Download Cellular respiration occurs in three stages

Cellular Respiration
The process by which your cells transfer the energy in organic compounds
(glucose, starch, carbohydrates) to ATP, the byproduct of this reaction is water
and carbon dioxide. It occurs in the cells mitochondria, which are the energy
producers for the cell.
Cellular respiration occurs in three stages
1. Glycolysis
2. Krebs Cycle
3. Electron Transport Chain
1. Glycolysis
 occurs in the cytosol
 glucose (6 carbons) is broken down
into two pyruvate molecules (3
carbons each)
 ATP consuming phase - 2 ATP are
consumed
 ATP producing phase - 4 ATP are
produced
 NET GAIN OF 2 ATP
 2 NADH (Nicotinamide) are produced
from two NAD+ (Nicotinamide
adenine dinucleotide) which can be
used to make more ATP in oxidative
phosphorylation
 NET GAIN OF 2 NADH
Animation of Glycolysis
*If you remember one thing about glycolysis,
remember that it yields 2 pyruvate, 2 ATP,
and 2 NADH
2. Krebs Cycle (a.k.a. the CITRIC ACID
CYCLE)
 occurs in the matrix of the
mitochondria
 the breakdown of glucose is
completed and CO2 is produced
in the presence of oxygen, the
two pyruvate molecules
produced by glycolysis travel to
mitochondria
 Krebs Cycle has 8 steps, each
step is catalyzed by a different
enzyme
 Each cycling requires the input
of 2-carbon acetyl-CoA and two
carbons are released as C02
 glycolysis results in the
production of 2 pyruvate
molecules which are converted to
acetyl-CoA, the Krebs cycle
needs only ONE acetyl-coA, so it
takes two complete turns of the
krebs cycle before you get the
products
 the NADH and FADH2 created
in the Krebs cycle are used in the electron transport system to create large
amounts of ATP
Animation of Krebs Cycle
*If you remember one thing about the Kreb's cycle, remember each pyruvate yields 4
NADH, 1 FADH2, and 1 ATP
* Double this number, for each glucose that's dropped into the process, the Krebs cycle
makes 2 turns, one for each pyruvate
3. The Electron Transport Chain (also known as oxidative phosphorylation)
 produces the energy that drives the synthesis of ATP in oxidative phosphorylation
 it consists of molecules (mostly proteins) that are embedded in the inner
mitochondria
 Sitting atop these proteins are molecules that are alternately reduced and oxidized
as they accept and donate electrons
 the initial electron acceptor in the chain is a flavoprotein (FMN) and it accepts an
electron from NADH. The electron is then passed down a series of molecules to
oxygen, which is the final electron acceptor. It is then combined with a couple of
hydrogen atoms to form water. The process will not function in the absence of
oxygen.
 FADH2 and NADH both donate electrons to the chain
the electron transport chain doesn't make any ATP itself, instead these reactions
are coupled to others to produce ATP, a process called CHEMIOSMOSIS
Animation of Electron Transport Chain <--- View this! It will totally help you
understand.
The NET RESULTS of the Aerobic Respiration
1. Each NADH produces 3 ATP (remember 8 NADH were created in the Krebs Cycle
and 2 in Glycolysis)
2. Each FADH2 produces 2 ATP (remember 2 FADH2 were created in the Kreb's Cycle)
3. Do the math, 34 ATP produced in the ETC + 2 from glycolysis + 2 from Krebs = 38
total ATP from each glucose
4. 2 ATP are used to move NADH to the mitochondria -- > for a grand total of 36 ATP
produced from each glucose molecule
Anaerobic Respiration
In the absence of oxygen (remember that oxygen is the final electron acceptor)
the cell goes through a process called FERMENTATION
Fermentation takes place under
anaerobic conditions (no oxygen
present). Two types:
Alcohol fermentation - occurs in
yeasts, fungi and some bacteria. 2
Pyruvate --> 2 Acetaldehyde --> 2
ethanol
Lactic acid fermentation - occurs in
oxygen deprived human muscle cells
where lactate is produced as a waste
product. Muscle cramps are caused by
increased acidity caused by the lactate
build up.
Anaerobic Respiration Steps
1. Glycolysis occurs, and pyruvate is
produced, the pyruvate enters the
Krebs cycle and produces NADH2 and
FADH2, and some ATP
2. The problem occurs in the ETC,
because there is no oxygen to be the
final electron acceptor
3. NADH bulids up in the system, and
NAD+ cannot be regenerated normally
4. Fermentation occurs to regenerate the NAD+ and create some ATP, but it is
much less efficient than aerobic respiration