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Introduction What Is Cell Respiration? ATP – The Energy Currency Types of Respiration Structure of the Mitochondrion Stages of Aerobic Respiration 1. Glycolysis 2. Link Reaction 3. Krebs Cycle 4. Electron Transport Chain Total ATP Production Anaerobic Respiration Role of Redox Reactions Metabolic Pathways Regulation of Respiration Relationship With Photosynthesis Benefits of Cell Respiration
Look around. You are breathing, your heart is beating, your brain is thinking, and your muscles are moving.
You may wonder, where does all this energy come from?
Food does provide us energy, but food is not directly usable by our cells. Your cells have to convert the food into chemical energy that is usable by the cell. That usable energy currency of the cell is called ATP.
Cell respiration is the process by which cells extract energy from organic molecules, primarily glucose, and convert it into ATP.
Life cannot exist without respiration.
Cell respiration is a series of chemical reactions that are largely controlled to break down the organic molecules to yield ATP.
Respiration is defined as:
Aerobic respiration occurs in the cell and requires the following chemicals to occur and to complete the cycle to produce energy for the cell (in the form of ATP) or to produce energy for the cell, the following equation is accomplished:
Glucose + Oxygen → Carbon dioxide + Water + Energy (in form of ATP)
In chemical equation form:
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP
Although the equation seems simple, a complex series of chemical reactions occurs in the cell in order to complete the process.
ATP is known as the energy currency of the cell and is known as the source of immediate energy for the cell. In the ATP molecule, there is a total of three phosphate groups. When one of the phosphate groups is removed, ATP becomes ADP (adenosine diphosphate) and energy is released.
ATP → ADP + Pi + Energy
The short answer is that ATP is used in the following processes:
The process of respiration is to regenerate ADP to ATP. Thus it is more accurate to say that the fuel source of the cell is ADP.
Respiration can be divided into two major processes:
To carry out Aerobic Respiration, one would need the following:
In contrast, Anaerobic Respiration occurs in the Cytoplasm of the cell, and as such releases a smaller amount of ATP molecules when compared to Aerobic Respiration.
In the case of humans, Anaerobic Respiration ultimately produces the molecule known as Lactate, whereas in the case of Yeast Anaerobic Respiration ultimately produces the molecules known as Ethanol and Carbon dioxide.
The various steps of the process of Aerobic Respiration occur in the Mitochondria of the cell, and as such, it is known as the powerhouse of the cell.
A mitochondrion has five parts:
The folds of the mitochondria increase the surface area for important reactions. The inner membrane has some proteins that are critical for ATP production.
Aerobic respiration has four main parts:
Let us understand each step.
Glycolysis takes place in the cytoplasm and does not need oxygen. A single glucose molecule (expected to have 6 carbons) gets broken down into two pyruvate molecules (3 carbons each). During this step in glycolysis:
Glycolysis is the first step in both aerobic and anaerobic respiration.
The Link Reaction acts as a bridge that connects Glycolysis to the Krebs Cycle. This takes place in the mitochondrial matrix.
Each pyruvate:
The resulting product is called acetyl-CoA.
For one glucose molecule (which is broken down into 2 pyruvate molecules):
The Krebs Cycle is also called the citric acid cycle.
For each cycle of glucose (2 turns of the cycle):
At this point, the greatest amount of final energy is remaining in the NADH and FADH₂.
This stage happens on the inner mitochondrial membrane.
This is the most crucial stage in terms of ATP yield.
In this part, the most ATP (about 28–34) is produced.
With aerobic respiration, this includes:
So, total ATP produced ≈ 32-38 (all cellular types)
When oxygen is not available, anaerobic respiration kicks in.
Pyruvate is converted into lactate. This leads to NAD being regenerated, and glycolysis can continue. When this occurs, only 2 ATP is produced per glucose molecule.
Lactate accumulation in muscles can also lead to fatigue.
Pyruvate is converted into ethanol and CO₂. This is called alcoholic fermentation.
While Anaerobic respiration can be fast, it is also very inefficient.
In respiration, there are also oxidation and reduction reactions.
Carriers of electrons like NAD and FAD also play very important roles in respiration.
They safely transfer the energy in small steps, instead of it being released all at once.
Respiration is a metabolic pathway.
Enzymes:
This ensures respiration is controlled and efficient.
Cells regulate respiration based on ATP demand.
One of the most important regulatory enzymes of glycolysis is called phosphofructokinase. This enzyme increases the efficiency of cellular respiration by preventing the waste of cell energy.
Photosynthesis and respiration are interdependent processes. The reactants for cellular respiration are the products of photosynthesis, which occur simultaneously within the cell.
Carbon dioxide + Water + Light → Glucose + Oxygen
Glucose + Oxygen → Carbon dioxide + Water + ATP
This is how energy is transferred in an ecosystem.
Cellular respiration is important for the cellular processes of:
Cellular respiration is the process by which ATP is generated. Without cellular respiration, the cellular processes come to a standstill, thereby causing inefficiency. Life, as we know it, depends on the continuous cycle of cellular respiration and energy generation.
The processes of cellular respiration may seem complicated, but they are based on clear principles.