Download Metabolism Teaching Notes ***Print off slides 7,12,13, 16, 20, 23, 24

Metabolism Teaching Notes
***Print off slides 7,12,13, 16, 20, 23, 24, and 29 and expect students to write on these ***
Slide 1
The sunlight is absorbed in the ecosystem and converted to energy by the process of photosynthesis.
The Calvin Cycle, or dark reactions, fix CO2 into carbohydrates. Plants fix carbon and to make glucose
and expire oxygen.
Then glucose and oxygen is used to make ATP in cellular respiration, much like gasoline and oxygen is
used to create energy in a vehicle.
The ATP is used to do work inside the cell creates heat.
Slide 2
At the end of this process , 1 molecule of glucose is used to make we have 6 molecules of CO2 and 6
molecules of H2O, and ATP. Instead of an inefficient “fast burn,” this occurs in a stepwise fashion that
converts the energy in the bonds of glucose into ATP in an efficient manner that minimizes energy lost
as heat.
Slide 3
Overview of the Process Cellular respiration is aerobic respiration that requires eventually oxygen to complete. It ends in
oxidative phosphorylation which is fed by electron carriers (NADH and FADH2). So most of the
ATP in the cell is made by making these electron carriers.
 The enzymes needed for cellular respiration are geographically located to regions of the cell, and
thus the biochemical pathways they regulate are carried-out in those regions.
 Geographical localization of enzymes helps to facilitate the slow successive use of bonds from
glucose makes ATP very efficiently in cells (“slow burn”) vs the “fast burn” of combustion.
 The name of the game is to create as much electron carriers (NADH and FADH2) as possible to
feed into oxidative phosphorylation to create ATP, b/c oxidative phosphorylation is much more
efficient at making ATP than any other method in the cell.
o glycolysis- carried-out in the cytoplasm
 converts glucose to pyruvate thorough many steps. Each step controlled by an
enzyme
 overall glycolysis also makes some ATP (2 net and 4 gross) and used to
convert NAD+ to NADH. The NADH is transported into the mitochondria
for oxidative phosphorylation (will discuss in detail later).
o Pyruvate is transported into the mitochondria as well and used to make acetyl CoA,
NADH and CO2 in a process called pyruvate decarboxylation (AKA pyruvate oxidation)
o Acetyl CoA is fed into the citric acid cycle (AKA Kreb’s Cycle or Tricarboxylic Acid Cycle) in
the matrix of the mitochondria.
o several enzymes in succession create some ATP, CO2, H2O, FADH2 and tons of NADH.
-NADH and FADH2 are used to make ATP in oxidative phosphorylation (will
discussed in detail later)
o
oxidative phosphorylaton is carried-out on the inner membrane of the mitochondria via
electron transport chain and chemiosmosis
Overall 3 sources of electron carriers in this process are glycolysis, pyruvate decaroxylation and Kreb’s
Cycle. The electron carriers are fed into oxidative phosphorylation to make ATP. These are made in
Metabolism Teaching Notes
coupled redox reactions where something is oxidized (looses electrons) and those electrons are
transferred to electron carriers. Thus the electron carriers are reduced (gain electrons). During
oxidative phosphorylation the electron carriers are oxidized again and give-up their electrons.
Slide 4
Why have electron carriers at all?
 The NADH and FADH2 are electron carriers and products of redox reactions. They are generated
by gaining electrons (i.e. they converted from NAD+ or FADH respectively by being reduced)
during glycolysis, pyruvate decarboxylation and Kreb’s Cycle.
o NADH and FADH2 are then fed into electron transport system where they are oxidized
slowly and thus lose their electrons slowly to create proton motive force (will discuss
later). This controlled release of energy is harnessed to make ATP. The final electron
acceptor is oxygen to make water. This is what makes aerobic respiration aerobic!
Slide 5
While oxidative phosphorylation is used to make most ATP, there is another way to make ATP in cellular
respiration known as substrate level phosphorylation. In this case, an enzyme that uses a chemical that
has a high energy phosphate as a source of a phosphate to add on to ADP.
