CELLULAR RESPIRATION:
HARVESTING CHEMICAL ENERGY
Section A: The Principles of Energy Harvest
1
‫مـراحـل الـتـنـفـــس‬
‫حويصالت‬
‫هوائية‬
‫‪ -1‬تـنـفـس خـارجـي‬
‫الــدم‬
‫‪2‬‬
‫خاليا‬
‫الجـســ‬
‫م‬
‫‪ -3‬تـنـفـس خـلـوي‬
‫‪ -2‬تـنـفـس داخـلــي‬
Overall process
a)
Organic compounds + O2 → CO2 + H2O + energy
b)
Food is the fuel for cellular respiration.
c)
Cellular respiration is a catabolic pathway: it releases
energy by breaking down complex molecules.
d)
Cellular respiration involves movement of electrons
(gain or loss).
e)
We will study the breakdown of glucose as an
example.
Section A: The Principles of Energy Harvest
1. Cellular respiration and fermentation ‫ التخمر‬are catabolic,
energy-yielding ‫ ه ْدم ُمنتِج للطاقة‬pathways.
2. Cells recycle the ATP they use for work.
3. Redox reactions ‫اإلختزال‬-‫ تفاعالت األكسدة‬release energy when
electrons move closer to electronegative atoms.
4. Electrons “fall” ‫ تنتقل‬from organic molecules to oxygen
during cellular respiration.
5. The “fall” of electrons during respiration is stepwise ‫ َم ْر َحلي‬,
via NAD+ and an Electron Transport Chain.
1. Cellular respiration and fermentation are
catabolic, energy-yielding ‫ ُمنتج للطاقة‬pathways
•
Organic molecules store energy in their arrangement of atoms.
•
Enzymes catalyze the systematic degradation of organic molecules that
are rich in energy to simpler products with less energy.
•
Some of the released energy is used to do work and the rest is dissipated
as heat.
•
Metabolic pathways that release the energy stored in complex organic
molecules are catabolic ‫ه ْدمي‬.
•
Fermentation is a type of catabolic process leads to the partial degradation
‫ التحلل الجزئي‬of sugars in the absence of oxygen.
•
Cellular respiration is a more important catabolic process, uses oxygen as
a reactant to complete the breakdown of a variety of organic molecules.
•
This process is:
• Organic compounds + O2 -> CO2 + H2O + Energy
•
Carbohydrates, fats, and proteins can all be used as the fuel, but we will
start learning with glucose.
• C6H12O6 + 6O2 -> 6CO2 + 6H2O + Energy (ATP + heat)
Cellular Respiration
Food
O2
(Fuel of energy)
Respiration
O2
H2O
Energy
+
CO2
Cellular Activities
Organic compounds + O2
Energy + CO2 + H2O
2. Cells recycle the ATP they use for work
• ATP (Adenosine Tri-Phosphate) is the important
molecule in cellular energetics ‫عمليات إنتاج الطاقة‬.
– The attachment of three negatively-charged phosphate groups (P) is an
unstable ‫عير مستقر‬, energy-storing ‫ مخزن للطاقة‬arrangement.
– Loss of the end phosphate group release energy.
– Thus, it can diffuse to any part of the cell and and release energy.
• The price of most cellular work is the conversion of ATP
to ADP and phosphate (P).
• An animal cell regenerates ‫ تعيد إنتاج‬ATP from ADP by adding P via
the catabolism ‫ هدم‬of organic molecules.
Adenosine Tri-Phosphate (ATP)
Adenosine
P
P
+ H2O
P
Triphosphate
Energy
P
P
P
Adenosine Di-Phosphate
The transfer of the terminal phosphate group from ATP to
another molecule is phosphorylation ‫فـَ ْسـفـَرة‬.
This changes the shape
of the receiving molecule
in order to work
(transport, mechanical,
or chemical).
When the phosphate
groups leaves the
molecule, the
molecule returns to
its original shape (stop).
How dose ATP drive cellular work ?
P P P
Organelle
Motor
Protein
P
Microtubule
Energy
3. Redox reactions release energy when electrons
move closer to electronegative atoms
•
•
•
•
Catabolic pathways relocate ‫ يبدل أماكن‬the electrons stored in food molecules,
releasing energy that is used to synthesize ‫ لتخليق‬ATP.
