Organelles
An animal cell, the organelles are small,
membranous cellular inclusion, floated in
the cytosol.
They keep various cellular activities
separated from one to another.
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Nucleus
Nucleus is a largest organelle, has a dia
meter of about 5 μm.
Prominent organelle in eukaryotic cell
Stores genetic information
Separated from the cytoplasm by nuclear
envelope.
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 Nuclear
envelope or nuclear membrane
consists of inner membrane and outer
membrane.
 The
space between inner and outer
membrane is continues with the lumen of
rough endoplasmic reticulum.
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The two nuclear membranes fuse at the
nuclear pores.
Nuclear pores are constructive of specific
set of membrane protein.
It functions as channel between the
nucleus and the cytosol.
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 It
regulates the movement of the material
from and to the nucleus.
 Protein
fibers associated with the inner
membrane of the nuclear envelope

Protein fibers maintain the shape of
nucleus and provide chromatin
attachment.
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The nucleus contains the nucleoplasm,
the nucleolus, fibrous matrix, DNA-protein
complex, chromatine-chromosome.
Chromatine looks grainy, but actually it is
thread like material.
Chemical analysis shows that chromatine
and chromosomes contain DNA, protein
and some RNA
.
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 Chromatin
undergoes coiling into
chromosome just before the cell divides
 It
is immersed in the nucleoplasm
 Nucleoplasm
is sugested has a different
composition from cytosol
 The
DNA of all chromosomes is packaged
into a compact structure with the aid of
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specialized proteins.
 It
is traditional to divide the DNA-binding
proteins in eucaryotes into two general
classes: the histones and the nonhistone
chromosomal proteins.
 The
complex of both classes of proteins
with the nuclear DNA of eucaryotic cells is
known as chromatin.
 Histones
are unique to eucaryotes.
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DNA
DNA is the hereditary or genetic material.
DNA stores information regarding its own
replication and the order in which amino
acid are to the joined to make protein
Nucleotide is a molecular complex of three
types of molecule: phosphate, pentose
sugar and a nitrogen containing base.
DNA is double stranded, the two strands
twisted about each other in the form of
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 The sugar in DNA is deoxyribose →
deoxy ribonucleic acid.
 The bases in DNA consist of purine (two
rings) and pyrimidine (one ring).
 The purine: Adenine (A) and Guanine (G)
 The pyrimidine:Thymine (T) and Cytosin (C)
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 The
sugar and phosphate as the
backbone of the strand and the bases
project to one side of the backbone.

Between the strands, Thymine (T)
always paired with Adenine (A) and
Guanine (G), with Cytosin (C).

 It
is called complementary.
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NUCLEOLUS
 Usually one nucleus has one nucleolus, but
sometime one nucleus has more than one
nucleolus or nucleoli.
 Nucleolus is the one or two dark regions of
the chromatine, where ribosomal RNA
(rRNA) is produced.

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 rRNA
joints with protein to form
subunits of the ribosomes.


The subunits of the ribosome leave
the nucleus enter the cytoplasm.
The subunits joint together in the
protein synthesis.
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Endoplasmic Reticulum
ER is an interconnected network of internal
membrane
Has a number of functions in synthesis of
many membrane lipid and proteins
Smooth ER (sER) it lacks ribosomes.
Rough ER (rER) are studded with ribosomes
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 The
smooth ER is the site of
synthesis and metabolism of fatty
acids and phospholipids.
 The
rough ER synthesize certain
membrane protein and organelle
proteins
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Secretory polypeptide from ribosom,
passes through rER, accumulate in the
lumen of rER before transported.
Rough ER is particularly abundant in cells
that specialized to produce secreted
proteins.
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 The
pancreatic acinar cells synthesize
digestive enzyme such as chymotrypsin,
because the cytosol filled with rER.
 The
plasma cells produce antibodies also
caused by abundant rER in the cytosol.
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Smooth ER are abundant in hepatocyte.
Enzyme in sER of the liver modify or
detoxify chemicals.
High doses of pesticides or carcinogens
result in a large proliferation of sER in the
liver.
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 Smooth
ER also forms transport
vesicles, in which large molecules
are transported.
 The
secretory proteins are found in
the lumen of rER will be transfered
to the Golgi vesicles.
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Ribosome.
Small particles composed of RNA and
proteins.
Composed of 2 subunits, a large subunit
and a small subunit.
Perform a very important function, they
carry out the protein synthesis.
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 Several
ribosom synthesizing the
same protein are called polysome.
 Polysome
can lie freely in the cytosol
or attached to ER.
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Cells that produce proteins for secretion,
contain a ten million ribosomes.
The ribosomal RNA is produced in the
nucleolus and the subunits of ribosomes
are assembled.
The subunits of ribosoms pass through the
nuclear envelope at nuclear pore.
Some remains free within cytoplasm and
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some attached to ER.
Most proteins in mitochondria and all of the
protein in the other organelles, membrane
etc. are encode by nuclear DNA and are
synthesized on ribosome in the cytosol.
The membrane attached and membrane
unattached ribosomes synthesized different
protein.
.
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 On
membrane attached, the protein
synthesized are those that enter the
secretory pathway during
synthesized
 This
include secretory protein,
lysosomal enzymes, and proteins in
the lumen of ER, Golgi vesicles,
secretory vesicles and plasma
membrane
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Golgi Apparatus
Discovered by Camillo Golgi → named
Golgi apparatus.
Consists of a stack of 3 – 20 curved
saccules.
The inner face is directed toward the ER
and the outer face toward the plasma
membrane.
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 Vesicles
can frequently be seen at the
edges of the saccules.
 Protein
or lipid filled vesicles that bud
from the sER are received at the inner
face or cis face.
 Golgi
Apparatus contains enzymes that
alter the carbohydrate chains of glycoproteins from rER.
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The monomer carbohydrates could be
modified or phosphate might be added
The products in vesicles depart the Golgi
apparatus at the outer face or trans face.
The vesicles move to the other organelles
such as lisosome.
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Some vesicles proceed to plasma
membrane and discharge their contents as
secretion.
The secretion is termed exocytosis.
Some of secretory proteins are secreted
continuously.
Collagen secretion by fibroblast and
serum protein by hepatocytes are
continuous secretion.
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 Continuous
secretion also termed as
constitutive secretion.
 In
certain cells the secretion is not continuous but stored inside the vesicles,
 The
secretory vesicles.
 The
stimulus for exocytosis triggered the
secretory vesicles to release the secretion.
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The secretion is termed as regulated
secretion.
Examples of this: exocrine cells of pancreas
which secrete precursor of digestive enzyme,
hormone secreting endocrine cells synthesize
insulin and other hormones and store them in
the vesicle secretory.
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 Maturation of secretory protein: from ER →
cis Golgi reticulum: modification on carbohydrate chains.
 From Golgi face, trough Golgi vesicles
migrate to further modification to medial
Golgi → trans Golgi reticulum.
 The proteins are shuttled between Golgi
vesicles by small transport vesicle.

