Why cell respiration?
It controls the release of energy from organic compounds in cells to form ATP
Oxidation and Reduction
Cell respiration involves the oxidation and reduction of compounds
Oxidation and reduction are chemical processes that always occur together. This happens because the involve the transferring of electrons from one substance to another. Oxidation is the loss of electrons from a substances and reduction is the gain of electrons. Oxidation normally involves gaining oxygen or losing hydrogen, while reduction usually involves losing oxygen or gaining hydrogen.
It controls the release of energy from organic compounds in cells to form ATP
Oxidation and Reduction
Cell respiration involves the oxidation and reduction of compounds
Oxidation and reduction are chemical processes that always occur together. This happens because the involve the transferring of electrons from one substance to another. Oxidation is the loss of electrons from a substances and reduction is the gain of electrons. Oxidation normally involves gaining oxygen or losing hydrogen, while reduction usually involves losing oxygen or gaining hydrogen.
Electron carriers are substances than can accept and give up electrons as required. They often link oxidations and reductions in cells. The main electron carriers in respiration are NAD and FAD. The energy that is released from oxidation is carried to cristae of the mitochondria by NAD and FAD, which have been reduced
ANAEROBIC RESPIRATION
This type of respiration occurs without the presence of oxygen and If there is no oxygen during glycolysis, the net gain of ATP is very small (2 ATPs), lactate is produced in humans and yeast in animals, and reactions don't continue in the mitochondria. This is because in the absence of oxygen, glycolysis is the only source of ATP for cellular functions. Glycolysis reduces NAD+ to NADH+H+, depleting the supply NAD+, and without NAD+, glycolysis will stop.
AEROBIC RESPIRATION
This type of respiration occurs in the presence of oxygen, which is why aerobic reactions continue to happen in the mitochondria of a cell. Aerobic respiration in the cell consists of 5 steps:
1. Glycolysis
- Phosphorylation
Meaning: Phosphorylation is the addition of a phosphate molecule to an organic molecule.
Certain amino acids sequences tend to act as binding sites for the phosphate molecule on proteins. In many reactions, the purpose of phosphorylation is to make the molecule more unstable, which makes it more likely to react.
Glucose is reduced with 2 ATP
- Glycolysis and ATP
+ If there is oxygen, glucose is broken down to form two molecules of pyruvate (two 3-carbon molecules= total 6 carbon molecules) in the cytoplasm and reactions continue in the mitochondria.
+ Glucose is oxidized to pyruvate, for this NAD+ is reduced to NADH+H+
+ The production of pyruvate generates four ATP molecules because its two molecules of ATP per pyruvate
ANAEROBIC RESPIRATION
This type of respiration occurs without the presence of oxygen and If there is no oxygen during glycolysis, the net gain of ATP is very small (2 ATPs), lactate is produced in humans and yeast in animals, and reactions don't continue in the mitochondria. This is because in the absence of oxygen, glycolysis is the only source of ATP for cellular functions. Glycolysis reduces NAD+ to NADH+H+, depleting the supply NAD+, and without NAD+, glycolysis will stop.
AEROBIC RESPIRATION
This type of respiration occurs in the presence of oxygen, which is why aerobic reactions continue to happen in the mitochondria of a cell. Aerobic respiration in the cell consists of 5 steps:
1. Glycolysis
- Phosphorylation
Meaning: Phosphorylation is the addition of a phosphate molecule to an organic molecule.
Certain amino acids sequences tend to act as binding sites for the phosphate molecule on proteins. In many reactions, the purpose of phosphorylation is to make the molecule more unstable, which makes it more likely to react.
Glucose is reduced with 2 ATP
- Glycolysis and ATP
+ If there is oxygen, glucose is broken down to form two molecules of pyruvate (two 3-carbon molecules= total 6 carbon molecules) in the cytoplasm and reactions continue in the mitochondria.
