Cellular Respiration Part A

Purpose of Cellular respiration:

TO transfer chemical energy stored in glucose into ATP which is used to power cellular reaction.

Why ATP is used mto provide energy

• ATP is used because energy can be easily released in a single step
  

• ATP also has fast turn over rate

WHY not just use glucose

THe release of energy from glucose occurs via conmplext multistep pathway which is much slower

Energy in glucose is high (3000kj) compared to ATP (30kj)

Two types of cellular respiration:

Aerobic cellular respiration

• requires oxygen

• produces 30 or 32 ATP molecules per one glucose molecule

Anerobic Fermentation:

• does not require oxygen

• produces 2 ATP molecules per one glucose molecule

• produces harmful by-products (lactic acid or ethanol)

Aerobic Cellular Respiration

Not a simple process, instead there are many enzyme controlled reaction which are need to convert glucose and oxygen into water CO2 and ATP

3 stages

1. Glycolysis

2. The Krebs cycle

3. The electron Transport chain

Role of mitochondria in aerobic cellular respiration

Mitochondria are crucial to aerobic cellular respiration as they are the site at which stages two and three occur

Mitochondria are complex organelles made up of many different structures

Aerobic cellular respiration vs Photosynthesis

Cellular respiration and photosynthesis are related but they are not direct counterparts

Glycolysis

• occurs in Cytosol of cells

• involves the breakdown of 6 carbon glucose in two 3 carbon pyruvate molecules via a sequence of 10 enzyme regulated reaction

• results in net production 2 ATP molecules

  As glucose is broken down into pyruvate, energy is released

ATP is free to power cellular reactions

Pyruvate and NADPH move to mitochondria to assist in the second stage of aerobic cellular respirations: The Krebs Cycle

Link Reaction

TO link Glycolysis and the Krebs cycle, Pyruvate moves from cytosol to matrix of mitochondrial and combines with coenzyme A (CoA) to form acetyl coenzyme A (acetyl-CoA)

Krebs Cycle ( also known as the Citric Acid Cycle)

• takes place in mitochondrial matrix

• consists of 8 reactions that break down acetyl CoA
  - the breaking down of acetyl CoA results in the release of protons and high energy electrons which are loaded onto NAD+ and FAD to generate high energy coenzymes NADH and FADH2

• produces 2 ATP

During formation of acetyl-CoA from pyruvate - 1 CO2 molecule is produced

During one full turn of the Krebs cycle - 2 CO2 molecules are produced

In Summary:

In ONE turn of the Krebs Cycle, acetyl-CoA is metabolised into:

• 2 Co2 molecules

• 1 ATP molecule

• 3 NADH molecules

• 1 FADH2 molecule

In TWO turns of the Krebs cycle, these values are doubled

The Electron Transport Chain - ETC

• takes place on inner membrane of mitochondria (Cristae)

• place where majority of ATP is produced

• converts high-energy coenzymes NADH and FADH2 back to NAD+ and FAD forms which are then recycled for continued use in glycolysis and the Krebs cycle

  

Steps involved in making ATP at Electron Transport Chain:

1. NADH and FADH unload protons and electrons at first and second protein of ETC

   • NADH converted to NAD+

   • FADH2 converted to FAD

     
     

2. Excitedd electrons power active transport of protons from mitochondirial matrix into narrow intermembrane space

3. Concentration of protons increases

   

4. To move down concentration gradient, protons need to move through protein channel (ATP synthase) - ADP + P > ATP

5. Large amounts of ATP are made

6. Unbound protons and electrons bind with oxygen to produce water

   

   
   
   In Summery:
   for every glucose molecule metabolized, 30 or 32 ATP molecules are formed:

   • 2 ATP (from glycolysis)

   • 2 ATP (from Krebs Cycle)

   • 26 or 28 ATP (from ETC)

     

   Glycolysis:

   

   
   
   Krebs Cycle:

   
   Electron Transport CHain:
   
   
   Enzymes and coenzymes in cellular respiration:

   • Enzymes, with the help of their coenzymes, catalyse the reactions of cellular respiration to allow them to proceed at a fast rate.

   • This means that cells can breakdown and extract energy from glucose at a rate fast enough to sustain energy-dependent processes

   • Since each enzyme is only capable of catalysing one specific reaction, there is a wide range of enzymes involved in cellular respiration
     
     
     
     
     EXAMPLES OF SOME KEY ENZYMES IN CELULLAR RESPIRATION: