Transcript releases energy

CELLULAR RESPIRATION & FERMENTATION
CHAPTER 7 BIOLOGY IN FOCUS
AP BIO 2014
Living systems require energy
-- Life is work
• Complex organic molecules have potential
energy stored in their covalent bonds (think
“energized” electrons)
• This form of potential energy is called chemical energy
• We can use chemical energy to perform cellular work
inside our cells
• Our cells generate and depend upon one final usable
energy source  ATP
Remember the 1st Law –
energy cannot be created or
destroyed but only transferred.
Energy from the sun is used to
convert carbon dioxide and water
to glucose (chemical energy)
which is then converted to ATP
(usable chemical energy),
releasing carbon dioxide and
water.
The BIG energy transfers…
Catabolism of large organic molecules releases chemical
energy which can be captured by the cell and stored in
the form of ATP via cellular respiration and
fermentation.
Transferring energy means moving
electrons – called REDOX reactions
• When bonds are broken and remade, electrons and H+
are transferred
• A molecule that gains electrons and hydrogen is
reduced and a molecule that loses electrons and
hydrogen is oxidized (Just remember OIL RIG!)
A pair of redox reactions (they are
always paired!)
More redox vocab…
• The molecule that gives up electrons is called the
reducing agent
• The molecule that takes the electrons is called an
oxidizing agent. Because oxygen is so electronegative, it
is one of the most powerful oxidizing agents.
Oxidizing a sugar molecule (taking away its energized
electrons) and reducing oxygen releases a LOT of energy
• We can literally burn sugar – reducing oxygen to H20 and oxidizing
C6H12O6 to CO2 – this releases heat energy very rapidly. Little
sugar fires wouldn’t be very helpful or good for our cells…
• So instead we release the energy a little bit at a time and harness it
to make ATP at the end
Releasing the energy in
controlled small steps…
versus burning 
Electron carriers = energy wheelbarrows
• Transferring the energy from glucose involves multiple redox reactions
in which high energy electrons are harvested.
• These electrons are received and shuttled inside the cells by special
electron carriers.
• A coenzyme called NAD+ (nicotinamide adenine dinucleotide)
functions as a major electron carrier.
NAD+ + H+ + e-  NADH
oxidized form  reduced form
Let’s review…
• Objective: To harvest the energy stored in food and
transfer to a molecule that we can use – ATP
• Where is the energy stored? In bonds, in the form of
high energy electrons. So we need to get these high
energy electrons from food to ATP
• When electrons are transferred, it’s called a redox
reaction. The molecule that loses the electrons is
oxidized and the molecule that gains the electrons is
reduced.
• The big electron carrier in cellular respiration is
NAD+/NADH but it gets some help from FAD/FADH2
Aerobic cellular respiration summary
Overview of Cellular Respiration
It occurs in three main stages…
Glycolysis Cliff Notes (in cytoplasm)
•Glycolysis has an energy
investment phase and an
energy payoff phase – it takes
some ATP to get it running but
you end up with more than
you put in.
•Here’s the payoff. The first
part “costs” 2 ATP and here
we make 4 ATP, giving us a
net of 2 ATP
We also transfer our first
electrons to NADH which
can then dump these
electrons into our electron
transport chain!
Substrate level phosphorylation: when
a phosphate from a substrate molecule is
added to ADP to form ATP
Glycolysis…
Glycolysis, in a nut shell…
• Converts 6-carbon glucose to two 3-carbon pyruvic
•
•
•
•
acids (aka pyruvate)
Produces 2 ATP and 2 NADH
Occurs in the cytoplasm
Does not require oxygen as a reactant! Anaerobic
Prokaryotic cells (bacteria) and eukaryotic cells all
perform glycolysis (everybody’s doin’ it….)
Glycolysis, the movie
Glycolysis videos
• https://www.youtube.com/watch?v=8Kn6BVGqKd8
• Ha! Glycolysis rap:
https://www.youtube.com/watch?v=EfGlznwfu9U
Before we enter the next step (the citric acid
cycle or Krebs cycle), pyruvate must be
prepared – stuck onto a chaperone…
Step 2: The Citric Acid/Krebs cycle
• Occurs in the matrix of
•
•
•
•
the mitochondria (see
next slide)
Involves a bohemoth
enzyme complex
The point – to finish
completely oxidizing
what’s left of glucose by
transferring the electrons
and H+ to NAD+ and FAD
Products per one acetylCoA: 3 NADH, 1 ATP,
and 1 FADH2 and CO2 as
waste.
Remember – there are 2
acetyl-CoA’s per
glucose!
Here ‘tis – the “powerhouse” of the eukaryotic cell
• Matrix: where the
Krebs cycle occurs
• Intermembrane
space: where the H+
will be pumped
during the next stage
of cellular respiration
• Outer membrane is
pretty porous – inner
membrane is VERY
selective (you’ve
gotta be on the A-list)
Citric acid cycle -- aka Krebs cycle…
Krebs cycle, the movie
Where are we now?
• Glycolysis occurred in the cytoplasm, Krebs cycle was in
the matrix of the mitochondria and now the electron
transport chain is a series of proteins and proton (H+)
pumps located in the inner membrane of the mitochondria
So what do we do with all of the electrons now on
NADH and FADH2? Time to use them to make a
boatload of ATP!! Chemiosmosis
In an electron transport system, electrons pass from carrier to
carrier through a series of oxidation-reduction reactions. During
each transfer, some energy is released.
• During each of those transfers, the energy released is used to
pump H+ ions against their concentration gradient.
• The end result is a high concentration of H+ in the
intermembrane space.
• Now which way do they want to diffuse?
You know this stuff…
• Diffusion of something down its concentration
gradient is favorable – AND thus it releases
energy
• When H+ diffuses back into the matrix through the
ATP synthase, it releases energy and this energy
drives the production of ATP from ADP and Pi
• So here we’re coupling an exergonic (H+
diffusing into the matrix) with an endergonic
(making ATP from ADP) reaction
Electron transport, the movie
ETC videos
• https://www.youtube.com/watch?v=xbJ0nbzt5Kw
• https://www.youtube.com/watch?v=6W-7FG9KlpA
ATP synthase (Or F0/F1 ATPase)
• https://www.youtube.com/watch?v=3y1dO4nNaKY
• https://www.youtube.com/watch?v=Shs3lFU_OFM
Argh, poisons attack mitochondria!!
Glycolysis = 2 ATP
add Krebs and chemiosmosis and you’ve got 38 ATP
Uh oh. No oxygen. Ack!
No problemo… just ferment-O!
Alcoholic fermentation (yeast)
Lactic acid fermentation (animal cells)
We eat –
and it all comes down to makin’ ATP
What do we do
with ATP and some
of the byproducts
of catabolism
(breakdown)?
Make more
biomolecules!!
• Crash Course video:
https://www.youtube.com/watch?v=00jbG_cfGuQ