Cell Respiration (2.8, 8.2) Flashcards
What are the two forms of ATP?
ADP and ATP. ADP is the empty energy carrier. When another phosphate group is added it becomes ATP.
Define cellular respiration.
The controlled release of energy from food (eg. carbohydrates) to produce ATP.
What is decarboxylation?
The removal of carbon atoms from the organic molecule to produce carbon dioxide. Aerobic respiration produces 6 CO₂ molecules.
What is oxidation?
The loss of electrons during a reaction.
What is phosphorylation?
The addition of a phosphate group to a molecule. Used in cellular respiration to convert ADP to ATP.
What is aerobic respiration?
Respiration with oxygen. Slower process than anaerobic respiration
Glucose + oxygen -> carbon dioxide + water + energy
C₆H₁₂O₆ + 6O₂ -> 6CO₂ + 6H₂O + 38ATP
Give the steps of aerobic respiration.
1) Glycolysis
2) The link reaction
3) The Krebs cycle
4) The electron transport system
Describe the first stage of aerobic respiration.
1) Glycolysis (occurs in the cytoplasm)
Think PLOAO.
- Phosphorylation
A hexose (6C) sugar, typically glycose, is phosphorylated using 2ATP to become hexose biphosphate. This makes the molecule more reactive. - Lysis
The hexose biphosphate splits into two triose (3C) phosphates. - Oxidation (loss of electrons)
The hydrogen is removed from the triose phosphates via oxidation. NAD+ is reduced to NADH (+ H+) - ATP formation
The triose phosphate molecules are converted into pyruvate released 4ATP molecules. - Overall
One molecule of glucose produces 2 pyruvate molecules, 2 NADH + H+ molecules and 2ATP (net gain).
Describe the second stage of aerobic respiration.
2) The link reaction (occurs in the matrix of the mitochondria).
The pyruvate molecules enter the matrix and lose a carbon. This carbon bonds to O₂ and forms CO₂. This is called decarboxylation of pyruvate. The pyruvate then becomes a 2C acetyl group via oxidation reactions where it loses hydrogen atoms. This cannot exist by itself so is held together by the carrier coenzyme A, forming acetyl coenzyme A.
- Overall
Per glucose molecule (two pyruvate molecules) 2 CO₂ molecules, 2 NADH + H+ molecules and 2 acetyl CoA groups are produced.
Describe the third stage of aerobic respiration.
3) The Krebs cycle (occurs in the matrix of the mitochondria).
In a complicated series of oxidation reactions the acetyl group (2C) joins with oxaloaetate (4C) to form citrate (6C). Coenzyme A is released and returns back to the link reaction. In other reactions in the cycle citrate is converted back into oxaloacetate. In these reactions 2C are released which form two molecules of CO₂ (decarboxylation). The oxidation reactions result in the reduction of hydrogen carriers (3 x NADH + H+) and (1 x FADH₂). These carry hydrogen to the electron transport system. One molecule of ATP is produced by phosphorylation.
Overall:
The Krebs Cycle occurs twice for each glucose molecule because there are two acetyl CoA molecules produced in the link reaction. So per glucose molecule 4CO₂ molecules, 6 NADH + H+, 2 FADH₂ and 2 ATP are produced.
Describe the fourth stage of aerobic respiration.
4) The electron transport system (occurs on the folded surface of the cristae in the mitochondria).
As electrons pass through the electron transport chain they lose energy. This energy is used to pump protons (H+ ions) across the membrane. As the hydrogen moves down the concentration gradient ATP is produced. This is called chemiosmosis and is facilitated by ATP synthase, a transmembrane enzyme. ATP synthase uses the energy released by H+ ions to convert ADP and Pi into ATP molecules. In total approx. 34 molecules of ATP are produced. At the end of the electron transport chain oxygen binds with the de-energised electrons and the protons (H+ ions) forming water. It does this to prevent the electron transport chain from being blocked and to maintain the hydrogen gradient.
What is anaerobic respiration?
If there is no oxygen present then only glycolysis occurs. This only produces 2 ATP molecules however it is a much faster process than aerobic respiration. It is often referred to as fermentation.
What are the products of anaerobic respiration in plants?
The pyruvate molecules produced in glycolysis are converted to ethanol and carbon dioxide.
What are the products of anaerobic respiration in animals?
The pyruvate molecules produced in glycolysis are converted to lactic acid. Very few animals use anaerobic respiration as their only way of getting energy. Some switch to anaerobic respiration during exercise. The build up of lactic acid is what causes fatigue in muscles.
Give the differences between aerobic and anaerobic respiration in terms of the overall energy yield, end products formed and location of the processes.
Aerobic respiration produces 38 ATP molecules, where anaerobic produces only 2 ATP. The end products formed in aerobic respiration are CO₂ and H₂O molecules and that of anaerobic respiration are ethanol and CO₂ in plants and lactic acid in animals. Aerobic respiration occurs in the cytoplasm and mitochondria where anaerobic respiration only occurs in the cytoplasm.
