Chapter 8.2 Cell Respiration Flashcards Preview

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Flashcards in Chapter 8.2 Cell Respiration Deck (24):
1

Cell respiration

Oxidation and reduction of electron carriers

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Phosphorylation

- a phosphoryl group (phosphate) is added to ADP, thus forming ATP.
- makes molecules less stable

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Brief overview of Glycolysis

-occurs in the cytoplasm of the cell
-small net gain of ATP without the use of oxygen
-end with product pyruvate
- if no oxygen available then pyruvate enters into anaerobic respiration --> products are lactate or ethanol and carbon dioxide
- if oxygen available, pyruvate enter aerobic respiration in the mitochondria of the cell --> production of large number of ATPs, carbon dioxide and water

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Application 1.1: Electron tomography used to produce images of active mitochondria

not yet found

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Oxidation

-Loss of electrons
-Gain of oxygen
-Loss of Hydrogen
-Results in many C-O bonds
-Results in a compound with lower potential energy

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Reduction

-Gain of electrons
-Loss of oxygen
-Gain of hydrogen
-Results in many C-H bonds
-Results in a compound with higher potential energy

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Oxidation and Reduction together

Redox reactions. When redox reactions take place, the reduced form of a molecule always has more potential energy that the oxidized form of the molecule. Play a key role in the flow of energy through living systems.

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Glycolysis

-Sugar splitting
-uses no oxygen and occurs in the cytosol of the cell, no organelles required, and sugar splitting proceeds efficiently in aerobic and anaerobic environments

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Glycolysis step 1

With a 6-carbon glucose, 2 molecules of ATP are used to begin. In 1st reaction, the phosphates from the ATPs are added to glucose to form fructose-1,6-biphosphate, a process called phosphorylation, which creates a less stable molecule

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Glycolysis step 2

the less stable 6-carbon phosphorylated fructose is split into two 3-carbon sugars called glyceraldehyde-3-phosphate (G3P). This splitting is known as lysis

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Glycolysis step 3

Once the two G3P molecules are formed, each G3P or triose phosphate molecule undergo oxidation to form a reduced molecule of NAD+, which is NADH. As this is being formed, released energy is used to add an inorganic phosphate to the remaining 3-carbon compound --> compound with 2 phosphate groups. Enzymes remove the phosphate groups so that they can be added to ADP to produce ATP. End result is 4 molecules of ATP, 2 molecules of NADP and 2 molecules of pyruvate. Pyruvate is the ionized form of pyruvic acid

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Summary of Glycolysis

- 2 ATPs are used to start
- 4 ATPS are produced, with a net gain of 2
- 2 molecules of NADH are produced
- pathway involves substrate-level phosphorylation, lysis, oxidation and ATP formation
- pathway occurs in the cytoplasm of the cell.
- metabolic pathway is controlled by enzymes. Whenever ATP levels in the cell are high, feedback inhibition will block the 1st enzyme of the pathway. This will slow or stop the process.
- 2 pyruvate molecules are present at the end of the pathway

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Importance of Mitochondria

the rest of cellular respiration takes place here and in the presence of oxygen

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The link reaction

After glycolysis and oxygen is present, pyruvate enters the matrix of the mitochondria via active transport. Inside, pyruvate is decarboxylated, a reaction involving the loss of a carbon in the form of carbon dioxide, to form the 2-carbon acetyl group. The removed carbon is released as carbon dioxide, a waste gas. The acetyl group is then oxidized with the formation of reduced NAD+. The acetyl group combines with coenzyme A (coA) to form acetyl CoA.
It is controlled by a system of enzymes. Acetyl CoA may then enter the Krebs cycle to continue the aerobic respiration process

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Decarboxylation

The removal of the carbon element of a molecule.

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coenzyme

a nonprotein compound that is necessary for the functioning of an enzyme.

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Hexose

any of the class of simple sugars whose molecules contain six carbon atoms, such as glucose and fructose. They generally have the chemical formula C6H12O6.

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Krebs Cycle Conditions

If ATP levels are low, the acetyl CoA enters this cycle. Also called the tricarboxylic acid cycle, occurring in the matrix of the mitochondrion. Starts with the same thing it ends with

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Krebs Cyle steps

1. Acetyl CoA combines with a 4-carbon compound called oxaloacetate. The result is a 6-carbon compound called citrate.
2. Citrate (6-carbon) is oxidized to from a 5-carbon compound. The carbon is released from the cell as carbon dioxide. While the 6-carbon compound is oxidized, NAD+ is reduced to from NADH.
3. The 5-carbon compound is oxidized and decarboxylated to from a 4-carbon compound. Again, the removed carbon combines with oxygen and is released as carbon dioxide. Another NAD+ is reduced to form NADH.
4. The 4-carbon compound undergoes various changes resulting in several products, one being NADH. The coenzyme FAD is reduced to form FADH2. There is also a reduction of an ADP to form ATP. The 4-carbon compound is changed during these steps to re-form the starting compound of the cycle oxaloacetate, which may start the cycle again.

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Krebs Cycle overview

- Krebs cycle will run twice for each glucose molecule entering cellular respiration because a glucose molecule forms two pyruvate molecules. Each pyruvate produces 1 acetyl CoA that enters the cycle. The breakdown of glucose results in these products: 2 ATP molecules per molecule of glucose, 6 molecules of NADH (which allow energy storage and transfer), 2 molecules of FADH2, 4 molecules of carbon dioxide (released).
- 4 ATPs have been gained, 6 generated (4 from glycolysis and 2 from Krebs cycle) but 2 are used to start the process of glycolysis. The breakdown of each glucose molecule results in a net gain of 36 ATPs.

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Electron Transport Chain

This is where most of the ATPs from glucose catabolism are produced. It is 1st stage of cellular respiration where oxygen is needed, and occurs within the mitochondrion, however unlike the Krebs cycle, which occurred in the matrix, the electron transport chain occurs on the inner mitochondrial membrane and on the membranes of the cristae.
Carriers of electrons (energy) are close together and pass the electrons from one to another because of an energy gradient. Each carrier molecule has a slightly different electron electronegativity, and different attraction for electrons. Most of these carriers are proteins with haem groups and are referred to as cytochromes. One carrier is not a protein and is called coenzyme Q.
In this chain, electrons pass from one carrier to another because the receiving molecule has a higher electronegativity and, therefore, a stronger attraction for electrons. In the process, small amounts of energy are released. The sources of the electrons that move down the electron transport chain are the coenzymes NADH and FADH2 from the previous stages of cellular respiration.

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haem group of the carrier

part that is easily reduced and oxidized

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not yet found

The electrons are stepping down in potential energy as they pass from one carrier to another. FADH2 enters the electron transport chain at a lower free energy level than NADH, thus FADH2 allows the production of 2 ATPS while NADH allows the production of 3 ATPs.
At the end of chain, the de-energized electrons combine with available oxygen, which is the final electron acceptor beach it has a very high electronegativity and a strong attraction for electrons. Water is created when hydrogen ions combine with oxygen as well.

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Structure of Mitochondrion for electron transport chain

Matrix is the area where the Krebs cycle occurs → cristae provides a large surface area for the electron transport chain to function on. The membranes provide a barrier, allowing proton accumulation on one side. Embedded in the membranes are the enzymes and other compounds necessary for the processes of the electron transport chain and chemiosmosis to occur. The inner membranes of the mitochondria have numerous copies of an enzyme called ATP synthase