Cell is the base of life

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Cell is the base of life
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The Endomembrane system
A membranous system of interconnected tubules and
cisternae Membranes of the endomembrane system
vary in structure, composition, thickness and
behavior The endomembrane system
includes Nuclear envelope Endoplasmatic
reticulum Golgi apparatus Lysosomes Vacuoles Plasm
a membrane (related to endomembrane)
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ER manufactures membranes
Endoplasmatic reticulum (ER) network within the
cytoplasm extensive membranous network of
tubules and sacs (cisternae) which sequesters its
internal lumen (cisternal space) from the
cytosol. Consist of smooth and rough ER.
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Smooth ER
Participates in the synthesis of lipids,
phospholipids and steroids Participates in
carbohydrate metabolism Detoxifies drugs and
poisons Stores calcium ion necessary for muscle
contraction
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Rough ER
Manufactures secretory proteins and membranes
Proteins to be secreted are synthesized by
ribosomes attached to rough ER
Polypeptide chain is threaded through ER membrane
into the lumen or cisternal space
Protein folds into its native conformation
Undergo modification oligosaccharide are added
to the proteins in order to make glycoprotein
Proteins departs in a transport vesicle pinched
off from transitional ER adjacent to the rough ER
site production
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Rough ER
Glycoproteins protein covalently bonded to
carbohydrate Oligosaccharide small polymer of
sugar units Transport vesicle membrane vesicle
in transit from one part of the cell to another
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Rough ER and membrane production
Membrane proteins are produced by
ribosomes. Growing polypeptide anchors by
hydrophobic regions into the ER membrane Enzymes
within the ER membrane synthesize phospholipids
from raw materials in the cytosol Newly expanded
ER membrane can be transported as a vesicle to
other parts of the cell
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Apparatus Golgi
Golgi apparatus organelle made of stacked,
flattened membranous sacs (cisternae), that
modifies, stores and routes products of the ER
Has a distinct polarity. Membranes of cisternae
at opposite ends differ in thickness and
composition.
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Apparatus Golgi
Two poles are called the cis face (forming face)
and the trans face (maturing face) Cis face,
which is closely associated with transitional ER,
receives products by accepting transport vesicles
from the ER. Trans face pinches off vesicles
from the Golgi and transports molecules to other
sites
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Apparatus Golgi
Golgi products in transit from one cisternae to
the next, are carried in transport vesicles. The
Golgi alters some membrane phospholipids modifie
s the oligosaccharide portion of
glycoproteins target products for various parts
of the cell sorts products for secretion
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Apparatus Golgi
Many polysaccharides including hyaluronic acid
are Golgi products
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Lysosomes
Lysosomes are relatively large vesicles formed by
the Golgi - organelles which are
membrane-enclosed bag of hydrolytic enzymes that
digest all major classes of macromolecules. Enzym
es include lipases, carbohydrases, proteases, and
nucleases
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Lysosomes
Lysosomal membrane performs two important
functions Sequesters potentially destructive
hydrolytic enzymes from the cytosol Maintains
the optimal acidic environment for enzyme
activity by pumping Hs inward from the cytosol
to the lumen
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Function of the lysosomes

• Intracellular digestion
• Phagocytosis cellular process of
  ingestion, in which the plasma membrane engulfs
  substances and pinches off to form a
  particle-containing vacuole
• Lysosomes may fuse with food-filled
  vacuoles, and their hydrolytic enzymes digest the
  food
• Amoeba and other protists
• Human macrophages

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Function of the lysosomes

• Recycle cells own organic material
• Lysosomes may engulf other cellular
  organelles or part of the cytosol and digest them
  (autophagy)
• Resulting monomers are released into the cytosol
  where they can be recycled into new
  macromolecules
• c. Programmed cell destruction
• This process is important during
  metamorphosis and development

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The formation and functions of lysosomes
The cell encloses food in a vacuole. The food
vacuole fuses with a lysosome, and hydrolytic
enzymes digest the food.
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The formation and functions of lysosomes
After hydrolysis, simple sugars, amino acids, and
other monomers pass across the lysosomal membrane
into the cytosol as nutrients for the cell.
Lysosomes recycle the molecular ingredients of
organelles (autophagy). The cell continually
renews itself
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Lysosomes and human disease
Symptoms of inherited storage diseases result
from impaired lysosomal function. Lack of a
specific lysosomal enzymes causes substrate
accumulation which interferes with lysosomal
metabolism and other cellular functions
Pompes disease the missing enzyme is a
carbohydrase that breaks down glycogen glycogen
accumulation damages the liver Tay-Sachs
disease brain impairment by accumulation of
lipids
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The formation and functions of lysosomes
Transformation of a tadpole into a frog
and Disappearance of tissue between the hands
fingers of human embryos
are done by digestion with lysosomes
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Diverse function of vacuoles
Food vacuoles vacuole formed by
phagocytosis Contractile vacuoles pump water
excess out of the cell (in protozoa) Central
vacuole enclosed by a membrane (tonoplast) exist
in mature plants.
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Diverse function of vacuoles

• Central vacuole
• is the major food storage (protein storage in
  seeds)
• stores inorganic ions (K and Cl-)
• sequesters dangerous metabolic by-products from
  the cytoplasm
• contains soluble pigments in some cells

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Diverse function of vacuoles

• Central vacuole
• helps against predators by containing poisonous
  compounds
• plays a role in plant growth by absorbing water
  and elongating the cell

