Download Cellular Respiration I. Cellular Respiration and Fermentation are

Cellular Respiration
I. Cellular Respiration and Fermentation are catabolic
A. Fermentation
1. ATP producing
2. e- donors are organic compounds
3. e- acceptors are organic
4. can be anaerobic
5. partial degradation of sugar
B. Respiration
1. ATP producing
2. e- donors are organic compounds
3. e- acceptors are inorganic
4. cannot be anaerobic
5. fully degrades sugar
Most efficient and
prevalent catabolic
pathway
II. Cells recycle ATP for work
A. ATP (Adenosine TriPhosphate) provides the energy for bioenergetics. ATP is our
energy currency.
B. Phosphorylation – The addition of a P (phosphate group) to a molecule.
Where does this phosphate group come from? The hydrolysis of ATP.
ATP transfers a P to Glu and becomes ADP. This energizes Glu.
ATP must be regenerated by phosphorylating ADP.
C. Cellular respiration provides the energy to regenerate ATP
III. Redox Reactions release energy when electrons(e-s) move closer to
electronegative atoms
A. Redox reaction - partial or complete transfer of e- from 1 reactant to another
1. reduction - partial or complete gain of e2. oxidation - partial or complete loss of e-
B. Since e-s lose potential energy when they shift toward more electronegative atoms,
redox reactions that move e-s closer to oxygen release energy because oxygen is so
electronegative.
IV. Electrons fall from organic molecules to oxygen during cellular respiration
A. the formula for cellular respiration of glucose is:
B. Carbohydrates and Fats are excellent energy stores because they are rich in C to H
bonds.
C. The activation barrier holds glucose back from spontaneously combining with
oxygen.
D. Enzymes lower the activation energy so that glucose can be SLOWLY oxidized in
steps.
V. The fall of electrons during respiration is stepwise via NAD+ and an electron
transport chain
A. e-s are first passed to NAD+ (2 e-s and 1 p+) which makes NADH
B.
C. The e-s are then passed down the electron transport chain which releases the energy
very slowly in small steps.
VI. Cellular respiration is the cumulative function of:
A. Glycolysis
1. occurs in the cytosol (outside the mitochondria)
2. partially oxidizes one glucose(one 6-carbon molecule) into two pyruvates(two
3-carbon molecules)
B. The Krebs Cycle
1. occurs in the mitochondrial matrix
2. completes the oxidizing of glucose by breaking down the pyruvates into six
carbon dioxide molecules
C. The Electron Transport Chain
1. occurs at the inner membrane of the mitochondria
2. accepts the e-s from NADH and FADH 2
3. oxygen pulls the e-s down the chain
4. e-s combine with H+ and Oxygen to form water
5. synthesizes 90% ATP by oxidative phosphorylation (powered by redox
reactions that transfer the e-s from food to oxygen – we’ll talk about this later)
6. the other 10% of ATP is from glycolysis and the Krebs cycle by substrate level
phosphorylation (enzymatic transfer of a P from a substrate to ADP)
Assignment: Write a short review of the journey of e-s from food to ATP.
VII. Glycolosis
A. Glycolysis – Glyco = sugar, lysis = to split
B. The 6 Carbon (6C) sugar glucose is split into two 3C sugars. These 3C sugars are
then transformed into two pyruvates.
C. Catalyzed by enzymes in the cytosol
D. Occurs with or without oxygen (ie. it is anaerobic)
E. Glycolysis is a two part process - energy investment and energy yielding
F. Summary reaction of glycolysis:
Glucose
2 pyruvate + 2 H2O + 2 ATP + 2 NADH
VIII.The Krebs Cycle
A. More than three quarters of the original energy in glucose is still present in two
molecules of pyruvate.
B. The Krebs Cycle (occurring in the mitochondrial matrix) extracts this energy.
C. Before entering the Krebs Cycle, the pyruvate is first converted into Acetyl
Coenzyme A (Acetyl CoA) in a 3 step process.