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Some
proteins are stored in
secretory vesicle awaiting a
signal for secretion.
Proteins are also sorted in the
trans Golgi vesicle to lysosome.

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Lysosome
 Vesicles produced by Golgi apparatus.
 Contains hydrolytic digestive enzymes.
 Molecules are brought into cell → fuse with
lysosome → digested by enzyme → simple
subunits → cytoplasm.

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

Bacteria are engulfed by white blood cell
fuse with lysosome → digested.
→
Autodigestion:parts of the cells are digested by
its own enzymes → rejuvenation, during
development, apoptosis or programmed cell
death.
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 A metabolic disorder: a missing or inactive
lysosomal enzymes → macromolecules
cannot be broken down → full of lysosome
→ die.
 The lysosomal enzymes are precursors:
proenzyme → maturation →
enzymatically active polypeptide.
 Maturation occurs in the acidic endosome
or lysosome.
.
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 lysosomal
enzyme inserted into the
ER lumen, receive olygosaccharide.
from ER move to cis Golgi
 In the cis Golgi the olygosaccharide
become phosphorilated → mannose 6
phosphate
 In order the lysosomal enzyme
diverted to lysosome it must bind to
receptor M6P
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PEROXISOME
Microbodies are small vesicle bounded
by membrane contain specific enzymes.
Peroxisomes are microbodies that contain
enzymes for oxidizing small organic
molecules with the formation of hydrogen
peroxide (H2O2).
Peroxisomes are present in all eukaryotic
cells.
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
The size and enzyme composition vary
considerably, but peroxisomes are always contain
catalase or peroxidase
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Microbodies are produced by ER. Their
proteins are encoded by nuclear genes.
Peroxisomes lead to progressive
enlargement and divided into new ones.
Peroxisomes membrane are also synthe
sized on free ribosomes.
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Receptor and transport proteins in the
peroxisome membrane are also required.
Mutation → defective peroxisome assembly.
Zellweger syndrome → the transport of all
proteins in the peroxisome matrix is
impaired.
The cells contain empty peroxisome
The mutation → defect in the receptor or
transport protein.
The patients has defective in the oxidation
of the very long chains fatty acids.
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Mitochondria
Most eukaryotic cells, plants and animals
contain mitochondria.
Mitochondria → formation of ATP
(adenosine triphosphate).
The size and the shape is variable
usually 0.5-1.0 um in diameter and 2-5 um
in length.
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

Mitochondria as the nucleus is bounded by two
different membrane, the inner and the outer
membrane.
The outer membrane contains the protein porin,
→ form transmembrane channels → freely
permeable to small molecules, particularly to
protons.
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The inner membrane contains cardiolipin,
the lipid concentrated → reduce the
permeability to protons → permeability
barrier between cytosol and matrix.
The inner membrane invaginates → cristae
→ provide a much greater surface area.
The cristae project into the matrix, the inner
space filled with semifluid medium contains
enzymes.
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The enzymes break down carbohydrates
and lipids products → ATP production.
The matrix also contains DNA and
ribosome → synthesize its own protein.
Metabolism of pyruvate and fatty acids.
In the cytosol, glucose by glycolysis is
converted to pyruvate and lipids are
hydrolyzed to fatty acids and glycerol.
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.
Pyruvate and fatty acids transported into matrix
→ oxidized to acetyl CoA
 The final stage of the oxidation is the citric acid
cycle or Krebs cycle → NADH and FADH2


The free energy released during oxidation of
NADH and FADH2 → ATP from ADP.
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The inner membrane and the matrix are
the sites of the synthesis of ATP from
ADP and P.
The processes are very complicated.
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