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Respiration

Respiration is a set of metabolic reations and processes that take place with in the cells of organisms. It converts biochemical energy into adenosine triphosphate (ATP). There are two types of respiration, aerobic and anaerobic. Respiration is also the process of making ATP rather that breaking it down.

Quick notes

Two types of respiration aerobic and anaerobic.
Respiration is the process of making ATP rather than breaking it down.

ATP (Adenosine triphosphate)

ATP is the main energy storage and transfer molecule in the cell. It's a nucleic acid similar to RNA.
It's formed from ADP (Adenosine diphosphate) + Pι and consists of a ribose sugar, a nitrogenous base (adenine) and three phosphate groups each carrying a negative charge.
ATP + H₂O = ADP + Pι + H⁺ = 30.6Kj
(This reaction is catalysed by the enzyme ATPase)

Mitochondria

1. Glycolysis

This is the first stage of three in respiration and takes place within the cytoplasm of the cell.
This is the same process for aerobic and anaerobic respiration.
The conversion to phosphorylated is simply to make it more reactive and the conversion to sugar phosphate easier.
In this process the cell gains a net of 2 ATP molecules.

2. Krebs Cycle

Also known as the tricarboxyl acid.
Takes place within the matrix of the mitochondria.
Has two parts, firstly the link reaction (shown below) and then the main cycle.
NADH₂ and FADH₂ produced by the Kreb cycle are used under aerobic conditions to supply electrons for the electron transport chain but also to supply protons for the proton pumps, across the inner membrane.
At the end of this process you are left with 6 CO₂ compounds, 4 ATP molecules, 10 NADH₂ and 2 FADH₂.
The Kreb cycle happens twice as much as glycolysis because two, three carbon pyruvates are formed from glycolysis.
Has two parts, firstly the link reaction (shown below) and then the main cycle.

The Link Reaction - Part 1

The Krebs Cycle - Part 2

3. Electron Transport Chain

The third stage consists mainly of the movement of H⁺, carried by NADH₂, across the mitochondrias inner membrane, from the matrix into the intermembrane space via proton pumps.
There is a higher H⁺ concentration in the inter-membrane space which is why the proton pumps are required.
Once the H⁺ are in the intermembrane space they can then pass through the ATPase back into the matrix releasing more ATP. As you can see from the diagram below ADP is used in this reaction along with Pι to form ATP.
Once the electrons loose their energy they can be used in the formation of H₂O
The NADH₂ from the Kreb cycle when beginning the electron transport cycle get converted into two electrons (e^-) and two hydrogen's (H⁺).

Anaerobic Respiration

The process of anaerobic respiration is similar to the aerobic respiration. The first stage, glycolysis, is the same because it doesn't require oxygen but it does require NAD⁺.

In aerobic respiration the electron transport chain turns NADH back into NAD with the aid of oxygen and thus recycles the NAD. With anaerobic respiration the shortage of oxygen in the cells means that they must find another way to convert NADH back into NAD, this process is called fermentation.
Lactate fermentation occurs in mammals when there is a deficiency of oxygen. It has many advantages including strenuous exercise and oxygen demand under water. It works by each pyruvate molecule produced taking up two hydrogen molecules (from glycolysis) to form lactate. This then leaves the NAD⁺ to be recycled.
The lactate produced can cause problems in itself, it's a toxic chemical and can form cramp in muscles. This lactate can be taken away from the cells by the blood to the liver to be converted into glycogen.

Anaerobic Respiration reaction in Plants

In plants fermentation occurs but not in the form of lactate but instead producing ethanol and CO₂.

The Respiring of Fats and Proteins

How Fats and Proteins get respired without oxygen

(click to enlarge)

Fats and proteins can also be used to respire. When fats are about to be respired they are broken down into fatty acids and glycerol. The glycerol is converted into triose phosphate and enters the glycolysis stage. The fatty acids are broken down into two carbon fragments and entered into the Krebs cycle via acetyl co-enzyme A.
Proteins cannot be stored by mammals so have to either be used or excreted.
The respiration of proteins only occurs when there is a excess of them in the diet. To begin their process the amino group is removed (called deamination). The amino group then combines with CO₂ forming urea, later to be excreted. The remains of the amino acid, without a amino group, are organic acids and are is feed back into the Krebs cycle.

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