Transcript combne etc citric photo

C0 5: Cellular respiration
(processes by which cells consume O2 and produce CO2)
CITRIC ACID CYCLE
Electron transport
PHOSPHORYLATION
PHOTOSYNTHESIS
Types of Cell Respirations:
Obligate anaerobes,
organisms that grow only in the absence of oxygen, avoid the gas by living in
highly reduced environments such as soil. They use fermentative processes to
satisfy their energy requirements.
Aerotolerant anaerobes,
also depend on fermentation for their energy needs, possess detoxifying
enzymes and antioxidant molecules that protect against oxygen's toxic
products.
Facul- tative anaerobes
not only possess the mechanisms needed for detoxifying oxygen metabolites,
they can also generate energy by using oxygen as an electron acceptor when
the gas is present.
Obligate aerobes
highly dependent on oxygen for energy production. They protect themselves
from the potentially dangerous consequences of exposure to oxygen with
elaborate mechanisms composed of enzymes and antioxidant molecules.
Respiration Main steps:
1. Oxidation of organic fuels (fatty acids, glucose, and some
amino acids) yields acetyl-CoA.
2. Oxidation of acetyl groups in the citric acid cycle includes
four steps in which electrons are abstracted.
3. Electrons carried by NADH and FADH2 are funneled into
a respiratory chain, ultimately reducing O2 to H2O. This
electron flow drives the production of ATP.
In the course of electron transfer, the large amount of energy released is
conserved in the form of ATP, by a process called oxidative phosphorylation
Explanation:
The citric acid cycle is a metabolic pathway in which two carbon
fragments derived from organic fuel molecules are oxidized to form
CO2 and the coenzymes NAD+ and FAD are reduced to form
NADH and FADH2, which act as electron carriers.
The electron transport pathway, also referred to as the electron
transport chain (ETC), is a mechanism by which electrons are
transferred from reduced coenzymes to an acceptor (usually O2).
Oxidative phosphorylation, synthesis of ATP from ADP ( the
energy released by electron transport is captured in the form of a
proton gradient that drives the synthesis of ATP, the energy
currency of living organisms.
Main Reactions of the Citric Acid Cycle.
Oxaloacetate, (4 C ) condenses with acetyl-CoA to form
citrate (6 C).
Also formed :
2 molecules of CO,
3 molecules of NADH,
1 molecule of FADH2,
In each turn of the citric acid cycle, 2 carbon atoms enter as
the acetyl group of acetyl-CoA and 2 molecules of CO2 are
released.
OVERALL REACTION
glycolysis
After its transport into the mitochondrial matrix, pyruvate is converted to
acetyl- CoA in a series of reactions catalyzed by the enzymes in the pyruvate
dehydrogenase complex. The net reaction, an oxidative decarboxylation, is as
follows:
The net reaction for the citric acid cycle is as follows:
Amphibolic
TCA is Amphibolic : ( function in both anabolic and catabolic processes)
catabolic pathway a series of biochemical reactions in which large
complex molecules are degraded into smaller, simpler products
anabolic pathway a series of biochemical reactions in which large
complex molecules are synthesized from smaller precursors
anabolism energy-requiring biosynthetic pathways
The citric acid cycle is obviously catabolic, because acetyl groups are
oxidized to form CO2 and energy is conserved in reduced coenzyme
molecules.
The citric acid cycle is also anabolic, because several citric acid cycle
intermediates are precursors in biosynthetic pathways
ETC is a series of electron carriers in the inner membrane of the mitochondria of eukaryotes and the plasma membrane of aerobic prokaryotes.
Electron Transport Chain.
Complexes I and II transfer electrons from NADH and succinate, respectively, to
UQ. Complex III transfers electrons from UQH2 to cytochrome c. Complex IV
transfers electrons from cytochrome c to O2.
Complex I, also referred to as the NADH dehydrogenase complex, catalyzes
the transfer of electrons from NADH to UQ. The major sources of NADH include
several reactions of the citric acid
complex II ( The succinate dehydrogenase complex ) consists primarily of the
citric acid cycle enzyme succinate dehydrogenase and two iron-sulfur proteins. Complex II mediates the transfer of electrons from succinate to UQ.
