DEFINITION

The process of breakdown of glucose in the presence of oxygen to release carbon dioxide and energy in the form of ATP ( Adenosine triphosphate).

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TYPES OF RESPIRATION

There are two types of respiration:

• Aerobic respiration: occurs in the presence of oxygen. There is a complete breakdown of glucose to release carbon dioxide and 38 molecules Of ATP.

• Anaerobic respiration: occurs in the absence of oxygen. Incomplete breakdown of glucose with the release of 2 molecules Of ATP. End products are ethanol/ alcohol.

* During exercise due to the lack of oxygen in the body, muscles  respire anaerobically  and produces lactic acid

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STEPS OF CELLULAR RESPIRATION

1. GLYCOLYSIS

2. OXIDATIVE DECARBOXYLATION

3. KREB’S CYCLE

4. ELECTRON TRANSPORT SYSTEM

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GLYCOLYSIS: Means splitting of sugars and is a release of energy within sugars. Glucose changes into 2 Molecules of pyruvate with the release of 2 molecules of ATP and two molecules of NADH (Nicotinamide adenine dinucleotide).

It takes place in the cytoplasm. It occurs with or without oxygen. In the presence of oxygen it is first step of cellular respiration and in the absence of oxygen it allows cells to release less ATP through fermentation. In this process two molecules of carbon dioxide are produced.

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OXIDATIVE DECARBOXYLATION: Two molecules of pyruvate enters in oxidative decarboxylation and changes into 2 molecules of Acetyl CoA  with the liberation of 2 molecules of NADH ( one from each pryuvate)

( NOTE: THIS STEP OCCURS ONLY IN AEROBIC RESPIRATION)

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KREB CYCLE: it is also known as citric acid cycle or TCA. It is a process of oxidation of  Acetyl CoA into ATP and carbon dioxide

it produces NADH by oxidizing NAD and produces 2 molecules of carbon dioxide as a waste product.

It occurs in the matrix of mitochondria. Overall yield of energy containing compounds is 3NADH , 1 FADH (Flavin adenine dinucleotide) and 1 ATP in each cycle from each acetyl CoA.

* It occurs only in aerobic respiration.

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NET ENERGY GAIN IN RESPIRATION

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IN GLYCOLYSIS:

2ATP + 2NADH   (i.e 2 + 2X3 = 8) [Total – 8 ATP]

(NOTE: 1 NADH RELEASES 3 ATP AND 1 FADH RELEASES 2 ATP]

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IN OXIDATIVE DECARBOXYLATION:

2 NADH     (i.e  2X3=6) [Total – 6ATP]

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IN KREB CYCLE:

1ATP +3 NADH + 1FADH ( FROM EACH Acetyl CoA)

TOTAL IN KREB CYCLE

2ATP + 6NADH + 2FADH   (i.e 2 + 6X3 + 2x2 = 24) [TOTAL – 24 ATPs]

 

NET GAIN= 8+6+24= 38 ATP. (AEROBIC RESPIRATION)