Download Metabolism part 2

Metabolism
Part 2
I teach a simplified version of Glycolysis and Tricarboxylic Acid
Cycle (Kreb Cycle). I don’t want to you spend any time memorizing
chemical structures, I simply want you to understand the concepts
behind the 2 cycles. Once you understand the concepts behind the
cycles then you will better understand them in more detail. (Which
you will get in other classes, not this one.)
Glycolysis
• Here are a couple of important definitions for you to
know before we begin.
– Oxidation: this means that a molecule has lost electrons
– Reduction: this means that a molecule has gained electrons
• Glycolysis is the is the process of breaking glucose down
into 2 molecules of pyruvate (also referred to as pyruvic
acid).
• Glucose is a sugar that is composed of 6 carbons (6 Cs)
and multiple oxygen (O) and hydrogen (H).
• Pyruvate is a molecule that is composed of 3 Cs, O, and
H.
• Simply put, Glycolysis is the formation of 2 molecules of
pyruvate through the oxidation of glucose. (A 6C
molecule is split into 2, 3 carbon molecules.
Glucose
O
OH
OH
OH
OH
H
H
C
C
C
C
C
C
H
OH
Lose 1
H2O
C
C
Pyruvate
Lose 1
H2O
C
C
C
Pyruvate
C
• In the process of forming pyruvate some H
and O molecules are lost as water.
• 2 molecules of ATP are used in the
process of splitting glucose.
• By the time the process is finished, 4 ATP
are made.
• The Net Energy that is produced by this
process is 2 ATP.
• Before pyruvate can then enter the Tricarboxylic
Acid Cycle (TCA Cycle) it has to be changed
slightly. It changes from a 3 C molecule to a 2 C
molecule.
• The first CO2 is released and Coenzyme A is
added on. If the acetyl CoA is not added, the
molecule can’t fit into the TCA cycle because it is
not the right shape.
O
OH
C
C
O
Pyruvate
H
C
O
H
H
C
H
C
S-CoA
CO2 is
lost
H
Acetyl CoA
H
TCA Cycle
• Now the Acetyl CoA can fit into the TCA cycle
and continue it’s journey.
• Remember that each glucose gives us 2
molecules of pyruvate. Each pyruvate is
converted to Acetyl CoA. During the conversion
process 1CO2 is lost from each pyruvate. So,
from the original 6 Cs of glucose we now have 4
remaining. We have also lost some H and O as
water during Glycolysis, as well as some
additional O as CO2.
• The TCA results in the complete oxidation of acetyl CoA
to CO2. In other words, all 4 Cs and the O from the
acetyl CoA are lost as CO2 by the time it is finished with
the TCA cycle.
• 1 ATP is made per Acetyl CoA molecule that enters the
TCA Cycle. So a total of 2 ATP are made during the TCA
Cycle per molecule of glucose.
• Once the C and O are gone, there are still a few H left.
Normally a H molecule is a composed of 1 proton and 1
neutron and 0 electrons. During the TCA Cycle, the H
molecules are left with 1 electron each.
• These H molecules with their corresponding
electrons are the most important part of aerobic
metabolism!
• Special taxis called, NAD+ and FAD,
come and pick up the molecules of H
with their corresponding electrons
and take them to the Electron
Transport Chain.
• NAD+ can carry 1 H with its
corresponding electron and FAD can
carry 2 Hs with their corresponding
electrons.
Electron Transport Chain
• The carrier molecules NAD+ and FAD bring the
H’s to cell membrane (in prokaryotes) or the
mitochondrial membrane (in eukaryotes).
• The H’s and their corresponding electrons are
released into the cell membrane at the sight of a
proton that specializes in pumping the H’s
outside of the cell membrane.
• The electrons are passed through a series of
proteins (via oxidation and reduction reactions)
inside of the cell membrane, called the Electron
Transport Chain.
Outside the Cell
Cell Wall
H
+
Cell Memrane
H
+
e-
H
H
+
+
e-
H
H
+
+
H
H
+
+
H
+
ATP Synthase
e-
ee-
H
oxygen
NAD-H
H
+
NAD+
-
H
+
Inside the Cell
e
++ oxygen
=
H2O
• Once the electrons have moved through the electron
transport chain they are transported to a molecule called,
the Terminal Electron Acceptor. In the case of Aerobic
Respiration, the Terminal Electron Acceptor is oxygen.
• Excess H’s (now called protons because they are no
longer carrying an electron) outside the cell membrane
create potential energy because there is a high positive
charge on one side of membrane.
• These protons are then pumped back inside the cell
through the enzyme ATP Synthase. The movement of
the protons through ATP Synthase powers the enzyme to
make ATP.
• Then the protons, electrons and terminal electron
acceptor combine to form water.
• Net result = 34 ATP + 4 ATP from glycolysis and kreb
cycle = 38 ATP in prokaryotes. In addition, H2O and CO2
are given off as the by products of
respiration/metabolism.
Summary of Glycolysis
Start
with
End
With
Net ATP
Generated
Glycolysis
1, 6C
glucose
2 ATP
2, 3C
pyruvate
4 ATP
2 ATP
TCA Cycle
2, 3C
Pyruvate
Co2, ATP,
H with e-s
2 ATP
Electron
Transport
Chain
H with e-s
H2O, ATP
34 ATP
Total=38 ATP
Anaerobic Respiration
• Anaerobic Respiration is essentially the
same as aerobic respiration. The main
difference is that the terminal electron
acceptor is a compound other than O2. It
is usually some compound that contains
nitrogen, sulfur, or carbon.
– Ie. Nitrate, nitrite, sulfate, or carbonate
• It does not generate as many ATP as
aerobic respiration.
Fermentation
• Anaerobic Respiration and Fermentation are
not the same thing.
– Anaerobic Respiration still utilizes the TCA cycle but
fermentation only utilizes glycolysis.
– After pyruvate is generated through glycolysis, it is
then converted to some acid or alcohol by product.
– Fermentation does not require oxygen to occur.
– Fermentation does not require the TCA cycle.
– It uses organic compounds as the terminal electron
acceptor.
– It produces only small amounts of ATP.
• Examples of end products are lactic acid or ethanol
• This completes the lecture material for
Unit 1.
• I will be happy to stay after lab and answer
any questions regarding the material for
Test 1 or to conduct a review.
• I will post a review sheet Monday morning,
Sept. 25.