Oxidation-reduction reactions (Redox reactions):
Are reactions that result in the transfer of one or more electrons from one reactant to
another
Redox reactions require
Oxidation: Is the loss ‫ فقـد‬of electrons.
Reduction: Is the addition ‫ إكتساب‬of electrons.
both a donor and acceptor of e.
X e-
+
Oxidation
(Reducing agent)
Reduction
(Oxidizing agent)
Lose electrons
Gain electrons
Lose hydrogen
Gain hydrogen
Gain oxygen
Lose oxygen
Y
+
X
Oxidation
Na + Cl
Na+ + Cl-
Y
+
(reducing agent)
Reduction
(oxidizing agent)
Energy
4. Electrons “fall” from organic molecules
to oxygen during cellular respiration
•
In cellular respiration, glucose and other fuel molecules are oxidized, releasing
energy.
e
C6H12O6 + 6O2
Reducing
agent
•
•
•
Oxidizing
agent
6CO2 + 6H2O + (ATP + Heat)
Energy = 686 kcal/mol
Energy
•
Glucose is oxidized, oxygen is reduced, and electrons loose potential energy.
H is the source of electrons that transfere to O.
Thus, molecules that have an abundance of ‫ وفرة من‬hydrogen are excellent fuels
because their bonds are a source of electrons that “fall” closer to oxygen.
Enzymes lower the barrier of activation energy, allowing these fuels to be
oxidized slowly.
When H moves to O, it leaves bonds which degenerated to release energy.
•
The resulting energy is used by the cell to synthesis ATP .
•
5. The “fall” of electrons ‫ اإلنحدار اإلليكتروني‬during respiration is
stepwise ‫مرحلي‬, by NAD+ and an electron transport chain
•
Cellular respiration does not oxidize glucose in a single step that transfers
all the hydrogen in glucose to oxygen at one time.
•
Rather, glucose and other fuels are broken down gradually ‫ تدريجيا‬in a
series of steps, each catalyzed by a specific enzyme.
•
At key steps ‫فى الخطوات األساسية‬, hydrogen atoms move from glucose and
passed first to the coenzyme NAD+ (Nicotinamide Adenine Dinucleotide).
•
Dehydrogenase enzymes strip two hydrogen atoms from the fuel (e.g.,
glucose), pass two electrons to NAD+ and release H+.
This changes the oxidized form, NAD+, to the reduced form
NADH. Thus, NAD+ is oxidizing agent as it accept electrons.
•
–
NAD+ functions as the oxidizing agent in many of the redox
steps during the catabolism of glucose.
H-C-OH + NAD+
Dehydrogenase
C=O + NADH + H+
As electrons “fall” from NADH to oxygen, their energy is used to synthesize
ATP.
•
•
•
•
The most common carrier is NAD+
H atoms have one proton and one electron
When two H atoms are removed from a
substrate NAD+ accepts the electrons
from both atoms and a proton from one of
them
NAD+ + 2H→ NADH + H+
• Cellular respiration uses an electron transport chain ‫سلسلة نقل اإلليكترونات‬
to break ‫ يـُقـَسم‬the fall of electrons to O2 into several steps ‫عدة خطوات‬.
• The electron transport chain, consisting
of several molecules (primarily proteins),
is built into the inner membrane of a
mitochondrion.
• NADH takes electrons from food to the
“top” of the chain.
• At the “bottom”, oxygen captures the
electrons and H+ to form water.
• The free energy change from “top” to
“bottom” is -53 kcal/mole of NADH.
• Electrons are passed by increasingly
electronegative molecules in the chain
until they are caught by oxygen (the
most electronegative).
Summary of electron “Fall” steps during respiration
- Falling of all H atoms from glucose to O is gradually not at once.
- It occurs in steps, each one is catalyzed by an enzyme.
- H atoms of glucose pass first to the co-enzyme NAD+ to form NADH
- Then from NADH to electron transport chain, and finally to O and
releases energy to form ATP.
Food
NAD+
H
NADH
e
Mitochondrion
e
Transport chain
ATP
ADP
Oxygen
Energy