one of the TCA
cycle intermediates
WHY? Brain needs glucose
CARBS refill the TCA cycle by converting pyruvic acid to
oxaloacetate
Amino acids refill the TCA cycle by transamination reactions
increases the amount of ammonia that kidneys must excrete
decreases the availability of amino acids for structure
increases the amount of ketones in the blood requiring more
excretion and more water
GLUCONEOGENESIS
Kindof reverse glycolysis
TCA  pyruvate  glucose
or
lactate  pyruvate  glucose
glucose
glucose
pyruvate
pyruvate
lactate
lactate
ACTIVE MUSCLE
LIVER
Lipid Metabolism
Fatty acids are broken down two carbons at a time
A typical fatty acid has the formula C18H34O2
Each two carbons go to Acetyl CoA which enters the TCA
cycle and then Electron Transport Chain
So a typical fatty acid spins the TCA cycle 9 times
No wonder fats have so much energy associated with them
glucose = 36 – 38 ATPs 16 carbon FA = 129 ATPs
Adipose fat  HDL  cells  cytosol  mitochondria
hormone sensitive lipase
carnitine
Incomplete burning of fatty acids happens
when carbohydrates are not present
Carbohydrate metabolism replenishes the TCA cycle with
intermediates OXALOACETATE is most important
Fatty acid metabolism depletes the TCA cycle of intermediates
Burning only fat without any carbs results in incomplete
oxidation of fatty acids this results in KETOSIS
Low Carb intake
low insulin production
FASTING, ATKINS
Fatty acids mobilized for energy
move to the liver
Ketone production
CO2 + H2O
Ketogenesis
Ketone bodies are formed in response to
low insulin production – diabetes, fasting
low carbohydrate intake
low carb intake results in elevated utilization of storage lipid
low carb intake results in lowered levels of Oxaloacetate
carbs  pyruvate  Oxaloacetate
fatty acids  lots of acetyl CoA + lots of ATP
no reason to run the TCA cycle
Acetyl CoA goes to ketones
X
ketones go into urine pulling potassium and sodium
pH changes in blood, increased urine output etc…
Ketogenesis in Diabetes
Insufficient insulin
Fatty acids flood the liver
Acetyl-CoA
Many Acetyl-CoA
Limited
Acetyl-CoA
Ketones, ketones
Citric Acid
Ketones, ketones,
Cycle
Urine
Not enough insulin
produced
CHO metabolism is
limited
Oxaloacetate is needed
to produce glucose
Citric Acid Cycle is
limited
More ketones produced;
ketones spill into urine
Blood becomes acidic
Protein Metabolism
Proteins  amino acids
Amino acids  to intermediates by transamination and
deamination reactions
Amino acids
ketogenic – get converted to Acetyl CoA
glucogenic – get converted to pyruvate or TCA cycle
intermediates