Kate Fullerton & Deborah Bakshiyev

B9 - Respiration

B.9.1 - Compare aerobic and anaerobic respiration of glucose in terms of oxidation/reduction and energy

released.

Respiration for Chemists

• Respiration is the controlled breakdown of energy-rich substances into usable forms• Ex. Glucose ATP

Glycolysis

• Glucose (C6H12O6) and NAD+ react to form Pyruvate (C3H3O3

-), NADH, H+, and energy

C6H12O6 + 2 NAD+ 2C3H3O3- + 2NADH + 4H+

• Half equations:

C6H12O6 2 C3H3O3- + 6H+ + 5e-

NAD+ + 2H+ + 2e- NADH

Reduction:

Oxidation:

It’s anaerobic!

Aerobic Respiration

This process requires O2 from the air• O2 acts as the oxidizing agent• It is the ultimate terminal electron acceptor and is

reduced to water• Final products are CO2, H2O, and energy• Pyruvate to CO2 and H2O:

C3H3O3- + NADH + 2H+ + 3O2

3CO2 + 3H2O + NAD+

Aerobic RespirationHalf-Equations:

3O2 + 12H+ + 12e- 6H2O

C3H3O3- + 3H2O 3CO2 + 9H+ + 9e-

NADH is also oxidized

Reduction:

Oxidation:

Aerobic RespirationOverall equation (glucose products):

C6H12O6 + 6O2 6CO2 + 6H2O

Glucose is oxidized while oxygen is reducedThis equation should look familiar…

The overall equation is the same as combustionHowever this process is much more complex with

many steps and is controlled by enzymes

Anerobic RespirationWhen no oxygen is present, anerobic

respiration (or fermentation) occursIn humans, pyruvate is converted into lactic

acid (C3H6O3)In yeast, pyruvate is converted into ethanol

and CO2

Anerobic RespirationPyruvate Lactic Acid

C3H3O3- + NADH + 2H+ C3H6O3 + NAD+

Half equations:

C3H3O3- + 3H+ + 2e- C3H6O3

NADH NAD+ + 2H+ + 2e-

• Lactic acid causes your muscles to feel sore• NAD+ is used to reduce more pyruvate (cyclic)

Reduction:

Oxidation:

Anerobic RespirationPyruvate Ethanol and CO2

C3H3O3- + NADH + 2H+ C2H5OH + CO2 + NAD+

Half equations:

C3H3O3- + 3H+ + 2e- C2H5OH + CO2

NADH NAD+ + 2H+ + 2e-

NAD+ is used to reduce more pyruvate (cyclic)

Reduction:

Oxidation:

Anerobic RespirationOverall equations:

Glucose Lactic AcidC6H12O6 2C3H6O3

Glucose EthanolC6H12O6 2C2H5OH + 2CO2

Energy ReleaseAerobic respiration releases about 40% of the

energy in glucoseAnerobic respiration releases about 2% of the

energy in glucose

*This is because aerobic respiration oxidizes glucose more fully than anaerobic respiration*

B.9.2 - Outline the role of copper ions in electron transport and iron

ions in oxygen transport

Role of Copperin electron transport In the electron transport chain at the end of respiration electrons are

passed between proteins in a membrane. – These proteins are called transport carriers

Many of these types of electron transport carriers are cytochromes. – They are proteins that contain a non-protein component called a

prosthetic group– contain iron and copper – reduced by electrons (in the electron chain) • Remember: RIG reduction is gain of electrons!

• Later, they are re-oxidized (continue passing along the electron transport chain)– HEME groups are the receptors of the electrons– The iron in the heme group is oxidized from +2 to +3.

Diagram of the heme structure of cytochromes

Role of Copperin electron transportThe terminal electron carrier in the electron transport

chain is cytochrome oxidase and contains copper as well as Fe. – copper receives the electron • The Cu changes its oxidation state from +1 to +2 as it

is oxidized.• Binds the electron to O 2 forms water

Danger of Cyanide (CN-)CN- binds to the cytochrome oxidase

backs up the electron transport chainslows respiration

Role of Iron in oxygen transport• Hemoglobin

– made of 4 polypeptides• Each polypeptide has its own HEME group

– HEME group = a complex ion! – Each HEME group contains Fe2+

• So, there are 4 Fe2+ in each hemoglobin molecule• In hemoglobin (blood) and myoglobin (muscles) oxygen is transported in a similar

heme structure. – Hydrophobic environment allows oxygen to bind to Fe2+ without oxidizing it (the

Fe stays in the +2 state) So, hemoglobin is described as being oxygenated to oxyhemoglobin rather than

oxidized. • Quick review: there are 4 HEME groups that means there are 4 Fe2+ so, every

hemoglobin can bind to 4 O2

The reversible equation is:– Hb + 4O2 Hb(O2) 4

Danger of Carbon monoxide (CO)• CO binds more tightly to Fe2+ –So you can think that the CO sort of steals

the oxygen’s spot with the Fe2+ • Causes lack of oxygen– If CO is not displaced asphyxiation