Cellular Biology

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Cellular Biology
School of Life Sciences Shaanxi Normal University
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CHAPTER 6 MITOCHONDRION AND CHLOROPLAST
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I. Mitochondrion Structure and distribution
Usually, mitochondrion is like a particle or
rod and others composed of proteins (65-70) and
lipids (25-30) at 0.51µm diameter and 1.53.0µm
length. The mitochondria in the cells of pancreas
can be 1020µm at length called huge
mitochondrion. The number of mitochondrion in a
cell can be hundreds to thousands, and less in
plant cell than in animal cell because of
chloroplast. Some unicellular organism contains
500,000 mitochondria inside, but mammalian
erythrocytes contain no any mitochondrion inside.
Mitochondrion can migrate in cell along
micro tube, and motorprotein supplies energy for
that.
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1. Outer membrane Outer membrane contains
lipids (40) and proteins (60). There are the
hydrophilic tunnels composed of porin that allows
the molecules lighter than 5KD passed through.
2. Inner membrane Inner membrane
contains more than 100 types of polypeptide with
a low permeability. The electron transmission
chain of oxidative phosphorylation is located in
inner membrane. Cytochrome C reductase is the
marker enzyme for inner membrane. Inner
membrane can be pleated into inside to form
cristae. The cristaes enlarge the area of inner
membrane to 5 10 folds. Cristae can be two
types of shape lamella or tube. Elementary
particles are located on cristae, and composed of
head part (F1 conjugate factor) and elemantary
part (F0 conjugate factor). F0 inserts into
inner membrane. 3. Intermembrane space
It is between inner membrane and outer membrane
with 6-8nm width. Adenylate kinase is the marker
enzyme for intermembrane space.
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Photo of mitochondrion
Inner membrane
Outer membrane
Intermembrane space
Lamella critae
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Matrix
A model structure of mitochondrion
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4. Matrix The area surrounded by cristae,
intermembrane space and inner membrane. Excepting
glycolysis (in plasma), other bio-oxidation
reactions are carried out in mitochondrion (in
matrix). Malic dehydrogenase (MDH) is the marker
enzyme for the matrix of mitochondrion.
The matrix contains a complete system for
transcription and translation including
mitochondrion DNA (mtDNA), 70s ribosome, tRNA,
rRNA, and DNA polymerase.
Tube cristae
Matrix
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The molecule basis of oxidative
phosphorylation Electronic vectors for the
respiratory chain 1.  Nicotinamide adenine
dinucleotide (NAD) NAD is a coenzyme for many
dehydrogenases and linked to tricarboxylic acids
cycle. NAD present H to flavoprotein.
2.  Flavoprotein. 3.  Cytochromes Types
a?a3?b?c?c1. 4.  Three Copper atoms on the
protein located on inner membrane.
5.  Ferredoxin. 6.  Coenzyme Q.
A model structure for ferredoxin
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Two major respiratory chains
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ATP synthetase Molecule weight 500KD.
Two parts a spherical head (F1), and the
basement (F0) inserted membrane. Each liver cell
mitochondrion contains 15,000 molecules of ATP
synthetase. Each ATP synthetase can make 100 ATP
molecules per second. For the detail about ATP
synthetase, see your biochemistry text book.
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Model structure for ATP synthetase
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The inhibitors for oxidative phosphorylation 1.In
hibitors for electronic transmission ?  Inhibit
NADH?CoQ amytal, rotenone, and piericidin.
?  Inhibit Cyt b?Cyt c actinomycin
A. ?  Inhibit cytochrome oxidase?O2 CO, CN,
NaN3, and H2S. 2.Inhibitors for phosphorylation
Oligomycin and dicyclohexyl carbodiimide
(DCC) can bind to F0 to block the H tunnel and
inhibit synthesis of ATP. 3.Uncoupler Some
reagents or medicines can separate the oxidation
and phosphorylation, oxidation is continued but
phosphorylation stopped. The uncoupler can cause
body temperature increased. Uncouplers include
DNP, FCCP, thermogenin, and aspirin.
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Mitochondrion is semiautonomous Mitochondrion
contains its whole system for DNA replication,
transcription, and translation. The system
includes mtDNA, RNA, DNA polymerase, RNA
polymerase, tRNA, ribosome, and others. That
means mitochondrion has the genetic way for
itself. So, we say that mitochondrion is a
semiautonomous organelle. mtDNA is double
strands and circle molecule as the below

Heavy chain (H)
Light chain (L) The
genes on mtDNA are located very closely without
introns. Each mitochondrion contains several
mtDNA molecules, and the length for each is about
16-20kb in animal. Most of gene are transcripted
from H chain. The genes on H chain encode two
rRNAs, 14 tRNAs, and 12 polypeptides. The genes
on L Chain encode other 8 tRNAs and 1 peptide.
The genes on mtDNA linked together, or
overlapped. Almost each reading frame has no any
region that is not translated. Many of them have
no stop codon, and end as T or TA. The stop codon
will be added during the modification after
transcription.
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Mitochondrion was originated from a bacterium
that parasited in cell probably because
mitochondrion has many features are almost same
to bacteria, for examples, morphology, staining,
chemical components, genetic system, and others.
