Transcript Metabolism and Energetics

Metabolic Pathways
How cells derive energy from organic fuel
Pathways that yield energy by burning fuel
Chapters
67-69
Metabolism
• Is the sum total of all chemical
reactions occurring throughout
the body. It includes
– Anabolic reactions-monomers to
polymers (making larger molecules
by attaching together many smaller
ones, ex. Amino acids linked to form
proteins.) Dehydration synthesis
reactions (ex. Growth)
– Catabolic reactions- polymers to
monomers (cutting larger molecules
into many smaller ones, ex.
Hydrolyzing a protein into amino
acids.) Hydrolysis reactions, ex.
Digestive system
Metabolic Pathways
• Cells quite literally “burn”
fuel, much like your car
engine burns gasoline, or
fireplace burns logs.
• It is a controlled burn – step
by step, releasing “packets of
energy” that can be stored in
chemical bonds.
• To burn anything completely
and get the highest yield of
energy, you require oxygen.
O2 is not a fuel!
Metabolic Pathways
• The more hydrogen atoms a
molecule has (the more highly
“reduced”), the more energy it
contains.
• Hydrogen atoms (and their electrons)
are stripped off energy rich
molecules and are passed on to O2.
Oxygen is the final electron
acceptor in the “oxidation”
process.
• Oxygen accepts the electrons, along
with the hydrogen ions, that are
stripped off any “energy rich”
molecule.
• The most commonly used,
immediately available, fuel
is glucose (dextrose) , but it
can be other substrates as
well, molecules like
– Fats (very highly reduced,
rich source of H)
– amino acids
– proteins (but this is reserved
for emergencies only, as this
actually burns down essential
molecules in cells.)
– Nucleic acids—in theory,
could be a source of fuel,
however the cell will NEVER
use its DNA as a fuel—why?
Metabolism
Cells and Mitochondria
• cells provide small organic
molecules (fuel) to their
mitochondria (the engines
that will “burn the fuel”)
• These molecules can come
from carbohydrates, fatty
acids or proteins
• Mitochondria use these
molecules to produce ATP
• ATP is the cell’s “currency”
used to perform cellular
functions
Metabolism
• cells carry out a “controlled burn”, otherwise you’d
blow up like the picture shown!
• cells burn their substrate-of-choice in a slow,
organized way. They shuttle the energy from each
step into a storage molecule.
• cells use the extracted energy to form energy-rich
chemical bonds.
• Energy is shuttled to and stored in the form of
chemical bonds, as in
ADP + Pi
ATP
• Each ATP molecule is a quantum of
energy formed by attaching a
phosphate group onto ADP.
• phosphate (Pi) is a bulky negatively
charged group,
• ADP is also highly negatively charged
• it takes much energy to overcome their
repulsion and tie them together.
• Forcing them together and linking them
requires energy. That’s where the
chemical energy is stored (“potential
energy.”)
• this energy can be recovered later by
breaking (hydrolyzing) the bond
(reversible reaction.)- this is kinetic
energy and can be used to do work—
that is the cell can use the released
energy to perform some other function
(Na+/K+ ATPase)
• This is the energy currency or “money”
of the cell.
Metabolism
Gylycolysis
• http://www.youtube
.com/watch?v=xstLxqPt6E
Glycolysis
•
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(“breaking down glucose”)
Anaerobic respiration (“in absence of oxygen”)
of glucose
Enzymes to carry this out are located in
cytoplasm of cells
In several steps, the atoms in a glucose
molecule are rearranged to a lower energy
state, the energy is then directly stored in the
bonds of ATP
Yields ATP directly, without the utilization of
oxygen, but only yields a small number of ATP
per glucose (2)
AND it yields two molecules of NADH—this is a
type of stored energy that can be “cashed in for
ATP” in the mitochondrion.
The end-product of this process is pyruvate (2
molecules for each burned glucose)
Often, pyruvate is sometimes converted to
lactate OR further hydrolyzed to acetate.
Acetate can be linked to a carrier, CoA, forming
acetyl-CoA-and this can be broken down for
even more energy....to be continued!
Glycolysis—the
breakdown of glucose to
pyruvic acid
• This process requires:
–
–
–
–
–
Glucose molecules
Cytoplasmic enzymes
ATP and ADP
Inorganic phosphate
NAD (nicotinamide adenine
dinucleotide)- a coenzyme!
It merely temporarily stores
energy from hydrogen ion
to cash it in for ATP in the
mitochondria! YOU
SHOULD KEEP TRACK
OF THE AMOUNTS OF
THESE CREATED (along
with FADH2)
Lactate fermentation vs alcoholic fermentation?
Are we talking humans or yeast?
• The overall reaction
is: •Glucose + 2 NAD + 2 ADP + 2Pi
 2 Pyruvic acid + 2 NADH + 2 ATP
http://trc.ucdavis.edu/biosci10v/bis10v/media/ch06/fermentation.html
glycolysis
http://trc.ucdavis.edu/biosci10v/bis10v/media/ch06/glycolysis.html
Krebs Cycle
• http://www.youtube
.com/watch?v=aCy
poN3X7KQ
Citric Acid Cycle (Krebs’ cycle) or TCA cycle
From glycolysis!