The biochemical pathways leading to the production of ATP (i.e. cellular respiration)
Slide 6
Overview of glycolysis
 a 6 carbon molecule (glucose) is converted over several reactions by enzymes into 2 3
carbon molecules (2 pyruvate). Pyruvate is fed on to other biochemical pathways to
make ATP
o so 1 molecule of glucose makes 2 pyruvate
o 2 molecules of glucose makes 4 pyruvates
o 4 molecules of glucose makes 8 pyruvtes
o 22 molecules of glucose makes ___ pyruvate
o 105 molecules of glucose makes ___ pyruvate
 In addition for each molecule of glucose. 2 molecules of ATP are used and 4 are
generated yielding a net of 2 ATP molecules
 AND for each molecule of glucose used in glycolysis there are redox reactions that
reduce 2 molecules of NAD+ to NADH
o The electron added to NAD+ is in the form of a hydronium ion (hydrogen with
an electron) so it is converted to NADH.
Slide 7 (slides 8-11 are just enlarged versions of this slide)
Glycolysis ReactionsGo over:
 1 molecule of glucose yielding 2 pyruvates
 the process highlighting the use of 2 ATPs, generation of 4 ATP and thus overall net of 2 ATPs
o a special focus on the production of PEP (phosphoenolpyruvate)
 redox reactions generating NADH from NAD+
 mentioning the reactant and products
 focus on the chemical structure of pyruvate and remind that each “corner” is a carbon atom
Metabolism Teaching Notes
Slide 12
Pyruvate Oxidation (AKA Pyruvate Decarboxylation)This is a redox reaction. Scientists are way too tired and too busy to be clever. Names are what they
are…So pyruvate decarboxylation is performed by the enzyme pyruvate decarboxylase by removing a
carboxyl group (circled below) from pyruvate to make carbon dioxide. Thus, here pyruvate is oxidized
(loses electrons), and simultaneously NAD+ is reduced (gains electrons) to form NADH. The NADH is
transported into the mitochondria and is used in oxidative phosphorylation (refer the students back to
slide #3). The remaining part (acetyl group) from pyruvate is added to Coenzyme A to make Acetyl CoA.
carboxyl
group
CO2
Slide 13
Acetyl CoA is transported into the mitochondrial matrix is fed into Kreb’s Cycle if ATP is needed.
Alternatively it can be used to make fat if ATP is not needed by the organism.
Slide 14-17
Kreb’s Cycle (AKA Citric Acid Cycle or Tricarboxylic Acid Cycle)
 performed in the mitochondrial matrix (refer to slide #3)
 step 1-Acetyl CoA (2 carbon molecule) is fed into Kreb’s Cycle and the carbons are added to
oxaloactate (a 4 carbon molecule) to make a 6 carbon molecule.
 step 2- redox reaction- Citrate is oxidized by removing CO2 and NAD+ is reduced to NADH
(which is fed into oxidative phosphorylation) and alpha-ketoglutarate is made (5 carbon
molecule)
 step 3- redox reaction- CO2 is removed from alpha-ketoglutarate and ATP is made (by substrate
level phosphorylation). More NADH and succinate is made
 steps 4-5- redox reactions- more NADH or FADH2 is made and oxaloacetate is regenerated
Metabolism Teaching Notes
Thinking exercisesIf 3 molecule of glucose is ingested, how many molecules is made of:
a) acetyl CoA
b) pyruvate
c) ATP in Kreb Cycle
d) NADH in Kreb Cycle
e) CO2 in Kreb Cycle
From glycolysis, pyruvate decarboxylation through Kreb’s Cycle, if 5 molecules of glucose is ingested,
how many molecules overall in the entire process is made of:
a) pyruvate
b) NADH
c) CO2
d) FADH2
-the students will be expected to make such predictions on exams.
Slides 18-19
ATP in this process uses substrate-level phosphorylation to make ATP. This done by an enzyme binding
a substrate with a phosphate group and adding it directly to ADP.
