Cellular Respiration - Krebs Cycle Quiz

The Krebs Cycle takes place in the mitochondria, a cellular organelle responsible for producing energy through various metabolic processes, including the citric acid cycle (Krebs Cycle) and oxidative phosphorylation.

Succinyl-CoA is an intermediate molecule found in the Krebs Cycle (citric acid cycle). It is formed during the conversion of alpha-ketoglutarate to succinate in the cycle.

When isocitrate loses a carbon atom in the form of carbon dioxide (CO2), it undergoes a chemical reaction within the citric acid cycle (also known as the Krebs cycle or TCA cycle). The resulting molecule is called alpha-ketoglutarate or α-ketoglutarate.

Key acids in the Krebs Cycle: Citric acid (citrate), α-ketoglutaric acid (α-ketoglutarate), succinic acid (succinate), fumaric acid (fumarate), malic acid (malate), oxaloacetic acid (oxaloacetate).

Succinyl-CoA is converted into succinate through a series of enzymatic reactions in the citric acid cycle. Succinate is an important intermediate molecule in this cycle, and it plays a key role in the production of energy through cellular respiration. Therefore, the correct answer is Succinate.

Fumarate contains four carbon atoms, making it a four-carbon compound in the Krebs Cycle.

Oxaloacetate is a four-carbon molecule.

In the Krebs Cycle, citrate molecules are formed before alpha-ketoglutarate. The cycle begins with the condensation of acetyl-CoA and oxaloacetate to form citrate. Subsequent reactions then lead to the conversion of citrate into other intermediates, eventually resulting in the formation of alpha-ketoglutarate.

Acetyl CoA is broken down in the Krebs Cycle to produce carbon dioxide (CO2), energy-rich molecules NADH and FADH2, and a small amount of ATP through substrate-level phosphorylation.

The diagram attached to the question shows the citric acid cycle, also known as the Krebs cycle. This cycle involves a series of chemical reactions that occur in the mitochondria of cells. The molecule found between citrate and isocitrate in this cycle is cis-Aconitate. This molecule is formed from citrate through a dehydration reaction and is then converted to isocitrate. Therefore, cis-Aconitate is the correct answer.

The electron acceptor molecule that aids in the transformation of succinate to fumarate in the Krebs Cycle is FAD (flavin adenine dinucleotide). It is reduced to FADH2 during this reaction.

The enzyme fumarase (also known as fumarate hydratase) is used in the Krebs Cycle to convert fumarate into malate. This reaction involves the addition of a water molecule to fumarate, resulting in the formation of malate.

Glycolysis produces two molecules of pyruvate from one molecule of glucose.

Each molecule of pyruvate entering the Krebs cycle releases one molecule of carbon dioxide.

Therefore, two molecules of pyruvate entering the Krebs cycle will release two molecules of carbon dioxide.

However, the complete oxidation of glucose requires two turns of the Krebs cycle to process both pyruvate molecules generated from one glucose molecule.

In two turns of the Krebs cycle, a total of four molecules of carbon dioxide are released (two from each pyruvate molecule).

Therefore, the statement is true: 4 molecules of carbon dioxide are released in 2 turns of the Krebs cycle to convert both molecules of pyruvate from glycolysis.

Fumarate and malate have four carbon atoms each, while citrate has six carbon atoms.

The Krebs Cycle needs to run twice to completely utilize one molecule of glucose. This is because glucose is initially broken down into two molecules of pyruvate through glycolysis, and each pyruvate molecule enters the Krebs Cycle separately, resulting in two turns of the cycle for one glucose molecule.

Citrate contains six carbon atoms.

In the reaction that converts alpha-ketoglutarate into succinyl-CoA within the Krebs Cycle, one molecule of carbon dioxide (CO2) is released, along with the reduction of a molecule of nicotinamide adenine dinucleotide (NAD+) to form NADH. This reaction is catalyzed by the enzyme alpha-ketoglutarate dehydrogenase complex.

The Krebs Cycle initiates with the combination of acetyl-CoA and a four-carbon molecule known as oxaloacetate (OAA). This union leads to the formation of citric acid, a six-carbon compound, which is why the Krebs Cycle is sometimes referred to as the citric acid cycle.

After the complete breakdown of one pyruvate molecule, 10 ATP molecules are produced through the processes associated with the Krebs Cycle, including the electron transport chain's contribution from NADH and FADH2 generated by the cycle. This takes into account the typical ATP yield values from oxidative phosphorylation, reflecting efficiencies seen in eukaryotic cells.

Water is not used as a reactant in the Krebs Cycle before carbon dioxide. In the Krebs Cycle, also known as the citric acid cycle, the reactants are acetyl-CoA and oxaloacetate. These reactants undergo a series of chemical reactions that result in the production of carbon dioxide, ATP, and reduced electron carriers such as NADH and FADH2. Water is not directly involved as a reactant in this cycle. Therefore, the statement is false.

GTP and ATP are molecules used to transform Succinyl-CoA into Succinate. GTP (guanosine triphosphate) and ATP (adenosine triphosphate) are both high-energy molecules that provide the necessary energy for the conversion process. CoA-SH (coenzyme A thiol) is not directly involved in this specific transformation, and GDP (guanosine diphosphate) is not used in the process either.