The following genetic features are same to a
bacteriums ? circle DNA without intron. ? 70S
ribosome. ? RNA polymerase can be inhibited by
EB, not by actinomycin D. ? Sensitive to
chloromycetin that inhibits bacterial protein
synthesis, not to actidione that inhibits the
cellular protein synthesis. The genetic codons
of mammalian mtDNA are different from universal
genetic codons ? UGA is not a stop codon here,
it is a codon for Tryptophan. ? Methionine is
encoded by codon AUG, AUA, AUU and AUC. ? AGA and
AGG are not codons for arginine, they are stop
codons here. There are 4 stop codons in
mitochondrion UAA, UAG, AGA, and AGG. mtDNA is
transferred to new generation from parental
generation with a matrilinear inheritance way,
and its mutation rate is higher than nucleus DNA
(nDNA) without efficient repairing function. So,
mtDNA is easy to be mutated and cause mutation
genetic diseases, such as Leber optic nerve
disease (optic nerve denaturation and atrophy)
and myoclonus epilepsy (convulsive seizure and
loss of consciousness).
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Proliferation of mitochondrion Mitochondrion is
proliferated by the cleavage styles include 1.
Septate division The mitochondrion membrane
forms a ligature ditch rounding the middle of
membrane, then separated to two new mitochondria.
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2. Contracting division The ligature ditch
become slender and is pulled to longer further,
the divided off to new mitochondria. 3. Budding
division Germinated firstly, the small
mitochondrion will fall off from its mother
mitochondrion, grow up and develop to a new
mitochondrion.
Contracting division of mitochondrion
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II. Chloroplast We can say that all energy
utilized by every life event is originally from
sun. But, how to utilize and transform it? We,
human body can not take energy from sun, but we
have to use it by other way. Chloroplast plays
key role here! Chloroplast take and transform the
sun energy for plant growth, animals take energy
and nutrition from plants (or other animal). As a
energy transformer, chloroplast can combine
carbon dioxide and water to form sugar and
release oxygen. So, the photosynthesis of green
plants is the basic energy resource for all bio
organs including human being in the world.

Sunlight 6CO26H2O
C6H12O66O2
Chloroplast Struct
ure The size of chloroplast is about 510um
24um 23um. 50 200 chloroplasts are
contained in each plant cell usually. The size
and shape are different in different plant
species. Chloroplast is composed of envelope,
thylakoid and stroma. Chloroplast contains 3
types of membranes (outer membrane, inner
membrane and thylakoid membrane) and 3 types of
cavities (intermembrane space, stroma cavity and
thylakoid space).
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Structure of chloroplast
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Envelope Envelope is composed of bilayer
of lipid membrane with a 1020nm intermembrane
space. The outer layer allows almost all large or
small molecules pass through, but the inner layer
allows molecules pass through selectively. Thylak
oid Thylakoid is a vesicle formed by a
monolayer membrane with some components of
photosynthetic pigments and electronic
transmission, we call this layer as
photosynthetic membrane. 10 100
thylakoids are overlapped together to form a
basic particles, so we call these thylakoids as
basic particle thylakoids. Each chloroplast
contains 40 60 basic particles. The thylakoids
that located between basic particles and did not
overlap together are called stroma thylakoids
that form stroma lamella. The basic particles
are linked by stroma thylakoids. So, all
thylakoids form a closed system. The
membrane of thylakoid is composed of protein and
lipid(6040). The light energy is transformed
into chemical energy on thylakoid membrane. The
proteins contained in the thylakoid membrane are
the complex of cytochrome b6/f, flavoprotein,
complex of photosystem I, complex of photosystem
II, and others.
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Stroma Stroma is the area between inner membrane
and thylakoid. The components of stroma include
Enzymes associated with carbon assimilation, The
system for protein synthesis chloroplast DNA
(ctDNA), RNAs, ribosome, and others. The
mechanism of photosynthesis Photosynthesis is a
course for the transformation of energy and
substance
Electronic transmission Light energy
Electric Chemical
energy Store in (Sun energy)
power (ATP and
NADPH) sugars The course can be divided
as two parts light reaction (the reaction needs
light) and dark reaction (the reaction does not
need light). The photosynthetic pigments and
electronic transmission components
Photosynthetic pigments Thylakoid contains two
pigments green chlorophyll and red carotinoid
(31). Chlorophyll includes two types
chlorophyll a and b. All chlorophylls and
carotinoid are embedded in thylakoid membrane.
So, thylakoid membrane is a very important place
where the photosynthesis and energy exchange are
carried out.
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Chlorophyll
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Light harvesting complex Light harvesting complex
is composed of about 200 chlorophylls and some
peptides. Most of chlorophyll a and all
chlorophyll b can capture light, they are called
as antenna pigment. Carotinoid and xanthophyll
are the helper pigments. Antenna pigments
transfer the light energy to central chlorophyll
by a resonance energy transmission way.