D. Notice that some NADH is produced as well as some CO2.
E. The Acetyl CoA is then fed into the Krebs Cycle
The Krebs Cycle:
1. Is an 8 step process
2. Occurs in the mitochondrial matrix
3. There are 2 turns for every 1 molecule of glucose
4. Each cycle produces one ATP (by substrate-level phosphorylation), three
NADH, and one FADH2 (another electron carrier) and 2 CO2 per acetyl
CoA.
Notice that the beginning molecule (oxaloacetate) is regenerated.
This is why it’s know as the Krebs cycle.
To summarize everything so far, 1 molecule of glucose yields 6CO2, 10NADH, 2FADH2
and only 4ATP. Remember that the goal of cellular respiration is to use the energy in
glucose to replenish the cell’s supply of ATP. So far, we haven’t done a very good job of
that (we have only made 4 ATP).
Not to worry, we still have all of those excited e-s housed in NADH and FADH2.
IX. Electron Transport Chain (ETC)
A. There are thousands of copies of the electron transport chain (ETC) found in the
extensive surface of the inner mitochondrial membrane.
B. Each ETC is made of a series of
molecules, (each one more
electronegative than the previous one)
with the most electronegative of all,
Oxygen, being at the end.
C. The excited e- are transferred into the
ETC by NADH and FADH2
D. As the e- moves from molecule to
molecule, it loses some of its potential
energy because it is getting closer and
closer to the positive nucleus.
E. This loss of potential energy is coupled
with the pumping of Hydrogen ions (H+)
from the matrix into the inter membrane
space.
F. Thus, the ETC does not make ATP
directly. Rather, it generates an area of
high concentration of H+ in the space between the two membranes. This is known as
the proton-motive force, and, like water behind a damn, it has the ability to do work.
“What work?” you ask.
The phosphorylation of ADP.
X. ATP Synthesis & Chemiosmosis
A. The proton-motive force generated by the ETC is used to make ATP.
B. The Hydrogen ions concentrated in the inter membrane space want to diffuse down
their concentration gradient
C. What is keeping them from moving across the membrane?
The H+ is electrically charged and cannot move through the hydrophobic (fatty acid)
interior of the membrane.
D. The channel protein ATP Synthase provides a route for the H+ to move down its
concentration gradient. As it does so, it loses potential energy.
E. This loss of potential energy is used by ATP Synthase to phosphorylate ADP to make
ATP.
F. This is known as oxydative phosphorylation because Oxygen is used to move the e-s in
the ETC.
To summarize Cellular Respiration:
X. Fermentation
A. anerobic catabolism of organic nutrients (without oxygen)
aerobic- with oxygen
B. Glycolosis makes pyruvate using NAD+ not oxygen and 2 ATPs
1. if oxygen is present(aerobic), pyruvate is oxidized further
2. if oxygen is absent (anerobic), pyruvate is reduced and NAD+ is regenerated
C. Alcohol fermentation pyruvate to ethanol
D. Lactic Acid Fermentation pyruvate to lactate
1. human muscle do this when oxygen supply is getting low
2. Ex. Lance Armstron
E. Comparison of Fermentation to Cellular respiration
1. NADH -> NAD+
Fermentation Cellular Respiration2. Final Electron Acceptor
Fermentation Cellular Respiration3. Amount of energy
Fermentation Cellular Respiration4. Oxygen required?
Fermentation Cellular RespirationF. Facultive Anareobes - can use oxygen or not
1. Strict ( obligate) aerobes - require oxygen
2. Strict (obligate) anareobes - will die if in the presence of oxygen
XI. Connections to other metabolic pathways
A. Other organic molecules besides glucose
1. Carbohydrates ->
2. Proteins->
3. Fats->
B. Biosynthesis - Anabolic pathway
1. consume ATP
2. build carbon skeletons of cells
3. use some molecules formed as intermediates to glycolosis and Krebs Cycle
XII. Feedback Mechanisms control Cellular Respiration
A. Anabolic pathways controlled by the products they produce
B. Catabolic pathways controlled by regulatory enzymes
C. Allosteric control of enzymes
- inhibited by citrate and ATP
- activated by ADP and AMP