+ Glucose is oxidized to pyruvate, for this NAD+ is reduced to NADH+H+
+ The production of pyruvate generates four ATP molecules because its two molecules of ATP per pyruvate
2. The Link Reaction
Once the pyruvate enters the mitochondria, enzymes in the matrix of the mitochondria remove hydrogen and carbon dioxide from the pyruvate. These are the processes of oxidation and decarboxylation. That is why the process together is called oxidative decarboxylation. Once the hydrogen is removed, the NAD+ accepts it, thus forming an acetyl group. Later, this acetyl group joins CoA and forms acetyl CoA
Once the pyruvate enters the mitochondria, enzymes in the matrix of the mitochondria remove hydrogen and carbon dioxide from the pyruvate. These are the processes of oxidation and decarboxylation. That is why the process together is called oxidative decarboxylation. Once the hydrogen is removed, the NAD+ accepts it, thus forming an acetyl group. Later, this acetyl group joins CoA and forms acetyl CoA
3. The Krebs Cycle
Step 1 - In the first stage of the Krebs cycle, the acetyl group from acetyl CoA is transferred to a four carbon compound. This forms a six carbon compound.
Step 2 - This six carbon compound then undergoes decarboxylation (CO2 is removed) and oxidation (hydrogen is removed) to form a five carbon compound. The hydrogen is accepted by NAD+ and forms NADH + H+.
Step 3 - The five carbon compound undergoes decarboxylation and oxidation (hydrogen is removed) again to form a four carbon compound. The hydrogen is accepted by NAD+ and forms NADH + H+.
Step 4 - The four carbon compound then undergoes substrate-level phosphorylation and during this reaction it produces ATP. Oxidation also occurs twice (2 hydrogens are removed). The one hydrogen is accepted by NAD+ and forms NADH + H+. The other is accepted by FAD and forms FADH2. The four carbon compound is then ready to accept a new acetyl group and the cycle is repeated.
The carbon dioxide that is removed in these reactions is a waste product and is excreted from the body. The oxidations release energy which is then stored by the carriers when they accept the hydrogen. This energy is then later on used by the electron transport chain to produce ATP.
Step 1 - In the first stage of the Krebs cycle, the acetyl group from acetyl CoA is transferred to a four carbon compound. This forms a six carbon compound.
Step 2 - This six carbon compound then undergoes decarboxylation (CO2 is removed) and oxidation (hydrogen is removed) to form a five carbon compound. The hydrogen is accepted by NAD+ and forms NADH + H+.
Step 3 - The five carbon compound undergoes decarboxylation and oxidation (hydrogen is removed) again to form a four carbon compound. The hydrogen is accepted by NAD+ and forms NADH + H+.
Step 4 - The four carbon compound then undergoes substrate-level phosphorylation and during this reaction it produces ATP. Oxidation also occurs twice (2 hydrogens are removed). The one hydrogen is accepted by NAD+ and forms NADH + H+. The other is accepted by FAD and forms FADH2. The four carbon compound is then ready to accept a new acetyl group and the cycle is repeated.
The carbon dioxide that is removed in these reactions is a waste product and is excreted from the body. The oxidations release energy which is then stored by the carriers when they accept the hydrogen. This energy is then later on used by the electron transport chain to produce ATP.