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Actually, there are 3 plant pigments in
thylakoid green chlorophyll, red carotene plus
carotinoid, and yellow xanthophyll. The 3
pigments form 3 basic colors to figure out so
colorful and beautiful world to us that we can
not love her enough forever! Photosystem II
(PS?) PS II is called as P680 also. PS II
includes 12 peptide chains at least. PS II is
located in thylakoid membrane, and contains one
light-hawesting comnplex ? (LHC ?), one central
chlorophyll, and one oxygen evolving complex. D1
and D2 are the key peptide chains combined to
P680?pheophytin and plastoquinone. Cytochrome
b6/f complex (cyt b6/f complex) Cytochrome b6/f
complex exists in dimer style. Each monomer
contains four subunits cytochrome b6 (b563),
cytochrome f, ferredoxin, and subunit
?. Photosystem I (PS I) PS I is called as P700
also. PS I is located in stroma and thylakoid
membrane. PS I is composed of light harvesting
complex I and a reaction center formed by some
special chlorophylls, electron vectors.
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Light capturing reaction and electron
transmission Light capture
Electron
trnasfer Light energy P680 (ground state)
P680e(excited state)
Pheophytin QA on D2 QB on D1
Plastoquinone of PS II Complex of
cytochrome b6/f Cu2 on plastocyanin
P700 of PS I A0 A1
4Fe-4S Ferredoxin NADP
NADPH The Z way of electron
transmission above is called as non-cycle
photosynthetic phosphorylation. Both ATP and
NADPH are released out here.
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Non-cycle photosynthetic phosphorylation
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If the NADP is inefficient in plant, electron
will cycle in PS I to form ATP only, no NADPH
synthesized at this time. We call this
transmission as cycle photosynthetic
phosphorylation shown as the fig below.
Cycle photosynthetic phosphorylation
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The cooperation of PS I and PS II (The fig just
show you the Z way)
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Photosynthetic phosphorylation Just like the
described as above, a pair of electrons is
transferred from P680 to NADP, this transmission
will put 4 H ions into the cavity of thylakoid
making the pH here low (about 5) and forming H
force. Under the ATP synthetase enhancing, the H
force will push ADP combined by Pi to form ATP.
Oxidative phosphorylation and photosynthetic
phosphorylation
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Semiautonomy of chloroplast Like mitochondrion,
chloroplast is the energy station in plant cell.
Chloroplast is a semiautonomous organelle also.
Chloroplast DNA (ctDNA) is cycle DNA with
200Kb-2500Kb length usually. Like mitochondrion,
chloroplast synthesizes the some of proteins that
chloroplast needs. Other needed proteins must be
synthesized in cell plasma. So, we say that
chloroplast is a semiautonomous organelle also.
The proliferation of chloroplast The
proliferation of chloroplast is very similar to
the septate division of mitochondrion. The
chloroplast membrane forms a ligature ditch
rounding the middle of membrane, then separated
two new chloroplasts. Chloroplast cleavage is
easier to be found in baby plant or leaf than in
adult plant or leaf usually. A adult chloroplast
will not start division again almost.
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Directive transportation of proteins in
mitochondrion and chloroplast Transportation of
mitochondrion proteins Most of mitochondrion
proteins are synthesized in plasma and
transported into mitochondrion directionally. The
signal sequence (leader sequence, presequence or
transit-peptide) at N terminal of protein will
lead the transportation specifically. After the
transportation, the signal sequence will be cut
off by signal peptidase. We call this splicing as
posttranslation modification.
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The protein transportation signal
sequence is not specific to target protein. Any
protein with the signal sequence can be
transported into mitochondrion. Many
protein complexes are associated with the protein
transportation These complexes are the
translocators actually including the follows
?TOM complex Protein can enter
intermembrane space by this complex. The
important human TOMs are TOM34, TOM40, TOM22,
TOM7, TOM6, and Tom5. The tunnel of TOM complex
is called as general import pore (GIP).
?TIM complex TIM23 can transport protein to
stroma or insert some proteins into inner
membrane. TIM22 can insert the transportation
proteins for metabolism needed substances into
inner membrane. ?OXA complex OXA can
insert both the proteins synthesized by
mitochondrion and the proteins passed through
TOM/TIM into inner membrane. The
proteins entered outer membrane contain a N
terminal signal that will not be cut off and will
be inserted into outer membrane by TOM complex.
For stroma proteins, they have to be transported
into intermembrane space by TOM complex firstly,
then inserted into stroma by TIM complex. As
another choice, they can enter stroma by the
cooperation of TOM and TIM at the site where the
mitochondrion inner and outer membranes are
touched each other.
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The complex of TOM and TIM (Proteins can pass
through outer membrane and inner membrane here
with one step only)
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The touched sites of the outer membrane and inner
membrane of mitochondrion
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Protein enter inner membrane and intermembrane
space A. The protein contains two signal
sequences enter stroma by first signal for
TOM/TIM23, then, inserted into inner membrane by
second signal for OXA complex. B. The proteins
entered intermembrane space can be inserted inner
membrane by the stop-transfer sequence for TIM23.
C. The inserted proteins can be modified by the
protease as soluble proteins. D. The transporter
for metabolized substance can be inserted
into inner membrane byTIM22.