The Cellular Level of Organization

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The Cellular Level of Organization
Living things are constructed of cells. Living
things may be unicellular or multicellular. Cell
structure is diverse but all cells share common
characteristics.
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The cell theory states All organisms are
composed of one or more cells. Cells are the
basic unit of structure and function in
organisms. All cells come only from other cells.
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Cells are small so they can exchange materials
with their surroundings.
Surface area relative to the volume decreases as
size of cell increases. - limits the size of
cells
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Sizes of living things
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Eukaryotic Cells
All cells are surrounded by a plasma membrane
made of phospholipids and proteins. Eukaryotic
cells have membrane bound intracellular
organelles. The most prominent is the nucleus
that controls the workings of the cell.
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The plasma membrane regulates what enters and
exits the cell. Inside the plasma membrane, the
nucleus is surrounded by cytoplasm. Plant cells
have a cell wall in addition to the plasma
membrane.
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Animal and plant cells have organelles. Organelle
s compartmentalize functions within the
cell. The organelles of animal and plant cells
are similar to each other except that centrioles
are present only in animal cells, and
chloroplasts are present only in plant cells.
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Animal cell anatomy
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Plant cell anatomy
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Structure of the Nucleus
Chromatin DNA and proteins Nucleolus
Chromatin and ribosomal subunits Nuclear
envelope Double membrane with
pores Nucleoplasm semifluid medium inside the
nucleus.
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The nucleus and the nuclear envelope
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Ribosomes
Protein synthesis occurs at tiny organelles
called ribosomes. Ribosomes are composed of a
large subunit and a small subunit. Ribosomes can
be found alone in the cytoplasm, in groups called
polyribosomes, or attached to the endoplasmic
reticulum.
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The endomembrane system consists of
Nuclear envelope Endoplasmic reticulum Golgi
apparatus Vesicles
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The endoplasmic reticulum
The endoplasmic reticulum (ER) is a system of
membranous channels and saccules. Rough ER is
studded with ribosomes and is the site of protein
synthesis and processing. Smooth ER lacks
ribosomes and is the site of synthesis of
phospholipids and the packaging of proteins into
vesicles, among other functions.
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The Golgi apparatus
The Golgi apparatus consists of a stack of curved
saccules. The Golgi apparatus receives protein
and also lipid-filled vesicles from the ER,
packages, processes, and distributes them within
the cell. This organelle may also be involved in
secretion.
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Lysosomes and vacuoles
Lysosomes are vesicles produced by the Golgi
apparatus. Lysosomes contain hydrolytic enzymes
and are involved in intracellular
digestion. Vacuoles (large) and vesicles (small)
are membranous sacs in the cell that store
substances.
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Peroxisomes
Peroxisomes are vesicles than contain
enzymes. The enzymes in these organelles use up
oxygen and produce hydrogen peroxide. Peroxisomes
are abundant in the liver where they produce
bile salts and cholesterol and break down fats.
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Energy-Related Organelles
The two energy-related organelles of eukaryotes
are chloroplasts and mitochondria. Both
organelles house energy in the form of ATP.
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Chloroplasts
A chloroplast is bounded by two membranes
enclosing a fluid-filled stroma that contains
enzymes. Membranes inside the stroma are
organized into thylakoids that house
chlorophyll. Chlorophyll absorbs solar energy
and carbohydrates are made in the stroma.
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Mitochondria
Mitochondria are found in plant and animal
cells. Mitochondria are bounded by a double
membrane surrounding fluid-filled matrix. The
inner membranes of mitochondria are cristae. The
matrix contains enzymes that break down
carbohydrates and the cristae house protein
complexes that produce ATP.
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The Cytoskeleton
The eukaryotic cytoskeleton is a network of
filaments and tubules that extends from the
nucleus to the plasma membrane. The cytoskeleton
contains three types of elements responsible for
cell shape, movement within the cell, and
movement of the cell Actin
filaments Microtubules Intermediate filaments
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Actin filaments occur in bundles or mesh-like
networks. Actin filaments play a structural role
in intestinal microvilli and also interact with
motor molecules, such as myosin.
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Microtubles are small hollow cylinders made of
the globular protein tubulin. Microtubules help
maintain the shape of the cell and act as tracks
along which organelles can move.
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Centrioles
Centrioles are short cylinders with a 9 0
pattern of microtubule triplets. Centrioles may
be involved in microtubule formation and
disassembly during cell division and in the
organization of cilia and flagella.
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Cilia and flagella
Cilia (small and numerous) and flagella (large
and single) have a 9 2 pattern of microtubules
and are involved in cell movement. Cilia and
flagella move when the microtubule doublets slide
past one another. Each cilium and flagellum has
a basal body at its base.
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Prokaryotic Cells
Prokaryotic cells include the bacteria and
archaea. Bacterial cells have these constant
features Outer Boundary Cell wall
Plasma membrane Cytoplasm
Ribosomes
Thylakoids (Cyanobacteria)
Innumerable enzymes Nucleoid
Chromosome (DNA only)
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Bacterial cells may have plasmids, small
accessory rings of DNA. Some bacteria have a
capsule or a slime layer. Most bacteria have
flagella. Some also have fimbriae that help
cells attach to surfaces. Bacteria have a great
metabolic diversity.
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Evolution of the Eukaryotic Cell
Endosymbiotic hypothesis. Eukaryotes arose from
a symbiotic relationship between various
prokaryotes. Heterotrophic bacteria became
mitochondria. Cyanobacteria became
chloroplasts. Host cell was a large eukaryotic
cell.
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Evolution of the eukaryotic cell