Cellular Respiration
...or, how one good meal provides the energy for the work of 75 trillion cells...
January 31, 2000

Readings Starr text: Ch 7 front page, 7.1- 7.5, 7.7.
CD Rom: Good animations and explanations!
Note: Slight change from syllabus; we will do Ch. 7 first (Monday) and Ch. 3 Wednesday

"Like this old Earth that lolls through sun and shade.
Our part is less to make than to be made." -
--- Sir Charles S. Sherrington


I . Overview of respiration
II. Mitochondria
III. Cellular respiration - aerobic

1. Glycolysis = cytosol (cytoplasm)
2. Transition reaction = transport into mitochondria
3. Krebs cycle = mitochondrial matrix
4. Electron transport / chemiosmosis = mitochondrial cristae

IV. Fermentation - anaerobic respiration


I . Overview of respiration

Photosynthesis (you recall...) is the process by which food is formed that is used as "fuel" by most organisms.





During Cellular Respiration, energy stored within the bonds of glucose is extracted and used to make ATP needed for cellular work



The overall reaction for cellular respiration: (does this reaction look familiar?)

C6H12O6 + 6O2 -------------------> 6CO2 + 6H2O + 38 ATP


Chemically, what happens during respiration is that electrons (and H+, protons) are stripped from sugars and other foods, oxidizing them to water and CO2 gas, a waste product.

A note: Although "breaking down glucose" is the major pathway for energy, all macromolecules - glycogen, fats, proteins (but not cellulose!) - are broken down in this way. They just enter the pathway at a later step (or a different step) than glucose (See Fig 7.12)


II. Mitochondria

Anatomy of the mitochondrion: Each of the approximately 75 trillion cells that make up the human body have their own "cellular furnaces" where fuel (food) is burned to produce energy. These "furnaces" are organelles called mitochondria. Cells from tissues that are highly metabolically active - muscles, liver - contain hundreds of mitochondria per cell!




Just like the chloroplast, the mitochondrian is a double membrane bound organelle, with an inner series of membranes (the christae, shown boxed in) and a liquid-y area, the inner compartment (the matrix) that contains enzymes for breaking down glucose.






Do plants have mitochndria? YES!...they need to break down sugars for energy too! Remember that there is no net gain of energy from photosynthesis - just sugar. They went through that whole process to get enough sugar so that they could then break it down for cellular work!

If you look closely, you will see evidence of their work outside the undergraduate library...the dafodills are starting to peek up! They are using the sugar reserves they have stored in the bulb (underground) and metabolizing it (breaking it down to glucose, and then to CO2, H2O and ATP) to give energy for growth! Very soon they will undergo a very energy-intensive process - flowering!



III. Cellular respiration - aerobic (in the presence of oxygen)

The Goal: Make ATP through the oxidation (removal of hydrogens and electrons) of glucose until only CO2 and H2O remain ...

Cellular respiration can be broken down into 4 stages:

1: Glycolysis ("splitting of sugar"): in the cytosol

2: Transition Reaction: getting pyruvate into the mitochondria

3: The Krebs Cycle, or Citric Acid Cycle:

4: The Electron Transport Chain and Chemiosmosis ("the big ATP payoff")













IV. Fermentation

Or, how to extract a little bit of ATP (2, to be precise) out of glucose when O2 is not present!



In the absence of oxygen, one of two waste products typically result:

Plants: Ethanol: wine, beer, etc

Animals: Lactic acid: sore muscles after exercising

Not a lot of energy, but better than nothing!


Learning Objectives:

1. Be able to write the overall equation for glucose metabolism.

2. Be able to list the 4 major steps in Cellular Respiration, their location in the cell, and the products generated.

3. Know the difference between Glycolysis and Fermentation in terms of energy production, location in cell, and end products