Mitochondria

Introduction

Energy is a requirement for all living organisms to function. Energy is why we consume food, breathe air and undergo all the processes that make us alive. The synthesis of energy is a highly complicated and nuanced process that requires a complex series of steps and a lot of complex pathways. These pathways are all regulated by a single cell organelle, the chief energy producer. This is where the  mitochondria comes in. Colloquially known as the cell’s energy centre, it is the chief source of ATP or Adenosine Triphosphate, the primary chemical energy source for all cellular processes. ATP is generated through complicated processes that require a certain degree of autonomy to execute. This is why Mitochondria are considered partially independent, with their DNA and their replicating mechanism. Mitochondria are colourless organelles; therefore, they cannot be seen under a microscope unless they are dyed. So, Richard Altman used a dye, observed these organelles under a microscope, and explained that these structures are the basic units of cellular activity. In 1898, Carl Benda coined the term ‘Mitochondria’ for these organelles. The number of mitochondria in a cell can vary significantly with life, tissue and cell type. The adult red blood cell has no mitochondria, while the liver cell can be over 2000. The mitochondrion is made up of compounds that perform special functions. These components or regions include the outer membrane, the intermembrane space, the inner membrane, the cristae and the matrix. Red Blood Cells or RBCs lack mitochondria. RBC uses none of the oxygen they transport in the body so they do not possess mitochondria. Instead, they derive energy from a different chemical process called glycolysis.

Features of mitochondria

• Semi-Autonomous in nature
• Double membrane-bound
• Only found in Eukaryotes
• They have their DNA
• Size ranging from 0.5-1 micrometres
• The structure comprises an inner membrane, an outer membrane and a gel-like material called the matrix
• The membrane is formed by Phospholipid layers that are Semi-Permeable
• The outer membrane covers the surface of the mitochondrion and has a large number of special proteins known as porins

Mitochondria Structure

The inner structure of mitochondria have  fold-like structures called Cristae. This helps increase the surface area inside the organelle: the cristae and the proteins of the inner membrane aids in the production of ATP molecules. The inner membrane is only permeable to oxygen and ATP molecules. Many chemical reactions take place within the inner membrane of mitochondria.

Mitochondria Functions

The essential function of mitochondria is to produce energy through oxidative phosphorylation. It is also involved in the following processes:

• Regulates the cell’s metabolism
• Promotes new cell growth & multiplication
• Detoxifies NH3 in animal’s liver cells
• Plays an important role in programmed cell death, also known as Apoptosis
• Helps to develop various hormones like estrogen and testosterone
• Keeps a regular check for Ca+ ion concentration within each cell of the body
• It is also involved in various cellular activities like cell signalling,  cellular differentiation, controlling the cell cycle, cell senescence, and cell growth

Cellular Respiration

The process of cellular respiration involves two significant steps. These two steps are vital as they help oxidise glucose and convert stored chemical energy to ATP, the form in which our cells can actively consume it. The two steps of Cellular respiration are as follows.

1. Glycolysis.
2. Citric Acid Cycle.

An intermediate also acts between the two, known as Oxidative decarboxylation. It functions as a bridge between the two steps.

Glycolysis

• Glycolysis is a cytoplasmic pathway that helps glucose break into two three-carbon compounds to generate energy. The process of phosphorylation helps to trap Glucose in the presence of Hexokinase enzyme
• There are ten steps in Glycolysis. Five are for the preparatory phase, and five are for the pay-off phase
• ATP is generated by substrate-level phosphorylation by high-energy compounds, such as 1,3-bisphosphoglycerate and phosphoenolpyruvate
• All cells of a living body use the process of Glycolysis to generate energy. There are two products of Glycolysis:
  • Aerobic Conditions: Pyruvate
  • Anaerobic conditions: Lactate
• Also, Pyruvate enters the Citric acid cycle for further energy production

Citric Acid Cycle

The Tricarboxylic Acid Cycle (TCA cycle), also known as the Citric Acid Cycle and Kreb’s cycle is cellular respiration’s second stage out of the total three-stage process. (Note: The three stages help living cells process and break down organic fuel molecules to gain the threshold energy to grow and divide, only in the presence of oxygen molecule. This metabolic process occurs in most animals, plants, fungi, and many bacteria.) The TCA cycle consists of eight steps catalysed by eight different enzymes. Sir Hans Adolf Krebs proposed this cycle and named it the Citric Acid Cycle in 1937. He received the Nobel Prize for Medicine and Physiology in 1953 because of this research. In simple words, the TCA cycle is an important biochemical process that connects carbohydrates, fats and protein metabolism.

Conclusion

Mitochondria is the powerhouse of the cell. It is that organelle in the cell that is responsible for energy. Now, energy is in ATP molecules; ATP is an abbreviated form of Adenosine Triphosphate. ATP is the energy currency. The meaning of currency in the context of biology is that ATP is the acceptable or the standard form of energy for the cell. Just like a currency which is the standard value of transactions everywhere. ATP is to cell what currency is for the economy. The inner structure of the mitochondria has  matrix. Matrix is the site where the chemical processes take place. The organelle has an outer membrane as well as an inner membrane. Mitochondria has various functions; chief among them is the production of energy. Cellular respiration is another essential aspect when we study mitochondria. The reason is that it plays a critical role in the processes of cellular respiration. This process involves two steps- glycolysis, and citric acid cycle, which is also called TCA. Glycolysis is when glucose is broken down into ATP and pyruvic acid. TCA or citric acid cycle is another essential metabolic process, and it happens in the matrix of the mitochondria. It connects the pathways of carbohydrates, fats, and protein metabolism.