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Chap 6 Bio Exam

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oxidation-reduction reactions
A chemical reaction in which electrons are lost from one substance (oxidation) and added to another (reduction). O & R always occur together

LEO (the lion) says GER
LEO- loss of electrons is oxidation
GER- gain of electrons is reduction
Why do cells obtain energy via electron transport chains rather than through the instantaneous breakdown of glucose?
Complete oxidation of glucose through these pathways, releases more energy than glycolysis alone.
aerobic respiration
Process by which cells use oxygen to obtain usable energy from an energy source.

Uses oxygen in the atmosphere, or dissolved in water, as part of a complex process that releases and stores energy.
Process of initial energy-releasing reactions common to all cells?
Glycolysis
Overall summary equation for aerobic respiration.
Mitochondrion uses oxygen and glucose to harvest energy and generate ATP, while releasing carbon dioxide and water as the byproducts.
Chemical equation for the degradation of glucose.
Going On With Carbon.

Glucose + Oxygen --> Water + Carbon Dioxide + Energy

C6H12O6 + 6O2 -----> 6CO2 + 6H2O + Energy (ATP+Heat)
Role of ATP in aerobic respiration
ATP is basically an energy carrying molecule in our body. Aerobic respiration uses oxygen and glucose to produce ATP (ie. ATP is the desired product of aerobic respiration).

Cells recycle the ATP they use for work
Role of NAD+ and FAD in aerobic respiration.
N-A-D and F-A-D take H and e to the E-T-C to make A-T-P
Stages in aerobic respiration
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1) Glycolysis- cytoplasm
1a) Pyruvate Oxidation - matrix
2) Krebs Cycle, -inner compartment
3) Oxidative Phosphorylation (Electron Transport Chain) -inner membrane
Glycolysis
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Occurs in the cytoplasm.
Beaks glucose into two molecules of a three-carbon compound called pyruvate.
Harvests chemical energy by oxidizing glucose to pyruvate.
Pyruvate Oxidation
Pyruvate molecules are modified and transported into the matrix of the mitochondrion.
Produces:
Acetyl CoA
Carbon Dioxide
2 NADH
Krebs Cycle
Occurs in the inner compartment of the mitochondrion.
Completes breakdown of substrate/ oxidation of molecules.
Produces:
-molecules of NADH
-molecules of FADH2
-molecules of ATP
-CO2
Oxidative Phosphorylation (Electron Transport Chain)
-Inner membrane of the mitochondrion
-Accepts energized electrons from reduced coenzymes (NADH and FADH2) that are harvested during glycolysis and Krebs cycle. -Oxygen pulls these electrons down the electron transport chain to a lower energy state.

In mitochondria, electrons from NADH and FADH2, travel down electron transport chain to O2, which picks up H+ to form water. Energy released by these redox reactions is used to pump H+ from the mitochondrial matrix into the intermembrane space. In chemiosmosis, the H+ diffuses back across the inner membrane through ATP synthase complexes, driving the synthesis of ATP.

-Couples this exergonic slide of electrons to ATP synthesis or oxidative phosphorylation. This process produces most (90%) of the ATP.



Electron transport chain (ETC)
- energy from electron carriers drives formation of a proton (H+) gradient
-Form a staircase where the electrons pass from one to the next down the staircase
-At ETC- electron carries (NADH & FADH) are oxidized by molecules in the chain.
-The last electron acceptor in the ETC is oxygen


ATP synthase:
-Energy from proton gradient drives ATP production
ATP is produced by (___) energy released by the downhill fall of electrons from NADH and FADH to O2 to phosphorylate ADP.
and a process known as chemiosmosis. NADH & FADH2 shuttle electrons to an ETC) in the inner mitochondrion membrane.
Products of glycolysis
2 pyruvate molecules
2 NADH
4 ATP

______ results in a "net gain of two ATP molecules". This means that 2 ATP are used to split glucose and 4 ATP are produced.
Describe where pyruvate is oxidized to acetyl CoA, list the molecules produced, and how this process links glycolysis to the Krebs Cycle.
- Pyruvate is decarboxylated. The oxidized carboxyl group is converted to CO2 which is released.
- 2 remaining carbon molecules are oxidized into acetate. The e-s are stored temporarily in coenzyme NAD+ (NADH after reduction).
- Coenzyme A attaches to the acetate, forming Acetyl-CoA.
- Acetyl-CoA is the first substrate in the Krebs Cycle
-(Produces NADH and FADH2)


• The Krebs cycle and the conversion of pyruvate to Acetyl CoA produce 2 ATP's, 8
• NADH's, and 2FADH2's per glucose molecule
List the products formed during the Krebs cycle form one molecule of glucose. (Remember: 2 molecules of pyruvate are formed from one glucose molecules.)
For each molecule of glucose, glycolysis produces a net gain of 2 ATP molecules directly.
Distinguish between substrate-level phosphorylation and electron transfer (oxidative) phosphorylation.
Substrate level phosphorylation:
-Does not involve (electron transport chain),
-Involves the direct transfer of phosphate from a phosphate bearing molecule to ADP, thus yielding ATP.


