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CELLULAR RESPIRATION

Cellular Respiration

complex process whereby cells make ATP by breaking down organic

compounds

many rxns in aerobic respiration are redox: (one reactant is oxidized

while another is reduced)

location: mitochondrial cristae

Glycolysis (Glucose/breaking)

Process where one molecule of GLUCOSE (6 C) is broken

down into 2 molecules of PYRUVIC ACID(PYRUVATE) (3C)

- occurs in cytoplasm

- occurs before respiration or fermentation

- occurs in the absence of oxygen

Glycolysis: 4 Major Steps

1. glucose is phosphorylated by 2 ATP

(stable glucose glucose 6 phosphate [reactive compound] )

*** uses 2 ATP ***

2. glucose 6 phosphate breaks down into 2 PGAL (3 C)

3. phosphate group is added to each PGAL

H ions are removed

H picked up by NAD+

Since 2 PGAL formed……2 NADH formed

(coenzyme- elec. Acceptor)

4. phosphate bonds in step 3 broken

PGAL converted to PYRUVIC ACID

*** 2 ATP generated for each PGAL ***

*** TOTAL 4 ATP ***

End products

2 pyruvic acid (pyruvate), 2 NADH + net gain of 2 ATP

(2 used, 4 generated )

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2 Possible Pathways for 2 Pyruvic Acid

If O2 present If no O2 present

respiration fermentation

(aerobic) (anaerobic respiration)

mitochondria cytosol

If no oxygen is present the 2 pyruvic acid will

go into anaerobic respiration (fermentation)

FERMENTATION

1. Lactic Acid Fermentation (animals)

A. As O2 is comsumed in aerobic respiration, it becomes scarce

B. Without O2

- NADH (nicotinamide adenine dinucleotide) is oxidized and donates its H to pyruvic acid

C. resultant NAD returns to glycolysis where it is reduced to NADH

(cyclical- happens over and over again)

D. lactic acid forms from pyruvic acid which causes muscle pain and soreness ( muscle cells cytosol becomes acidic)

**eventually diffuses into liver where it is converted back to pyruvic acid when

O2 again present **

2. Alcoholic Fermentation (yeasts, plant cells, microorganisms)

- converts pyruvic acid to ethyl alcohol

A. CO2 molecule is removed from Pyruvic acid (3C) leaving a 2 C compound

B. 2 H (from NADH + H ion) are added to 2C compound to form

ethyl alcohol

C. NAD is formed (back to glycolysis)

***causes alcohol in beer and wine, air bubbles in bread, beer, and

wine*****

NO ATP FORMED IN

FERMENTATION

PURPOSE OF FERMENTATION:

TO REGENERATE NAD FOR

GLYCOLYSIS

Efficiency of Fermentation

- measured in kilocalories (1 kcal = 1000 calories)

- complete oxidation of glucose releases 686 kcal

- production of ATP from ADP uses 12 kcal

- 1 glucose molecule makes 2 ATP from glycolysis

Efficiency = ____energy required to make ATP_____ x 100%

energy released by oxidation of glucose

= 2 (ATP from glycolysis) x 12 kcal (used) x 100%

686 kcal

= 3.5% (this is the amount of energy from complete oxidation

of glucose)

*** contains almost as much energy as original glucose molecule***

- Anaerobic pathways only provide enough energy for unicellular and very

small multicellular organisms which have limited energy requirements

- Anaerobic pathways are very inefficient

RESPIRATION (aerobic)

C6H12O6 + 6 O2 6 H2O + 6 CO2 + 36 ATP

Process of breakdown of pyruvic acid in the

presence of oxygen

- prokaryotic cells: occurs in cytosol

- eukaryotic cells: occurs in mitochondria

- much more efficient than anaerobic respiration

2 Major Stages of Respiration

1. krebs cycle

- oxidation of glucose is completed

- NAD+ is reduced to NADH

2. electron transport chain

- NADH is used to make ATP via oxidative phosphorolation

- location where most ATP is made

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- process of extracting ATP from

NADH and FADH2

- also known as

oxidative phosphorylation

- cytochromes: proteins that act

as carriers in ETC

Efficiency of Aerobic Respiration

efficiency of

aerobic = energy required to make ATP______ x 100%

respiration energy released by oxidation of glucose

= 38 x 12 kcal x 100%

686 kcal

= 66%

**** aerobic respiration is almost 20 X more efficient

than glycolysis alone****

Alternative Energy Sources

What if the body runs out of sugar for glycolysis? Can the

body still make ATP?

YES

This is how the Atkins and South Beach diets work.

They are low carb, high protein/fat diets.

Alternative Energy Sources

Fats as fuel:

- Triacylglycerol reserves tend to be stored in adipose cells

- Lipases are released into the bloodstream and break down fats in the bloodstream (from the fats and oils we eat) or travel to adipose cells.

- Lipases break the glycerol head away from the fatty acids

- Glycerol is converted to PGAL, and enters cellular respiration in the cytoplasm

- The fatty acid tails are converted to Acetyl CoA and enter the Krebs cycle in the mitochondria

Result: Still ~32-38 or so ATPs, but from fats, not glucose!

Alternative Energy Sources

Proteins as fuel:

- Excess proteins in our diets cannot be stored like glycogen or fats can, and must be broken down by the body

- Proteases break the peptide bonds of proteins back down to amino acids

- Most of the amino acid can be rearranged in cells to enter cellular respiration either as pyruvate, as acetyl CoA, or directly into the Krebs cycle

Result: Still ~32-38 or so ATPs, but from proteins, not glucose!

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Remember...

photosynthesis and respiration are exact

opposite processes.

Look at the general equations for both………..what do you notice?

6 CO2 + 6 H2O + light energy C6H12O6 + 6 O2

C6H12O6 + 6 O2 6 H2O + 6 CO2 + 36 ATP

Both are needed for all of life’s activities.

Study for the test !!!