Transcript Metabolic Pathways - Centralia College

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A metabolic pathway or biochemical pathway
is where a substrate will convert to a product,
and that product will turn into a substrate for
a different enzyme
Exergonic Reaction is a reaction where energy
is released
Endergonic Reaction is where a reaction will
need to take in energy to occur
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Chemical reactions which break larger
molecules into smaller ones are catabolic
pathways.
◦ aerobic respiration, anaerobic respiration,
dehydration reaction
◦ These reactions are typically exergonic
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Chemical reactions which synthesize larger
molecules from smaller ones are anabolic
pathways.
◦ Protein synthesis, photosynthesis, condensation
reaction
◦ These reactions are typically endergonic.
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ATP stands for
adenosine triphospate,
which means that it
has three phosphate
groups attached to it.
ADP stands for
adenosine diphospate
AMP stands for
adenosine
monophosphate
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High-energy
phosphate bonds are
the bonds of the last 2
phosphate groups,
which are easily broken
to release energy for
cellular processes.
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ATP → ADP + P + energy
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Electron transport is where electrons give up
their energy as they move through a series of
electron transport reactions.
Oxidation-reduction reaction is where
molecules either gain or lose electrons.
◦ Oxidation is where a molecule loses electrons
◦ Reduction is where a molecule gains electrons
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Three important electron acceptors (carriers)
are NAD+, NADP+, and FAD
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One major way to generate ATP is via a proton pump.
The energy from high energy electrons is used to
pump H+ across a membrane, like pumping water
behind a dam.
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Autotrophs are able to take basic energy
sources to make energy-containing organic
molecules from inorganic molecules
◦ (auto-self, troph-feeding)
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Two types of autotrophs
◦ Chemosynthetic autotrophs are prokaryotic
organisms that use inorganic chemical reactions as
a source of energy to make larger, organic
molecules
◦ Photosynthetic autotrophs use sunlight to create
the organic molecules used for energy
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Heterotrophs do not make their own organic
molecules, so they must intake their energy
source through food
◦ (hetero-other, troph-feeding)
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In eukaryotic cells, certain biochemical processes
are carried out in certain organelles
◦ Chloroplasts are sites of photosynthesis
◦ Mitochondria are the sites of most cellular respiration
◦ Prokaryotes lack both chloroplasts and mitochondria, so
many biochemical processes occur in the cytoplasm
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Cellular Respiration is where organisms
control the release of chemical-bond energy
from large, organic molecules and use the
energy to sustain life
◦ Aerobic cellular respiration requires oxygen to
occur
◦ Anaerobic cellular respiration do not require
oxygen to occur
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In aerobic cellular respiration, ATP forms as
electrons are harvested, transferred along the
electron transport chain, and eventually
donated to oxygen gas.
C6H12O6 + 6O2 → 6CO2 + 6H20 + Energy
In glucose, the covalent bonds has chemical
potential energy. The easiest ones to get to
are the C-H and O-H bonds
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When the bonds from glucose are broken,
two things happen:
◦ The energy of electrons will phosphylate ADP to
make ATP
◦ Hydrogen ions (protons) are released
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Oxygen will be the final electron acceptor
Glucose will be oxidized, while oxygen will be
reduced.
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Aerobic respiration is divided into three
processes:
◦ Glycolysis
◦ Krebs Cycle
◦ Electron Transport System
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Glycolysis (glyco-sugar,lysis-split)
◦ Glucose + 2 ATP + NAD+ → 4 ATP + 2 NADH + 2 pyruvic acid
◦ Anaerobic
◦ Occurs in cytoplasm
◦ Requires 2 ATP
to start
glycolysis
◦ Has a net gain
of 2 ATP
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An inorganic phosphate
group is added to each
3C molecule.
This leaves each 3C
molecule with phosphate
groups at either end
Pi – C – C – C – Pi
Other enzymes pull off a
pair of high energy
electrons (and H+) and
pass them to our
electron delivery truck,
NAD+, producing NADH.
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Takes place in
mitochondrian
One carbon, in the
form of CO2, is
pulled off the 3C
molecules, leaving
2C.
And a pair of high
energy electrons are
loaded onto NAD+ to
produce NADH.
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A phosphate group is
added to each 2C
molecule and then
transferred to ADP,
forming ATP.
Enough high energy
electrons are pulled
off the 2C fragments
to load up 3 more
NAD+, forming 3
NADH.
A pair of slightly less
energetic electrons
are passed to
another carrier, FAD,
producing FADH2
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Pyruvic Acid + ADP + 4NAD+ + FAD →
3CO2 + 4NADH + FADH2 + ATP (for each pyruvic acid)
Also known as the Citric Acid Cycle
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Both glycolysis and the Krebs cycle pass
electrons to the electron carriers, NADH and
FADH2.
The carriers pass their electrons to transport
molecules in the inner mitochondrial
membrane.
◦ NAD+ and FAD leave to pick up another load.
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As electrons are passed from transport
molecule to transport molecule, H+ ions are
pumped across the membrane.
Finally, the electrons are passed to O2, which
combines with 2H+ to form H2O.
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The energy in the electrons carried by each
NADH can be cashed in for 3 ATPs
◦ 10 NADH x 3 ATP = 30 ATP.
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The energy in the electrons carried by FADH2
can be cashed in for 2 ATPs.
◦ 2 FADH2 x 2 ATP = 4 ATP.
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Total: 34 ATP from the ETS.
6 O2 are consumed to produce H2O.
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Starting with glucose (C6H12O6) and 6 O2
◦ Produce 6 CO2 and 6 H2O and up to 36 ATP
◦ However, 1/3 of energy is wasted in heat release,
yet still incredibly efficient source of energy
◦ The NAD+ and FAD are released to be used over
again
 Since oxygen is the final electron acceptor, H2O is
formed
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Fermentation is the term used to describe
anaerobic pathways that oxidize glucose to
generate ATP energy by using an organic
molecule as ultimate hydrogen acceptor
◦ Incomplete oxidation of glucose
 Lower amount of ATP produced
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The pyruvic acid may be turned into lactic
acid, ethyl alcohol or other molecules
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Alcoholic fermentation is the anaerobic
respiration pathway that yeast cells follow
when there is no oxygen in the environment
◦ Pyruvic Acid is converted into ethanol and carbon
dioxide
◦ In bread-making, the carbon dioxide is trapped in
the bread dough and called leavened
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Lactic Acid Fermentation is where pyruvic
acid is converted into lactic acid.
◦ Lactic Acid is considered a waste product to the
human body
◦ However, lactic acid is used to make yogurts, sour
cream and cheese
◦ When exercising, the skeletal muscle cells may have
to function anaerobically. The lactic acid will
ultimately be metabolized, which requires oxygen.
After finishing working out, our body will start to
metabolize the lactic acid.
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Both proteins and fats can
be catabolized via aerobic
respiration (but not
anaerobic respiration).
The glycerol (3C) from fats
enters glycolysis near the
end and then continues
through the Krebs cycle.
Fatty acids are split into 2C
fragments by the
peroxisomes.
The 2C fragments are
passed to the Krebs cycle
for conversion into CO2 and
generation of lots of ATP.
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Proteins are first split into
their amino acids.
The amine groups are
split off each amino acid,
forming NH3, ammonia.
Some organisms excrete
the toxic NH3
immediately, while others
convert it to urea.
The rest of the C skeleton
pass into various spots in
the Krebs cycle where
they are converted to CO2.