Question

Common to all living organism is (a) Kreb's cycle (b) EMP pathway (c) ETC (d) All of these

Short answer

All of these metabolic pathways can be found in almost all living organisms, therefore the answer is (d) All of these.

Step-by-step solution

Understanding the Kreb's Cycle

The Kreb's cycle, also known as the citric acid cycle or TCA cycle, is a part of cellular respiration where energy stored in organic molecules is transferred to ATP. This pathway is common in all aerobic organisms, thus it supports the statement.

Understanding the EMP pathway

The EMP pathway, also known as the Embden-Meyerhof-Parnas pathway or glycolysis, is the process of converting glucose into pyruvate and generating small amounts of ATP (energy) and NADH (reducing power). It occurs in nearly all living cells, supporting the statement.

Understanding the ETC

The electron transport chain (ETC) is a group of complexes that transfer electrons from electron donors to electron acceptors via redox reactions, and couples this electron transfer with the transfer of protons across a membrane. This process is found in all aerobic organisms, supporting the statement.

Key concepts

Kreb's Cycle

The Kreb's Cycle, also known as the Citric Acid Cycle or the Tricarboxylic Acid (TCA) Cycle, is a crucial part of cellular respiration. It is the pathway through which cells produce energy by breaking down organic molecules. This cycle takes place in the mitochondria of eukaryotic cells, where it plays a vital role in converting Acetyl-CoA, derived from carbohydrates, fats, and proteins, into energy.

The process begins when Acetyl-CoA combines with a four-carbon molecule, oxaloacetate, forming a six-carbon molecule known as citrate. Throughout the cycle, citrate is progressively broken down in a series of reactions, releasing two molecules of carbon dioxide and transferring energy to electron carriers such as NADH and FADH₂.

Each turn of the Kreb's Cycle generates:

• 3 NADH molecules
• 1 FADH₂ molecule
• 1 GTP (or ATP) molecule

These high-energy carriers are essential for the electron transport chain, where additional ATP is produced. The Kreb's Cycle is not only a pathway for energy production; it also provides intermediates for other biosynthetic pathways, highlighting its central role in cell metabolism.

EMP Pathway

The EMP Pathway, more commonly referred to as glycolysis, is the initial step of cellular respiration where glucose is catabolized into pyruvate. This process occurs in the cytoplasm, and it is universal across almost all living organisms, serving as a fundamental energy conversion pathway.

Glycolysis does not require oxygen, making it an anaerobic process. It consists of ten enzyme-catalyzed steps that efficiently convert one molecule of glucose (a six-carbon sugar) into two molecules of pyruvate (a three-carbon compound). Through these steps, a net gain of 2 ATP molecules and 2 NADH molecules is achieved per molecule of glucose.

Key features of the EMP Pathway include:

• Breaking down glucose through phosphorylation and splitting
• Producing energy as ATP via substrate-level phosphorylation
• Reducing NAD⁺ to NADH, which serves as an electron carrier for later stages of cellular respiration

The simplicity and efficiency of glycolysis, along with its evolutionary ancient origins, illustrate its pivotal role in energy metabolism across diverse life forms.

Electron Transport Chain (ETC)

The Electron Transport Chain (ETC) is the final phase of aerobic respiration and is pivotal for oxidative phosphorylation. This process takes place within the inner mitochondrial membrane in eukaryotes and the plasma membrane in prokaryotes.

The ETC is a series of protein complexes and other molecules that pass electrons down a gradient, ultimately transferring them to molecular oxygen, forming water. As electrons move through the chain, protons are pumped from the mitochondrial matrix to the intermembrane space, creating a proton gradient, also known as the proton motive force.

The energy stored in this gradient is used by ATP synthase, a membrane-bound enzyme, to produce ATP from ADP and inorganic phosphate. The electron transport chain is exceptionally efficient, producing most of the ATP generated during cellular respiration.

Important aspects of the ETC include:

• Electron transfer coupled with proton pumping
• Creation of a proton gradient
• Synthesis of ATP via chemiosmosis

Without the ETC, cells would not be able to efficiently extract energy from nutrients, underscoring its critical role in the survival of aerobic organisms.