Glycolysis and Cellular respiration

 

Photosynthesis primarily produces glucose

 

6 CO2  + 6 H20  + sunlight ® C6H12O6  + 6 O2

 

Cell respiration primarily breaks-down glucose to generate ATP.

 

C6H12O6  + 6 O2   ® 6 CO2  + 12 H20  + 36ATP

 

Both can use other molecules but glucose follows the most basic process.

 

Remember, the “in” energy from the sun > “out” energy in ATP.  What law?

 


Glycolysis and Cellular Respiration

 

Glucose metabolism has two general stages:

  1. Anaerobic metabolism- Glycolysis
  2. Aerobic metabolism- Cellular respiration

 

 

Glycolysis

 

Goal: Splits glucose into to 3-carbon molecules (pyruvate), releases little ATP.

-         Used by every living creature on earth.

 

Where: Mainly in cytoplasm of Cell, not in mitochondria.

 

Two stages of Glycolysis: (Fig 7-2)

 

  1. Glucose activation- ATP release phosphate that binds to glucose (make it unstable- Phosphorolized)

-         Consumed two ATP molecules (turn into ADP)

 

  1. Energy harvest- Phosphorolized glucose then readily splits into two pyruvate molecules (3-C) and produces 4 ATP and 2 NADH.

-         ATP can be used to drive metabolic reactions in cell.

-         Without oxygen NADH “ferments” by returning its electrons and H+ to pyruvate to produce “lactic acid” or in some cells, alcohol.

-         With oxygen NADH will drop off electrons and H+ in electron transport system that generates ATP through chemiosmosis.

 

Product: two Pyruvate molecules, 2 ATP (net), 2 NADH

 

 

II. Cellular Respiration (Fig 7-4)

-         Occurs only when O2 is present in cell!

 

Goal: To produce lots of ATP through further breakdown of pyruvate into CO2.

 

Where: In Mitochondria (matrix and inner membrane)

 

Two stages:

  1. Krebs Cycle
  2. Electron transport

 

Krebs Cycle (Fig 7-5):

1.      Pair of pyruvate from glycolysis migrates (diffusion) into mitochondria inner matrix

2.      It binds with Co-enzyme A, releasing 2 CO2 & 2 NADH (one per pyruvate).

3.      acetyle CoA then enters the Krebs Cycle

-         Krebs cycle finishes breaking down carbon molecule into CO2 and produces an ATP and several electron carrier molecules: (1 FADH2 and 3 NADH per acetyl CoA).

-         CO2 diffuses out of mitochondria and cell.

-         Carrier molecule enter the electron transport system:

 

Products- 6 CO2, 8 NADH, 2 FADH2 2 ATP (Krebs and a-CoA); Consumes 2 Pyruvates

 

Electron Transport System (Fig 7-6):

4.      Electron carrier molecules carry their cargo (2e- and H+) to the inner membrane (cristae).

5.      There the electrons are released in electron transport system (similar to photosynthesis). (Fig 7-6)

6.      This transport system pumps Hydrogen ions out of matrix to create H+ gradient.

7.       H+ gradient drives production of ATP ions tries to reenter the matrix region through ATP-producing transport proteins. (process is called Chemiosmosis).

§         The vast majority of ATP is produce here! (32-34 ATP)

8.      At the end of the electron transport system the electrons bind with oxygen (from the air you breath!) and H+ to produce water.

 

Products: 32-34 ATP, #? H20 (consumes Oxygen gas)

 

 

Summary (Table 7-1, Fig 7-7)

-         All together 36-38 ATP are produced from a single glucose molecule.

 

Notes:  Why Cyanide is deadly.  Cyanide will bind permanently to the site at the end of the electron transport chain where Oxygen would bind.  This causes a back-up of electrons that eventually stop the entire process (like an accident on the highway).

 

Metabolism of other Nutrients-

 

You body is quite capable of metabolizing other substance other than glucose.  These substances go through a series of intermediate steps and may enter the pathway at different points.

 

In addition, when ATP supplies are sufficient the system can work in reverse converting glucose to carbohydrates, proteins, and especially Fats (from acetyl CoA).  Thus if you don’t use your ATP your likely to build up fat.  Thus it may not necessarily be what you eat but what you do.  That’s why exercise (hence ATP consumption) is always the key to weight loss. (Fig E7-1)

 

Notice that this strategy is adaptive- That is, it is to a persons advantage in terms of survival to store fat (energy reserves) in case food becomes short as would have before the agricultural revolution.  Only very recently has this adaptive advantage turned against us.  (lesson- what may be evolutionarily adaptive now isn’t necessarily always going to be adaptive.)

 

Discussion questions: #5 and #6