Transcript cellular respiration

Cellular Respiration
By the end of this class you should understand:
• The major processes that living things use to
make energy
• The relationship between photosynthesis and
cellular respiration
• The key differences between aerobic and
anaerobic processes
• The three steps of eukaryotic cellular
respiration
What is needed to make ATP?
• ADP (nucleic acid) and
phosphate
– There is plenty of this in the cell
already since it gets reused a lot
• Energy source (carbohydrate,
protein, lipid)
• Oxygen (for aerobic
respiration only)
– Anaerobic respiration requires
no oxygen
Which cells do this?
• All cells need energy
• All cells with mitochondria
perform complete cellular
respiration (aerobic)
• Cells with no
mitochondria (i.e. red
blood cells, most
prokaryotes) can only
perform anaerobic
respiration or
fermentation
Complete Cellular Respiration
C6H12O6 + 6O2  6CO2 + 6H2O + ATP
Technically a Combustion Reaction:
C6H12O6 + 6O2  6CO2 + 6H2O + Heat
Photosynthesis in Reverse!
• Water is split into O2
to extract electrons
• Electron transport
chain creates proton
gradient
• Glucose is broken down with
enzymes to make 3-carbon
sugar (glycolysis)
• 3-carbon sugar enters Krebs
cycle, is broken down into CO2
– Used by ATP synthase • Products of Krebs cycle are ATP
and electron carriers
• ATP and electron
carriers are used up • Electron carriers power electron
absorbing CO2 making transport chain which creates
3-carbon sugar in the
proton gradient
Calvin Cycle
– Used by ATP Synthase
• 3-carbon sugars made • Electrons are dumped onto O2
into glucose
to make water
Fermentation
• Breakdown of sugar is nearuniversal to living things
• Many different chemical
pathways available
• Anaerobic pathways (lacking
oxygen) include producing
ethanol and lactic acid
– How do you think your beer
was made?
– Yogurt also made this way
Glycolysis
• Fermentation typically takes
place with no oxygen
• Most eukaryotes (and a few
aerobic prokaryotes) use
oxygen to complete
metabolism of sugar
• The first step is glycolysis, or
breaking down the sugar
with enzymes, into pyruvate
Human Fermentation
• If no oxygen is present,
pyruvate buildup in cell
can become toxic
• Pyruvate is instead
converted to lactic acid
• Lactic acid enters
bloodstream and
creates the “burning”
feeling in your muscles
Krebs Cycle
• The Krebs Cycle is an enzymatic process
• Aerobic: requires oxygen to keep running
– If no oxygen, no electron carriers available
• Reactant: 1 Acetyl CoA
– Pyruvate is converted to Acetyl CoA first
• Product: 3 CO2
Krebs Cycle
• Performed in the
mitochondria
• Produces ATP and
high-energy
electrons
• Produces the CO2
that we breathe
out
– CO2 exits cell and
dissolves into
blood until we
breathe it out at
the lungs
Electron Transport Chain
• Electrons are pushed one by one through a
transport chain
• As the electron moves, its energy is used to
pump hydrogen ions into a special reservoir
– Sort of like using energy to pump water to a lake
above a dam
• As the hydrogen ions are released back, they
turn a “water wheel” that makes ATP
Electron Transport Chain
• Each of these
structures pulls
a little more
tightly on the
electron
• The final
recipient of the
electron is
oxygen, which
makes water
• This means the
entire chain is
aerobic
Electron Transport Chain
• The energy in the electron does work to
create a gradient of hydrogen ions
• The hydrogen ions move down their gradient
through an ATP Synthase enzyme
• This enzyme creates ATP when turned by
hydrogen ions
– This is called chemiosmosis
– This step makes a LOT of ATP (overall total for 1
glucose molecule: ~34 ATP)
ATP Synthase
Cellular Respiration Summary
Cellular Respiration Summary:
• Glucose
– is broken down by glycolysis to
• Pyruvate
– which enters the Krebs cycle and becomes
• CO2
– which leaves, but the released electrons power the
• Electron Transport Chain
– which makes fat stacks of ATP
– oxygen absorbs the electrons to become water
Alternative Energy
• This is the main sequence of energy for
metabolizing glucose
– All organisms with mitochondria perform this type
of cellular respiration
• Most organisms have alternatives as well
– Humans can convert fat into Acetyl CoA through a
process called beta oxidation
– One fat molecule can provide hundreds of ATP!
Part 2: Open Question Time!
• First exam is tomorrow! Yaaay…