Transcript Anaerobic Respiration

The Anaerobic Pathway
 Glycolysis allows organisms to obtain energy from
nutrients in the absence of oxygen. However, step 6
(G3P to BPB) of the glycolytic pathway reduces NAD to
NADH.
 If glycolysis continues without a mechanism to oxidize
NADH back into NAD, step 6 will be blocked and
glycolysis will come to a halt.
 Organisms have evolved several ways of recycling NAD
allowing glycolysis to continue when oxygen is not
available.
Fermentation
 There are two different ways in which fermentation occurs:
 One method involves transferring the hydrogen atoms of
NADH to certain organic molecules instead of the electron
transport chain. This process is called fermentation.
 Bacteria have evolved dozens of different forms of
fermentation, but eukaryotes primarily use two
methods: ethanol fermentation and lactate (lactic acid)
fermentation.
 This diagram shows where fermentation would start if there is a lack aerobic conditions.
Glycolysis occurs due to it’s ability to create energy anaerobically (with out oxygen) and
fermentation would occur at the end of the Glycolytic pathway. There are then two
different means in which energy can be produced depending on the organism.
Ethanol Fermentation
 Yeast when under anaerobic conditions converts glucose to
pyruvic acid (via the glycolysis pathway).
 NADH passes its hydrogen atoms to acetaldehyde, a
compound formed when a carbon dioxide molecule is
removed from pyruvate which forms ethanol. This process
allows NAD to be recycled and glycolysis to continue
and occurs in the cytoplasm.
 The two ATP molecules produced satisfy the organism’s
energy needs, and the ethanol and carbon dioxide are
released as waste products.
 *Note: *Yeast is a eukaryotic micro-organism classified as
a fungi
 As shown above, glucose is converted into 2 Pyruvate molecules, which is further converted
to 2 Acetaldehyde molcules where 2 Carbon Dioxide molecules and finally 2 Ethanol are
released. In order for this entire process to occur NAD+ must be converted to NADH and 2
H+ ions (vice versa) or this process will not occur.\
Applications of Fermentatio
 Bread is leavened by mixing live yeast cells with starches
and water. The yeast cells ferment the glucose from the
starch and release carbon dioxide and ethanol. Small
bubbles of carbon dioxide gas cause the bread to rise (or
leaven) and the ethanol evaporates away when the bread is
baked.
 In beer and wine making, yeast cells ferment the sugars
found in carbohydrate-rich fruit juices, such as grape juice.
The mixture bubbles as the yeast cells release carbon
dioxide gas and ethanol during fermentation. The
percentage of Ethanol in the solution stabilizes when the
increase in Ethanol kills the remaining yeast cells.
Lactate Fermentation
 Occurs when NADH reduces pyruvate directly to form
lactate as an end product.
 If one glucose molecule goes through glycolysis, 2 net
ATP and 2 pyruvate molecules are produced and 2
NAD+ molecules are consumed.
 2 NADH molecules and 2 H+ come and reduce the 2
pyruvate molecules in the cytoplasm of the cell,
forming 2 lactate molecules and 2 NAD+.
 The 2 NAD+ molecules are then reused in glycolysis,
enabling the cell to produce ATP even in the absence
of oxygen.
What happens with the Lactate
that is produced?
 The accumulation of lactate molecules in the blood
and in muscle tissue causes stiffness, soreness, and
fatigue.
 Lactate is transported through the bloodstream from
the muscles to the liver.
 When vigorous exercise ceases, lactate is oxidized back
to pyruvate,which then goes through the Krebs cycle
and oxidative phosphorylation.
VO2 and Lactate Threshold?
 Lactate fermentation occurs continuously as you
exercise. However, as exercise intensity increases,
lactate production increases. The increase in Lactate
also causes an interference between areas of muscle
fibres which inhibit muscular contraction.
 The lactate threshold (LT) is the value of exercise
intensity at which blood lactate concentration begins
to increase sharply.
 In this graph the amount of Lactate that remains with in the blood will sharply
increase as the intensity of an activity increases. This point is called the “Onset of
Blood Lactate” which is the area on the line where there is a dramatic increase. This
graph shows that levels of blood Lactate change as an individual trains more often.
This means the person can sustain a high work output for longer without the onset
of Lactate interfering with their performance.
 One measure of performance is the percentage of VO2
max (maximum oxygen consumption) at which the LT
is reached. This is the maximum volume of oxygen (in
mL) that the cells of the body can remove from the
bloodstream in one minute per kg of body mass.