Slide 20
Oxidative Phosphorylation most ATP is made using this method
 performed on the inner membrane of the mitochondria.
 draw a mitochondria and show matrix, inner membrane and intermembrane space.
 two partso use animations to show this more clearly
o electron transport system (ETS) or chain (ETC)- here electrons from NADH and FADH2
are “separated” from hydrogens to make “proton motive force” (pmf). The electrons
stay inside the inner membrane of the mitochondria and the protons are pumped into
the inter membrane space. Draw on your mitochondria. Pmf is a type of potential
energy.
 slide 21 to supplement as needed
 in the end, electrons are handed-off to oxygen which is the final electron
acceptor
 Tell them at all atoms seek electrical neutrality. And ask them if put a whole in
the inner membrane, what would they expect the hydrogens would do?
 Answer- move to the electrons to seek electrical neutrality
o chemiosmosis- ATP synthase takes advantage of this. It uses the potential energy of pmf
to make ATP by providing a channel for the hydrogens to move through. This drives
shape change in the enzyme that allows it to make ATP (animation).
Slide 22
Net reaction for Cellular Respirationnote redox nature in process
Slide 23
Relate back to:
 the cellular geography
Metabolism Teaching Notes
 Note the maximal gross amount of ATP per glucose molecule made
o ask what if it was 4 glucose molecules, what would be the maximal gross amount of ATP
made?
 Note the production and movement of NADH and FADH2 to make ATP in oxidative
phosphorylation
Slide 24
Tell them the maximal net ATP production per glucose molecule is 36.
 Ask them why?
o Answer- because 2 ATP/glucose molecule is used to begin glycolysis
Slide 25
sum-up slide
Slide 26-28
Feedback Inhibition
 Biochemical pathways are expensive in enzymes etc to run in organisms, so we don’t do it unless
we need to.
 Suppose you ate a cheesecake and slept. Do you need a lot of ATP?
answer- no- so cellular respiration should be slowed to reduce the amount of energy spent in
making ATP
 Feedback inhibition is a way to control biochemical pathways.
o an end product of the pathway becomes an inhibitor that “feeds back” to control the
activity of an enzyme earlier in the pathway.
o slide 27 for example:
 phsophofructokinase is down-regulated by high ATP levels
 pyruvate decarboxylase is down-regualted by high NADH levels
Slide 29
o many of these feedback inhibitors are allosteric inhibitors
 remind them what allosteric inhibition means again vs competitive inhibition
 Ask them why most feedback inhibitors are allosteric?
 answer- because the inhibitors have a very different shape than the
substrate (e.g. ATP vs fructose 6-phosphate) so they can’t bind to the
active site of the enzyme (Lock and Key Hypothesis)
Slides 30-32
Anaerobic vs Aerobic Respiration
 With O2 - aerobic respiration- here glycoylsis is used to make pyruvate which is run through
pyruvate decarboxylation, Kreb’s Cycle and ultimately oxidative phosphorylation. And the key is
that O2 is the final electron acceptor which accepts the electrons (reduced) to make water. This
is why oxygen is needed!
 Let’s say you run a marathon, what happens?
o short of breath, heart rate increases to deliver oxygen to muscle cells
o next day sore muscles
So what is going on here?
 Without O2 - anaerobic respiration- all in the cytoplasm- here glycolysis is used to make
pyruvate but little oxygen to serve as the final electron acceptor. So the pyruvate is shunted in
another route to make the ATP needed to run the marathon.
o What that route looks like depends on the enzymes which vary in different organisms:
Metabolism Teaching Notes



slide 31 - a redox reaction- in organisms like us, glycolysis makes pyruvate and
ATP. Lactate dehydrogenase uses pyruvate to make lactate using NADH as a
source of electrons leaving NAD+. NAD+ is now regenerated for glycolysis.
slide 32 - a redox reaction- in yeast, glycolysis makes ATP and forms pyruvate. A
pyruvate decarboxylase removes CO2 and alcohol dehydrogenase reduces the
resulting acetaldehyde to ethanol using NADH as a source of electrons and
leaving NAD+. NAD+ is now regenerated for glycolysis.
So basically, if we had the same enzymes as yeast, everyone would run
marathons!!
Slide 33- extra summation slide