Oxygen is super important for a process called oxidative phosphorylation. This process makes energy in the form of adenosine triphosphate (ATP). ATP is like money for cells - they need it to do stuff like moving and contracting. It all happens in the mitochondria, which are like little powerhouses inside cells. The more mitochondria a cell has, the more active it is!

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Oxidative phosphorylation definition

Oxidative phosphorylation is a process that happens when there's oxygen around. It's part of something called aerobic respiration. This process makes a lot of ATP, which is like energy for cells. It makes way more ATP than other processes like glycolysis and the Krebs cycle.

There are two really important parts of oxidative phosphorylation - the electron transport chain and chemiosmosis. The electron transport chain is made up of different proteins and molecules that live in the membrane of the mitochondria. In eukaryotic cells, these molecules are in the inner membrane of the mitochondria. pro, like bacteria, they're in the plasma membrane. The electron transport chain moves electrons around in a bunch of reactions called redox reactions.

Redox reactions are just when molecules give or take electrons from other molecules.

Structure of mitochondria

Mitochondria are small organelles that have two layers of membrane, an outer one and an inner one, with a space in between. They're really important for making energy in cells, especially in tissues like the heart that need a lot of energy. Each cell has around 2000 mitochondria, which take up around 25% of the cell's volume. They're called the powerhouse of the cell because they make a lot of ATP, which is like energy for cells.

One cool thing about mitochondria is that they have a lot of folds in their inner membrane, called cristae. This makes it easier for them to do a process called oxidative phosphorylation, which makes ATP. They also have something called the Krebs cycle in their inner membrane, which is another way they make ATP. The Krebs cycle has its own enzymes, DNA, RNA, ribosomes, and calcium granules.

Mitochondria are different from other organelles because they have their own DNA, which is arranged in a ring shape. They own ribosomes, which are like little factories that make proteins. Scientists think that mitochondria used to be their own bacteria, and then they became part of other cells a long time ago. 

Oxidative phosphorylation diagram

Visualising oxidative phosphorylation canbe really helpful in remembering the process and steps involved. Below is adiagram depicting oxidative phosphorylation.

Oxidative phosphorylation process and steps

The synthesis of ATP via oxidative phosphorylation follows four main steps:

Transport of electrons by NADH andFADH2Proton pumping and electron transfer Formation of water ATP synthesis

Transport of electrons by NADH and FADH2

Two important molecules in cellular respiration are NADH and FADH2. They're made during the early parts of the process, like glycolysis, pyruvate oxidation, and the Krebs cycle. They're important because they carry hydrogen atoms and give their electrons to other molecules in the electron transport chain, which is where cells make ATP.

NADH carries electrons with a lot of energy, and it gives them to Complex I in the electron transport chain. Complex I uses the energy from the electrons to move protons (H+) from inside the mitochondria to the space between the two mitochondrial membranes.

FADH2 carries electrons with less energy than NADH, so it doesn't give its electrons to Complex I. Instead, it gives them to Complex II in the electron

Proton pumping and electron transfer

The electron transport chain is where most of the ATP in cellular respiration is made. As electrons move down the chain, they lose energy, which is used to pump H+ out of the matrix and into the intermembrane space. This creates an electrochemical gradient, with the intermembrane space becoming more positive and the matrix becoming more negative.

FADH2 contributes less to the electrochemical gradient than NADH because it gives its electrons to Complex II, which doesn't pump H+ across the membrane. The electron transport chain is made up of four complexes, each containing different proteins and cofactors. Complex III contains cytochrome proteins with haem groups, and it passes its electrons to Cytochrome C, which carries the electrons to Complex IV. Complex IV is also made up of cytochrome proteins, and it's responsible for making water as part of the electron transport process.

Formation of water

When the electrons reach Complex IV, anoxygen molecule will accept H+ to form water in the equation:

2H+ + O2 H2O

ATP synthesis

The ATP synthase enzyme is responsible for using the electrochemical gradient created by the electron transport chain to make ATP. H+ ions flow back into the mitochondrial matrix through ATP synthase, and this process is called chemiosmosis. Cellular respiration produces between 30 and 32 molecules of ATP for each glucose molecule, with the majority of ATP being made through chemiosmosis.

NADH pumps 10 H+ into the intermembrane space, which equates to 2.5 molecules of ATP produced. FADH₂ only out 6 H+, so it only produces 1.5 molecules of ATP. Brown fat is a type of adipose tissue found in hibernating animals, and it uses an alternative pathway composed of uncoupling proteins to produce heat rather than ATP. This is an important strategy to keep animals warm during hibernation.

Oxidative phosphorylation products

In summary, oxidative phosphorylation is the process of making ATP through electron transport chain and chemiosmosis. This process requires oxygen and is part of aerobic respiration. Complex proteins in the electron transport chain generate an electrochemical gradient that drives the production of ATP through the flow of H+ ions through ATP synthase. Water is also produced during this process. NADH and FADH2 are recycled back into other processes such as glycolysis, where they act as coenzymes.

Oxidative phosphorylation

What is oxidative phosphorylation?
Oxidative phosphorylation refers to the series of redox reactions involving electrons and membrane-bound proteins to generate adenosine triphosphate (ATP).This process is involved in aerobic respiration and therefore requires the presence of oxygen. 
Where does oxidative phosphorylation take place?
It takes place in the inner mitochondrial membrane.
What are the products of oxidative phosphorylation?
The products of oxidative phosphorylation include ATP, water, NAD+ and FAD.
What is the main purpose of oxidative phosphorylation?
To generate ATP, which is the main source of energy in a cell.
Why is it called oxidative phosphorylation?
In oxidative phosphorylation, oxidation refers to the loss of electrons from NADH and FADH2. During the last steps of the process, ADP is phosphorylated with a phosphate group to generate ATP.

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