Metabolism



It’s important to know how we derive energy from food. Not an easy topic to explain in a single post. But, I try my level best to simplify the metabolism for an easy understanding.  

Metabolism is a complex chemical the process by which body converts the food and water into energy. Metabolism gives energy to move, adapt, repair, etc.

 

Metabolism is a well regulated mechanism. It conserves the energy (slow down) in the absence of food and vice-versa.   

 

Our body gets energy thru the food. But, metabolism doesn’t know the language of food, it only understands nutrients. Hence, food needs to be broken down (by the process digestion) into their molecules like carbs, proteins and fat (macro nutrients)

 

Further, these macro nutrients are further broken down into their component parts. Example :  Carbs are broken down into Glucose, proteins into Amino Acids, and Fats into Fatty Acids.

 

After breaking the macro nutrients into their component parts, depending on the need body uses them either Anabolism or Catabolism. Anabolism is known as the synthesis of all compounds needed by the cells. Catabolism is known as the breakdown of molecules to obtain energy.

 

There are three possible ways to use Glucose, Amino Acids, and Fatty Acids

1)      Process further and convert into energy (ATP)  -  Catabolism  

2)     Repair, rebuilt, adapt, heal, etc.  -   Structural Anabolism 
 
3)     Store (the energy) for later use.  -  Storage Anabolism  

 

Converting the excess glucose (after fed into cells) into glycogen and storing in the liver and muscle cells, converting fatty acids into triglyceride and storing into the fat cell and storing fat under adipose tissue is known as anabolism.


Deriving ATP from food is one of the chief purposes of catabolism. In the absence of food (calorie deficit), stored fuel sources (fat, protine & glycogen) also turned into ATP also known as catabolism.

 

ATP (Adenosine tri-phosphate) is known as energy currency of life and it’s a most important molecule in the human body, which transports chemical energy within cells for metabolism.

 

ATP = one molecule of adenosine and add three molecules of phosphate

ADP = one molecule of adenosine and add two molecules of phosphate

 

ATP should be hydrolyzed, to get ADP (adenosine di-phosphate) so that can be used as an active energy. Again, ADP gains one phosphate molecule and turns ATP. This repeated cycle  is the part of Cellular respiration.

Cellular respiration is the set of the metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy (ATP) from the food (nutrients) and then release waste products. In other words, Without the Cellular respiration, the most important biochemical (ATP) can’t be derived. Cellular respiration taking places each and every cells of the body and every second of the life.



Note : Don’t confuse the digestion with cellular respiration. Both are different. Digestion is the preliminary stage of cellular respiration that breaks down our macronutrients into their component parts. Cellular respiration begins after the digestion.

 

The word glycolysis is derived from Greek (glyco = sugar; lysis = breaking) Therefore, Glycolysis is a process for glucose only and it’s a first step of cellular respiration.




Glycolysis is the metabolic pathway that converts glucose (by enzymes) into pyruvic acid or glycolysis converts one six-carbon molecule of glucose into three-carbon molecules of pyruvate.



Further, the pyruvate will be oxidized (that’s why we breath) and becomes a compound called Acetyl CoA. This compound is right at the centre of all of the action in the Krebbs cycle.



In the absence of oxygen (during anaerobic exercise), those two pyruvates get reduced into lactate as part of a process called lactic acid fermentation. (faster and simpler alternative to the full cellular respiration process).

 

The second step of the cellular respiration is the Krebs Cycle (also known as citric acid cycle) is a series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetate derived from carbohydrates, fats and proteins into carbon dioxide and chemical energy in the form of ATP.


Amino acids directly broken down into Acetyl CoA or pyruvate, depending on the amino acid, and enter directly into the Krebs cycle (krebs cycle is always the same for carb, protein and fat)


When the amino acid makes this transition amine is given off and becomes one of the waste products in our urine. The rest is used for ATP.


Lipogenesis is the process by which glycerol is esterified with free fatty acids to form triglyceride.


Fats are made up of a glycerol backbone and long chains of fatty acids. The fatty acids have a two carbon backbone and enter the Krebs cycle at the level of acetyl-CoA, the glycerol has a three-carbon backbone and enters the cycle at the level of pyruvate and the ATP production continues like normal.

 

Electron Transport Chain is the (third) most complex part of cellular respiration It’s also at the cutting edge of biochemistry.

 

An electron transport chain is a series of compounds that transfer electrons from electron donors to electron acceptors via redox reactions, and couples this electron transfer with the transfer of protons across a membrane in order to produce ATP and ADP (an active energy)

 

Note: Stored fatty acids can be turned into glucose in the liver and go through glycolysis before entering the Krebs cycle. 

 

Note: Insulin is a peptide hormone that is critical for managing the body's metabolism. Insulin is released by the pancreas when blood sugar levels rise, and it has many effects that broadly promote the absorption and storage of sugars, including lipogenesis.


Hope, I managed to cover the "huge" topic in single post. If any further queries please refer the below links


Further Reading :

http://chemistry.elmhurst.edu/vchembook/601glycolysissum.html

http://bio100.class.uic.edu/lecturesf04am/lect12.htm

http://biology4isc.weebly.com/5-cell-respiration.html

http://www.wiley.com/legacy/college/boyer/0470003790/animations/tca/tca.htm

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