Energy-Releasing Pathways: Aerobic and Anaerobic Respiration

2. It is the main energy carrier for cells.
It is consists of:
a. Adenosine – a substance made up of the purine
adenine plus a five-carbon sugar ribose
b. Triphosphate Group
It is released from food molecules ingested by
organisms in the process of respiration.

3. The energy input from ATP formation can
come from sunlight, small inorganic
compound, or from the breakdown of
carbohydrates, lipids and proteins.
Of the foods we eat, carbohydrates are
the main source of energy. A good example is
glucose. Our cells use glucose first as long
as it is available, then lipids, and proteins as
the last resort.

4. A process where chemical energy is released from
various carbohydrates.
It has three pathways:
A. Aerobic Respiration
B. Anaerobic Electron Transport
C. Fermentation

5. Glucose (carbohydrate)
Glycolysis ATP
no oxygen with oxygen
Fermentation Aerobic Respiration

6. ‘Glyco’ means sugar.
‘Lysis’ means break.
This step doesn’t proceed without an energy input
from ATP

7. It takes place in the cytoplasm

8. In this process, Glucose is phosphorylated toglucose-6-phosphate. Then, breaks
into 2 three-carbon molecules of PGAL. ATP provides a phosphate group to each
PGAL and removes hydrogen atoms. NAD+ picks up the Hydrogen and
becomes reduced to NADH; 2 molecules are formed.
As a result, 4 ATP molecules and 2 NADH are generated from the PGAL
molecule and is converted to pyruvic acid.+

9. *aerobe- uses Oxygen as the final electron acceptor
in carbohydrate metabolism.
An Oxygen-dependent pathway which takes place
in the Mitochondrion

10. This pathway commonly yields 36 ATP molecules
for every glucose molecules degraded.
H+ and electrons are transferred to NAD+ and FAD
which in turn transfer them to an electron transport
system.
Occurs as a series of chemical reaction in which
Oxygen convert the chemical energy stores in
organic molecules to ATP and reduced H2
acceptors. E.g. NADH

11. The pyruvic acid must be converted first to Acetyl-
CoA; a two-carbon molecule of Acetyl Group.
During this transformation, the pyruvic acid loses
H2O and produces CO2 + NADH+ H+ (as NAD+
accept H2 ). Now, the 2 molecules of Acetyl-CoA
are ready to enter the Krebs Cycle.
P.A + CoA + NAD+ Acetyl-CoA +CO 2 + NADH + H +

13. Also known as Citric Acid Cycle
The cycle was named after a British biochemist
named Sir Hans Adolf Krebs.

14. This occurs in the inner matrix of Mitochondria

16. Step 1: Acetyl CoA combines with Oxaloacetic acid
to form citric acid (regenerates CoA)
Step 2: Citric acid releases CO2 and a H atom that
combines with NAD+ to form NADH + H+ to form 5
carbon compound.
Step 3: 5 carbon compound releases CO2 and a
Hydrogen atom (combines with NAD+ to form NADH
+ H+) to form a 4 carbon compound. A molecule of
ATP is formed.
Krebs Cycle

17. Step 4: 4 Carbon compound releases a hydrogen
atom ( combines with FAD to Form FADH2) and is
converted to another 4 carbon compound.
Step 5: The 4 carbon compound releases a
hydrogen atom and is (combines with NAD+ to
form NADH + H+)converted back into Oxaloacetic
acid.

18. In this stage, one acid is formed to another; Acetyl
CoA (2-C) reacts with oxloacetic acid (4-C). Citric
Acid is eventually reduced to other forms:
ketoglutaric acid (5-c)
succinic acid (4-c)
malic acid (4-c)
oxaloacetic acid (4-c)

19. Which become regenerated to start the cycle
all over again because it takes two preparatory
reaction sequences of Krebs Cycle to dismantle
the 2 pyruvates.
The breakdown of the pyruvates add only 2
ATP molecules (one for each) and many electron
carriers to the number that can be used in the
third stage, the Electron Transport Phosphoryatio.

21. The most impressive of all ATP-yielding mechanisms
This stage is carried out by enzymes embedded in the
inner membrane of the mitochondrion.
It involves two events:
1. The transfer of electrons and Hydrogen through a
membrane- bound transport system.
2. Actual formation of ATP

22. *anaerobes cannot ever use Oxygen as the final
electron acceptor thus, an inorganic compound is the
final acceptor.
In this pathway, NADH from Glycolysis transfers
electrons to a small transport system bound in the
plasma membrane and the NAD+ is thereby
regenerated.
The reaction do not add any more ATP.

23. The breakdown of pyruvates without Oxygen.
The net yield is 2 ATP. The remaining reactions
only serve to regenerate NAD+
It comes in 2 forms:
1. Alcoholic Fermentation
2. Lactic Acid Fermentation

24. 1. Alcoholic Fermentation
During this process, pyruvates are broken down
to acetyldehyde. This accepts electrons from
NADH and thereby becomes ethanol.
It occurs in some plants and some one-celled
organisms.

25. ALCOHOLIC FERMENTATION
Ex:
Production of beer and wine

26. 2. Lactic Acid Fermentation
It takes place when there is a short supply
of Oxygen in cells.

27. Example:
Occurs in muscle cell when strenuous exercise causes
muscle cells to use up all the oxygen available to them.
They switch to anaerobic respiration and lactic acid
builds up in the cells, changing the acidity of the
cytoplasm.
Production of cheese and yogurt