Monday, April 27, 2009

Review: Cellular Respiration

Today in class we did interactive slides on the smart board to start our review for the AP test.
Here are the topics the slides covered:
-sources and sinks
-hydrogen bonds
-the four properties of water:
+cohesion and adhesion (transpiration)
+the fact that water is less dense as a solid than as a liquid
+surface tension
+high speific heat
-modes of selection
-speciation (*a lot of people seemed to need to review this one)
-apoplastic and symplastic routes
-recombinant DNA and vectors
-guttation, xenophytes, C3 C4 and CAM plants
-stages of mitosis
-animal junctions
+tight junction
+gap junction
-plant junctions
-monomers, polymers, and bonds
-the structure of a protein

I, personally, feel that I need to brush up on CELLULAR RESPIRATION. Here is a quick review. Hopefully it helps everyone out!

Cellular respiration is the breakdown of sugars that occurs in teh presence of oxygen. Carbohydrates, fats, and proteins can all be broken down to release energy in cellular repsiration. However, glucose is the primary nutrient fuel molecule that is used in cellular respiration to release energy.

Below is the standard equation for cellular respiration:
C6H12O6 + O2CO2 + H2O + Energy (as ATP)

Cellular respiration is aerobic respiration (oxygen is present).
Glycolysis is the first process in cellular respiration:
Glycolysis is the decomposition of glucose to two pyruvate molecules. The 6-carbon glucose molecule is split into two 3-carbon sugars through a long series of steps.

There is an ATP consuming phase and an ATP producing phase.
First, 2 ATP are consumed. In the next phase, 4 ATP are produced as well as 2 NADH. The net gain of ATP is 2.
*NADG is a conenzyme that forms when NAD+ combines with two energy-rich electrons and H+.

The Krebs Cycle is the second process:
It occurs in the mitochondrial matrix. In it, glucose is completely broken down and the final product is CO2.
The cycle has 8 steps, and each is catalyzed by a different enzyme:
1. Acetyl CoA adds iots two-carbon acetyl group to oxoaloacetate, producing citrate.
2. Citrate is converted to its isomer, isocitrate, by removal of one water molecule and addition of another.
3. Isocitrate is oxidized, reducing NAD+ to NADH. Then the resultinf compound loses a CO2 molecule.
4. Another CO2 is lostm and the resulting compound is oxidized, reducing NAD+ to NADH. THe remaining molecule is then attached to coenzyme A by an unstable bond.
5. CoA is displaced by a phosphate group, which is transferred to GDP, forming GTP, a molecule with functions similar to ATP.
6. Two hydrogens are transferred to FAD, forming FADH2 and oxidizing succinate.
7. Addition of a water molecule rearranges bonds in the substrate.
8. The substrate is oxidized, reducing NAD+ to NADH and regenerating oxaloacetate.

Each cycling requires the input of a 2-carbon acetyl co-a molecule, and two carbons are released in the course of the cyle as CO2.
For every 1 turn of the cycle, the net results are:
2 CO2

For every 2 turns of the cylce, the net results are:
4 CO2
**Both glycolysis and the Krebs Cycle are substrate level phosphorylation. This means that a phosphate group and its associated energy is transferred to ADP to from ATP. The substrate molecule (the one with the phosphate group) donates the high energy phosphate group.

Oxidative phosphorylation is the last process of the cellular respiration:
Oxidative phosphorylation is the process of extracting ATP from NADH and FADH2. Electrons from NADH and FADH2 pass along an electron transport chain.

The electron transport chain consists of molecules (mainly proteins) embedded in teh inner mitochondrial membrane. Sitting on top of these proteins embedded in the membrane are associated molecules that are alternately reduced and oxidized as the accept and donate electrons.
* In oxidation, electrons are loast. In reduction, they are added.

The first electron acceptor in the ETC is a flavoprotein called flavin mononucleotide (FMN) and it accepts and electron from NADH.
The electron is passd down a series of molecules to oxygen, the final electron acceptor. Then, it is combined with hydrogen atoms to form water.
*FADH2 and NADH both donate electrons in the chain

The ETC does not make any ATP itself. Its reactions are coupled to others to make ATP in chemiosmosis.

In chemiosmosis, a hydrogen pump pumps H+ ions against their concentration gradient across the mitochondrial membrane. This creates a proton gradient. Protein complexes called ATP synthases embedded in the membrane use the energy from the proton gradient. The H+ ions flow back into the mitochondrial matrix through the ATP synthase. The flow drives the oxidative phosphorylation of ADP to ATP. Oxidative phosphorylation results in about 34 ATP molecules.

This makes the total number of ATP produced by cellular respiration about 38.

To sum it up, here are the products of each step of cellular respiration:



KREB'S CYCLE: 2 net ATP, 6 NADH, 2 FADH2, 4 CO2
* Here is a really good video that Mrs. Lyon showed us in class when we first learned cellular respiration:
1. Which of the following sequences correctly indicates the potential ATP yield of the indicated molecules from greatest ATP yield to least ATP yield?
a) Pyruvate, ethanol, glucose, acetyl CoA
b) Glucose, pyruvate, acetyl CoA, NADH
c) Glucose, pyruvate, NADH, acetyl CoA
d) Glucose, FADH2, acetyl CoA, pyruvate
e) Glucose, FADH2, NADH, pyruvate
2. Cells do not catabolize carbon dioxide because
a) its double bonds are too stable to be broken
b) CO2 has fewer bonding electrons than other organic compounds
c) CO2 is already completely reduced
d) CO2 is already completely oxidized
e) the molecule has too few atoms
3. In mitochondria, exergonic redox reactions
a) are the source of energy driving projaryotic ATP synthesis
b) are directly coupled ot substrate-level phosphorylation
c) provide the energy that establishes the proton gradient
d) reduce carbon atoms to carbon dioxide
e) are coupled via phosphorylated intermediates to endergonic processes
4. When electrons flow along the electron transport chains of mitochondria, which of the following changes occurs?
a) the pH of the matrix increases
b) ATP synthase pumps protons by active transport
c) the electrons gain free energy
d) the cytochromes phosphorylate ADP to form ATP
e) NAD+ is oxidized
5. The final electron acceptor of the ETC that functions in aerobic oxidative phosphorylation is
a) oxygen
b) water
c) NAD+
d) pyruvate
e) ADP
1- B
2- D
3- C
4- A
5- A
This Week:
Review, review, and more review.
Remember: Chapter 50 take home is due Friday.
Only 2 more weeks until the exam! Keep up the hard work!

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