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Cell respiration

Topic 8
...
2

Results in a compound with lower

Biology HL

Results in a compound with higher

potential energy

potential energy

➢ The reduced form of a molecule always has more potential energy than the oxidized
form of the molecule
➢ Redox reactions play a key role in the flow of energy through living systems
○

Because the electrons that are flowing from one molecule to the next are
carrying energy with them

Example:

C6H12O6 + 6O2 ⇒ 6CO2 + 6H2O + energy
○
○

C6H12O6 was oxidized since it lost hydrogen atoms to form carbon dioxide
6O2 was reduced since it gained hydrogen atoms to form water

Glycolysis
➢ Uses no oxygen and occurs in the cytoplasm
○

No organelles are required

○

It proceeds efficiently in both aerobic and anaerobic environments

➢ Occurs in both prokaryotic and eukaryotic cells
➢ Steps:
○

Two molecules of ATP are used to begin glycolysis
■

The phosphates from the ATPs are added to glucose to form another
sugar

○

Less stable molecule

●

The process is called phosphorylation

The less stable 6-carbon sugar is split into two 3-carbon sugars
■

○

●

This splitting process is known as lysis

These sugars enter an oxidation phase involving ATP formation and the
production of the reduced coenzyme NAD
■

Each of those phosphate molecules undergoes oxidation to form a
+

reduced NAD which becomes NADH
●

Energy is released and it is used to add an inorganic
phosphate to the 3-carbon compound

○

Enzymes remove the phosphate groups so that they can be added to ADP to
produce ATP

2

Cell respiration

Topic 8
...
2

Biology HL

➢ Steps:
○

Acetyl CoA combines with a 4-carbon compound called oxaloacetate
...

■

The lost carbon is combined with oxygen and leaves the cell as
carbon dioxide
...
4 CO2 are
released during the Krebs cycle
○

These account for all 6 carbon atoms that were present in the initial glucose
■

Glucose is completely catabolized and its original energy is now
carried by NADH and FADH2 or ATP

➢ Until now, a net gain of 4 ATPs has been produced by substrate-level
phosphorylation
○

We obtain the remaining 32 ATPs through oxidative phosphorylation
4

Cell respiration

Topic 8
...
2

Biology HL

Chemiosmosis is an oxidative phosphorylation, as it utilizes an ETC

➢ The protons will try to move back across the membrane to level out the
concentration gradient, but they are stopped by the membrane
○

Because of the hydrophilic region of the membrane, protons can only pass
through the ATP synthase

➢ ATP synthase is a protein that harness the energy of moving protons to
phosphorylate an ADP to ATP
○

ATP synthase lies on the inner membrane

➢ When protons enter the matrix again, they will react with a newly formed oxygen
ion to form water maintaining the gradient
Production of ATP - summary

Process

ATP used

ATP produced

Net ATP gain

Glycolysis

2

4

2

Krebs cycle

0

2

2

ETC +

0

32

32

2

38

36

chemiosmosis
Total

➢ In reality the number is closer to 30, because:
○

Some protons move back to the matrix without going through the ATP
synthase channel

○

Some of the energy of the proton movement is used to transport pyruvate
into the mitochondria

➢ The 30 ATPs account for approximately 30% of the energy present in the chemical
bonds of glucose

6



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