What is cellular respiration
Creatures need energy for their every activity in life. This energy is provided by the foods that they receive. The process of releasing energy from received nutrients is called cellular respiration.
C6H12O6 (s) + 6 O2 (g) + ADP + P → 6 CO2 (g) + 6 H2O (l) + ATP
This process with its written formulas shows the generation of aerobic cellular respiration. As an example stored energy in glucose form with oxygen gas are reactants and they synthesize ATP.
ATP stands for adenosine triphosphate, It’s an energy-carrying in cells and molecules. If oxygen gas doesn’t exist so anaerobic respiration will happen.
How does cellular respiration work
Most of the time cellular respiration backs to aerobic cellular respiration. Cellular respiration gets done in 3 steps:
- TCA cycle
- Oxidative phosphorylation
The first process of cellular respiration is glycolysis, also called the glycolytic pathway. Glycolysis takes place in the cytoplasm. Glycolysis breaks down done step by step in glycolysis.
Glucose converts into fructose 1,6- diphosphate by using the energies of two ATP ( two ATP release their energies and converted to two ADP).
Fructose 1,6- diphosphate breaks down into two molecules called glyceraldehyde 3- phosphate. Glyceraldehyde 3- phosphate converts to 1,3- bisphosphoglycerate, during this conversion NAD+ ( an electron carrier molecule that stands for nicotinamide adenine dinucleotide), converts to NADH (an electron carrier that stands for nicotinamide adenine dinucleotide (NAD) + hydrogen ( H) ) and a hydrogen ion, one phosphate also add to have a molecule with two phosphates.
At the end of glycolysis, two pyruvate molecules should be manufactured, each 1,3- bisphosphoglycerate converts two ADP to ATP and creates pyruvate.
Pyruvates enter the mitochondria to have a process called pyruvate oxidation. The result of pyruvate oxidation is producing two acetyl-coenzyme A. Each pyruvate release one carbon dioxide, receive CoA( coenzyme A), and convert one NAD+ to NADH, to produce acetyl COA.
Tricarboxylic acid cycle is also known as Krebs or citric acid cycle, take place in mitochondria. Then the main process of organic fuels breaks down. In pyruvate oxidation, two acetyl COA have produced so each of them enters the TCA cycle. Oxaloacetate catches the carbons of acetyl COA and converts to the six-carbon molecule called citrate.
Acetyl COA releases its CoA during this conversion. Citrate converts to the five-carbon molecule called α-ketoglutarate, citrate release one carbon dioxide as a waste product and uses an NAD+ and converts it to NADH. Now succinate going to be made from the α-ketoglutarate molecule, succinate is the four-carbon molecule. During this process, one ADP converts to ATP, one NAD+ converts to NADH, and one carbon dioxide is released as a waste product.
Succinate should be made fumarate, fumarate is a four-carbon molecule like succinate, here another electron carrier is produced. FADH2 is made by FAD (flavin adenine dinucleotide). As we mentioned this process was a cycle so here oxaloacetate has to be produced.
Oxaloacetate is the four-carbon molecule, fumarate got some changes and produces oxaloacetate, during this changing NAD+ converts to NADH. If we want to express it as a number, for two acetyl COA that has been produced in pyruvate oxidation, we going to have six NADH, four CO2, two ATP, and two FADH2.
This process is also called the electron transport chain because it includes four proteins that transport electrons. This chain takes place in the inner membrane of mitochondria. NADH and FADH2 that have been produced in glycolysis and the TCA cycle, now release their hydrogen atoms, which provide pair of electrons.
These electrons transport by proteins mentioned above until they reach the last protein, these electrons reduce oxygen atoms to manufacture water molecules, oxygen ions with hydrogen ions synthesize H2O.
During this transportation, proteins of the chain pump protons ( H+) from the matrix to the intermembrane space by using the energies of electrons released by electron carriers ( NADH and FADH2).
There’s a molecule out of the electron transport chain called ATP synthase. It transports protons that enter the intermembrane space to the matrix again. While this transportation ATP synthase, make ATP from ADP.
These processes got happened in the cytoplasm and mitochondria to provide energy, as u see glucose or any other organic fuels consume oxygen and produce carbon dioxide to have ATP from ADP, water manufactured as a waste product.
Types of cellular respiration
Cellular respiration has two types: aerobic cellular respiration and anaerobic cellular respiration.
Aerobic respiration got happened whenever oxygen is available but when cells don’t have any oxygen or don’t have enough oxygen so they break down molecules by anaerobic cellular respiration.
In the human body u can see anaerobic respiration in muscles, whenever hardsports are being done by someone muscles couldn’t receive enough oxygen so they try anaerobic respiration to break down glycogen.
As an example we can mention fermentation for anaerobic cellular respiration, fermentation has two types alcoholic fermentation and lactate fermentation, both of them has glycolysis step like aerobic cellular respiration because glycolysis doesn’t depend on oxygen existence.
Anaerobic cellular respiration in the type of fermentation is also done in some plants.
Why is cellular respiration important
Cellular respiration is part of the metabolism in living things including humans. Metabolism means providing energy and providing energy means continuing life, so cellular respiration is vital.
This process manufacture ATP, ATP is one of the most important units of energy that cells release its energy to use whenever they need it. During cellular respiration 30 to 32 ATP have been made, this amount is providing a large part of the energy requirements of body cells.
What is the role of oxygen in cellular respiration
In the last step of cellular respiration (oxidative phosphorylation or electron transport chain) oxygen received the electrons transported by proteins of the chain and manufactured water molecules.
It creates a gradient that causes that electron transportation doesn’t stop or completes with enough speed.
A certain amount of oxygen is a need for enough gradient if this gradient doesn’t exist ATP synthesizing will face problems and in general view cellular respiration won’t work well.
What is the purpose of cellular respiration
The purpose of cellular respiration is clearly showed in it’s process( C6H12O6 (s) + 6 O2 (g) + ADP + P → 6 CO2 (g) + 6 H2O (l) + ATP ) .
The main materials of this process are glucose (C6H12O6) and ATP. In general, the main purpose of cellular respiration is the conversion of the energies that have been stored in chemical bonds of glucose to ATP, the energy unit that cells can consume easily.
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