• Aerobic respiration (utilizes oxygen)
• Occurs inside mitochondria, where
necessary enzymes are located.
• Extracts hydrogen atoms, along with
their electrons from 6-C citric acid
(which is formed from 4-C
oxaloacetate and 2-C acetyl CoA.)
• 2ATP made here for every glucose
• These are passed to coenzymes
(temp storage of electrons), and
then later passed down to the ETS
to be completely oxidized (oxidative
phosphorylation)
• Total number of coenzyme carriers
to cash in for every glucose
(including preparatory phase):
– NADH (8)
– FADH2 (2)
http://trc.ucdavis.edu/biosci10v/bis10v/media/ch06/prep_and_krebs.html
Oxidative phosphorylation and the ETS
http://images.google.com/imgres?imgurl=http://vcell.ndsu.nodak.edu/animations/etc/images/etcmov.jpg&imgrefurl=http://vcell.ndsu.nodak.edu/animations/etc/index.htm&h=125&w=130&sz=9&hl=en&start=2&tbnid=HBWChNaHruPl9M:&tbnh=88&tbnw=91
&prev
See video at this web-site!! Very helpful!
• A chain of enzymes
(cytochromes) located inside
mitochondrial (matrix) attached
to the inner membrane (cristae)
• Involved in passing down
hydrogen atoms and their
accompanying electrons as
they extract the energy in them
and pass the energy on by
storing it in ATP bonds. (ADP
+ Pi
ATP)
• The last receiver in the chain is
oxygen.
• Oxygen will receive 2 hydrogen
atoms, to become a water
molecule (byproduct)
•
•
This is where we cash in the NADH
and FADH2
Get 2.5 ATP for every NADH and
1.5 ATP for every FADH2
http://www.stanford.edu/group/hopes/treatmt
s/ebuffer/f_j13electtrans.jpg
Energy yield per molecule of glucose
3
3
20
20
3
3
30
COH- 1:2:1
• Monosaccharides
– Simple sugar
– Up to seven carbons
– Isomers- D-, L- glucose,
fructose
• Disaccharides
– Two mono’s bound together
– Sucrose
• Polysaccharides
– Cellulose
– Starch
– glycogen
Why would it be important to store
sugar in a polymer form?
Hint: think osmotic gradient!
Lipids
• Very little oxygen (carbon and
hydrogen atoms abound—
Yeah! More fuel!)
• Give off more energy than
COH
– Fatty acids
– Eicosanoids- come from
arachadonic acid; prostaglandins
example
– Glycerides
– Steroids- sex hormones,
cholesterol, bile salts
– Phospholipids
– glycolipids
Glycerides
• Can be attached to
fatty acids
• Monoglyceride
• Diglyceride
• Triglyceride
– Energy source
– Insulation
– protection
Phospholipids and Glycolipids
• Phospholipids have
phosphate group
attached to diglyceride
• Glycolipids have a COH
attached to diglyceride
• Polar Heads
• Non-polar tails
(hydrophobic)
• Head to tail
configuration or micelle
Lipids- Fatty Acids
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COOH- head
Carbon tail
Saturated
Unsaturated
The process by which fatty acids are
burned to retrieve the energy stored in its
bonds.
Fatty acids are long chains of carbon
atoms (often 20 or more C’s) with many
hydrogen atoms attached.
Fatty acids are highly reduced (energy
rich) molecules.
Beta oxidation is a repeating 4 step
process in which sequential 2-C groups
(“acetyl groups”) are cut from the long
chain; they are attached to a carrier (CoA)
and then shuttled into the mitochondria
These 2-C groups are then burned in the
Krebs’ cycle.
Lipid catabolism
• Lipolysis
– Lipids broken down into pieces that can be converted
into pyruvate
– Triglycerides are split into glycerol and fatty acids
• Glycerol enters glycolytic pathways
• Fatty acids enter the mitochondrion via carnitine translocase
(rate limiting factor)
• Beta-oxidation
– Breakdown of fatty acid molecules into
2-carbon fragments
– Enter the TCA
• Lipids and energy production
– Cannot provide large amounts in ATP in a short amount
of time
– Used when glucose reserves are limited
•Fats burn in the
flame of
carbohydrates– if no
oxaloacetate, then
NO krebs cycle and
acetyl-CoA will
become ketone
bodies and lead to
ketoacidosis—
•Ketone bodies leads
to sweet breath
Acetoacetate
- hydroxybutyrate
acetone
Amino acid catabolism
• If other sources inadequate,
mitochondria can break down
amino acids
– TCA cycle
• removal of the amino group
– Deamination –generating
NH4+ and NADH
• Proteins are an impractical
source of ATP production
Nucleic Acids
• DNA
• RNA
• DNA is never catabolized for
energy
• RNA catabolism
– RNA molecules are routinely
broken down and replaced
– Generally recycled as nucleic
acids
– Can be catabolized to simple
sugars and nitrogenous bases
– Do not contribute significantly to
energy reserves
• Nitrogenous ring
– Pyrimidines (C,T, U)
– Purines (A, G)
• Pentose sugar
• Phosphate group--mono, di or tri