Complex III (cytochrome bcj complex).
transfers electrons from reduced coenzyme Q (UQH2) to cytochrome c.
Complex IV (Cytochrome oxidase)
is a protein complex that catalyzes the 4-electron reduction of O2 to form H2O.
ETC INHIBITOR
Several molecules specifically inhibit the electron transport process
The inhibition can be measured with an oxygen electrode. (Oxygen
consumption is a sensitive measure of electron transport.) When electron
transport is inhibited, oxygen consumption is reduced or eliminated.
Example of inhibitors:
•antimycin A inhibits cyt b..
•rotenone and amytal, which inhibit NADH dehydrogenase (complex I).
•Carbon monoxide (CO), azide (N3), and cyanide inhibit cytochrome oxidase.
Oxidative phosphorylation,
Oxidative phosphorylation
the process whereby the energy generated by the ETC is
conserved by the phosphorylation of ADP to yield ATP,
The Chemi osmotic Theory.
The flow of e through the ETC complexes is coupled to
the flow of protons across the inner membrane from the
matrix to the intermembrane space. This process raises
the matrix pH. In addition, the matrix becomes
negatively charged with respect to the intermembrane
space.
Oxidative stress
Oxygen can accept single electrons to form unstable derivatives, referred to as
reactive oxygen species (ROS). This ROS can seriously damage living cells
Examples of ROS : superoxide radical, hydrogen peroxide, the hydroxyl radical,
and singlet oxygen.
ROS formation is usually kept to a minimum by antioxidant defense mechanisms.
Examples of circumstances that may cause serious oxidative damage :
•overconsumption of certain drugs
•exposure to intense radiation,
•repeated contact with certain contaminants (e.g., tobacco smoke).
Antioxidants are substances that inhibit the reaction of molecules with oxygen radicals.
Antioxidants are effective because they are more easily oxidized than the atom or
molecule being protected.
To protect themselves from oxidative stress, living organisms
have developed several antioxidant defense mechanisms.
These mechanisms employ several metalloenzymes and
antioxidant molecules.
The major enzymatic defenses against oxidative stress are
provided by :
•superoxide dismutase,
•glutathione peroxidase,
•catalase.
Photosynthesis : the trapping of light energy and its conversion to chemical energy,
which then reduces carbon dioxide and incorporates it into organic molecules
Photorespiration: a light-dependent process occurring in plant cells actively
engaged in photosynthesis that consumes oxygen and liberates carbon dioxide
The essential feature of photosynthesis is the absorption of light energy by specialized pigment molecules.
The chlorophylls are green pigment molecules that play the principal role in
eukaryotic photosynthesis, because its absorption of light energy directly drives
photochemical events.
Chlorophyll b acts as a light-harvesting pigment by absorbing light energy and
passing it on to chlorophyll a.
The orange-colored carotenoids : molecules that either function as lightharvesting pigments (e.g., lutein, a xanthophyll, ) or protect against reactive
oxygen species (ROS)
PHOTOSYNTHETIC PIGMENTS
Photosynthetic pigments use primarily the
visible light portion of the electromagnetic
spectrum
1. Pigment is a substance that absorbs
visible light
2. Two major photosynthetic pigments are
chlorophyll a and chlorophyll b
3. Chlorophylls absorb violet, blue, and red
wavelengths; they reflect green, this is
why leaves appear green.
Photosynthesis takes place in chloroplasts.
Photosynthesis consists of two major phases: the light reactions and the
light-independent reactions.
During the light reactions, water is oxidized, O2 is evolved, and the ATP
and
NADPH required to drive carbon fixation are produced.
During the light-independent reactions, CO2 is incorporated into organic
molecules. The first stable product of carbon fixation is glycerate-3phosphate.
PHOTOSYNTHESIS
Virtually all energy on earth comes from
sunlight. Plants use energy from the sun to
make te bonds which hold organic molecules
together. When these bonds are broken the
energy is ultimately transferred to ATP, which
is then moved about cells and organisms to
power their needs.