Electron Transfer (oxidative) Phosphorylation.
-Involves (electron transport chain),
-Requires a protein, ATP synthase, to channel energy provided by a concentration of H ions; this energy results in the combining of phosphate with ADP.
what do NADH and FADH2 do with the electrons they carry in the final stage of aerobic respiration?
they carry electrons to the electron transport chain
Describe how a H+ gradient is formed as electrons move along the electron transport chain. & Describe how the formation of a H+ gradient is coupled to the synthesis of ATP.
The chain is an energy converter that uses the exergonic flow of electrons from NADH to FADH2 to pump H+ across the membranes from the mitochondrial matrix to the intermembrane space. The H+ has a tendency to move back across the membrane, diffusing own its gradient. And the ATP synthases are the only sites that provide a route through the membrane for H+.
What is the role of oxygen in aerobic respiration?
Oxygen serves as an electron acceptor. When food is completely metabolised in the organism, it is decomposed to electrons, protons and CO2. The electrons are carried by NADH to mitochondria, to electron-transport chain. At the end of the electron transport chain, oxygen receives electrons, thus providing for maximal yield of energy carried by those electrons (in the electron-transport chain, they are used for pumping protons across the mitochondrial membrane, thus proton gradient which empowers ATPase, is maintained). At last, the ATPase enzyme produces ATP, the usable form of energy.
Summarize the net ATP yield from the oxidation of a glucose molecule.
a. Glycolysis= 2 ATP, 0-2 NADH
b. Pyruvate dehydrogenase= 2 NADH
c. Krebs cycle= 2 ATP, 6 NADH, 2 FADH2
d. Oxidative phosphorylation= 32-34 ATP
e. Total 36-38 ATP
Simple break down of aerobic respiration stages...
Glycolysis: At this stage, some of the ATP molecules, some carbon molecules known as pyruvate or pyruvic acid, and some NADH molecules are created. Oxygen plays no part during this stage.
Krebs Cycle: In this stage, unused carbon molecules are used to initiate another series of chemical reactions to produce more NADH molecules, and another molecule known as FADH2.
Electron Transport Phosphorylation: In this stage, additional ATP molecules are created using the remainder of the reactant molecules.
Describe how anaerobic metabolic pathways differ from aerobic respiration.
*Aerobic respiration requires oxygen, whereas anaerobic respiration takes place in the absence of oxygen.
*Most of the plant and animal cells use aerobic respiration. On the other hand, anaerobic bacteria, yeast cells, prokaryotes, and muscle cells perform anaerobic respiration.
*Aerobic respiration is more efficient than anaerobic respiration. For one molecule of glucose, aerobic respiration produces 38 ATP molecules, whereas anaerobic respiration produces just 2 ATP molecules.
*Aerobic respiration usually takes place in the mitochondria, while anaerobic respiration takes place in the cytoplasm.
*In case of aerobic respiration, the end products are carbon dioxide and water. In anaerobic respiration, the end products are ethyl alcohol or lactic acid, and carbon dioxide.
*Aerobic respiration takes a longer time to release energy. Anaerobic respiration is a much faster process.
Compare the fate of pyruvate in alcohol fermentation and in lactic acid fermentation.
Alcohol Fermentation

Pyruvate is reduced to ethanol in two steps:
Pyruvate loses carbon dioxide and is converted to the two-carbon compound acetaldehyde.
NADH is oxidized to NAD+ and acetaldehyde is reduced to ethanol.
Many bacteria and yeast carry out alcohol fermentation under anaerobic conditions.

Lactic Acid Fermentation

Pyruvate is reduced to lactate.
NADH is oxidized to NAD+.
Commercially important products of lactic acid fermentation include cheese and yogurt.
When oxygen is scarce, human muscle cells switch from aerobic respiration to lactic acid fermentation. Lactate accumulates, but it is gradually carried to the liver where it is converted back to pyruvate when oxygen becomes available.
Compare the yield of ATP, per molecule of glucose, generated by fermentation with that produced by aerobic respiration.
Just 2 ATPs, which contrasts with the 36 yield by aerobic respiration.
Describe how food molecules other than glucose (including lipids, proteins, and other carbohydrates) can be oxidized to make ATP.
Energy can be extracted from molecules more complex than glucose such as proteins, carbohydrates and fats. These complex molecules are broken down into monomers, which then enter glycolysis or the Krebs Cycle at various positions.

Proteins: amino acids can feed into the Krebs Cycle by transamination reactions
.
Fatty acids: can feed into the Krebs Cycle via Acetyl CoA which is produced by the beta oxidation.

Lipids: Glycerol, derived from lipids, can feed into glycolysis at the 3-carbon stage (glyceraldehyde-3-phosphate).

Carbohydrates: (polysaccharides and starches) are usually taken into cells once they have been digested into monosaccharides (primarily glucose and fructose). Once inside the cell, they can be converted to glucose (if necessary) and/or shuttled directly into glycolysis.