Cellular Respiration

Unit 5: Plants, Photosynthesis, and Cellular Respiration

Overview !  Organisms obtain energy (ATP) by breaking down (catabolic

pathway, exergonic reaction) organic molecules (glucose) during cellular respiration.

!  The function of cellular respiration is to gather electrons from glucose and use their energy to create ATP.

!  Cellular respiration occurs in the cytoplasm and mitochondria.

(ATP)

Sugar (Glucose) ! ATP ! Available Energy

Anaerobic vs. Aerobic Respiration !  Anaerobic – oxygen (O2) not required !  Aerobic – oxygen (O2) required

Cellular Respiration

Oxygen unavailable Oxygen available

Fermentation (cytoplasm): a)  Lactic Acid Fermentation b)  Alcohol Fermentation

Aerobic Respiration (mitochondria): a)  Krebs Cycle b)  Electron Transport Chain (ETC) +

Chemiosmosis

Glycolysis (cytoplasm) Glycolysis (cytoplasm)

Aerobic Respiration !  Aerobic cellular respiration occurs in two main parts:

1.  Glycolysis !  This stage is anaerobic, meaning that it doesn’t require oxygen!

2.  Aerobic Respiration !  Aerobic mean that the process occurs with oxygen! !  Includes the Krebs Cycle, Electron Transport Chain, and

Chemiosmosis

Glycolysis !  Glycolysis (glyco = sugar,

lysis = to break) is the process of glucose being broken down in the cytoplasm of a cell.

!  What goes in? !  Glucose (6-carbon sugar) !  2 ATP

!  What comes out? !  4 ATP total, a net of 2 ATP !  2 NADH (electron carriers) !  2 Pyruvate (3-carbon sugar)

Glycolysis

Krebs Cycle

Electron Transport Chain

+ Chemiosmosis

Cellular Respiration: C6H12O6 + 6 O2 ! 6 CO2 + 6 H2O + ATP (36)

Goes IN Comes OUT C6H12O6

2 ATP 2 NADH 2 NAD+

4 ADP 4 ATP (2 net)

2 ADP

2 Pyruvate

Between Glycolysis and the Krebs Cycle !  After glycolysis, the cell is left with 2 pyruvate in the

cytoplasm.

!  Prior to entering the Krebs Cycle, pyruvate firsts reacts with coenzyme A (CoA) to form a 2-carbon molecule called Acetyl CoA.

!  Also during this time, one carbon dioxide is released and one NADH (electron carrier) is formed.

Glycolysis

Krebs Cycle

Electron Transport Chain

+ Chemiosmosis

Cellular Respiration: C6H1206 + 6 O2 ! 6 CO2 + 6 H20 + ATP (36)

Goes IN Comes OUT C6H12O6

2 ATP 2 NADH 2 NAD+

4 ADP 4 ATP (2 net)

2 ADP

2 NAD+ 2 Pyruvate 2 NADH 2 CO2

2 Acetyl CoA

The Krebs Cycle !  After glycolysis, most of the energy from the glucose is

still contained in the 2 pyruvate.

!  In the presence of oxygen, the pyruvate is transported into the mitochondria and converted to Acetyl CoA.

!  There it is broken down into carbon dioxide in a process known as the Krebs Cycle.

The Krebs Cycle !  What goes in?

!  Pyruvate !Aceytl CoA

!  What comes out? !  4 CO2

!  6 NADH (electron carrier) !  2 FADH2 (electron carrier) !  2 ATP

Glycolysis

Krebs Cycle

Electron Transport Chain

+ Chemiosmosis

Cellular Respiration: C6H1206 + 6 O2 ! 6 CO2 + 6 H20 + ATP (36)

Goes IN Comes OUT C6H12O6

2 ATP 2 NADH 2 NAD+

4 ADP 4 ATP (2 net)

2 ADP

2 NAD+ 2 Pyruvate 2 NADH 2 CO2

2 Acetyl CoA

2 FAD 2 ADP

6 NAD+ 6 NADH 2 FADH2

2 ATP

4 CO2

Electron Transport Chain !  This is the point at which most of the ATP of aerobic

cellular respiration is produced. !  The electrons carried by NADH and FADH2 are brought

to the ETC to convert ADP ! ATP. !  These electrons are release by NADH and FADH2 to

move along the mitochondrial membrane from one protein (cytochromes) to another.

!  This causes Hydrogen ions to be pumped across the mitochondrial membrane into the innermembrane space.

!  After the electrons have been passed down the chain they are accepted at the end by O2 to make H2O.

Chemiosmosis !  Because there are more Hydrogen ions (H+) in the

innermembrane space, they want to diffuse back across the membrane into the matrix.

!  They move back across the membrane through an enzyme called ATP synthase.

!  ATP synthase turns ADP into ATP!

Fig. 9-16

Protein complex of electron carriers

H+

H+ H+

Cyt c

Q

Ι

ΙΙ

ΙΙΙ

ΙV

FADH2 FAD

NAD+ NADH (carrying electrons from food)

Electron transport chain

2 H+ + 1/2O2 H2O

ADP + P i

Chemiosmosis

Oxidative phosphorylation

H+

H+

ATP synthase

ATP

2 1

Glycolysis

Krebs Cycle

Electron Transport Chain

+ Chemiosmosis

Cellular Respiration: C6H12O6 + 6 O2 ! 6 CO2 + 6 H20 + ATP (36)

Goes IN Comes OUT C6H12O6

2 ATP 2 NADH 2 NAD+

4 ADP 4 ATP (2 net)

2 ADP

2 NAD+ 2 Pyruvate 2 NADH 2 CO2

2 Acetyl CoA

2 FAD 2 ADP

6 NAD+ 6 NADH

2 FADH2

2 ATP

4 CO2

10 NADH 2 FADH2

6 O2

2 FAD

10 NAD+

32 ATP

6 H2O

Anaerobic Respiration !  Some cells can function for short periods of time when

oxygen levels are low or even exist without oxygen at all!

!  Recall, Glycolysis is an anaerobic process and occurs in the cytoplasm without oxygen.

!  If there is no oxygen after Glycolysis, the cell will carry out fermentation rather than aerobic cellular respiration.

!  Fermentation is the process in which NAD+ is regenerated, allowing cells to maintain Glycolysis and small amounts of ATP production in the absence of oxygen.

Fermentation !  There are two main types of fermentation:

1.  Lactic acid fermentation 2.  Alcohol fermentation

1. Lactic Acid Fermentation

!  At the end of Glycolysis, pyruvate is left. !  Lactic acid fermentation converts the pyruvate made

during Glycolysis to lactic acid using special enzymes. !  During Glycolysis NAD+ is converted to NADH. When

Pyruvate gets converted to Lactic acid, NADH gets converted back to NAD+ so Glycolysis can be repeated.

!  This is what occurs in your muscle cells when you are at lacking oxygen. It is hypothesized that Lactic acid can cause your muscles to feel fatigued or sore.

1. Lactic Acid Fermentation

2. Alcohol Fermentation !  This occurs in yeast (fungi) and some bacteria.

!  After Glycolysis, pyruvate is converted to ethanol and carbon dioxide.

!  This process also allows for NAD+ to be converted back to NADH.

!  This is why bread has holes in it!!!

Fig. 9-18a

2 ADP + 2 P i 2 ATP

Glucose Glycolysis

2 Pyruvate

2 NADH 2 NAD+ + 2 H+

CO2

2 Acetaldehyde 2 Ethanol

(a) Alcohol fermentation

2