Photosynthesis overview
12H20 + 6CO2 ----- light -----> 6O2+ C6H12O6 + 6H20
Photosynthesis - The Basic Reaction
CO2 +H2O +---Plants (Chloroplasts)
Light Energy---Simple
Sugars+ O2
PHOTOSYNTHETIC PIGMENTS
Photosynthetic pigments use primarily the
visible light portion of the electromagnetic
spectrum
1. Pigment is a substance that absorbs
visible light that behave as packets of
energy called photons.
2. Two major photosynthetic pigments are
chlorophyll a and chlorophyll b
3. Chlorophylls absorb violet, blue, and red
wavelengths; they reflect green, this is
why leaves appear green. Different
colors/wavelengths of light (ROYGBIV).
CAROTENOIDS
1. Carotenoids are yellow-orange
pigments which absorb light in
violet, blue, and green regions
2. When pigments absorb light,
electrons are boosted to a higher
energy level and the energy is
captured in a chemical bond
Photosynthesis occurs in
chloroplasts
Chloroplasts have two parts:
1. A double membrane encloses a fluid-filled space called
the stroma or ground substance
2. Thylakoids = flattened sacs organized into stacks called
grana
3. Chlorophylls and other pigments involved in absorption
of solar energy are embedded within thylakoid
membranes; these pigments absorb solar energy
REACTIONS IN PHOTOSYNTHESIS
Photosynthesis has two sets of reactions
1. Light-dependent reactions =
light energy is converted to chemical
energy (ATP&NADPH). Occur in the thylakoid
2. Light-independent reactions =
The energy in the ATP and NADPH are
used to power the light-independent
reactions (to make carbohydrates)
Light-independent reactions
• Takes place in the stroma of the chloroplast
• Energy from the light reactions (ATP, NADPH) is used to
form several molecules of 3-phosphoglyceraldehyde
(PGAL). This PGAL is then used to produce glucose
THE CALVIN CYCLE
• The incorporation of CO2 into carbohydtrate by
eukaryotes in the stroma, in the absence of light
and presence of ATP and NADPH produced by
light reactions, is often referred as Calvin cycle.
• It is light-independent reaction and also referred
as reductive pentose phosphate cycle (RPP
cycle) and photosynthetic carbon reduction cycle
(PCR cycle).
• The 3 phases of Calvin cycle are: carbon
fixation; reduction by NADPH; and regeneration
of glyceraldehyde-3-phosphate.
Carbon fixation
• It is a mechanism in which inorganic CO2 is
incorporated into organic molecules.
• Ribulose-1,5-biphosphate carboxylase (often
described as the world’s most abundant
enzyme) catalyzes the carboxylation of ribulose1,5-biphosphate to form 2 molecules of
glycerate-3-phosphate.
• Plants that produce glycerate-3-phosphate as
the first stable product of photosynthesis are
referred as C3 plants.
Photorespiration
• It is a light-dependent process consuming
oxygen (both ATP and NADPH) and
releasing fixed CO2. Hence it is a wasteful
process.
• It is a serious problem for C3 plants (e.g.
Soy-beans and oats) in hot, dry
environments, where these plants close
stomata to conserve water and reduce the
CO2 concentration within the leaf tissue
C4 plants (e.g. Sugar-cane and
maize)
• These plants develop C4 metabolism to surpress
photorespiration and in hot weather open their stomata
only in the cooler night temperature.
• In the C4 biochemical pathway in the mesophyll cells,
that are in direct contact with the air space in the leaf,
take up CO2, and use it to synthesize oxaloacetate,
which is then reduced to malate
• Malate diffuses to bundle sheath cells where it is
reconverted to pyruvate and the CO2 released in the
reaction is used in the Calvin cycle to yield triose
phosphate molecules
• Triose phosphate is converted to starch or sucrose.
• Pyruvate returns to the mesophyll.
Crassulacean Acid Metabolism
• CAM plants (e.g. Succulent Cacti) that grow in
high light intensity and limited water supply,
employ C4 metabolism, by opening their
stomata in the night, when CO2 is incorporated
into oxaloacetate by PEP
(phosphoenolpyruvate) carboxylase to form
malate.
• Malate is stored in the vacuole until
photosynthesis begins the next morning, when
CO2 is regenerated
• Malic acid accumulated in the leaves of the plant
may give an unpleasant taste.