Tag: biology

TCA or Krebs' cycle is amphibolic (both catabolic and anabolic) because it provides a number of intermediates for anabolic pathways.

Mechanism of aerobic respiration was given by Kreb. Thus it was named as Krebs cycle. Aerobic respiration is the respiration, which involves the breakdown of the substrate in the presence of oxygen (oxidation process).

The conversion of pyruvate to acetyl-CoA is a linker step between glycolysis and Krebs cycle. After the entry of pyruvate in the mitochondria the acetylation takes place in the perimitochondrial space which is the space between the inner and outer mitochondrial membrane. Each molecule of pyruvic acid is oxidatively decarboxylated to acetyl coA by the action of an enzyme complex pyruvate dehydrogenase. The acetyl coA then enters the Krebs cycle.  Thus the correct answer is option C.

The pyruvic acid enters Krebs cycle in form of acetyl CoA where it is oxidatively decarboxylated into CO$ _2$. The complete Kreb cycle leads to the net formation of 2 molecules of ATP by substrate-level phosphorylation, 8 molecules of NADH plus 2 molecules of FADH$ _2$ (via succinate dehydrogenase). The NADH and FADH$ _2$ then enter the ETS to drive ATP production by substrate level phosphorylation. 

Kreb's cycle consists of 8 cyclic steps which take place in the mitochondrial matrix. Each step is catalyzed by a specific enzyme. In Kreb's cycle, the entrant molecule is 2- carbon acetyl coenzyme A and the receptor molecule is 4- carbon oxaloacetate. Since the process involves both catabolic and anabolic reactions. it is an amphibolic pathway. It degrades acetyl coenzyme A and yields carbon dioxide and energy which is used to produce NADH, H+, and FADH+

• The citric acid cycle is also known as the TCA cycle (tricarboxylic acid cycle) or the Krebs cycle. 
• It is a series of chemical reactions used by all aerobic organisms to release stored energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins, into adenosine triphosphate (ATP) and carbon dioxide.
•  In eukaryotic cells, the citric acid cycle occurs in the matrix of the mitochondrion.
•  In prokaryotic cells, such as bacteria, which lack mitochondria, the citric acid cycle reaction sequence is performed in the cytosol. 
• Hence, Mitochondria is the site for the Krebs cycle.
• So, the correct answer is 'Krebs cycle'.

Olfactory receptors are found in nose. They are associated with the perception of smell. Olfactory receptors expressed in the cell membranes of olfactory receptor neurons are responsible for the detection of odor molecules. Activated olfactory receptors are the initial player in a signal transduction cascade which ultimately produces a nerve impulse which is transmitted to the brain.

• Olfactory receptors are also known as odorant receptors. 
• They are present in the cell membranes of olfactory receptor neurons and are responsible for the detection of odour which gives rise to the sense of smell.
• Hence,  Olfactory receptor organs are sensitive to Smell.
• So, the correct answer is 'Smell'.