4. Electron Transport Chain
In the mitochondria, there is a chain of electron carriers, which is best known as the electron transport chain. It is through this chain that electrons from the oxidative reactions before pass along the chain. NADH donates two electrons to the first carrier in the chain. Then, these two electrons go along the chain releasing energy from one carrier to the next. At the third location of the chain, enough energy has been released to produce ATP with the usage of the ATP synthase, which is an enzyme that is found in the inner mitochondrial membrane as well. FADH2 donates electrons but at later stage than NADH. Enough energy is released at only two locations of the chain by electrons from FADH2. The ATP production relies on the released energy by oxidation and it is thus called oxidative phosphorylation
In the mitochondria, there is a chain of electron carriers, which is best known as the electron transport chain. It is through this chain that electrons from the oxidative reactions before pass along the chain. NADH donates two electrons to the first carrier in the chain. Then, these two electrons go along the chain releasing energy from one carrier to the next. At the third location of the chain, enough energy has been released to produce ATP with the usage of the ATP synthase, which is an enzyme that is found in the inner mitochondrial membrane as well. FADH2 donates electrons but at later stage than NADH. Enough energy is released at only two locations of the chain by electrons from FADH2. The ATP production relies on the released energy by oxidation and it is thus called oxidative phosphorylation
5. Oxidative Phosphorylation
Once electrons go through the electron transport chain, they release energy. Then, this energy is used to pump protons (H+) from the matrix to the inner mitochondrial membrane and into the space between the inner and outer mitochondrial membranes. This space has a very small volume and thus as the protons move into it they create a concentration gradient quickly. This is the process of chemiosmosis. Now, there is a high concentration of protons in the space between the inner and outer membranes and a low concentration of protons in the matrix
Once electrons go through the electron transport chain, they release energy. Then, this energy is used to pump protons (H+) from the matrix to the inner mitochondrial membrane and into the space between the inner and outer mitochondrial membranes. This space has a very small volume and thus as the protons move into it they create a concentration gradient quickly. This is the process of chemiosmosis. Now, there is a high concentration of protons in the space between the inner and outer membranes and a low concentration of protons in the matrix
The energy used to pump these protons across the inner membrane comes from the energy released by the electrons passing through the electron transport chain.
Afterwards, the protons move down the concentration gradient from the space between the inner and outer membrane into the matrix. These protons can only go back to the matrix through an enzyme called ATP synthase which is embedded in the inner membrane. As the protons go through the channels of the ATP synthase, they release energy, which is then used by ATP synthase to convert ADP to ATP. This process is called oxidative phosphorylation because the electrons come from previous oxidation reactions and the ATP synthase catalyses the phosphorylation of ADP into ATP.
•Therefore: H+: remains in the intermembrane space, lowering pH and contributing to the chemiosmotic gradient --> ATP phosphorylation
•H+ diffuse down chemiosmotic gradient from intermembrane space (pH = 4) through proton channel and into matrix (pH = 8)
•Product
–each NADH + H+ pumped 3 pairs of H+s, which produces 3 ATP
–each FADH2 pumps 2 pairs of H+s, which produces 2 ATP
Afterwards, the protons move down the concentration gradient from the space between the inner and outer membrane into the matrix. These protons can only go back to the matrix through an enzyme called ATP synthase which is embedded in the inner membrane. As the protons go through the channels of the ATP synthase, they release energy, which is then used by ATP synthase to convert ADP to ATP. This process is called oxidative phosphorylation because the electrons come from previous oxidation reactions and the ATP synthase catalyses the phosphorylation of ADP into ATP.
•Therefore: H+: remains in the intermembrane space, lowering pH and contributing to the chemiosmotic gradient --> ATP phosphorylation
•H+ diffuse down chemiosmotic gradient from intermembrane space (pH = 4) through proton channel and into matrix (pH = 8)
•Product
–each NADH + H+ pumped 3 pairs of H+s, which produces 3 ATP
–each FADH2 pumps 2 pairs of H+s, which produces 2 ATP
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Theory of knowledge: Peter Mitchell’s chemiosmotic theory encountered years of opposition before it was finally accepted. For what reasons does falsification not always result in an immediate acceptance of new theories or a paradigm shift?
This because even though a theory might be tested over and over, which is the process of falsification, each time results can be different; they can either support the theory or the opposite. For something to be scientific, it has to be tested a vast amount of times so that scientists are aware that what they are trying to prove actually is what they thought, and that it does not change over time.
This because even though a theory might be tested over and over, which is the process of falsification, each time results can be different; they can either support the theory or the opposite. For something to be scientific, it has to be tested a vast amount of times so that scientists are aware that what they are trying to prove actually is what they thought, and that it does not change over time.