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Relationships between endomembranes
Membrane and secretory proteins produced by the
ER flows in the form of transport vesicles to the
Golgi. Golgi pinches off vesicles
Vesicles give rise to lysosomes and vacuoles
and fuse with and add to plasma membrane. The
membrane expends and releases secretory proteins
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Other membranous organelles
Mitochondria and chloroplasts the main energy
transformers of cells Mitochondria and
chloroplasts are organelles that transduce energy
acquired from the surroundings into forms useable
for cellular work
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Other membranous organelles
Mitochondria are the sites of cellular
respiration catabolic process that generates ATP
by extracting energy from sugars, fats and other
molecules Chloroplasts the sites of
photosynthesis they convert solar energy to
chemical energy by absorbing sunlight and using
it to drive the synthesis of organic compounds
from CO2 and H2O
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Mitochondria
Enclosed by double membranes that are not part of
endomembrane system (the membrane proteins are
synthesized by free ribosomes) Contain ribosomes
and some DNA that programs a small portion of
their own protein synthesis Are semiautonomous
organelles that grow and reproduce within the cell
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Mitochondria
outer membrane
inner membrane
Cristae
Matrix
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Mitochondria
Found in nearly all eukaryotes cells Number of
mitochondria depends on the cells metabolic
activity Are about 1 µm in diameter and 1-10 µm
in length Are dynamic structures that move,
change their shape and divide Mitochondria
contain their own DNA (termed mDNA) and are
thought to represent bacteria-like organisms
incorporated into eukaryotic cells over 700
million years ago (perhaps even as far back as
1.5 billion years ago).
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Mitochondria
They function as the sites of energy release
(following glycolysis in the cytoplasm) and ATP
formation (by chemiosmosis). Smooth outer
membrane is highly permeable to small solutes,
but it blocks passage of proteins and other
macromolecules Convoluted inner membrane
contains embedded enzymes that are involved in
cellular respiration. It folds into a series of
cristae, which are the surfaces on which ATP is
generated.
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Mitochondria
Intermembrane space a narrow region between the
inner and outer mitochondrial membranes Reflects
the solute composition of the cytoplasm, because
the outer membrane is permeable Mitochondrial
matrix compartment enclosed by the inner
membrane, contains enzymes that catalyze many
metabolic steps of cellular respiration. Some
enzymes of respiration and ATP production are
actually embedded in the inner membrane.
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Muscle Cell Mitochondria
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Plastids
Plastids are also membrane-bound organelles that
only occur in plants and photosynthetic
eukaryotes. They include amyloplasts,
chromoplasts and chloroplasts. Amyloplasts
colorless plastids that store starch in roots and
tubers Chromoplasts plastids containing
pigments other than chlorophyll responsible for
fruits and flowers color. Chloroplasts
chlorophyll-containing plastids which are the
sites of photosynthesis in eukaryotes.
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Plastids
Chloroplasts are found in eukaryotic algae,
leaves and other green plant organs Are
lens-shaped and measure about 2-5?m Are dynamic
structures that change shape, move and
divide. Functional compartments Intermembrane
space separates the two membranes Inside the
chloroplast is another membranous system
thylakoids segregates the interior of the
chloroplast into two compartments thylakoid
space and stroma.
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Plastids
Thylakoids function in the steps of
photosynthesis that initially convert light
energy to chemical energy Collectively a stack
of thylakoids are a granum plural grana)
floating in a fluid termed the stroma.
Photosynthetic reactions that use chemical
energy to convert carbon dioxide to sugar occur
in the stroma
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Chloroplasts
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Chloroplasts
Like mitochondria, chloroplasts have their own
DNA, termed cpDNA. Chloroplasts of Green Algae
(Protista) and Plants (descendants of some Green
Algae) are thought to have originated by
endosymbiosis of a prokaryotic alga similar to
living Prochloron (Prochlorobacteria).
Chloroplasts of Red Algae (Protista) are very
similar biochemically to cyanobacteria (also
known as blue-green bacteria.
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Peroxisomes
Peroxisomes are roughly spherical and often have
a granular or crystalline core that is probably a
dense collection of enzymes. This peroxisome is
in a leaf cell.
Notice its proximity to two chloroplasts and a
mitochondrion. These organelles cooperate with
peroxisomes in certain metabolic functions (TEM).
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Peroxisomes
Peroxisomes do not bud from the endomembrane
system. They grow by incorporating proteins and
lipids made in the cytosol.
They increase in number by splitting in two when
they reach a certain size.
Peroxisomes in liver detoxify alcohol by
transferring H to O and producing
H2O2 Peroxidase destroys toxic H2O2 by
converting it to H2O
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Peroxisomes
Peroxisomes convert fatty acids to smaller
molecules that can be used by mitochondria in the
process of cellular respiration. In plant seeds
glyoxysomes, special peroxisomes, convert fatty
acids to sugar. This provides growing seedlings
with energy and carbon source.
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Cytoplasm
The cytoplasm was defined earlier as the material
between the plasma membrane (cell membrane) and
the nuclear envelope. Fibrous proteins that
occur in the cytoplasm, referred to as the
cytoskeleton maintain the shape of the cell.
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Cytoplasm
Microtubules function in cell division and serve
as a "temporary scaffolding" for other
organelles. Actin filaments are thin threads
that function in cell division and cell motility.
Intermediate filaments are between the size of
the microtubules and the actin filaments.
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Reading
Ch. 6 pp. 108-111